During sexual reproduction, two haploid gametes fuse to form the zygote, and the acrosome is essential to this fusion process (fertilization) in animals. The acrosome is a special kind of organelle with a cap-like structure that covers the anterior portion of the head of the spermatozoon. The acrosome is derived from the Golgi apparatus and contains digestive enzymes. With the progress of our understanding of acrosome biogenesis, a number of models have been proposed to address the origin of the acrosome. The acrosome has been regarded as a lysosome-related organelle, and it has been proposed to have originated from the lysosome or the autolysosome. Our review will provide a brief historical overview and highlight recent findings on acrosome biogenesis in mammals. Copyright © 2019 Khawar, Gao and Li. KEYWORDS: acrosome biogenesis; autolysosome; globozoospermia; lysosomes; spermiogenesis PMID: 31620437 PMCID: PMC6759486 DOI: 10.3389/fcell.2019.00195
The dynamics and regulation of chromatin remodeling during spermiogenesis
Gene. 2019 Jul 20;706:201-210. doi: 10.1016/j.gene.2019.05.027. Epub 2019 May 11.
Hao SL1, Ni FD1, Yang WX2.
The functional sperm is the key factor for species continuation. The process spermatogenesis, to produce mature sperm is quite complex. It begins with the proliferation and differentiation of spermatogonia, which develop from primary spermatocytes to secondary spermatocytes and round spermatids, which eventually develop into fertile mature sperm. Spermiogenesis is the latest stage of spermatogenesis, where the round spermatids undergo a series of dramatic morphological changes and extreme condensation of chromatin to construct mature sperm with species-specific shape. During spermiogenesis, chromatin remodeling is a unique progress. It leads the nucleosome from a histone-based structure to a mostly protamine-based configuration. The main events of chromatin remodeling are the replacement of histone by histone variants, hyperacetylation, transient DNA strand breaks and repair, variants by transition proteins and finally by protamines. In this review, we synthesize and summarize the current knowledge on the progress of chromatin remodeling during spermiogenesis. We straighten out the chronological order of chromatin remodeling and illustrate the possible regulation mechanisms of each step. Copyright © 2019 Elsevier B.V. All rights reserved. KEYWORDS: Chromatin remodeling; Histone variants; Hyperacetylation; Protamine; Transition proteins PMID: 31085275 DOI: 10.1016/j.gene.2019.05.027
Deficiency of fibroblast growth factor 2 (FGF-2) leads to abnormal spermatogenesis and altered sperm physiology
J Cell Physiol. 2018 Jul 27. doi: 10.1002/jcp.26876. [Epub ahead of print]
Saucedo L1, Rumpel R2, Sobarzo C3, Schreiner D2, Brandes G2, Lustig L3, Vazquez-Levin MH1, Grothe C2, Marín-Briggiler C1.
In previous studies, we described the presence of fibroblast growth factor 2 (FGF-2) and its receptors (FGFRs) in human testis and sperm, which are involved in spermatogenesis and in motility regulation. The aim of the present study was to analyze the role of FGF-2 in the maintenance of sperm physiology using FGF-2 knockout (KO) mice. Our results showed that in wild-type (WT) animals, FGF-2 is expressed in germ cells of the seminiferous epithelium, in epithelial cells of the epididymis, and in the flagellum and acrosomal region of epididymal sperm. In the FGF-2 KO mice, we found alterations in spermatogenesis kinetics, higher numbers of spermatids per testis, and enhanced daily sperm production compared with the WT males. No difference in the percentage of sperm motility was detected, but a significant increase in sperm concentration and in sperm head abnormalities was observed in FGF-2 KO animals. Sperm from KO mice depicted reduced phosphorylation on tyrosine residues (a phenomenon that was associated with sperm capacitation) and increased acrosomal loss after incubation under capacitating conditions. However, the FGF-2 KO males displayed no apparent fertility defects, since their mating with WT females showed no differences in the time to delivery, litter size, and pup weight in comparison with WT males. Overall, our findings suggest that FGF-2 exerts a role in mammalian spermatogenesis and that the lack of FGF-2 leads to dysregulated sperm production and altered sperm morphology and function. FGF-2-deficient mice constitute a model for the study of the complex mechanisms underlying mammalian spermatogenesis. KEYWORDS:
FGF-2 knockout (FGF-2 KO); fibroblast growth factor 2 (FGF-2); sperm; spermatogenesis
PMID: 30054911 DOI:10.1002/jcp.26876
Small RNAs Are Trafficked from the Epididymis to Developing Mammalian Sperm
Dev Cell. 2018 Jul 16. pii: S1534-5807(18)30540-9. doi: 10.1016/j.devcel.2018.06.023. [Epub ahead of print]
Sharma U1, Sun F1, Conine CC1, Reichholf B2, Kukreja S1, Herzog VA2, Ameres SL2, Rando OJ3.
The biogenesis of the RNA payload of mature sperm is of great interest, because RNAs delivered to the zygote at fertilization can affect early development. Here, we tested the hypothesis that small RNAs are trafficked to mammalian sperm during the process of post-testicular maturation in the epididymis. By characterizing small RNA dynamics during germ cell maturation in mice, we confirm and extend prior observations that sperm undergo a dramatic switch in the RNA payload from piRNAs to tRNA fragments (tRFs) upon exiting the testis and entering the epididymis. Small RNA delivery to sperm could be recapitulated in vitro by incubating testicular spermatozoa with caput epididymosomes. Finally, tissue-specific metabolic labeling of RNAs in intact mice definitively shows that mature sperm carry RNAs that were originally synthesized in the epididymal epithelium. These data demonstrate that soma-germline RNA transfer occurs in male mammals, most likely via vesicular transport from the epididymis to maturing sperm. KEYWORDS:
epigenetics; small RNAs; spermatogenesis
PMID: 30057273 DOI: 10.1016/j.devcel.2018.06.023
Sperm nuclear protamines: A checkpoint to control sperm chromatin quality
Anat Histol Embryol. 2018 Aug;47(4):273-279. doi: 10.1111/ahe.12361. Epub 2018 May 23.
Steger K1, Balhorn R2.
