Transcriptional Repression of reaper by Stand Still Safeguards Female Germline Development in Drosophila

Apoptosis plays a central role in shaping tissues and preserving cellular integrity across developmental stages. In the germline, its precise regulation is critical to ensure both the elimination of aberrant cells and the maintenance of reproductive capacity. However, the molecular mechanisms that control apoptotic susceptibility in germline cells remain poorly defined. Here, we identifystand still(stil) as a female germline-specific regulator of apoptosis inDrosophila. Loss ofstilleads to near-complete depletion of germline cells at the time of eclosion, associated with upregulation of the pro-apoptotic genereaper(rpr) and activation of caspase-dependent cell death. Reporter assays in S2 cells show that Stil directly repressesrprtranscription through its N-terminal BED-type zinc finger domain. Despite the absence ofstil, undifferentiated germline cells remain resistant to apoptosis. Analysis of publicly available chromatin data reveals that therprlocus in these cells resides in a closed, H3K9me3-enriched chromatin state, suggesting a Stil-independent mode of transcriptional silencing. Together, our findings uncover two distinct mechanisms that protects the female germline fromrpr-dependent apoptosis: Stil-mediated transcriptional repression that operates in both undifferentiated and differentiated germline cells, and an additional chromatin-based silencing mechanism that functions specifically in undifferentiated cells. This work provides new insights into the interplay between transcriptional and chromatin-based regulations that maintain germline cell identity and survival.