Sexual Differentiation
"The process of development of the differences between males and females from an undifferentiated zygote." (3)
Sexual differentiation is the realization of gender. In humans, during the early stages of fetal development there is no discernible difference between genders, rather both are in a "sexually indifferent stage" and have the capacity to develop into either sex. Sexually indifferent gonads are flanked by developing ducts: Wolffian and Müllerian. Wolffian ducts appear closer to the gonads, and will be differentiated into the epididymis, the vas deferens, the seminal vesicle and the ejaculatory duct. The Müllerian duct will become the fallopian tubes, the uterus and the top of the vagina (3).
Sexual determination is based on the presence of the SRY gene, or sex-determining region of the Y-chromosome. Presence of the SRY gene will spur differentiation of the gonads into testes, which in its absence become the ovaries. In males, two types of support cells will then begin to develop: Sertoli cells and Leydig cells. Leydig cells produce testosterone which assists in the development and differentiation of the Wolffian ducts. Sertoli cells produce Müllerian inhibiting substance (MIS), also known as Anti-Müllerian hormone (AMH). This hormone causes the Müllerian ducts to degenerate. In females, the absence of either MIS or testosterone leads to the differentiation of the Müllerian ducts and causes the Wolffian ducts to recede (3).
The Dmrt Gene
In addition to humans, many mammals, insects and even some plants have XY sex-determination systems (5). Another highly conserved component of sexual determination is the Dmrt gene. This gene is most important for maintaining "testis identity" after differentiation of gonads. Maintaining a differentiated state is controlled in part by a competition between two transcription factors. Foxl2 or female-specific forkhead box L2, promotes the development of female granulosa, ovarian cells which aid in oocyte development (1), and theca cells, which produce androstenedione that is converted to a form of estradiol by granulosa cells (4). Its competitor Sox9 or Sry-related box 9, promotes the development of Sertoli cells. The SRY gene targets Dmrt1 and Sox9, which leads to male development and represses female specific genes such as "Foxl2, the Wnt4 and R-spondin-1 signaling proteins, and estrogen receptors" (2).
Works Cited
1. "Granulosa Cell." Wikipedia 2015. Web. 27 Apr 2015.
2. Kopp, Artyom. "Dmrt Genes in the Development and Evolution of Sexual Dimorphism." Trends Genet. 28.4 (2012): 175-84. Web.
3. Linder, Melby. "Sexual Differentiation." University of Washington 2014. Web. 27 Apr 2015.
4. "Theca of Follicle." Wikipedia 2014. Web. 27 Apr 2015.
5. "XY Sex-Determination System." Wikipedia 2015. Web. 27 Apr 2015.
Images:
Banner: http://wideshut.co.uk/the-power-of-dna-and-the-potential-for-misuse/
1. http://www.nytimes.com/health/guides/surgery/vasectomy/print.html
2. http://everydayscienceforall.blogspot.com/2012/07/female-reproductive-system.html
3. & 4. http://courses.washington.edu/conj/bess/differentiation/differentiation.htm
2. Kopp, Artyom. "Dmrt Genes in the Development and Evolution of Sexual Dimorphism." Trends Genet. 28.4 (2012): 175-84. Web.
3. Linder, Melby. "Sexual Differentiation." University of Washington 2014. Web. 27 Apr 2015.
4. "Theca of Follicle." Wikipedia 2014. Web. 27 Apr 2015.
5. "XY Sex-Determination System." Wikipedia 2015. Web. 27 Apr 2015.
Images:
Banner: http://wideshut.co.uk/the-power-of-dna-and-the-potential-for-misuse/
1. http://www.nytimes.com/health/guides/surgery/vasectomy/print.html
2. http://everydayscienceforall.blogspot.com/2012/07/female-reproductive-system.html
3. & 4. http://courses.washington.edu/conj/bess/differentiation/differentiation.htm