Protamines are nuclear proteins which are specifically expressed in haploid male germ cells. Their replacement of histones and binding to DNA is followed by chromatin hypercondensation that protects DNA from negative influences by environmental factors. Mammalian sperm contain two types of protamines: PRM1 and PRM2. While the proportion of the two protamines is highly variable between different species, abnormal ratios within a species are known to be associated with male subfertility. Therefore, it is more than likely that correct protamine expression represents a kind of chromatin checkpoint during sperm development rendering protamines as suitable biomarkers for the estimation of sperm quality. This review presents an overview of our current knowledge on protamines comparing gene and protein structures between different mammalian species with particular consideration given to man, mouse and stallion. At last, recent insights into the possible role of inherited sperm histones for early embryo development are provided. KEYWORDS:
histology; horse; molecular biology
PMID: 29797354 DOI: 10.1111/ahe.12361
Perinatal exposure to 2,2',4'4' -Tetrabromodiphenyl ether induces testicular toxicity in adult rats
Toxicology. 2017 Jul 13;389:21-30. doi: 10.1016/j.tox.2017.07.006. [Epub ahead of print]
Khalil A1, Parker M2, Brown SE3, Cevik SE4, Guo LW5, Jensen J6, Olmsted A7, Portman D8, Wu H9, Suvorov A10.
Since 1965, polybrominated diphenyl ethers (PBDEs) have been used internationally as flame-retardant additives. PBDEs were recently withdrawn from commerce in North America and Europe due to their environmental persistence, bioaccumulative properties and endocrine-disrupting effects. Generations exposed perinatally to the highest environmental doses of PBDE account for one-fifth of the total United States population. While, toxicity of PBDE for the male reproductive system has been demonstrated in several human and animal studies, the long-lasting effects of perinatal exposures on male reproduction are still poorly understood. In this study, pregnant Wistar rats were exposed to 0.2mg/kg 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) from gestation day 8 until postnatal day 21. Male reproductive outcomes were analyzed on postnatal day 120 in offspring. Exposed animals had significantly smaller testes, displayed decreased sperm production per testis weight, had significantly increased percentage of morphologically abnormal spermatozoa, and showed an increase in spermatozoa head size. Perinatal BDE-47 exposure led to significant changes in testes transcriptome, including suppression of genes essential for spermatogenesis and activation of immune response genes. In particular, we observed a 4-fold average decrease in expression of protamine and transition protein genes in testes, suggesting that histone-protamine exchange may be dysregulated during spermatogenesis, resulting in an aberrant sperm epigenome. The possibility of long-lasting effects of developmental PBDE exposures calls for additional studies to build a foundation for the development of preventive and protective interventions against the environmentally-induced decline in fertility. Copyright © 2017 Elsevier B.V. All rights reserved.
KEYWORDS: 2,2′,4,4′-tetrabromodiphenyl ether; Male reproduction; PBDE; Protamine; Sperm; Transcriptome PMID: 28712647 DOI: 10.1016/j.tox.2017.07.006
Temporal trends in sperm count- a systematic review and meta-regression analysis
25 July 2017 - Review Sperm Counts in Western Men May Have Decreased by 50 Percent Over 40 Years Temporal trends in sperm count- a systematic review and meta-regression analysis "This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by SC and TSC) between 1973 and 2011, driven by a 50–60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand."
Spermatogenesis: The Commitment to Meiosis
Physiol Rev. 2016 Jan;96(1):1-17. doi: 10.1152/physrev.00013.2015.
Mammalian spermatogenesis requires a stem cell pool, a period of amplification of cell numbers, the completion of reduction division to haploid cells (meiosis), and the morphological transformation of the haploid cells into spermatozoa (spermiogenesis). The net result of these processes is the production of massive numbers of spermatozoa over the reproductive lifetime of the animal. One study that utilized homogenization-resistant spermatids as the standard determined that human daily sperm production (dsp) was at 45 million per day per testis (60). For each human that means ∼1,000 sperm are produced per second. A key to this level of gamete production is the organization and architecture of the mammalian testes that results in continuous sperm production. The seemingly complex repetitious relationship of cells termed the "cycle of the seminiferous epithelium" is driven by the continuous commitment of undifferentiated spermatogonia to meiosis and the period of time required to form spermatozoa. This commitment termed the A to A1 transition requires the action of retinoic acid (RA) on the undifferentiated spermatogonia or prospermatogonia. In stages VII to IX of the cycle of the seminiferous epithelium, Sertoli cells and germ cells are influenced by pulses of RA. These pulses of RA move along the seminiferous tubules coincident with the spermatogenic wave, presumably undergoing constant synthesis and degradation. The RA pulse then serves as a trigger to commit undifferentiated progenitor cells to the rigidly timed pathway into meiosis and spermatid differentiation. Copyright © 2016 the American Physiological Society.
Sperm function test
J Hum Reprod Sci. 2015 Apr-Jun;8(2):61-9. doi: 10.4103/0974-1208.158588.
Talwar P1, Hayatnagarkar S1.
With absolute normal semen analysis parameters it may not be necessary to shift to specialized tests early but in cases with borderline parameters or with history of fertilization failure in past it becomes necessary to do a battery of tests to evaluate different parameters of spermatozoa. Various sperm function tests are proposed and endorsed by different researchers in addition to the routine evaluation of fertility. These tests detect function of a certain part of spermatozoon and give insight on the events in fertilization of the oocyte. The sperms need to get nutrition from the seminal plasma in the form of fructose and citrate (this can be assessed by fructose qualitative and quantitative estimation, citrate estimation). They should be protected from the bad effects of pus cells and reactive oxygen species (ROS) (leukocyte detection test, ROS estimation). Their number should be in sufficient in terms of (count), structure normal to be able to fertilize eggs (semen morphology). Sperms should have intact and functioning membrane to survive harsh environment of vagina and uterine fluids (vitality and hypo-osmotic swelling test), should have good mitochondrial function to be able to provide energy (mitochondrial activity index test). They should also have satisfactory acrosome function to be able to burrow a hole in zona pellucida (acrosome intactness test, zona penetration test). Finally, they should have properly packed DNA in the nucleus to be able to transfer the male genes (nuclear chromatic decondensation test) to the oocyte during fertilization. KEYWORDS: Fertilization; sperm function test; spermatozoa
Pachytene piRNAs instruct massive mRNA elimination during late spermiogenesis
Cell Res. 2014 Jun;24(6):680-700. doi: 10.1038/cr.2014.41. Epub 2014 May 2.
Gou LT1, Dai P1, Yang JH2, Xue Y3, Hu YP1, Zhou Y3, Kang JY1, Wang X1, Li H3, Hua MM1, Zhao S1, Hu SD1, Wu LG1, Shi HJ4, Li Y5, Fu XD3, Qu LH2, Wang ED6, Liu MF1.
