Osterix functions downstream of anti-Mullerian hormone signaling to regulate Mullerian duct regression

Abstract

In mammals, the developing reproductive tract primordium of male and female fetuses consists of the Wolffian duct and the Mullerian duct (MD), two epithelial tube pairs surrounded by mesenchyme. During male development, mesenchyme-epithelia interactions mediate MD regression to prevent its development into a uterus, oviduct and upper vagina. It is well established that transforming growth factor-beta family member anti-Mullerian hormone (AMH) secreted from the fetal testis and its type 1 and 2 receptors expressed in MD mesenchyme regulate MD regression. However, little is known about the molecular network regulating downstream actions of AMH signaling. To identify potential AMH-induced genes and regulatory networks controlling MD regression in a global non-biased manner, we examined transcriptome differences in MD mesenchyme between males (AMH signaling on) and females (AMH signaling off) by RNA-Seq analysis of purified fetal MD mesenchymal cells. This analysis found 82 genes up-regulated in males during MD regression and identified Osterix (Osx)/Sp7, a key transcriptional regulator of osteoblast differentiation and bone formation, as a novel downstream effector of AMH signaling during MD regression. Osx/OSX was expressed in a male-specific pattern in MD mesenchyme during MD regression. OSX expression was lost in mutant males without AMH signaling. In addition, transgenic mice ectopically expressing human AMH in females induced a male pattern of Osx expression. Together these results indicate that AMH signaling is necessary and sufficient for Osx expression in the MD mesenchyme. In addition, MD regression was delayed in Osx null males, identifying Osx as a new factor that regulates MD regression.\n\nSignificanceIn mammals, each embryo forms both male and female reproductive tract organ progenitor tissues. Anti-Mullerian hormone (AMH) secreted by fetal testes acts on mesenchyme cells adjacent to the Mullerian duct (MD) epithelium, the progenitor tissue of the female reproductive tract, to induce MD regression. While AMH and early AMH signaling components are elucidated, downstream gene networks directing this process are largely unknown. A global non-biased approach using whole transcriptome sequencing of fetal MD mesenchymal cells identified 82 factors as potential target genes of AMH including Osterix (Osx). Our findings provide in vivo evidence Osx is an AMH-induced gene that regulates MD regression. Identification of Osx may provide key insights into gene regulatory networks underlying MD regression and male sex differentiation.