Testis Development
Introduction
The male gonad is the testis. The initial difference in male and female gonad development are dependent on testis-determining factor (TDF) the protein product of the Y chromosome SRY gene. Recent studies have indicated that additional factors may also be required for full differentiation. Within the developing testis the three main differentiating cell types are: gamete forming cells (spermatogonia), support cells (Sertoli cells) and hormone secreting cells (Leydig or interstitial cells).
The seminiferous tubules are considered the parenchyma of the testis.
| Y Chromosome | Puberty | original page
Some Recent Findings
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Development Overview
Sex Determination
- Humans (week 5-6)
- Germ cells migrate into gonadal ridge
- Gonads (male/female) identical at this stage, Indifferent
Gonad Development
- dependent on sex chromosome
- Y testes
- No Y ovary
SRY
SRY protein (Testes determining factor, TDF) binds DNA Transcription factor, Bends DNA 70-80 degrees
Internal Genital Organs
- All embryos form paired
- Mesonephric duct, see kidney development
- Paramesonephric duct, Humans 7th week Invagination of coelomic epithelium Cord grows and terminates on urogenital sinus
- Male Gonad (testes) secretes Mullerian duct inhibitory factor (MDIF) which causes regression of paramesonephric duct
- Male Gonad (testes) secretes Testosterone which retains mesonephric duct
External Genital Organs
- All embryos initially same (indifferent)
- Testosterone differentiates male
Sertoli Cells
These are the support cells located within the seminiferous tubule. Their differentiation is regulated by the presence of a Y chromosome and in turn regulates Leydig cell differentiation. At puberty the immature Sertoli cells cease to proliferate and differentiate.
Molecular factors: Follicle Stimulating Hormone (FSH) -> Krüppel-like factor 4 (KLF4)
Krüppel-like factor 4 (KLF4) - zinc finger transcription factor, terminal differentiation of epithelial cells.
Epidermal Growth Factor (EGF)
Transforming Growth Factor-beta (TGFbeta)
Leydig Cells
Interstitial or Leydig cells, named after german zoologist Franz von Leydig (1821 - 1908).
These cells produce the male testicular androgens and have a role during life prenatally (fetal) and postnatally during puberty onward.
Fetal Leydig Cells
Have a hormonal role in male genitalia differentiation and are lost postnatally. These cells arise approximately at 6 weeks (human) and 12.5 dpc (mouse) and there appears to be differences in hormonal sensitivity between the species. Their initial differentiation requires both luteinizing hormone (LH) and adrenocorticotrophic hormone (ACTH) and therefore normal pituitary development.
(More? Endocrine - Pituitary Development)
Adult Leydig Cells
Have a hormonal role in puberty, secondary sex characteristics and sexual maturation. Their initial differentiation from peritubular mesenchymal cells does not require gonadotropin, but development and function are dependent upon luteinizing hormone (LH).
The cells differentiate with three discrete stages (newly formed, immature, mature) leading to a decrease in proliferation and increasing testosterone biosynthetic capacity. Insulin-like growth factor I (IGF-I) stimulates proliferation of immature cells and promotes their maturation. Testosterone and estrogen inhibit the process of precursor cell differentiation and may be responsible for the cessation of proliferation in the adult Leydig cells.
Testis Descent
Before Descent | End of Descent | Testis Descent Movie |
Puberty
In humans at puberty, hormonal and morphological changes occur within the gonad and other systems (secondary sex characteristics). Within the testis the immature Sertoli cells cease to proliferate and differentiate. Spermatogonium proliferate and spermatogenesis begins, and it takes about 70 days for cells to mature from the diploid spermatogonium to a primary spermatocyte. This maturation occurs in waves along the seminiferous tubules.
Links: Puberty Development
References
- ↑ <pubmed>20040496</pubmed>
Reviews
Articles
<pubmed>20664245</pubmed> <pubmed>20610195</pubmed>
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| Y Chromosome | Week 1 - Spermatogenesis | Ovary | Puberty | original page
Cite this page: Hill, M.A. (2024, May 21) Embryology Testis Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Testis_Development
- © Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G