Spermatogenesis in mammals is characterized by two waves of Piwi-interacting RNA (piRNA) expression: one corresponds to classic piRNAs responsible for silencing retrotransponsons and the second wave is predominantly derived from nontransposon intergenic regions in pachytene spermatocytes, but the function of these pachytene piRNAs is largely unknown. Here, we report the involvement of pachytene piRNAs in instructing massive mRNA elimination in mouse elongating spermatids (ES). We demonstrate that a piRNA-induced silencing complex (pi-RISC) containing murine PIWI (MIWI) and deadenylase CAF1 is selectively assembled in ES, which is responsible for inducing mRNA deadenylation and decay via a mechanism that resembles the action of miRNAs in somatic cells. Such a highly orchestrated program appears to take full advantage of the enormous repertoire of diversified targeting capacity of pachytene piRNAs derived from nontransposon intergenic regions. These findings suggest that pachytene piRNAs are responsible for inactivating vast cellular programs in preparation for sperm production from ES. Comment in piRNAs, master regulators of gene expression. [Cell Res. 2014]
Chromatin dynamics during spermiogenesis
Biochim Biophys Acta. 2014 Mar;1839(3):155-68. doi: 10.1016/j.bbagrm.2013.08.004. Epub 2013 Sep 30.
Rathke C1, Baarends WM2, Awe S3, Renkawitz-Pohl R4.
The function of sperm is to safely transport the haploid paternal genome to the egg containing the maternal genome. The subsequent fertilization leads to transmission of a new unique diploid genome to the next generation. Before the sperm can set out on its adventurous journey, remarkable arrangements need to be made during the post-meiotic stages of spermatogenesis. Haploid spermatids undergo extensive morphological changes, including a striking reorganization and compaction of their chromatin. Thereby, the nucleosomal, histone-based structure is nearly completely substituted by a protamine-based structure. This replacement is likely facilitated by incorporation of histone variants, post-translational histone modifications, chromatin-remodeling complexes, as well as transient DNA strand breaks. The consequences of mutations have revealed that a protamine-based chromatin is essential for fertility in mice but not in Drosophila. Nevertheless, loss of protamines in Drosophila increases the sensitivity to X-rays and thus supports the hypothesis that protamines are necessary to protect the paternal genome. Pharmaceutical approaches have provided the first mechanistic insights and have shown that hyperacetylation of histones just before their displacement is vital for progress in chromatin reorganization but is clearly not the sole inducer. In this review, we highlight the current knowledge on post-meiotic chromatin reorganization and reveal for the first time intriguing parallels in this process in Drosophila and mammals. We conclude with a model that illustrates the possible mechanisms that lead from a histone-based chromatin to a mainly protamine-based structure during spermatid differentiation. This article is part of a Special Issue entitled: Chromatin and epigenetic regulation of animal development. © 2013. Published by Elsevier B.V. All rights reserved. KEYWORDS: Chromatin remodeling; Histone modification; Histone variant; Protamine; Spermiogenesis; Transition protein
Testicular Development From Birth To Puberty. Systematic Evaluation Of The Prepubertal Testis
Pediatr Dev Pathol. 2014 Jul 30. [Epub ahead of print]
Nistal M1, Gonzalez-Peramato P, Paniagua R, Reyes-Múgica M.
Abstract The appropriate interpretation of testicular biopsies from infants and children we requires to keep in mind that the testis, as the rest of the child, is an organ in dynamic development, undergoing significant remodeling from birth to puberty in most of its components, featuring active and variably regulated proliferation and differentiation at certain ages [1, 2]. The use of morphometric analyses based in proven stereological methods, together with the performance of endocrinological studies in infants and children have demonstrated that in this period, the numbers of both Sertoli cells and germ cells increase, and an important production of AMH and inhibin occurs [3, 4]. Through the course of the prepubertal period, germ cells in the seminiferous epithelium undergo three proliferative waves, but only the third wave, which takes place at puberty, will achieve forming spermatozoa and result in the adult histological pattern of the testis. In addition, two Leydig cell waves provide the necessary androgen supply for the waves of germ cell proliferation and differentiation.
Actin binding proteins, spermatid transport and spermiation
Semin Cell Dev Biol. 2014 Apr 13. pii: S1084-9521(14)00089-5. doi: 10.1016/j.semcdb.2014.04.018. [Epub ahead of print]
Qian X1, Mruk DD2, Cheng YH3, Tang EI2, Han D4, Lee WM5, Wong EW2, Cheng CY6. Author information
The transport of germ cells across the seminiferous epithelium is composed of a series of cellular events during the epithelial cycle essential to the completion of spermatogenesis. Without the timely transport of spermatids during spermiogenesis, spermatozoa that are transformed from step 19 spermatids in the rat testis fail to reach the luminal edge of the apical compartment and enter the tubule lumen at spermiation, thereby arriving the epididymis for further maturation. Step 19 spermatids and/or sperms that remain in the epithelium beyond stage VIII of the epithelial cycle will be removed by the Sertoli cell via phagocytosis to form phagosomes and be degraded by lysosomes, leading to subfertility and/or infertility. However, the biology of spermatid transport, in particular the final events that lead to spermiation remain elusive. Based on recent data in the field, we critically evaluate the biology of spermiation herein by focusing on the actin binding proteins (ABPs) that regulate the organization of actin microfilaments at the Sertoli-spermatid interface, which is crucial for spermatid transport during this event. The hypothesis we put forth herein also highlights some specific areas of research that can be pursued by investigators in the years to come. Copyright © 2014 Elsevier Ltd. All rights reserved. KEYWORDS: Actin binding proteins, Actin bundling proteins, Branched actin polymerization inducing proteins, Ectoplasmic specialization, Spermatogenesis, Spermiation, Spermiogenesis, Testis
WHO Laboratory Manual for the Examination and Processing of Human Semen
WHO. WHO Laboratory Manual for the Examination and Processing of Human Semen. 5 ed. Geneva, Switzerland: World Health Organization; 2010. Available online. Accessed 10-11-12.
The rate of change in Ca(2+) concentration controls sperm chemotaxis
J Cell Biol. 2012 Mar 5;196(5):653-63. Epub 2012 Feb 27.
