Fertilization

Embryology - 5 Dec 2023        Expand to Translate
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Introduction

Human Fertilization

Early Human Zygote

Fertilization is the fusion of haploid gametes, egg and sperm, to form the diploid zygote. Note though there can be subtle differences in the fertilization process which occurs naturally within the body or through reproductive technologies outside the body, the overall product in both cases is a diplod zygote. In fertilization research, after humans the mouse is the most studied species followed by domestic and farm animals. The process of fertilization involves components of, and signaling between, both sperm (spermatozoa) and egg (oocyte).

In addition to in vivo fertilization there are many new in vitro technologies related to human infertility (Assisted Reproductive Technology) and animal production somatic cell nuclear transfer (SCNT) to generate a zygote.

Note different spelling - USA spelling "fertilization", Australian spelling "fertilisation".

Some Recent Findings

Acrosin is essential for sperm penetration through the zona pellucida in hamsters PNAS February 4, 2020 117 (5) 2513-2518 "Mammalian oocytes are surrounded by the zona pellucida, a glycoprotein coat that protects the oocyte and embryo from mechanical damage during their preimplantation development within the oviduct. Fertilizing spermatozoa must penetrate the zona, but we do not know the exact mechanisms underlying this process. Sperm proteases were thought to work as zona lysins, but gene-knockout studies in mice did not support this assumption. In this study, we generated hamsters without acrosin, the major acrosomal protease, to examine its role in both in vivo and in vitro fertilization. Surprisingly, mutant male hamsters were completely infertile because their spermatozoa were unable to penetrate the zona. We thus demonstrated that, at least in hamsters, acrosin is essential for sperm penetration through the zona." OMIM - crosin Zinc sparks induce physiochemical changes in the egg zona pellucida that prevent polyspermy "During fertilization or chemically-induced egg activation, the mouse egg releases billions of zinc atoms in brief bursts known as 'zinc sparks.' The zona pellucida (ZP), a glycoprotein matrix surrounding the egg, is the first structure zinc ions encounter as they diffuse away from the plasma membrane. Following fertilization, the ZP undergoes changes described as 'hardening', which prevent multiple sperm from fertilizing the egg and thereby establish a block to polyspermy. A major event in zona hardening is cleavage of ZP2 proteins by ovastacin; however, the overall physiochemical changes contributing to zona hardening are not well understood. These results provide a paradigm-shifting model in which fertilization-induced zinc sparks contribute to the polyspermy block by altering conformations of the ZP matrix. This adds a previously unrecognized factor, namely zinc, to the process of ZP hardening."

More recent papers

This table allows an automated computer search of the external PubMed database using the listed "Search term" text link. This search now requires a manual link as the original PubMed extension has been disabled. The displayed list of references do not reflect any editorial selection of material based on content or relevance. References also appear on this list based upon the date of the actual page viewing. References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability. More? References | Discussion Page | Journal Searches | 2019 References | 2020 References Search term: Fertilization | In vitro Fertilization | Polar Body

