Sry gene & Testis determining factor in Y chromosome -How they exert influences on Sertoloii cells primarily ??

 

Ans:    Sry encodes a gene-regulatory protein (Sry) that activates the transcription of other gene-regulatory proteins required for Sertoli cell development, including the Sry-related protein Sox9. 

In the absence of either Sry or Sox9, the genital ridge develops into an ovary. The supporting cells become follicle cells instead of Sertoli cells. The other somatic cells become theca cells instead of Leydig cells and, beginning at puberty secrete the female sex hormone estrogen instead of testosterone. The primordial germ cells develop into eggs instead of sperm and the fetus develops as a female.

Influence of Sry on gonad development. The germ line cells are shaded in red,and the somatic cells are shaded in green and blue. The change from light to darker color indicates that the cell has matured or differentiated. The Sry gene acts in a subpopulation 

The Y chromosome influences the sex of the individual by inducing the somatic cells of the genital ridge to develop into a testis instead of an ovary. The crucial gene on the Y chromosome that has this testis determining function is called Sry , for “sex-determining region of Y.” Remarkably, when this gene is introduced into the genome of an XX mouse zygote, the transgenic embryo produced develops as a male, even though it lacks all of the other genes on the Y chromosome. Such mice, however, cannot produce sperm, in part, at least, because the presence of two X chromosomes suppresses sperm development.

 

The Sry gene, injected into the nucleus of an XX female zygote, caused the transgenic embryo produced to develop into a male. The external genitalia of the transgenic mouse are indistinguishable from those of a normal XY male mouse.

Sry is expressed only in a subset of the somatic cells of the developing gonad, and it causes these cells to differentiate into Sertoli cells, which are the main type of supporting cells found in the testis. The Sertoli cells direct sexual development along a male pathway by affecting other cells in the genital ridge in at least four ways:

 

They stimulate the newly arriving primordial germ cells of male foetus to develop along a pathway that produces sperm.

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They secrete anti-Müllerian hormone, which suppresses the development of the female reproductive tract by causing the Müllerian duct to regress (this duct otherwise gives rise to the oviduct, uterus, and upper part of the vagina).

They stimulate particular somatic cells that lie adjacent to the developing gonad to migrate into the gonad and form critical connective tissue structures that are required for normal sperm production.

They help to induce other somatic cells in the developing gonad to become Leydig cells, which secrete the male sex hormone testosterone; this hormone is responsible for inducing all male secondary sexual characteristics. These include the structures of the male reproductive tract, such as the prostate and seminal vesicles, which develop from another duct, called the Wolffian duct system.

What happens in female?? Ans:  This duct system degenerates in the developing female because it requires testosterone to survive and develop. The testosterone also masculinizes the early developing brain and thereby plays a major part in determining male sexual identity and orientation, and thereby behavior: female rats that are treated with testosterone around birth, for example, later display male like sexual behavior.