RT Journal Article SR Electronic T1 Direct control of somatic stem cell proliferation by the Drosophila testis stem cell niche JF bioRxiv FD Cold Spring Harbor Laboratory SP 110619 DO 10.1101/110619 A1 Eugene A. Albert A1 Olga A. Puretskaia A1 Nadezhda V. Terekhanova A1 Christian Bökel YR 2017 UL http://biorxiv.org/content/early/2017/06/19/110619.abstract AB Niches have traditionally been characterized as signalling microenvironments that allow stem cells to maintain their fate. This definition implicitly assumes that the various niche signals are integrated towards a binary fate decision between stemness and differentiation. However, observations in multiple systems have demonstrated that stem cell properties such as proliferation and self renewal can be uncoupled at the level of niche signalling input, which is incompatible with this simplified view. We have studied the role of the transcriptional regulator Zfh1, a shared target of the Hedgehog and Jak/Stat niche signalling pathways, in the somatic stem cells of the Drosophila testis. We found that Zfh1 binds and downregulates salvador and kibra, two tumour suppressor genes of the Hippo/Wts/Yki pathway, thereby restricting Yki activation and proliferation to the Zfh1 positive stem cells. These observations provide an unbroken link from niche signal input to an individual aspect of stem cell behaviour that does not, at any step, involve a fate decision. We discuss the relevance of our observations and other reports in the literature for an overall concept of stemness and niche function.Summary statement We demonstrate that the fly testis niche controls stem cell proliferation by repressing Hippo pathway genes independent of a binary cell fate decision between stemness and proliferation.