Older papers

These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table. See also the Discussion Page for other references listed by year and References on this current page. Versatile action of picomolar gradients of progesterone on different sperm subpopulations "High step concentrations of progesterone may stimulate various sperm physiological processes, such as priming and the acrosome reaction. However, approaching the egg, spermatozoa face increasing concentrations of the hormone, as it is secreted by the cumulus cells and then passively diffuses along the cumulus matrix and beyond. ... The results suggest a versatile role of the gradual distribution of very low doses of progesterone, which selectively stimulate the priming and the acrosome reaction in different sperm subpopulations." Juno is the egg Izumo receptor and is essential for mammalian fertilization "Fertilization occurs when sperm and egg recognize each other and fuse to form a new, genetically distinct organism. The molecular basis of sperm–egg recognition is unknown, but is likely to require interactions between receptor proteins displayed on their surface. Izumo1 is an essential sperm cell-surface protein, but its receptor on the egg has not been described. Here we identify folate receptor 4 (Folr4) as the receptor for Izumo1 on the mouse egg, and propose to rename it Juno. We show that the Izumo1–Juno interaction is conserved within several mammalian species, including humans. Female mice lacking Juno are infertile and Juno-deficient eggs do not fuse with normal sperm. Rapid shedding of Juno from the oolemma after fertilization suggests a mechanism for the membrane block to polyspermy, ensuring eggs normally fuse with just a single sperm." Non-genetic contributions of the sperm nucleus to embryonic development "Recent data from several laboratories have provided evidence that the newly fertilized oocyte inherits epigenetic signals from the sperm chromatin that are required for proper embryonic development. For the purposes of this review, the term epigenetic is used to describe all types of molecular information that are transmitted from the sperm cell to the embryo. There are at least six different forms of epigenetic information that have already been established as being required for proper embryogenesis in mammals or for which there is evidence that it may do so. These are (i) DNA methylation; (ii) sperm-specific histones, (iii) other chromatin-associated proteins; (iv) the perinuclear theca proteins; (v) sperm-born RNAs and, the focus of this review; and (vi) the DNA loop domain organization by the sperm nuclear matrix. These epigenetic signals should be considered when designing protocols for the manipulation and cryopreservation of spermatozoa for assisted reproductive technology as necessary components for effective fertilization and subsequent embryo development." CD9 tetraspanin generates fusion competent sites on the egg membrane for mammalian fertilization "CD9 tetraspanin is the only egg membrane protein known to be essential for fertilization. To investigate its role, we have measured, on a unique acrosome reacted sperm brought in contact with an egg, the adhesion probability and strength with a sensitivity of a single molecule attachment. Probing the binding events at different locations of wild-type egg we described different modes of interaction. Here, we show that more gamete adhesion events occur on Cd9 null eggs but that the strongest interaction mode disappears. We propose that sperm-egg fusion is a direct consequence of CD9 controlled sperm-egg adhesion properties. CD9 generates adhesion sites responsible for the strongest of the observed gamete interaction. These strong adhesion sites impose, during the whole interaction lifetime, a tight proximity of the gamete membranes, which is a requirement for fusion to take place. The CD9-induced adhesion sites would be the actual location where fusion occurs." Gamete recognition in mice depends on the cleavage status of an egg's zona pellucida protein "sperm-egg recognition depends on the cleavage status of ZP2 and that binding at the surface of the zona is not sufficient to induce sperm acrosome exocytosis."

Objectives

The first polar body deforms the mammalian egg away from its encapsulating zona pellucida

• Understand the mechanisms of gamete formation.
• Understand the mechanisms of cell division.
• Describe the differences between mitosis and meiosis.
• Understand the mechanisms of fertilization, both in vivo and in vitro.
• Describe the cleavage of the zygote.
• Have a preliminary understanding of the role and process in male sex determination and X inactivation.
• Understand the abnormalities that occur during this period of development.

Movies

‎‎Ovulation Page | Play	‎‎Spermatozoa Page | Play	‎‎Spermatozoa Motility Page | Play	‎‎Fertilisation to 4 Blastomere Page | Play	‎‎Fertilization Page | Play
‎‎Fertilization Page | Play	‎‎Mouse Fertilisation Page | Play	‎‎Pronuclear Fusion Page | Play	‎‎Week 1 Page | Play

Fertilization Preparation

Prior to the fertilization process commencing both the gametes oocyte (egg) and spermatozoa (sperm) require completion of a number of biological processes.

• Oocyte meiosis - completes Meiosis 1 and commences Meiosis 2 (arrests at Metaphase II).
• Spermatozoa Capacitation - following release (ejaculation) and mixing with other glandular secretions, activates motility and acrosome preparation.
• Migration - both oocyte and spermatozoa.
  • oocyte ovulation and release with associated cells, from ovary into fimbria then into uterine tube (oviduct, uterine horn, fallopian tube) and epithelial cilia mediated movement.
  • spermatozoa ejaculation, deposited in vagina, movement of tail to "swim" in uterine secretions through cervix, uterine body and into uterine tube, have approximately 24-72h to fertilize oocyte.

