%0 Journal Article
%T Unmasking a role for sex chromosomes in gene silencing
%A Danielle M Maatouk
%A Blanche Capel
%J Genome Biology
%D 2010
%I BioMed Central
%R 10.1186/gb-2010-11-9-134
%X During mammalian development, sexual development is initiated in the embryonic gonad. Male gonadal cells express the Sry gene (sex determining region Y), a Y-linked gene which triggers differentiation of the testis. Steroidogenic Leydig cells, within the testis, produce testosterone, masculinizing non-gonadal tissues including the sex ducts, the external genitalia and parts of the brain. The dominant role of hormones in masculinizing the brain was shown about 50 years ago by Alfred Jost. By treating female guinea pigs with testosterone prenatally, he demonstrated irreversible male-type behavioral changes. This early research suggested that XX and XY cells were equivalent and that sexual dimorphisms resulted from exposure to male or female gonadal hormones [1]. However, the question of whether sexual dimorphism is completely reliant on hormones or whether there is also a genetic component has remained an area of interest.Heteromorphic sex chromosomes make cells in the male and female intrinsically different in terms of the dose of sex-linked genes (as the female has two X chromosomes and the male has an X and a Y chromosome). This difference is balanced in part by inactivating one X-chromosome in females, which equalizes X gene dosage between males and females. However, in mice and humans, many genes escape inactivation, increasing the gene dosage of these loci in XX cells [2]. Therefore, it is not inconceivable that intrinsic chromosomal differences affect the differentiation of XX and XY cells. Brain and nerve cells seem to be sensitive to this inherent difference in gene dosage. For example, in cultures of mouse midbrains, where the effect of hormones is probably negligible, XY explants develop more dopamine neurons than do XX explants. Similarly, the density of vasopressin fibers correlates with the presence of the Y chromosome, and not with phenotypic sex (female or male) [3]. However, Sry expression has been reported in regions of the mouse brain, challenging t
%U http://genomebiology.com/2010/11/9/134