A personal message from Dr Mark Hill (May 2020) contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!

Introduction

Urogenital Male

The male and female reproductive systems develop initially "indifferently", it is the product of the Y chromosome SRY gene that makes the "difference".



The paired mesonephric ducts (Wolffian ducts) contributes the majority of male internal genital tract.



Embryonic gonad development leads to the mesonephric/paramesonephric duct changes, while the external genitaila remain indeterminate in appearance through to the fetal period.



Importantly its sex chromosome dependence, late embryonic/fetal differential development, complex morphogenic changes, long time-course, hormonal sensitivity and hormonal influences make it a system prone to many different abnormalities.



There are also separate pages describing: Y Chromosome | spermatozoa | testis | epididymis | ductus deferens | prostate | penis | Category:Male



Historic Embryology Caspar Friedrich Wolff (1734-1794) was a German embryologist and anatomist best known today for identifying the Wolffian duct (mesonephric duct; ductus deferens, epididymis), Wolffian body (mesonephros) and Wolffian cyst (mesonephric origin uterine broad ligament cyst) that bear his name. Thought also to be a founder of the germ layer theory. His doctorate dissertation Theoria generationis (1774) discarded the developmental theory of preformation. Later in his career, his teaching in Berlin was opposed by the professors of the Medical-Surgical College, who had guild privileges to teach medicine.





Some Recent Findings

[1] Model male second trimester androsterone synthesis

Alternative (backdoor) androgen production and masculinization in the human fetus[1] "Masculinization of the external genitalia in humans is dependent on formation of 5α-dihydrotestosterone (DHT) through both the canonical androgenic pathway and an alternative (backdoor) pathway. The fetal testes are essential for canonical androgen production, but little is known about the synthesis of backdoor androgens, despite their known critical role in masculinization. ...Results show that androsterone is the principal backdoor androgen in the male fetal circulation and that DHT is undetectable (<1 ng/mL), while in female fetuses, there are significantly lower levels of androsterone and testosterone. In the male, intermediates in the backdoor pathway are found primarily in the placenta and fetal liver, with significant androsterone levels also in the fetal adrenal. Backdoor intermediates, including androsterone, are only present at very low levels in the fetal testes. This is consistent with transcript levels of enzymes involved in the alternate pathway (steroid 5α-reductase type 1 [SRD5A1], aldo-keto reductase type 1C2 [AKR1C2], aldo-keto reductase type 1C4 [AKR1C4], cytochrome P450 17A1 [CYP17A1]), as measured by quantitative PCR (qPCR). These data identify androsterone as the predominant backdoor androgen in the human fetus and show that circulating levels are sex dependent, but also that there is little de novo synthesis in the testis. Instead, the data indicate that placental progesterone acts as substrate for synthesis of backdoor androgens, which occurs across several tissues. Masculinization of the human fetus depends, therefore, on testosterone and androsterone synthesis by both the fetal testes and nongonadal tissues, leading to DHT formation at the genital tubercle. Our findings also provide a solid basis to explain why placental insufficiency is associated with disorders of sex development in humans." Alterations of sex determination pathway in the genital ridges of males with limited Y chromosome genes[2] "We previously demonstrated that in the mouse only two Y chromosome genes are required for a male to produce an offspring with the help of assisted reproduction technologies (ART): testis determinant Sry and spermatogonial proliferation factor Eif2s3y. Subsequently, we have shown that the function of these genes can be replaced by transgenic overexpression of their homologues, autosomally encoded Sox9 and X-chromosome encoded Eif2s3x. Males with Y chromosome contribution limited to two (XEif2s3yOSry), one (XEif2s3yOSox9 and XOSry, Eif2s3x) and no genes (XOSox9, Eif2s3x) produced haploid germ cells and sired offspring after ART. However, despite successful assisted reproductive outcome, they had smaller testes and displayed abnormal development of the seminiferous epithelium and testicular interstitium. Here we explored whether these testicular defects originated from altered pro-testis and pro-ovary factor signaling in genital ridges at the time of sex determination."