Endocrinology - Diagram of the comparative anatomy of the male and female reproductive tracts

Oogenesis

Histology of the Ovary

Preantral Follicle

Antral Follicle and Oocyte

• Process of oogonia mature into oocytes (ova, ovum, egg)
• all oogonia form primary oocytes before birth, therefore a maturation of preexisting cells in the female gonad, ovary

• humans usually only 1 ovum released every menstrual cycle (IVF- superovulation)
• oocyte and its surrounding cells = follicle
• primary -> secondary -> ovulation releases

Ovary- Histology - whole transverse section (cortex, medulla)

Menstrual Cycle

• Primary Oocyte - arrested at early Meiosis 1
  • diploid: 22 chromosome pairs + 1 pair X chromosomes (46, XX)
  • autosomes and sex chromosome

• Oogenesis- pre-antral then antral follicle (Graafian follicle is mature antral follicle released)
• Secondary oocyte
  • 1 Day before ovulation completes (stim by LH) Meiosis 1
  • haploid: 22 chromosomes + 1 X chromosome (23, X)
  • nondisjunction- abnormal chromosome segregation
  • begins Meiosis 2 and arrests at metaphase
  • note no interphase replication of DNA, only fertilization will complete Meiosis 2

Ovulation (HPG Axis)

• Hypothalmus releases gonadotropin releasing hormone (GRH, luteinizing hormone–releasing hormone, LHRH) -> Pituitary releases follicle stimulating hormone (FSH) and lutenizing hormone (LH) -> ovary follicle development and ovulation.
  • release of the secondary oocyte and formation of corpus luteum
  • secondary oocyte encased in zona pellucida and corona radiata
• Ovulation associated with follicle rupture and ampulla movement.

Zona Pellucida

Mouse zona pellucida

zona pellucida glycoprotein shell ZP1, ZP2, ZP3, ZP4 (mouse only ZP1-3)

1. mechanical protection of egg
2. involved in the fertilization process
3. sperm binding
4. adhesion of sperm to egg
5. acrosome reaction
6. releases enzymes to locally breakdown
7. cortical granules modify to block of polyspermy
8. altered to prevent more than 1 sperm penetrating
9. mechanical protection of zygote, blastomeres, morula and blastocyst
10. role in development of the blastocyst

Links: zona pellucida | MBoC - Figure 20-21. The zona pellucida

Corona Radiata

Mouse granulosa cells

• granulosa cells and extracellular matrix
• protective and nutritional role for cells during transport
• cells are also lost during transport along oviduct

Spermatogenesis

• process of spermatagonia mature into spermatozoa (sperm)
• continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes)
• at puberty spermatagonia activate and proliferate (mitosis)
• primary spermatocyte -> secondary spermatocyte-> spermatid->sperm
• Seminiferous Tubule is site of maturation involving meiosis and spermiogenesis

• Spermatogenesis- Meiosis
• meiosis is reductive cell division
  • 1 spermatagonia (diploid) 46, XY (also written 44+XY) = 4 sperm (haploid); 23, X 23, X 23, Y 23, Y

Spermiogenesis

• morphological (shape) change from round spermatids to elongated sperm
• loose cytoplasm
• Transform golgi apparatus into acrosome (in head)
• Organize microtubules for motility (in tail, flagellum)
• Segregate mitochondria for energy (in tail)

Links: spermatozoa

Ejaculate

• Human Ejaculate
  • By volume <10 % sperm and accessory glands contribute majority of volume (60 % seminal vesicle, 10 % bulbourethral, 30 % prostate)
  • 3.5 ml, 200-600 million sperm.
• Capacitation is the removal of glycoprotein coat and seminal proteins and alteration of sperm mitochondria.
• Ovulation-inducing factor identified in several species.
• Infertility can be due to Oligospermia, Azoospermia, Immotile Cilia Syndrome
  • Oligospermia (Low Sperm Count) - less than 20 million sperm after 72 hour abstinence from sex
  • Azoospermia (Absent Sperm) - blockage of duct network
  • Immotile Cilia Syndrome - lack of sperm motility

Links: spermatozoa | prostate

Fertility Window

Probability of women with regular or irregular cycles being in their fertile window

Clinical guidelines have typically identified the "fertile window" between days 10 and 17 within the typical 28 day menstrual cycle.

Data from a large USA NIEHS - Early Pregnancy Study (1982-86) identified the timing of the “fertile window” within a range of different menstrual cycles.

• fertile window occurred during a broad range of days in the menstrual cycle.
• between days 6 and 21 women had at minimum a 10% probability of being in their fertile window.
• women cannot predict a sporadic late ovulation; 4 - 6% of women whose cycles had not yet resumed were potentially fertile in the fifth week of their cycle.
• only about 30% of women is the fertile window entirely within the days of the menstrual cycle identified by clinical guidelines (between days 10 and 17)
• most women reach their fertile window earlier and others much later.
• women should be advised that the timing of their fertile window can be highly unpredictable, even if their cycles are usually regular.

