Genes of Hippo signaling network act unconventionally in the control of germline proliferation in Drosophila.

Hippo pathway and its related genes are required for growth control in various somatic tissues. The mutations of Hippo pathway components lead to tissue overgrowth cell-autonomously. Surprisingly, when we generated germline mutant clones of Hippo-network genes such as fat, expanded, hippo, salvador, and warts, we did not observe any overgrowth of these mutant cells. Consistently, overexpression of the progrowth gene yorkie, which is normally inhibited by Hippo signaling, did not lead to germline overgrowth either. In contrast to previous studies in epithelial tissues, these tumor suppressor genes are dispensable in germline cells for their proliferation control. Furthermore, we demonstrate that expanded functions nonautonomously to regulate spermatogonial proliferation. It appears that expanded acts from the somatic support cells surrounding the germline to restrict spermatogonial amplification.