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. Tissue-specific roles of Fgfr2 in development of the external genitalia[3] "Congenital anomalies frequently occur in organs that undergo tubulogenesis. Hypospadias is a urethral tube defect defined by mislocalized, oversized, or multiple openings of the penile urethra. Deletion of Fgfr2 or its ligand Fgf10 results in severe hypospadias in mice, in which the entire urethral plate is open along the ventral side of the penis. In the genital tubercle, the embryonic precursor of the penis and clitoris, Fgfr2 is expressed in two epithelial populations: the endodermally derived urethral epithelium and the ectodermally derived surface epithelium. Here, we investigate the tissue-specific roles of Fgfr2 in external genital development by generating conditional deletions of Fgfr2 in each of these cell types. These results demonstrate that urethral tubulogenesis, prepuce morphogenesis, and sexually dimorphic patterning of the lower urethra are controlled by discrete regions of Fgfr2 activity." Fibroblast Growth Factor Penile biometry on prenatal MR imaging [4]"Mean length values, including 95% confidence intervals and percentiles, were defined. Penile length as a function of gestational age was expressed by the regression equation: outer mean length= -5.514 + 0.622 *, and total mean length= -8.865 + 1.312 * (*= gestational weeks). The correlation coefficients were statistically significant (p < .001). The comparison between outer length on MRI and US data showed no significant differences, whereas total length on MRI and US data demonstrated significant differences (p< .001)." penis Male reproductive tract abnormalities: More common after assisted reproduction?[5] "IVF and ICSI, by increasing the risks of prematurity, low birthweight, and multiple gestation, are indirect risk factors for developing male genital malformations. In infants with normal birhtweight or from singleton pregnancies, ICSI is a specific risk factor for hypospadias." Temporal and spatial dissection of Shh signaling in genital tubercle development.[6] "Genital tubercle (GT) initiation and outgrowth involve coordinated morphogenesis of surface ectoderm, cloacal mesoderm and hindgut endoderm. GT development appears to mirror that of the limb. Although Shh is essential for the development of both appendages, its role in GT development is much less clear than in the limb. Here, by removing Shh at different stages during GT development in mice, we demonstrate a continuous requirement for Shh in GT initiation and subsequent androgen-independent GT growth." Bmp7 expression and null phenotype in the urogenital system suggest a role in re-organization of the urethral epithelium. [7] "Signaling by Bone morphogenetic proteins (Bmps) has multiple and diverse roles in patterning and morphogenesis of the kidney, eye, limbs and the neural tube. ...Together, our analysis of Bmp7 expression and the null phenotype, indicates that Bmp7 may play an important role in re-organization of the epithelium during cloacal septation and morphogenesis of the genital tubercle."

Textbooks

Historic drawing of the testis

Human Embryology (2nd ed.) Larson Chapter 10 p261-306

(2nd ed.) Larson Chapter 10 p261-306 The Developing Human: Clinically Oriented Embryology (6th ed.) Moore and Persaud Chapter 13 p303-346

(6th ed.) Moore and Persaud Chapter 13 p303-346 Before We Are Born (5th ed.) Moore and Persaud Chapter 14 p289-326

(5th ed.) Moore and Persaud Chapter 14 p289-326 Essentials of Human Embryology , Larson Chapter 10 p173-205

, Larson Chapter 10 p173-205 Human Embryology , Fitzgerald and Fitzgerald Chapter 21-22 p134-152

, Fitzgerald and Fitzgerald Chapter 21-22 p134-152 Developmental Biology (6th ed.) Gilbert Chapter 14 Intermediate Mesoderm





Movies

‎‎Testis Page | Play ‎‎Urogenital Septum Page | Play ‎‎Male External Page | Play ‎‎Testis Descent Page | Play ‎‎Gonad Vascular Page | Play

Mouse Primordial Germ Cell Migration ‎‎Germ Cell E9.0 Page | Play ‎‎Germ Cell E9.5 Page | Play ‎‎Germ Cell E10.5 Page | Play

Development Overview

Three main stages during development, mesonephric/paramesonephric duct changes are one of the first male/female differences that occur in development, while external genitaila remain indeterminate in appearance for quite a while.