Links: menstrual cycle

Fertilization Site

Week 1

• Fertilization usually occurs in first 1/3 of oviduct
• Fertilization can also occur outside oviduct, associated with In Vitro Fertilization (IVF, GIFT, ZIFT...) and ectopic pregnancy
• The majority of fertilized eggs do not go on to form an embryo

Fertilization - Spermatozoa

• Sperm Binding - zona pellucida protein ZP2 acts as receptor for sperm
• Acrosome Reaction - exyocytosis of acrosome contents (Calcium mediated) MBoC - Figure 20-31. The acrosome reaction that occurs when a mammalian sperm fertilizes an egg
  • enzymes to digest the zona pellucida
  • exposes sperm surface proteins to bind ZP2
• Membrane Fusion - between sperm and egg, allows sperm nuclei passage into egg cytoplasm

• Contact between spermatozoa and oocyte egg coat (zona pellucida [ZP]) glycoproteins triggers increases in intracellular calcium ion (iCa²⁺) concentration in spermatozoa
• CATSPER channels on the distal portion of sperm (the principal piece) are required for the ZP-induced iCa²⁺ increases
• iCa²⁺ increase starts from the spermatozoa tail and propagates toward the head
• Store depletion-activated Ca²⁺ entry is thought to mediate the sustained phase

Fertilization - Oocyte

• Membrane Depolarization - in non-mammalian species, caused by sperm membrane fusion, acts as a primary block to polyspermy.
• Cortical Reaction - IP3 pathway elevates intracellular Calcium, exocytosis of cortical granules MBoC - Figure 20-32. How the cortical reaction in a mouse egg is thought to prevent additional sperm from entering the egg
  • enzyme alters ZP2 so it will no longer bind sperm plasma membrane
• Meiosis 2 - completion of 2nd meiotic division
  • forms second polar body (a third polar body may be formed by meiotic division of the first polar body)

Spermatozoa - Oocyte Interaction

Membrane Fusion

Spermatozoa and oocyte fusion in the membrane adhesion area requires the presence of 3 membrane proteins (spermatozoa Izumo1; oocyte receptor Juno and Cd9).

Izumo

The sperm-specific protein Izumo is named for a Japanese shrine dedicated to marriage and is essential for sperm-egg plasma membrane binding and fusion. It interacts with the spermatozoa folate receptor 4 (Folr4).

Links: OMIM 609278

Juno

folate receptor 4 (Folr4)

Folate receptors are also known as the folic acid (FA) binding protein and bind of 5-methyltetrahydrofolate (5-MeTHF).

CD9

Oocyte cell surface protein acts as a receptor for pregnancy-specific glycoprotein 17 (Psg17).

Links: OMIM 143030

Ovastacin

(Astacin-Like Metalloendopeptidase, ASTL) An oocyte enzyme (zinc-dependent metalloprotease) involved in altering zona pellucida structure, by cleaving zona pellucida glycoprotein (ZP2), following fertilisation. This change in zona pellucida structure is one of the blockers to polyspermy.

Mouse oocyte cortical granule (green) ovastacin (red) staining.

Formation of the Zygote

Early human zygote showing Pronuclei

• Pronuclei - Male and Female haploid nuclei approach each other and nuclear membranes break down
• chromosomal pairing, DNA replicates, first mitotic division

• Spermatozoa contributes - centriole which organizes mitotic spindle
• Oocyte contributes - mitochondria (maternally inherited)

Mitochondria

• Mitochondria of the spermatozoa are specifically destroyed in early development by proteolysis (mouse 4 to 8 cell transition).
• Metaphase II oocytes in rats have an average mitochondrial DNA (mtDNA) copy number of 147,600 (+/-3000) that only increases at the 8-cell stage.

