Zfh-1 controls somatic stem cell self-renewal in the Drosophila testis and nonautonomously influences germline stem cell self-renewal

The ability of adult stem cells to maintain their undifferentiated state depends upon residence in their niche. While simple models of a single self-renewal signal are attractive, niche-stem cell interactions are likely to be more complex. Many niches have multiple cell types, and the Drosophila testis is one such complex niche with two stem cell types, germline stem cells (GSCs) and somatic cyst progenitor cells (CPCs). These stem cells require chemokine activation of Jak/STAT signaling for self-renewal. We identified the transcriptional repressor Zfh-1 as a presumptive somatic target of Jak/STAT signaling, demonstrating that it is necessary and sufficient to maintain CPCs. Surprisingly, sustained Ah-1 expression or intrinsic STAT activation in somatic cells caused neighboring germ cells to self-renew outside their niche. In contrast, germline-intrinsic STAT activation was insufficient for GSC renewal. These data reveal unexpected complexity in cell interactions in the niche, implicating CPCs in GSC self-renewal.