Differentiation of gonad (Sex determination) Differentiation of internal genital organs Differentiation of external genital organs

The 2nd and 3rd stages dependent on endocrine gonad. Reproductive development has a long maturation timecourse, begining in the embryo and finishing in puberty. (More? Puberty Development)

Historic Images of Genital Changes

Urogenital indifferent Urogenital male Urogenital female

SRY

Sry (sex-determining region on the Y chromosome) gene was found in 1990 on the Y and the first SOX gene identified, the sry gene encodes a "testis-determining factor" a 204aa protein (Mr 23884 Da).

Sry acts as a transcriptional activator (HMG type-high mobility group) binding to DNA and initiating male sex determination then regulating male development. The protein sequence is shown on this current page and the full genebank entry can also be seen. The sry protein has a HMG box that binds DNA by intercalating in the minor groove. Read about the mapping of the testis determining factor which is SRY.

The actual gene targets of SRY are still being determined but at least one downstream gene Sox9 has been identified. Another gene Dax1 (nuclear hormone-receptor superfamily member) when expressed as a transgene will antagonize Sry and also force dosage-sensitive sex reversal.



Mouse sex determination genes[8]









SRY Nuclear Import

A model for nuclear import of SRY from normal males and XY females.[9]

The distinct nuclear localization signals (NLSs) of SRY use different import pathways.

cNLS - recognized by IMPβ, docks the transport complex at the nuclear pore complex (NPC) and is then translocation through. After nuclear entry of the complex, RanGTP binds to IMPβ to trigger release of SRY; DNA binding by SRY may also facilitate the release process.

nNLS - mediates nuclear import through a novel pathway not utilizing conventional nuclear import factors such as IMPs but an unidentified "transport factor" (TF) suggested to be calcium-calmodulin.

Sry Target Genes

Cerebellin 4 precursor (Cbln4) - encodes a secreted protein expressed in Sertoli cells in the developing gonad.[10]

Androgen receptor - SRY interacts with and negatively regulates this receptor transcriptional activity.[11]





Gonad - Testis

See the detailed notes on testis development.

Internal Genital

Mesonephric duct or Wolffian duct differentiates to form the male internal genital tract the vas deferens (ductus deferens, vas deferens or simply vas). Associated with the duct are the male prostate and accessory glands.

Human Mesonephric Duct position (week 6 to 11) Schematic representations of the descent of the mesonephric duct (Wolffian duct, WD) or vas deferens. Anterior view.[12]

6 weeks - (A) the WD opens to the urogenital sinus at a site adjacent to the ureteral orifice (UR).

7–8 weeks - (B, C) rather than descent, there are individual variations in the WD position along the mediolateral axis as well as in left/right difference in morphology of the urogenital sinus (URS). The future bladder and urethra are not discriminated in the sinus.

8–9 weeks - the bilateral upper angles (arrows) of the URS start upward growth toward the umbilicus.

9 weeks - (D) depending on development of smooth muscles in the bladder as well as rhapdosphincter muscles of the urethra (RS), the descent of the vas deferens becomes evident. However, the epithelium is still same (arrowheads) between the future bladder and urethra.

10–11 weeks - (E) a drastic upward growth of bladder smooth muscles as well as a developing prostate (PR) accelerates the descent of the vas.

Adult Ductus deferens Adult Prostate Human prostate histology Corpora Amylacea Submucosal gland (adult, low power overview) (adult, detail) (adult, high power detail)

External Genital

Historic diagram of external development (male left)

external genitalia are initially identical and undergo male and female differentiation under the influence or absence of steroidal sex hormones.

Indifferent stage ‐ cloaca divided by proliferating mesenchyme forming the urorectal septum which separates the ventral urogenital sinus from the dorsal rectum.