Alvarez L, Dai L, Friedrich BM, Kashikar ND, Gregor I, Pascal R, Kaupp UB. Source Department of Molecular Sensory Systems, Center of Advanced European Studies and Research (caesar), 53175 Bonn, Germany. firstname.lastname@example.org
During chemotaxis and phototaxis, sperm, algae, marine zooplankton, and other microswimmers move on helical paths or drifting circles by rhythmically bending cell protrusions called motile cilia or flagella. Sperm of marine invertebrates navigate in a chemoattractant gradient by adjusting the flagellar waveform and, thereby, the swimming path. The waveform is periodically modulated by Ca(2+) oscillations. How Ca(2+) signals elicit steering responses and shape the path is unknown. We unveil the signal transfer between the changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) and path curvature (κ). We show that κ is modulated by the time derivative d[Ca(2+)](i)/dt rather than the absolute [Ca(2+)](i). Furthermore, simulation of swimming paths using various Ca(2+) waveforms reproduces the wealth of swimming paths observed for sperm of marine invertebrates. We propose a cellular mechanism for a chemical differentiator that computes a time derivative. The cytoskeleton of cilia, the axoneme, is highly conserved. Thus, motile ciliated cells in general might use a similar cellular computation to translate changes of [Ca(2+)](i) into motion.
The relative contributions of propulsive forces and receptor-ligand binding forces during early contact between spermatozoa and zona pellucida of oocytes
J Theor Biol. 2012 Feb 7;294:139-43. Epub 2011 Nov 15.
Kozlovsky P, Gefen A. Source Department of Biomedical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel.
When reaching the zona pellucida (ZP) of the oocyte, spermatozoa apply propulsive forces produced by the motion of their flagella, which push against the ZP and theoretically should contribute to their penetration into the ZP. Additionally, specific receptors on the spermatozoon head bind to ZP3 ligands located on the surface of the ZP, which locks the sperm's head onto the oocyte. Both mechanisms are important cofactors in the initial sperm penetration into the ZP, which is required for successful fertilization of the oocyte, but it is unclear which forces-mechanical thrust or biochemical binding-are more influential at this stage. To address this question, we developed a biomechanical sperm-oocyte contact model, which is based on the Johnson-Kendall-Roberts model adopted from the contact mechanics theory. The modeling predicted that during the early stage of penetration into the ZP, biochemical binding forces acting on spermatozoa, which are swimming at a (normal) velocity of 100μm/s are ∼4.2-times to ∼16.7-times less than the mechanically-generated propulsive forces. In a simulated pathology of a low number of properly functioning receptors (50 out of 300receptors/μm(2)), the biochemical binding forces are ∼63-times less than the propulsive forces for the normally swimming sperm. It is suggested that such dominance of the propulsive forces over the biochemical binding forces can prevent efficient binding of spermatozoa to the ZP of the oocyte due to continuous movement of the sperm (which is not necessarily perpendicular to the ZP surface, and can cause sliding of sperm over the ZP). Thus, our theoretical analysis indicates that a sufficiently large density of receptors to ZP3 ligands on the sperm head is critical at the stage of early sperm-oocyte contact, in order to allow an efficient acrosome reaction to follow, so that the spermatozoon can start penetrating into the ZP. Copyright © 2011 Elsevier Ltd. All rights reserved.
MNS1 is essential for spermiogenesis and motile ciliary functions in mice
PLoS Genet. 2012 Mar;8(3):e1002516. Epub 2012 Mar 1.
Zhou J, Yang F, Leu NA, Wang PJ. Source Department of Animal Biology, Center for Animal Transgenesis and Germ Cell Research, University of Pennsylvania School of Veterinary Medicine, Philadelphia, Pennsylvania, United States of America. Abstract
During spermiogenesis, haploid round spermatids undergo dramatic cell differentiation and morphogenesis to give rise to mature spermatozoa for fertilization, including nuclear elongation, chromatin remodeling, acrosome formation, and development of flagella. The molecular mechanisms underlining these fundamental processes remain poorly understood. Here, we report that MNS1, a coiled-coil protein of unknown function, is essential for spermiogenesis. We find that MNS1 is expressed in the germ cells in the testes and localizes to sperm flagella in a detergent-resistant manner, indicating that it is an integral component of flagella. MNS1-deficient males are sterile, as they exhibit a sharp reduction in sperm production and the remnant sperm are immotile with abnormal short tails. In MNS1-deficient sperm flagella, the characteristic arrangement of "9+2" microtubules and outer dense fibers are completely disrupted. In addition, MNS1-deficient mice display situs inversus and hydrocephalus. MNS1-deficient tracheal motile cilia lack some outer dynein arms in the axoneme. Moreover, MNS1 monomers interact with each other and are able to form polymers in cultured somatic cells. These results demonstrate that MNS1 is essential for spermiogenesis, the assembly of sperm flagella, and motile ciliary functions.
PLoS Genet. 2012 Mar;8(3):e1002516. Epub 2012 Mar 1.
The generation of spermatogonial stem cells and spermatogonia in mammals
Reprod Biol. 2012 Mar;12(1):5-23.
Kolasa A, Misiakiewicz K, Marchlewicz M, Wiszniewska B. Source Department of Histology and Embryology, Pomeranian Medical University in Szczecin, 72 Powstańców Wielkopolskich Str., 70-111 Szczecin, Poland; e-mail: email@example.com. Abstract Spermatogenesis is a complex series of cellular changes leading to the formation of haploid male gametes (spermatozoa) and includes mitotic, meiotic and post-meiotic phases. Spermatogonial stem cells (SSCs) are essential for the continuous lifelong production of spermatozoa. Spermatogenesis is initiated when SSC is triggered to undergo mitosis that gives rise to progenitors, which further differentiate into spermatogonia. In this review, we describe the origin of SSCs and other spermatogonia populations and summarize the knowledge concerning their markers.
The role of the septin family in spermiogenesis
Spermatogenesis. 2011 Oct;1(4):298-302. Epub 2011 Oct 1.
Lin YH, Kuo YC, Chiang HS, Kuo PL. Source Graduate Institute of Basic Medicine; Fu Jen Catholic University; Taipei, Taiwan. Abstract SEPTINS (FULL NAME: Septin; symbol name: SEPT) belong to a family of polymerizing GTP-binding proteins that are required for many cellular functions, including membrane compartmentalization, vesicle trafficking, mitosis and cytoskeletal remodeling. Two of the 14 family members in the mammalian species, Septin12 and 14 are expressed specifically in the testis. In the mouse, knockout of Septin4 and Septin12 leads to male sterility with distinctive sperm pathology (defective annulus or bent neck). In humans, sperm with abnormal expression patterns of SEPT4, 7 and 12 are more prevalent in infertile men. How septin filament is assembled/dissembled and how the SEPT-related complex regulates spermatogenesis still await further investigation.
