The proliferation and differentiation of stem cells is influenced by the surrounding niche, which includes the basement membrane (BM), a specialised extracellular matrix. Although cells in direct contact with the BM can receive signals via cell surface receptors, such as integrins, it is not clear how signals from the BM are relayed to cells that it does not contact. Previously, Daniel McIntyre and Jeremy Nance showed in C. elegans that depletion of the BM component laminin from the primordial germ cell (PGC) niche causes PGCs to exit quiescence and proliferate, despite being enwrapped by somatic gonadal precursor cells (SGPs). In this study, they now investigate how SGPs transduce BM signals to PGCs. Here, they show that in the absence of laminin, SGPs relay proliferation-inducing signals from the BM to PGCs via integrin receptors. This requires interactions of integrin with the BM component perlecan, because reducing perlecan levels blocks PGC proliferation. Furthermore, reducing perlecan levels in larvae in the presence of laminin attenuates germline growth, suggesting perlecan also regulate PGC proliferation under physiological conditions. Together, these findings reveal how, despite not being in direct contact with the BM, signals from the BM can be transduced via SGPs to regulate stem cell quiescence.