Difference stage ‐ locally in this region the presence or absence of dihydrotestosterone (DHT), generated from testosterone, determines male/female development.

Testosterone

Dihydrotestosterone

Hormones

Anti-Müllerian Hormone

Anti-Müllerian Hormone (AMH, Müllerian Inhibiting Substance, MIS, Müllerian Inhibiting Factor, MIF) is a secreted glycoprotein factor of the transforming growth factor-beta, TGF-beta superfamily, that regulates gonadal and genital tract development. (Gene locus 19p13.3)

In the male embryo, the Sertoli cell secrete AMH and inhibit paramesonephric (Mullerian) duct development. This secreted hormone also acts to differentiate the Leydig cells (interstitial cells).

Ligand of TGF-beta (transforming growth factor-beta) superfamily and receptor binds to the anti-Mullerian hormone receptor type 2. Signalling pathway activate SMAD family transcription factors that regulate gene expression.

In postnatal males, AMH increases during the first month, reaching peak level at 6 months of age, and then slowly declines during childhood falling to low levels in puberty.



In reproductive age women, AMH is produced in the ovary by the granulosa cells surrounding preantral and small antral follicles and serum levels may reflect the remaining follicle cohort and decrease with age.

Sertoli cells release mainly a prohormone (proAMH), that is cleaved by subtilisin/kexin-type proprotein convertases or serine proteinases. The cleaved protein forms a stable complex (AMHN,C). Therefore the circulating AMH is a mixture of proAMH and AMHN,C. It has been suggested that proAMH may be activated within the gonads and also by its endocrine target-cells.



Preproprotein proteolytically processed to generate N- and C-terminal cleavage products, that homodimerize and associate to form a biologically active noncovalent complex. (see Protein Atlas)





Male testosterone and AMH levels

Ovary AMH

During ovary follicle development, the granulosa cells secrete AMH and it may have a role in follicular recruitment and development.[14] and may also function in postnatal elevation of FSH secretion in females.[15]

Other AMH Tissues

The placenta has also been shown to both synthesise AMH and express its receptors. [16]

AMH receptors have been identified in both the pituitary and brain.[15]



Links: TGF-beta | OMIM - AMH

Dihydrotestosterone (DHT)

Male presence of Dihydrotestosterone (DHT, 5α-dihydrotestosterone, androstanolone, 5α-androstan-17β-ol-3-one). locally in this region leads to genital tubercle growth, form

genital folds (urethral) initial maintenance and then fusion, forming perineal and penile raphe.

labioscrotal swellings become the scrotum.









Histology





Androgen and Digit ratio (2D:4D)

Androgen and Digit ratio (2D:4D

The ratio of 2nd and 4th finger (D, digit) length. This ratio has been suggested to relate to high fetal testosterone concentration (males have lower 2D:4D than females) and has been shown for several species.[17] Although a study in mice has not shown the same correlation.[18] There have been some suggestions that the ratio may also be an indicator of various neurological abnormalities.

To measure (2D:4D) - using your right hand palm up, measure the index finger (2) and ring finger (4) length from palm to tip. Dividing the index finger by the ring finger gives the 2D:4D ratio, average women ratio is 1, average men is 0.98.

