- The mammalian genital ridge is bipotential. Which one of the following statements regarding determination of the fate of genital ridge is INCORRECT?
(1) The activation of Sox9 gene promotes testis determining pathway.
(2) The accumulation of β-catenin is critical for activating ovarian development.
(3) R-spondin 1 (Rspo1) stimulates the Disheveled protein, thus promoting testis determining
pathway.
(4) Though Wnt4 is expressed in the bipotential gonads, it is an important factor in ovary determination.
Introduction to the Bipotential Genital Ridge
In mammals, the genital ridge is initially bipotential, meaning it has the ability to differentiate into either a testis (male gonad) or an ovary (female gonad). The fate of this ridge depends on a tightly regulated interplay of genes and signaling pathways.
Correct Regulatory Factors in Sex Determination
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Sox9 Activation Promotes Testis Development:
The Sry gene on the Y chromosome triggers the expression of Sox9, a major testis-determining gene. Sox9 promotes differentiation of Sertoli cells and testis formation, a well-established principle in mammalian sex determination. -
β-Catenin Accumulation for Ovarian Development:
Stabilization and accumulation of β-catenin in the genital ridge cells promote ovarian development by activating ovary-specific gene expression and repressing testis pathways. -
Wnt4 Role in Ovary Determination:
Wnt4, expressed in bipotential gonads, is essential for female development and ovarian differentiation. It acts through the canonical Wnt/β-catenin pathway to support ovarian fate.
Incorrect Assumption Regarding R-spondin1 (Rspo1)
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The statement that R-spondin1 stimulates Disheveled protein to promote testis determination is incorrect.
-
In reality, Rspo1 acts upstream in the Wnt/β-catenin signaling pathway to promote ovarian development, not testis development.
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Rspo1 stabilizes β-catenin, facilitating the female pathway, opposing the testis-promoting Sox9 pathway.
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Disheveled is a cytoplasmic protein involved in Wnt signaling but its activation by Rspo1 promotes ovary differentiation rather than testis formation.
Summary of Correct vs Incorrect Statements
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(1) Sox9 promotes testis pathway — Correct
-
(2) β-catenin accumulation critical for ovarian development — Correct
-
(3) Rspo1 stimulates Disheveled to promote testis pathway — Incorrect
-
(4) Wnt4 important for ovary determination — Correct
Conclusion
The incorrect statement regarding determination of the fate of the mammalian bipotential genital ridge is:
(3) R-spondin 1 (Rspo1) stimulates the Disheveled protein, thus promoting testis determining pathway.
Rspo1 and Disheveled rather promote ovarian development.
Final Answer:
(3) R-spondin 1 (Rspo1) stimulates the Disheveled protein, thus promoting testis determining pathway. -