Sex Determination

• based upon whether an X or Y carrying sperm has fertilized the egg, should be 1.0 sex ratio.
• actually 1.05, 105 males for every 100 females, some studies show more males 2+ days after ovulation.
• cell totipotent (equivalent to a stem cell, can form any tissue of the body)

Men - Y Chromosome

• Y Chromosome carries Sry gene, protein product activates pathway for male gonad (covered in genital development)

Women - X Chromosome

• Gene dosage, one {ChrX}} chromosome in each female embryo cell has to be inactivated
• process is apparently random and therefore 50% of cells have father's X, 50% have mother's X
• Note that because men only have 1 X chromosome, if abnormal, this leads to X-linked diseases more common in male that female where bothe X's need to be abnormal.

Fertilization Protein Changes

A recent study in mice has shown that after fertilization the maternal proteins present in the original oocyte are quickly degraded by the zygote stage. MII oocytes have 185,643 different peptides while zygotes contain only 85,369 peptides.

Protein Expression Classified by Molecular Functions

MII oocyte	Zygote

Abnormalities

The abnormalities listed below relate to genetic abnormalities resulting in infertility or occurring during fertilisation. There are of course many additional genetic abnormalities inherited and introduced by the recombined maternal and paternal genomes, other than trisomy 21 these will not be covered here. Note the sex different genes responsible shown for the examples of male and female infertility.

Male Infertility Genes

Selected genes in Male Infertility

Gene abbreviation	Name	Gene Location	Online Mendelian Inheritance in Man (OMIM)	HUGO Gene Nomenclature Committee (HGNC)	GeneCards (GCID)	Diagnosis
AURKC	Aurora kinase C	19q13.43	603495	11391	GC19P057230	Macrozoospermia
CATSPER1	Cation channel sperm-associated 1	11q13.1	606389	17116	GC11M066034	Asthenozoospermia
CFTR	Cystic fibrosis transmembrane conductance regulator	7q31.2	602421	1884	GC07P117465	Obstructive azoospermia
DNAH1	Dynein axonemal heavy chain 1	3p21.1	603332	2940	GC03P052350	Asthenozoospermia
DPY19L2	Dpy-19-like 2 gene	12q14.2	613893	19414	GC12M063558	Globozoospermia
GALNTL5	Polypeptide N-acetylgalactosaminyltransferase-like 5	7q36.1	615133	21725	GC07P151956	Asthenozoospermia
MAGEB4	MAGE family member B4	Xp21.2	300153	6811	GC0XP030260	Azoospermia
NANOS1	Nanos C2HC-type zinc finger 1	10q26.11	608226	23044	GC10P119029	Azoospermia
NR0B1	Nuclear receptor subfamily 0 group B member 1	Xp21.2	300473	7960	GC0XM030322	Azoospermia
NR5A1	Nuclear receptor subfamily 5 group A member 1	9q33.3	184757	7983	GC09M124481	Azoospermia
SOHLH1	Spermatogenesis and oogenesis-specific basic helix–loop–helix 1	9q34.3	610224	27845	C09M135693	Azoospermia
vSPATA16	Spermatogenesis-associated 16	3q26.31	609856	29935	GC03M172889	Globozoospermia
SYCE1	Synaptonemal complex central element protein 1	10q26.3	611486	28852	GC10M133553	Azoospermia
TAF4B	TATA-box binding protein-associated factor 4b	18q11.2	601689	11538	GC18P026225	Azoospermia
TEX11	Testis expressed 11	Xq13.1	300311	11733	GC0XM070528	Azoospermia
TEX15	Testis expressed 15, meiosis and synapsis associated	8p12	605795	11738	GC08M030808	Azoospermia
WT1	Wilms tumour 1	8p12	607102	12796	GC11M032365	Azoospermia
ZMYND15	Zinc-finger MYND-type containing 15	17p13.2	614312	20997	GC17P004740	Azoospermia
Table data source (table 1)    Links: fertilization | spermatozoa | testis | Male Infertility Genes | Female Infertility Genes | oocyte | ovary | Genetic Abnormalities | ART   Asthenozoospermia - (asthenospermia) term for reduced spermatozoa motility. Azoospermia - term for no spermatozoa located in the ejaculate. Globozoospermia - term for spermatozoa with a round head and no acrosome.