Additional Images

Stages of primordial germ cell migration

References

1.0 1.1 PLoS Biol. , 17, e3000002. PMID: DOI. O'Shaughnessy PJ, Antignac JP, Le Bizec B, Morvan ML, Svechnikov K, Söder O, Savchuk I, Monteiro A, Soffientini U, Johnston ZC, Bellingham M, Hough D, Walker N, Filis P & Fowler PA. (2019). Alternative (backdoor) androgen production and masculinization in the human fetus., e3000002. PMID: 30763313 ↑ Biol. Reprod. , , . PMID: DOI. Ortega EA, Salvador Q, Fernandez M & Ward MA. (2018). Alterations of sex determination pathway in the genital ridges of males with limited Y chromosome genes., . PMID: 30285093 ↑ Development , 142, 2203-12. PMID: DOI. Gredler ML, Seifert AW & Cohn MJ. (2015). Tissue-specific roles of Fgfr2 in development of the external genitalia., 2203-12. PMID: 26081573 ↑ Seishin Shinkeigaku Zasshi , 94, 864-73. PMID: Ishiguro T, Tamagawa S & Ogawa H. (1992). [Changes of pupil size in brain death patients]., 864-73. PMID: 1484906 ↑ Early Hum. Dev. , 86, 547-50. PMID: DOI. Funke S, Flach E, Kiss I, Sándor J, Vida G, Bódis J & Ertl T. (2010). Male reproductive tract abnormalities: more common after assisted reproduction?., 547-50. PMID: 20674196 ↑ Development , 136, 3959-67. PMID: DOI. Lin C, Yin Y, Veith GM, Fisher AV, Long F & Ma L. (2009). Temporal and spatial dissection of Shh signaling in genital tubercle development., 3959-67. PMID: 19906863 ↑ Gene Expr. Patterns , 9, 224-30. PMID: DOI. Wu X, Ferrara C, Shapiro E & Grishina I. (2009). Bmp7 expression and null phenotype in the urogenital system suggest a role in re-organization of the urethral epithelium., 224-30. PMID: 19159697 ↑ Genome Biol. , 13, 242. PMID: DOI. de Lau WB, Snel B & Clevers HC. (2012). The R-spondin protein family., 242. PMID: 22439850 ↑ Proc. Natl. Acad. Sci. U.S.A. , 100, 7045-50. PMID: DOI. Harley VR, Layfield S, Mitchell CL, Forwood JK, John AP, Briggs LJ, McDowall SG & Jans DA. (2003). Defective importin beta recognition and nuclear import of the sex-determining factor SRY are associated with XY sex-reversing mutations., 7045-50. PMID: 12764225 ↑ Biol. Reprod. , 80, 1178-88. PMID: DOI. Bradford ST, Hiramatsu R, Maddugoda MP, Bernard P, Chaboissier MC, Sinclair A, Schedl A, Harley V, Kanai Y, Koopman P & Wilhelm D. (2009). The cerebellin 4 precursor gene is a direct target of SRY and SOX9 in mice., 1178-88. PMID: 19211811 ↑ J. Biol. Chem. , 276, 46647-54. PMID: DOI. Yuan X, Lu ML, Li T & Balk SP. (2001). SRY interacts with and negatively regulates androgen receptor transcriptional activity., 46647-54. PMID: 11585838 ↑ Anat Cell Biol , 49, 231-240. PMID: DOI. Jin ZW, Abe H, Hinata N, Li XW, Murakami G & Rodríguez-Vázquez JF. (2016). Descent of mesonephric duct to the final position of the vas deferens in human embryo and fetus., 231-240. PMID: 28127497 ↑ PLoS ONE , 6, e24152. PMID: DOI. Pang K, Ryan JF, Baxevanis AD & Martindale MQ. (2011). Evolution of the TGF-β signaling pathway and its potential role in the ctenophore, Mnemiopsis leidyi., e24152. PMID: 21931657 ↑ J. Endocrinol. , 226, R45-57. PMID: DOI. McLennan IS & Pankhurst MW. (2015). Anti-Müllerian hormone is a gonadal cytokine with two circulating forms and cryptic actions., R45-57. PMID: 26163524 15.0 15.1 Sci Rep , 6, 23790. PMID: DOI. Garrel G, Racine C, L'Hôte D, Denoyelle C, Guigon CJ, di Clemente N & Cohen-Tannoudji J. (2016). Anti-Müllerian hormone: a new actor of sexual dimorphism in pituitary gonadotrope activity before puberty., 23790. PMID: 27030385 ↑ Placenta , 36, 731-7. PMID: DOI. Novembri R, Funghi L, Voltolini C, Belmonte G, Vannuccini S, Torricelli M & Petraglia F. (2015). Placenta expresses anti-Müllerian hormone and its receptor: Sex-related difference in fetal membranes., 731-7. PMID: 25972076 ↑ Reprod. Biol. Endocrinol. , 4, 10. PMID: DOI. McIntyre MH. (2006). The use of digit ratios as markers for perinatal androgen action., 10. PMID: 16504142 ↑ PLoS ONE , 4, e5801. PMID: DOI. Yan RH, Bunning M, Wahlsten D & Hurd PL. (2009). Digit ratio (2Dratio4D) differences between 20 strains of inbred mice., e5801. PMID: 19495421





