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#SRY gene

8 public questions tagged with this topic.

Sex determination-l

Which transcription factor is activated by the SRY gene in mammals?

Sry encodes HMG-domain architectural transcription factor that does not itself complete Sertoli differentiation but initiates cascade by binding Sox9 testis-specific enhancer TESCO cooperatively with Sf1/Nr5a1. Protein induces DNA bending facilitating recruitment of coactivators, chromatin remodeling and sustained Sox9 transcription sufficient to commit supporting lineage. Sox9 fulfills most male functions including Fgf9, Amh induction and cord formation. Therefore immediate direct transcriptional target downstream of Sry is Sox9, functioning as hub for testis program. Other factors like Wnt4 and Foxl2 belong to opposing pathway suppressed.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: SRY activates SOX9 as primary target.

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Sex determination-l

In mammals, the presence of the Y chromosome leads to the development of:

Mammalian Y chromosome harbors Sry gene considered testis-determining factor. Presence of Y means presence of Sry whose timely expression in genital ridge precursors between six to seven weeks upregulates Sox9 in pre-Sertoli cells, activating Fgf9 loop, testis cord formation, anti-Müllerian hormone secretion and testosterone synthesis from Leydig cells. Wolffian ducts thus persist while Müllerian ducts regress, generating male phenotype. Absence leaves ovarian pathway established via Wnt4/Rspo1/β-catenin directing ovary formation. Therefore presence of Y chromosome leads anatomically and molecularly to development of testes in normal mammals.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Y chromosome and SRY in testis determination.

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sex determination-ll

Absence of SRY gene results in:

Absence of functional SRY in mammalian embryos prevents activation of testis pathway. Without Sry-mediated upregulation, Sox9 remains low, Fgf9 amplification loop fails, pre-Sertoli cells do not form and Amh and Dhh never expressed. Consequently antagonistic ovarian pathway driven by Wnt4, Rspo1, β-catenin and Foxl2 prevails, directing supporting lineage toward granulosa cells, allowing germ cells to enter meiosis and forming ovary with cortex-medulla organization. XY individuals with SRY deletions or loss-of-function mutations therefore develop as phenotypic females, while normal XX gonads naturally follow ovarian trajectory.

Ref: Alberts, Molecular Biology of the Cell, Chapter 22: Absence of SRY allows ovarian differentiation.

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sex determination-ll

The product of the SRY gene directly activates:

Sry gene on Y chromosome encodes HMG-box transcription factor transiently expressed in XY genital ridges between 10.5-12.5 days in mice. Protein binds with Sf1 and Wt1 to testis-specific enhancer element TESCO upstream of Sox9, causing chromatin bending, recruitment of coactivators and dramatic Sox9 transcriptional upregulation. Immediate induction commits pre-supporting cells to Sertoli lineage, initiating Amh expression, testis cord morphogenesis and repression of ovarian genes. No other autosomal genes are directly activated by Sry in this manner; Wnt4 and Foxl2 lie in opposing pathway actively suppressed following Sox9 induction.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Sry activates Sox9 enhancer TESCO.

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sex determination-ll

Which gene is crucial for testis determination pathway in mammals?

Testis determination in mammals absolutely requires Sox9, an HMG-box transcription factor functioning downstream of Sry. Sry expressed briefly in XY supporting precursors binds testis-specific enhancer TESCO together with Sf1 to trigger Sox9 transcriptional surge. Sox9 then establishes feed-forward loops with Fgf9 and prostaglandin D2, autoregulates, represses ovarian Wnt4/β-catenin pathway, activates Dhh, Amh, Sox8 and extracellular matrix genes driving testis cord formation. Loss-of-function XY gonads develop as ovaries, while ectopic Sox9 in XX gonads induces complete testes without Sry, proving central indispensability.

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 6: Sox9 and Sry in testis differentiation.

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Fertilization in mammals-lll

Absence of SRY gene results in:

SRY gene on Y chromosome encodes testis-determining factor transcription factor initiating male cascade. SRY upregulates SOX9 via SF1 synergy in bipotential gonad, driving Sertoli differentiation, AMH secretion and Leydig testosterone synthesis promoting Wolffian development and testis morphogenesis. In XX individuals lacking SRY, absence of SOX9 upregulation allows ovarian pathway via WNT4, RSPO1, FOXL2 activation leading to granulosa differentiation and ovary formation. Thus default or more accurately alternative WNT-driven pathway yields ovary when SRY absent. Absence does not cause testis, hermaphroditism or absolute sterility per se but leads to female differentiation; secondary infertility factors depend on karyotype.

Ref: Larney et al., Sex Dev 2014: SRY-SOX9 testis pathway versus WNT4-RSPO1 ovary pathway and gonadal sex determination.

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