Behavioral Mechanism during Human Sperm Chemotaxis: Involvement of Hyperactivation
Armon L, Eisenbach M. Source
Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel.
When mammalian spermatozoa become capacitated they acquire, among other activities, chemotactic responsiveness and the ability to exhibit occasional events of hyperactivated motility-a vigorous motility type with large amplitudes of head displacement. Although a number of roles have been proposed for this type of motility, its function is still obscure. Here we provide evidence suggesting that hyperactivation is part of the chemotactic response. By analyzing tracks of spermatozoa swimming in a spatial chemoattractant gradient we demonstrate that, in such a gradient, the level of hyperactivation events is significantly lower than in proper controls. This suggests that upon sensing an increase in the chemoattractant concentration capacitated cells repress their hyperactivation events and thus maintain their course of swimming toward the chemoattractant. Furthermore, in response to a temporal concentration jump achieved by photorelease of the chemoattractant progesterone from its caged form, the responsive cells exhibited a delayed turn, often accompanied by hyperactivation events or an even more intense response in the form of flagellar arrest. This study suggests that the function of hyperactivation is to cause a rather sharp turn during the chemotactic response of capacitated cells so as to assist them to reorient according to the chemoattractant gradient. On the basis of these results a model for the behavior of spermatozoa responding to a spatial chemoattractant gradient is proposed.
Doubly uniparental inheritance of mitochondria as a model system for studying germ line formation
PLoS One. 2011;6(11):e28194. Epub 2011 Nov 29.
Milani L, Ghiselli F, Maurizii MG, Passamonti M. Source Department of Biologia Evoluzionistica Sperimentale, University of Bologna, Bologna, Italy.
BACKGROUND: Doubly Uniparental Inheritance (DUI) of mitochondria occurs when both mothers and fathers are capable of transmitting mitochondria to their offspring, in contrast to the typical Strictly Maternal Inheritance (SMI). DUI was found in some bivalve molluscs, in which two mitochondrial genomes are inherited, one through eggs, the other through sperm. During male embryo development, spermatozoon mitochondria aggregate in proximity of the first cleavage furrow and end up in the primordial germ cells, while they are dispersed in female embryos. METHODOLOGY/PRINCIPAL FINDINGS: We used MitoTracker, microtubule staining and transmission electron microscopy to examine the mechanisms of this unusual distribution of sperm mitochondria in the DUI species Ruditapes philippinarum. Our results suggest that in male embryos the midbody deriving from the mitotic spindle of the first division concurs in positioning the aggregate of sperm mitochondria. Furthermore, an immunocytochemical analysis showed that the germ line determinant Vasa segregates close to the first cleavage furrow. CONCLUSIONS/SIGNIFICANCE: In DUI male embryos, spermatozoon mitochondria aggregate in a stable area on the animal-vegetal axis: in organisms with spiral segmentation this zone is not involved in cleavage, so the aggregation is maintained. Moreover, sperm mitochondria reach the same embryonic area in which also germ plasm is transferred. In 2-blastomere embryos, the segregation of sperm mitochondria in the same region with Vasa suggests their contribution in male germ line formation. In DUI male embryos, M-type mitochondria must be recognized by egg factors to be actively transferred in the germ line, where they become dominant replacing the Balbiani body mitochondria. The typical features of germ line assembly point to a common biological mechanism shared by DUI and SMI organisms. Although the molecular dynamics of the segregation of sperm mitochondria in DUI species are unknown, they could be a variation of the mechanism regulating the mitochondrial bottleneck in all metazoans.
The CatSper channel mediates progesterone-induced Ca2+ influx in human sperm
Nature. 2011 Mar 17;471(7338):382-6.
Strünker T, Goodwin N, Brenker C, Kashikar ND, Weyand I, Seifert R, Kaupp UB. Source Center of Advanced European Studies and Research, Abteilung Molekulare Neurosensorik, Ludwig-Erhard-Allee 2, 53175 Bonn, Germany. firstname.lastname@example.org
In the oviduct, cumulus cells that surround the oocyte release progesterone. In human sperm, progesterone stimulates a Ca(2+) increase by a non-genomic mechanism. The Ca(2+) signal has been proposed to control chemotaxis, hyperactivation and acrosomal exocytosis of sperm. However, the underlying signalling mechanism has remained mysterious. Here we show that progesterone activates the sperm-specific, pH-sensitive CatSper Ca(2+) channel. We found that both progesterone and alkaline pH stimulate a rapid Ca(2+) influx with almost no latency, incompatible with a signalling pathway involving metabotropic receptors and second messengers. The Ca(2+) signals evoked by alkaline pH and progesterone are inhibited by the Ca(v) channel blockers NNC 55-0396 and mibefradil. Patch-clamp recordings from sperm reveal an alkaline-activated current carried by mono- and divalent ions that exhibits all the hallmarks of sperm-specific CatSper Ca(2+) channels. Progesterone substantially enhances the CatSper current. The alkaline- and progesterone-activated CatSper current is inhibited by both drugs. Our results resolve a long-standing controversy over the non-genomic progesterone signalling. In human sperm, either the CatSper channel itself or an associated protein serves as the non-genomic progesterone receptor. The identification of CatSper channel blockers will greatly facilitate the study of Ca(2+) signalling in sperm and help to define further the physiological role of progesterone and CatSper.
Progesterone activates the principal Ca2+ channel of human sperm
Nature. 2011 Mar 17;471(7338):387-91.
Lishko PV, Botchkina IL, Kirichok Y. Source Department of Physiology, University of California San Francisco, UCSF Mail Code 2140, Genentech Hall Room N272F, 600 16th Street, San Francisco, California 94158, USA.