Reviews

Cohn MJ. (2011). Development of the external genitalia: conserved and divergent mechanisms of appendage patterning. Dev. Dyn. , 240, 1108-15. PMID: 21465625 DOI.

Larney C, Bailey TL & Koopman P. (2014). Switching on sex: transcriptional regulation of the testis-determining gene Sry. Development , 141, 2195-205. PMID: 24866114 DOI.

Rey RA & Grinspon RP. (2011). Normal male sexual differentiation and aetiology of disorders of sex development. Best Pract. Res. Clin. Endocrinol. Metab. , 25, 221-38. PMID: 21397195 DOI.

Biason-Lauber A. (2010). Control of sex development. Best Pract. Res. Clin. Endocrinol. Metab. , 24, 163-86. PMID: 20541146 DOI.

Koopman P. (2010). The delicate balance between male and female sex determining pathways: potential for disruption of early steps in sexual development. Int. J. Androl. , 33, 252-8. PMID: 19845801 DOI.

Wilhelm D, Palmer S & Koopman P. (2007). Sex determination and gonadal development in mammals. Physiol. Rev. , 87, 1-28. PMID: 17237341 DOI.

Sharpe RM. (2006). Pathways of endocrine disruption during male sexual differentiation and masculinization. Best Pract. Res. Clin. Endocrinol. Metab. , 20, 91-110. PMID: 16522522 DOI.

Warne GL & Kanumakala S. (2002). Molecular endocrinology of sex differentiation. Semin. Reprod. Med. , 20, 169-80. PMID: 12428197 DOI.

Adham IM, Emmen JM & Engel W. (2000). The role of the testicular factor INSL3 in establishing the gonadal position. Mol. Cell. Endocrinol. , 160, 11-6. PMID: 10715534

Hiort O & Holterhus PM. (2000). The molecular basis of male sexual differentiation. Eur. J. Endocrinol. , 142, 101-10. PMID: 10664515

Articles

Chawengsaksophak K, Svingen T, Ng ET, Epp T, Spiller CM, Clark C, Cooper H & Koopman P. (2012). Loss of Wnt5a disrupts primordial germ cell migration and male sexual development in mice. Biol. Reprod. , 86, 1-12. PMID: 21900680 DOI.

Cools M, Wolffenbuttel KP, Drop SL, Oosterhuis JW & Looijenga LH. (2011). Gonadal development and tumor formation at the crossroads of male and female sex determination. Sex Dev , 5, 167-80. PMID: 21791949 DOI.





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Search Pubmed: Male Genital System Development | mesonephric duct

Terms

mesonephric duct - (Wollfian duct) An early developing urogenital paired duct system that initially runs the length of the embryo, that will differentiate and form the male reproductive duct system (ductus deferens). In females, this duct degenerates occasionally some remnants may remain associated in broad ligament.

Wolffian duct - (mesonephric duct, preferred terminology), A developmental duct that runs from the mesonephros to cloaca. The duct in male differentiates to form the ductus deferens and in female the same structure regresses. Historically named after Caspar Friedrich Wolff (1733-1794), a German scientist and early embryology researcher and is said to have established the doctrine of germ layers. (More? Caspar Friedrich Wolff)









Cite this page: Hill, M.A. (2020, September 18) Embryology Genital - Male Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Genital_-_Male_Development