DLC3/Cv-c function in testis development in humans and Drosophila: implication for variants of sex development

Abstract

Identifying genes affecting gonad development is essential to understand the mechanisms causing Variants/Differences in Sex Development. Recently, a DLC3 mutation was associated with male gonadal dysgenesis in 46,XY DSD patients. We show that Cv-c, the Drosophila ortholog of DLC3, is also required to maintain testis integrity during fly development. We found that Cv-c and human DLC3 can perform the same function in fly embryos, as flies with wild type but not mutated DLC3 rescue gonadal dysgenesis, suggesting a functional conservation. Expression of different Cv-c protein variants demonstrated that the StART domain mediates the Cv-c function in the male gonad, independently from the GAP domain activity. This work demonstrates a role for DLC3/Cv-c in male gonadogenesis and highlights a novel StART-mediated function required for gonadal mesoderm-germ cell interaction during testis development. Significance Statement: Associating rare human genetic variants to specific conditions is complex. An amino acid change in the StART domain of the RhoGAP DLC3 protein has been found in female DSD patients with a 46,XY male karyotype. We present a second DSD patient with a mutation in the same region and show that the Cv-c/DLC3 homolog is also required in Drosophila testis. In cv-c mutant embryos the testis mesodermal cells display various defects: the testes are unable to retain the germ cells due to their abnormal ensheathment by mesodermal cells and the mesodermal sheet of cells surrounding the testis is discontinuous resulting in the liberation of the germ cells outside the gonad. Defects can be rescued by gonadal expression of Cv-c or DLC3 but not by the patients’ DLC3 protein variant. Testis development requires the StART lipid binding domain but not the GAP domain, revealing a novel function of this RhoGAP family.