Syndecan is critical for Drosophila CNS and PNS glia function

Glia are irreplaceable components for the nervous system development and function. However, the cellular mechanisms each glial layer utilizes to communicate with each other and the extracellular environment is not well characterized. Here, we investigated the role of a heparan-sulfate proteoglycan, Syndecan (Sdc), in regulating glial cell function and development in the Drosophila nervous system. Sdc is expressed throughout multiple glial layers and loss of Sdc in all glia resulted in disruption of both central and peripheral glia. Within the CNS loss of Sdc in all glia lead to reduced brain lobes and disruption of neuroblast proliferation. In the PNS, loss of Sdc in different glial layers resulted in impaired ensheathment in wrapping glia and abnormal septate junction morphology in subperineurial glia. We focused on the outer layer of perineurial glia and found ensheathment defects and a reduction in glial numbers with Sdc loss. These phenotypes mirror those previously observed with the loss of integrins and a mutation in the integrin {beta}-subunit enhanced the phenotypes observed with loss of Sdc within the perineurial. Thus, our results indicate Sdc has multiple roles in Drosophila nervous system development including as an integral component in regulating glial cell morphology, maintaining neuroblast populations within the optic lobe and in mediating glial-ECM interactions.