Stem cell-associated stromal cells create a signalling microenvironment– a niche – that sustains the self-renewing and asymmetric properties of stem cell divisions. The Drosophila ovary is an ideal system for investigating how these niches form and recruit stem cells. In their careful study on p. 2579, Zhu and Xie have analysed the occupation of the ovarian niche in flies by primordial germ cells (PGCs). They report that, as niche formation begins, one population of PGCs directly differentiates, while an anterior population, which lies adjacent to the cells that create the niche, develop into germline stem cells. These anterior PGCs exhibit distinctive division patterns and require dpp signalling to maintain normal proliferation. Importantly, lineage-tracing analyses revealed that a single PGC can occupy a whole niche through clonal expansion. Such findings offer valuable insights into how other niches might form.

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