The driving force of male (XY) sex determination in most mammals usually begins with Sry expression initiating Sox9¸which is expressed in early developing supporting cells of the testis and directs further testicular development. Conversely, in females (XX) the lack of Sry cannot promote Sox9 overexpression, and Sox9 is actively repressed and downregulated in the developing gonad by the complement of female-promoting factors (Foxl2, ER/E2, Wnt4/Rspo1). Many downstream direct targets of Sox9 that promote male gonadal development remain elusive, however through analysis of published RNA-seq, scRNA-seq, SOX9-ChIPseq and related gonadal-transcriptomic datasets, we identified Tyro3 as a likely SOX9 direct target gene.
TYRO3, together with AXL and MERTK, comprises the TAM family of receptor tyrosine kinases. Triple-knockout TAM family (TAM-/-) mice exhibit severe phenotypes, including male infertility. Tyro3 is more highly expressed in XY gonads than XX gonads at the time of sex differentiation in mice. Our RNA-seq on Tyro3-/-male and female E12.5 gonads demonstrate a surprising role for Tyro3 in XX gonadal development, with 975 differentially expressed genes (DEGs) identified in females (Tyro3+/-vs. Tyro3-/-), and 10 DEGs in males (Tyro3+/-vs. Tyro3-/-). The DEGs identified in females are involved in MAPK signalling, Aldosterone synthesis and secretion, ovarian steroidogenesis and more. Current literature suggests both Tyro3 and Axl contribute to normal reproductive function and cyclicity in the female through regulation of GnRH neuron survival. Our data present a novel role of Tyro3-only in ovarian development in the mouse.