Steroid hormone progesterone released by cumulus cells surrounding the egg is a potent stimulator of human spermatozoa. It attracts spermatozoa towards the egg and helps them penetrate the egg's protective vestments. Progesterone induces Ca(2+) influx into spermatozoa and triggers multiple Ca(2+)-dependent physiological responses essential for successful fertilization, such as sperm hyperactivation, acrosome reaction and chemotaxis towards the egg. As an ovarian hormone, progesterone acts by regulating gene expression through a well-characterized progesterone nuclear receptor. However, the effect of progesterone upon transcriptionally silent spermatozoa remains unexplained and is believed to be mediated by a specialized, non-genomic membrane progesterone receptor. The identity of this non-genomic progesterone receptor and the mechanism by which it causes Ca(2+) entry remain fundamental unresolved questions in human reproduction. Here we elucidate the mechanism of the non-genomic action of progesterone on human spermatozoa by identifying the Ca(2+) channel activated by progesterone. By applying the patch-clamp technique to mature human spermatozoa, we found that nanomolar concentrations of progesterone dramatically potentiate CatSper, a pH-dependent Ca(2+) channel of the sperm flagellum. We demonstrate that human CatSper is synergistically activated by elevation of intracellular pH and extracellular progesterone. Interestingly, human CatSper can be further potentiated by prostaglandins, but apparently through a binding site other than that of progesterone. Because our experimental conditions did not support second messenger signalling, CatSper or a directly associated protein serves as the elusive non-genomic progesterone receptor of sperm. Given that the CatSper-associated progesterone receptor is sperm specific and structurally different from the genomic progesterone receptor, it represents a promising target for the development of a new class of non-hormonal contraceptives.
Dimensions of human ejaculated spermatozoa in Papanicolaou-stained seminal and swim-up smears obtained from the Integrated Semen Analysis System (ISAS(®))
Asian J Androl. 2010 Sep 20. [Epub ahead of print]
Bellastella G, Cooper TG, Battaglia M, Ströse A, Torres I, Hellenkemper B, Soler C, Sinisi AA.
 Centre of Reproductive Medicine and Andrology of the University, Münster D-48149, Germany  Department of Clinical and Experimental Medicine and Surgery, Endocrinology and Medical Andrology Section, Seconda Universita`di Napoli, Napoli 80131, Italy.
Objective measurements are required for computer-aided sperm morphometric analysis (CASMA) machines to distinguish normal from abnormal sperm heads. The morphometric characteristics of spermatozoa in 72 samples of semen and of spermatozoa from 72 other semen samples after swim-up were quantified by the semi-automated Integrated Sperm Analysis System (ISAS) computer-aided system, which measured the sperm head parameters length (L), width (W), area (A), perimeter (P), acrosomal area (Ac), and the derived values L/W and P/A. For each man a homogeneous population of distributions characterized seminal spermatozoa (7 942 cells: median values L 4.4 μm, W 2.8 μm, A 9.8 μm(2), P 12.5 μm, Ac 47.5%, L/W 1.57, P/A 1.27), and there was no significant difference in within- and among-individual variation. Different men could have spermatozoa of significantly different dimensions. Head dimensions for swim-up spermatozoa from different men (4 812 cells) were similar to those in semen, differing only by 2%-5%. The values of L, W and L/W fell within the limits given by the World Health Organization (WHO). Although these samples were not biologically matched, linear mixed-effects statistical analyses permitted valid comparison of the groups. A subpopulation of 404 spermatozoa considered to fit the stringent criteria of WHO 'normal' seminal spermatozoa from both semen and swim-up were characterized by median values (and 95% confidence intervals) of L, 4.3 μm (3.8-4.9), W, 2.9 μm (2.6-3.3), A, 10.2 μm(2) (8.5-12.2), P, 12.4 μm (11.3-13.9), Ac, 49% (36-60), L/W, 1.49 (1.32-1.67) and P/A, 1.22 (1.11-1.35). These median values fall within the 95th centile confidence limits given by WHO, but the confidence intervals for L and W were larger. Although these differences in head dimensions among men and after swim-up could be detected by CASMA, the small differences make it unlikely that technicians would be able to distinguish them. The values could be used as default sperm head values for the CASMA machine used here.
Microgravity promotes differentiation and meiotic entry of postnatal mouse male germ cells
- "A critical step of spermatogenesis is the entry of mitotic spermatogonia into meiosis. Progresses on these topics are hampered by the lack of an in vitro culture system allowing mouse spermatogonia differentiation and entry into meiosis. Previous studies have shown that mouse pachytene spermatocytes cultured in simulated microgravity (SM) undergo a spontaneous meiotic progression. Here we report that mouse mitotic spermatogonia cultured under SM with a rotary cell culture system (RCCS) enter into meiosis in the absence of any added exogenous factor or contact with somatic cells."
The biology of spermatogenesis: the past, present and future
Philos Trans R Soc Lond B Biol Sci. 2010 May 27;365(1546):1459-63.
Cheng CY, Mruk DD. Source The Mary M. Wohlford Laboratory for Male Contraceptive Research, Population Council, 1230 York Avenue, New York, NY 10065, USA. email@example.com
The physiological function of spermatogenesis in Caenorhabditis elegans, Drosophila melanogaster and mammals is to produce spermatozoa (1n, haploid) that contain only half of the genetic material of spermatogonia (2n, diploid). This half number of chromosomes from a spermatozoon will then be reconstituted to become a diploid cell upon fertilization with an egg, which is also haploid. Thus, genetic information from two parental individuals can be passed onto their offspring. Spermatogenesis takes place in the seminiferous epithelium of the seminiferous tubule, the functional unit of the mammalian testis. In mammals, particularly in rodents, the fascinating morphological changes that occur during spermatogenesis involving cellular differentiation and transformation, mitosis, meiosis, germ cell movement, spermiogenesis and spermiation have been well documented from the 1950s through the 1980s. During this time, however, the regulation of, as well as the biochemical and molecular mechanisms underlying these diverse cellular events occurring throughout spermatogenesis, have remained largely unexplored. In the past two decades, important advancements have been made using new biochemical, cell and molecular biology techniques to understand how different genes, proteins and signalling pathways regulate various aspects of spermatogenesis. These include studies on the differentiation of spermatogonia from gonocytes; regulation of spermatogonial stem cells; regulation of spermatogonial mitosis; regulation of meiosis, spermiogenesis and spermiation; role of hormones (e.g. oestrogens, androgens) in spermatogenesis; transcriptional regulation of spermatogenesis; regulation of apoptosis; cell-cell interactions; and the biology of junction dynamics during spermatogenesis. The impact of environmental toxicants on spermatogenesis has also become an urgent issue in the field in light of declining fertility levels in males. Many of these studies have helped investigators to understand important similarities, differences and evolutionary relationships between C. elegans, D. melanogaster and mammals relating to spermatogenesis. In this Special Issue of the Philosophical Transactions of the Royal Society B: Biological Sciences, we have covered many of these areas, and in this Introduction, we highlight the topic of spermatogenesis by examining its past, present and future.