Female Infertility Genes

Selected Female Infertility Genes

Gene abbreviation	Name	Gene Location	Online Mendelian Inheritance in Man (OMIM)	HUGO Gene Nomenclature Committee (HGNC)	GeneCards (GCID)	Diagnosis
BMP15	Bone morphogenetic protein 15	Xp11.22	300247	1068	GC0XP050910	Primary ovarian insufficiency
CLPP	Caseinolytic mitochondrial matrix peptidase proteolytic subunit	19p13.3	601119	2084	GC19P006369	Primary ovarian insufficiency
EIF2B2	Eukaryotic translation initiation factor 2B subunit beta	14q24.3	606454	3258	GC14P075002	Primary ovarian insufficiency
FIGLA	Folliculogenesis-specific BHLH transcription factor	2p13.3	608697	24669	GC02M070741	Primary ovarian insufficiency
FMR1	Fragile X mental retardation 1	Xq27.3	309550	3775	GC0XP147912	Primary ovarian insufficiency
FOXL2	Forkhead box L2	3q22.3	605597	1092	GC03M138944	Primary ovarian insufficiency
FSHR	Follicle stimulating hormone receptor	2p16.3	136435	3969	GC02M048866	Primary ovarian insufficiency
GALT	Galactose-1-phosphate uridylyltransferase	9p13.3	606999	4135	GC09P034636	Primary ovarian insufficiency
GFD9	Growth differentiation factor 9	5q31.1	601918	4224	GC05M132861	Primary ovarian insufficiency
HARS2	Histidyl-TRNA synthetase 2, mitochondrial	5q31.3	600783	4817	GC05P141975	Primary ovarian insufficiency
HFM1	HFM1, ATP-dependent DNA helicase homolog	1p22.2	615684	20193	GC01M091260	Primary ovarian insufficiency
HSD17B4	Hydroxysteroid 17-beta dehydrogenase 4	5q23.1	601860	5213	GC05P119452	Primary ovarian insufficiency
LARS2	Leucyl-TRNA synthetase 2, mitochondrial	3p21.31	604544	17095	GC03P045405	Primary ovarian insufficiency
LHCGR	Luteinizing hormone/choriogonadotropin receptor	2p16.3	152790	6585	GC02M048647	Primary ovarian insufficiency
LHX8	LIM homeobox 8	1p31.1	604425	28838	GC01P075128	Primary ovarian insufficiency
MCM8	Minichromosome maintenance 8 homologous recombination repair factor	20p12.3	608187	16147	GC20P005926	Primary ovarian insufficiency
MCM9	Minichromosome maintenance 9 homologous recombination repair factor	6q22.31	610098	21484	GC06M118813	Primary ovarian insufficiency
NOBOX	NOBOX oogenesis homeobox	7q35	610934	22448	GC07M144397	Primary ovarian insufficiency
NOG	Noggin	17q22	602991	7866	GC17P056593	Primary ovarian insufficiency
PMM2	Phosphomannomutase 2	16p13.2	601785	9115	GC16P008788	Primary ovarian insufficiency
POLG	DNA polymerase gamma, catalytic subunit	15q26.1	174763	9179	GC15M089316	Primary ovarian insufficiency
REC8	REC8 meiotic recombination protein	14q12	608193	16879	GC14P024171	Primary ovarian insufficiency
SMC1B	Structural maintenance of chromosomes 1B	22q13.31	608685	11112	GC22M045344	Primary ovarian insufficiency
SOHLH1	Spermatogenesis and oogenesis-specific basic helix–loop–helix 1	9q34.3	610224	27845	GC09M135693	Primary ovarian insufficiency
STAG3	Stromal antigen 3	7q22.1	{{Chr 608489	11356	GC07P100177	Primary ovarian insufficiency
SYCE1	Synaptonemal Complex Central Element Protein 1	10q26.3	611486	28852	GC10M133553	Primary ovarian insufficiency
TLE6	Transducin-like enhancer of split 6	19p13.3	612399	30788	GC19P002976	Embryonic lethalithy
TUBB8	Tubulin beta 8 Class VIII	10p15.3	616768	20773	GC10M000048	Oocyte maturation arrest
TWNK	Twinkle MtDNA helicase	10q24.31	606075	1160	GC10P100991	Primary ovarian insufficiency
Table data source (table 1)    Links: fertilization | oocyte | ovary | | Female Infertility Genes | spermatozoa | testis | Male Infertility Genes | Genetic Abnormalities | ART  Primary ovarian insufficiency - depletion or dysfunction of ovarian follicles with cessation of menses before age 40 years.  Oocyte maturation arrest - arrest of human oocytes may occur at different stages of meiosis.

