Chinmo is a novel regulator of differential Hippo signaling response within a single developing organ.

Orchestrated control of proliferation of multiple cell types is essential for building a healthy organ. Here we use larval ovary development in Drosophila melanogaster as a model to understand the homeostasis of somatic and germ line cells in the formation of the female adult reproductive organ. We previously showed that the highly conserved Hippo signaling pathway regulates proliferation of both germ line and somatic cells in the D. melanogaster larval ovary. Response to Hippo signaling appeared to be mediated by different genetic mechanisms in germ line and soma, but the mechanism allowing distinct responses to the same signaling pathway remained unknown. Here we perform cell type-specific RNA-Seq of isolated germ line and somatic cells from the developing ovary at multiple time points spanning the formation of germ line stem cell niches, in either a Hippo signaling loss- or gain-of-function genetic background. Applying network analysis to these data revealed a novel regulator of ovarian development, the transcription factor chinmo. Subsequent experimental validation showed that chinmo acts as a key germ cell-specific translator of Hippo signaling in the developing ovary, allowing the Hippo signal to be transduced in cell type-specific ways in germ line and somatic cells within the same organ.