Interactions between tissue-specific stem cells and their local niche are vital for stem cell self-renewal and differentiation. But how are niches established? On p. , Tishina Okegbe and Stephen DiNardo provide new insights into testis stem cell niche development in Drosophila. The stem cells in the fly testis, which sustain spermatogenesis throughout life, are clustered around a group of somatic cells (hub cells) that serves as a niche. The researchers confirm a previous report that Notch signalling is necessary for specification of mesoderm-derived somatic gonadal precursor cells to the hub cell fate but, unexpectedly, show that the endoderm adjacent to the developing testis supplies the Notch-activating ligand Delta. They also report that niche cell specification occurs earlier than anticipated, well before the expression of known niche cell markers. Given that mammalian primordial germ cells also pass through endoderm on their way to the genital ridge, the researchers suggest that Delta-Notch signalling by the endoderm could be a conserved mechanism for specification of the germline niche.
