Stem cell niche organization in the Drosophila ovary requires the ECM component Perlecan

Stem cells reside in specialized microenvironments or niches that balance stem cell proliferation and differentiation.^1,23-11 Basement membranes (BMs) are thin ECM sheets that are constituted mainly by Laminins, Perlecan, Collagen IV, and Entactin/Nidogen and surround epithelia and other tissues.¹² Perlecans are secreted proteoglycans that interact with ECM proteins, ligands, receptors, and growth factors such as FGF, PDGF, VEGF, Hedgehog, and Wingless.^13-18 Thus, Perlecans have structural and signaling functions through the binding, storage, or sequestering of specific ligands. We have used the <i>Drosophila</i> ovary to assess the importance of Perlecan in the functioning of a stem cell niche. Ovarioles in the adult ovary are enveloped by an ECM sheath and possess a tapered structure at their anterior apex termed the germarium. The anterior tip of the germarium hosts the germline niche, where two to four germline stem cells (GSCs) reside together with a few somatic cells: terminal filament cells (TFCs), cap cells (CpCs), and escort cells (ECs).¹⁹ We report that niche architecture in the developing gonad requires <i>trol</i>, that niche cells secrete an isoform-specific Perlecan-rich interstitial matrix, and that <i>DE</i>-cadherin-dependent stem cell-niche adhesion necessitates <i>trol</i>. Hence, we provide evidence to support a structural role for Perlecan in germline niche establishment during larval stages and in the maintenance of a normal pool of stem cells in the adult niche.