PMID 20403863 [PubMed - indexed for MEDLINE] PMCID: PMC2871927
Capacity for stochastic self-renewal and differentiation in mammalian spermatogonial stem cells
J Cell Biol. 2009 Nov 16;187(4):513-24. Epub 2009 Nov 9.
Wu Z, Luby-Phelps K, Bugde A, Molyneux LA, Denard B, Li WH, Süel GM, Garbers DL. Source Cecil H. and Ida Green Center for Reproductive Biology Sciences, Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA. firstname.lastname@example.org Abstract Mammalian spermatogenesis is initiated and sustained by spermatogonial stem cells (SSCs) through self-renewal and differentiation. The basic question of whether SSCs have the potential to specify self-renewal and differentiation in a cell-autonomous manner has yet to be addressed. Here, we show that rat SSCs in ex vivo culture conditions consistently give rise to two distinct types of progeny: new SSCs and differentiating germ cells, even when they have been exposed to virtually identical microenvironments. Quantitative experimental measurements and mathematical modeling indicates that fate decision is stochastic, with constant probability. These results reveal an unexpected ability in a mammalian SSC to specify both self-renewal and differentiation through a self-directed mechanism, and further suggest that this mechanism operates according to stochastic principles. These findings provide an experimental basis for autonomous and stochastic fate choice as an alternative strategy for SSC fate bifurcation, which may also be relevant to other stem cell types.
PMCID: PMC2779229 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2779229
New insights into epididymal biology and function
Hum Reprod Update. 2009 Mar-Apr;15(2):213-27. Epub 2009 Jan 8.
Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, 79430, USA. email@example.com Abstract BACKGROUND: The epididymis performs an important role in the maturation of spermatozoa including their acquisition of progressive motility and fertilizing ability. However, the molecular mechanisms that govern these maturational events are still poorly defined. This review focuses on recent progress in our understanding of epididymal function including its development, role of the luminal microenvironment in sperm maturation, regulation and novel mechanisms the epididymis utilizes to carry out some of its functions.
METHODS: A systematic search of Pubmed was carried out using the search term 'epididymis'. Articles that were published in the English language until the end of August 2008 and that focused on the specific topics described above were included. Additional papers cited in the primary reference were also included.
RESULTS: While the majority of these findings were the result of studies in animal models, recent studies in the human epididymis are also presented including gene profiling studies to examine regionalized expression in normal epididymides as well as in those from vasectomized patients.
CONCLUSIONS: Significant progress has been made in our understanding of epididymal function providing new insights that ultimately could improve human health. The data also indicate that the human epididymis plays an important role in sperm maturation but has unique properties compared with animal models.
All You Wanted to Know About Spermatogonia but Were Afraid to Ask
"During mammalian spermiogenesis, histones at the onset of the differentiation process are gradually replaced by transition proteins and protamines (14,22) and although the replacement is almost complete in most species, in humans ~15% of the mature sperm chromatin remains associated with histone variants"
Sequence-specific packaging of DNA in human sperm chromatin
"The DNA in human sperm chromatin is packaged into nucleoprotamine (approximately 85%) and nucleohistone (approximately 15%). Whether these two chromatin fractions are sequence-specific subsets of the spermatozoon genome is the question addressed in this report. Sequence-specific packaging would suggest distinct structural and functional roles for the nucleohistone and nucleoprotamine in late spermatogenesis or early development or both. After removal of histones with 0.65M NaCl, exposed DNA was cleaved with Bam HI restriction endonuclease and separated by centrifugation from insoluble nucleoprotamine. The DNA sequence distribution of nucleohistone DNA in the supernatant and nucleoprotamine DNA in the pellet was compared by cloning size-selected single-copy sequences and by using the derived clones as probes of nucleohistone DNA and nucleoprotamine DNA. Two clones derived from nucleohistone DNA preferentially hybridized to nucleohistone DNA, and two clones derived from nucleoprotamine DNA preferentially hybridized to nucleoprotamine DNA, which demonstrated the existence of sequence-specific nucleohistone and nucleoprotamine components within the human spermatozoon."
Mechanisms of sperm chemotaxis
Annu Rev Physiol. 2008;70:93-117.
Kaupp UB1, Kashikar ND, Weyand I.
Sperm are attracted by chemical factors that are released by the egg-a process called chemotaxis. Most of our knowledge on sperm chemotaxis originates from the study of marine invertebrates. In recent years, the main features of the chemotactic signaling pathway and the swimming behavior evoked by chemoattractants have been elucidated in sea urchins. In contrast, our understanding of mammalian sperm chemotaxis is still rudimentary and subject to an ongoing debate. In this review, we raise new questions and discuss current concepts of sperm chemotaxis. Finally, we highlight commonalities and differences of sensory signaling in sperm, photoreceptors, and olfactory neurons.
Partial wave in human seminiferous tubules appears to be a random occurrence
Tissue Cell. 1996 Apr;28(2):127-36.
Johnson L, Mckenzie KS, Snell JR. Source Department of Veterinary Anatomy and Public Health, College Veterinary Medicine, Faculty of Toxicology, Texas A&M University, College Station 77843-4458, USA. LJohnson@VETMED.TAMU.EDU
Serial cross sections were evaluated to determine the architectural arrangement of stages among men with varied spermatogenic efficiencies. Using autopsy specimens, glutaraldehyde-perfused testes from men with low or high daily sperm production per g parenchyma were compared. Lobes of testicular parenchyma were teased from connective tissue septa, further fixed in osmium, and embedded such that the straight portions of tubules could be sectioned perpendicularly. Unstained 22 microns serial sections were sectioned optically with Nomarski optics. Paired photomicrographs of each tubular cross section were taken under a 40 x objective, and stages of the spermatogenic cycle were mapped by two observers using Clermont's criteria (Clermont, 1963). For comparison, numbers (1-6) were assigned randomly to the stages, the stages were plotted in two dimensions (length and circumference of tubule) as if the tubule were cut down its length and laid flat, and geometric centers were plotted for each stage. Geometric centers consecutive and/or non-consecutive stages appeared to form an angle down the length of the tubule. When considering helical patterns along the tubule, men with neither low nor high spermatogenic efficiency had a complete wave composed of all six consecutive stages. The helical pattern of geometric centers indicated only 2-4 consecutive stages when the actual values of stages were used or when random numbers were substituted for actual numerical value of stages. The number of consecutive stages in tubules from these men was not different from consecutiveness found when stages were assigned random numbers. Given that no complete wave was found, regardless of spermatogenic efficiency, and that the degree of consecutiveness of stages down a helical pattern in human seminiferous tubules could be generated from random numbers, the arrangement of stages in human seminiferous tubules may simply be a random occurrence.
