Sexual Dimorphism of Body Size Is Controlled by Dosage of the X-Chromosomal Gene Myc and by the Sex-Determining Gene tra in Drosophila

摘要

Drosophila females are larger than males. In this article, we describe how X -chromosome dosage drives sexual dimorphism of body size through two means: first, through unbalanced expression of a key X -linked growth-regulating gene, and second, through female-specific activation of the sex-determination pathway. X -chromosome dosage determines phenotypic sex by regulating the genes of the sex-determining pathway. In the presence of two sets of X -chromosome signal elements (XSEs), Sex-lethal ( [Sxl][1] ) is activated in female ( XX ) but not male ( XY ) animals. Sxl activates [transformer][2] ( [tra][2] ), a gene that encodes a splicing factor essential for female-specific development. It has previously been shown that null mutations in the [tra][2] gene result in only a partial reduction of body size of XX animals, which shows that other factors must contribute to size determination. We tested whether X dosage directly affects animal size by analyzing males with duplications of X -chromosomal segments. Upon tiling across the X chromosome, we found four duplications that increase male size by 9%. Within these, we identified several genes that promote growth as a result of duplication. Only one of these, [Myc][3] , was found not to be dosage compensated. Together, our results indicate that both [Myc][3] dosage and [tra][2] expression play crucial roles in determining sex-specific size in Drosophila larvae and adult tissue. Since [Myc][3] also acts as an XSE that contributes to [tra][2] activation in early development, a double dose of [Myc][3] in females serves at least twice in development to promote sexual size dimorphism. [1]: http://flybase.org/reports/FBgn0264270.html [2]: http://flybase.org/reports/FBgn0003741.html [3]: http://flybase.org/reports/FBgn0262656.html