Complete Hydatidiform Mole

• Chromosomal genetic material from the oocyte (ovum, egg) is lost, by an unknown process.
• Fertilization then occurs with one or two spermatozoa and an androgenic (from the male only) conceptus (fertilized oocyte) is formed.
• The embryo (fetus, baby) does not develop at all but the placenta does grow.

Links: hydatidiform mole

Partial Hydatidiform Mole

Three sets of chromosomes instead of the usual two and this is called triploidy.

• chromosomal (genetic) material from the oocyte (ovum, egg) is retained and the egg is fertilized by one or two spermatozoa.
• with partial mole there are maternal chromosomes and there is a fetus.
• the three sets of chromosomes means the fetus is always grossly abnormal and will not survive.

Links: hydatidiform mole

Parthenogenesis

(Greek, parthenos = virgin, genesis = birth) The development of an unfertilized oocyte (no spermatozoa). Other than mammals, many different species (plants, insects, reptiles) can develop from unfertilized eggs. An embryo so formed without sperm contribution. Blocking of parthenogenesis in mammals appears to be related to genomic imprinting. Abnormal parthenogenic processes can occur in mammals, and more recently a parthenogenic mouse has been made in the laboratory.

Trisomy 21

Trisomy 21 (Down's or Down syndrome) is caused by nondisjunction of chromosome 21 in a parent who is chromosomally normal and is one of the most common chromosomal aneuploidy abnormalities in liveborn children. The frequency of trisomy 21 in the population is approximately 1 in 650 to 1,000 live births, in Australia between 1991-97 there were 2,358 Trisomy 21 infants. There are other less frequently occurring trisomies (Trisomy 18, Trisomy 13 and Trisomy X).

Links: Trisomy 21

References

Textbooks

• Human Embryology (2nd ed.) Larson Ch1 p1-32
• The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud
• Before we Are Born (5th ed.) Moore and Persaud Ch 2 p14-33
• Essentials of Human Embryology Larson Ch1 p1-16
• Human Embryology Fitzgerald and Fitzgerald Ch2 p8-14

Search NCBI Bookshelf fertilization | fertilisation

Reviews

Bianchi E & Wright GJ. (2016). Sperm Meets Egg: The Genetics of Mammalian Fertilization. Annu. Rev. Genet. , 50, 93-111. PMID: 27617973 DOI.

Mou L & Xie N. (2017). Male infertility-related molecules involved in sperm-oocyte fusion. J. Reprod. Dev. , 63, 1-7. PMID: 27904014 DOI.

• IJDB Vol. 52 Nos. 5/6 (2008) Fertilization

Articles

Suzuki B, Sugano Y, Ito J, Saito H, Niimura S & Yamashiro H. (2017). Location and expression of Juno in mice oocytes during maturation. JBRA Assist Reprod , 21, 321-326. PMID: 29124919 DOI.

Duncan FE, Que EL, Zhang N, Feinberg EC, O'Halloran TV & Woodruff TK. (2016). The zinc spark is an inorganic signature of human egg activation. Sci Rep , 6, 24737. PMID: 27113677 DOI.

Wilcox AJ, Weinberg CR & Baird DD. (1998). Post-ovulatory ageing of the human oocyte and embryo failure. Hum. Reprod. , 13, 394-7. PMID: 9557845

Search Pubmed

April 2010

• fertilization - All (51803) Review (5928) Free Full Text (11715)

Search Pubmed Now: fertilization | fertilisation | zona pellucida | zygote

Additional Images

• 

  Mouse - Oocyte polar body

• 

  Mouse - Spermatozoa Swims within the Previtelline space (PVS) Prior to Fertilization

External Links

External Links Notice - The dynamic nature of the internet may mean that some of these listed links may no longer function. If the link no longer works search the web with the link text or name. Links to any external commercial sites are provided for information purposes only and should never be considered an endorsement. UNSW Embryology is provided as an educational resource with no clinical information or commercial affiliation.

• PBS - First Human Eggs Fertilized in a Laboratory 1944.

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Cite this page: Hill, M.A. (2023, December 5) Embryology Fertilization. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Fertilization

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© Dr Mark Hill 2023, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G