An analysis of human sperm chromosome aneuploidy
Cytogenet Cell Genet. 1996;74(3):194-200.
Templado C, Márquez C, Munné S, Colls P, Martorell MR, Cieply K, Benet J, Van Kirk V, Navarro J, Estop AM.
Departamento de Biología Celular, Facultad de Medicina, Universidad Autónoma, Barcelona, Spain. Cristina@cc.uab.es Abstract A sperm chromosome analysis of 24 men with normal or balanced karyotypes was carried out to study the frequency of sperm chromosome aneuploidy. A total of 3,446 human sperm complements (36-315 per donor) was analyzed after in vitro penetration of hamster eggs. Two sets of donors were studied at two different centers in the United States (center 1) and Spain (center 2). The frequencies of hyperhaploidy and hypohaploidy in control donors were similar between center 1 (1.9% vs. 7.7%) and center 2 (1.8% vs. 10.3%). In carrier donors there were no significant differences between the two centers in the frequency of hyperhaploidy (0.8% vs. 1.9%), but that of hypohaploidy was significantly higher in center 2 (11.0%) than in center 1 (4.6%). A significant excess of hypohaploid complements, as compared to hyperhaploid complements, was found in both centers in both control and carrier donors. The sex ratio was similar in both centers and did not differ significantly from a 1:1 sex ratio. The larger chromosomes in the complement (1, 2, 3, 4, 5, 7, and 10) presented a significantly lower frequency of hypohaploidy, while some of the smaller chromosomes (13, 19, and 21) showed a higher frequency of hypohaploidy than expected. Chromosome 21 and the sex chromosomes showed an increase in the percentage of hyperhaploidy, as compared to other chromosomes, that was close to statistical significance (P = 0.08). Our results reflect a preferential loss of small chromosomes during slide preparation and suggest that chromosome 21 and the sex chromosomes could be more frequently involved in aneuploidy.
A comparative view of sperm ultrastructure
Fawcett DW. Biol Reprod. 1970 Jun;2:Suppl 2:90-127. PMID: 5521054
Spermatogenesis-Specific Features of the Meiotic Program in Caenorhabditis elegans
(excellent meiosis images) http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2720455/?tool=pmcentrez
Daily spermatozoal production and epididymal spermatozoal reserves of the human male
J Urol. 1980 Aug;124(2):211-5.
Amann RP, Howards SS.
- Testicular and epididymal spermatozoal reserves were determined for 11 healthy men, a vasectomized man and 12 other men.
- For healthy men testis weight (19 testes) averaged 16.9 plus or minus 1.2 gm. and daily spermatozoal production was 4.25 times 10(6) per gm. (range equals 1.4 to 6.3 times 10(6) per gm.). Based on our total sample (23 patients) 67 per cent of the men 20 to 50 years old probably produce between 45 times 10(6) and 207 times 10(6) spermatozoa per day.
- Daily spermatozoal production was normal in 1 vasectomized man. Epididymal reserves of healthy men totaled 182 times 10(6) spermatozoa per epididymis, of which 26 per cent were in the caput, 23 per cent in the corpus and 52 per cent in the cauda. The interval between any previous ejaculation and death was unknown but we assumed that these values are typical for men copulating or masturbating every 1 to 7 days. Extragonadal spermatozoal reserves totaled approximately 440 times 10(6), of which less than 225 times 10(6) would be available for ejaculation in the ductuli deferentia and caudae epididymides.
- Transit time of spermatozoa through the caput, corpus and cauda epididymidis was estimated as 0.72, 0.71 and 1.76 days.
- In a vasectomized man extragonadal reserves totaled 7 times 10(9) spermatozoa or about 75 days of production by the testes.
- Thus, spermatozoal production in man is much less efficient than in other mammals, the extragonadal reserves of spermatozoa are small and maturation of spermatozoa in the caput plus corpus epididymidis occurs in less than 2 days.
- In terms of these quantitative characteristics the reproductive capacity of man is considerably less than that of a rhesus monkey.
PMID: 6772801 http://www.ncbi.nlm.nih.gov/pubmed/6772801
Efficiency of spermatogenesis
Microsc Res Tech. 1995 Dec 1;32(5):385-422.
Department of Veterinary Anatomy and Public Health, College of Veterinary Medicine, Texas A&M University, College Station 77843-4458, USA. Abstract Spermatogenesis is a process of division and differentiation by which spermatozoa are produced in seminiferous tubules. A measure of efficiency of spermatogenesis is the estimated number of spermatozoa produced per day per gram of testicular parenchyma. This measure is not influenced by species differences in testicular size; however, it is influenced by species differences in the numerical density of germ cells and in the life spans of these cells. Seminiferous tubules are composed of somatic cells (myoid cells and Sertoli cells), and germ cells (spermatogonia, spermatocytes, and spermatids). Activity of these three germ cells divide spermatogenesis into spermatocytogenesis, meiosis, and spermiogenesis, respectively. Spermatocytegenesis involves mitotic cell division to increase the yield of spermatogenesis and to produce stem cells and primary spermatocytes. Meiosis involves duplication and exchange of genetic material and two cell divisions that reduce the chromosome number and yield four spermatids. Spermiogenesis is the differentiation of spherical spermatids into mature spermatids which are released at the luminal free surface as spermatozoa. The spermatogenic cycle is superimposed on the three major divisions of spermatogenesis. Spermatogenesis and germ cell degeneration can be quantified from numbers of germ cells in various steps of development throughout spermatogenesis, and quantitative measures are related to number of spermatozoa in the ejaculate. Germ cell degeneration occurs throughout spermatogenesis; however, the greatest impact occurs during spermatocytogenesis and meiosis. Efficiency of spermatogenesis is related to the amount of germ cell degeneration, pubertal development, season of the year, and aging of humans and animals. Number of Sertoli cells and amount of smooth endoplasmic reticulum of Leydig cells (but not Leydig cell number) are related to efficiency of spermatogenesis. In humans, efficiency of spermatogenesis is reflected in number of spermatogenic stages per cross-section and number of missing generations within each stage; however, the arrangement of stages along the tubular length does not reflect differences in the efficiency of spermatogenesis. In short, spermatogenesis involves both mitotic and meiotic cell divisions and an unsurpassed example of cell differentiation in the production of the spermatozoon, and daily sperm production per g parenchyma is a measure of its efficiency.