Fig. 1. LanA is expressed throughout the third instar larval PNS. Peripheral nerves expressing ECM proteins in longitudinal view and accompanying cross sections (site indicated with yellow line). Scale bars: 5 μm A-B: LanA::GFP with continuous (A), or discontinuous strands (B) in the nerve interior (yellow arrowheads) as well as to the outer ECM (white arrowheads). C-H: LanA::GFP (green) and axons immunolabeled with anti-futsch (22C10; magenta). In early third instar larva (C,D), feeding third instar larva (E,F), and wandering third instar larva (G,H). Development • Accepted manuscript I-N: Trol::GFP (green), Ndg::GFP (green), and Vkg::GFP (green) are localized to the outer ECM, and absent from the nerve interior. Axons immunolabeled with anti-futsch (22C10; magenta). O-T: LanA::GFP (green) localization relative to the three glial layers. O-P: Relative to the PG membranes (46F>mCD8::RFP, magenta). Q,R: Relative to SPG membranes (SPG>mCD8::RFP, magenta), with LanA exterior to the SPG within the PG (white arrowheads) S,T: Relative to WG membranes (Nrv2>mCD8::RFP, magenta), with LanA localization to WG processes (yellow arrowheads)
Abstract
The Drosophila peripheral nerve contains multiple layers of glial cells and an overlying extracellular matrix (ECM), which together support neuronal survival and function. The innermost glial layer, the wrapping glia (WG), ensheathes axons and facilitates action potential conduction. Recent work has identified involvement of laminin, a heterotrimeric ECM protein complex in WG development. However, the localization and function of laminin in the WG remains poorly understood. Here, we found that the alpha subunit, LamininA (LanA), is dynamically expressed by WG, and loss of LanA results in a reduction in WG-axon contact. The deposition of LanA by WG is concentrated between WG and axons and deposited preferentially around motor axons versus sensory axons. We identified Crag, a GDP-GTP exchange protein, that controls LanA deposition. We found Dystroglycan also controls LanA deposition by the WG, and that both Dystroglycan and Dystrophin are present and necessary for WG ensheathment of axons. Thus, WG contain the highly conserved Dystroglycan/Dystrophin complex that not only associates with deposited laminin but is necessary for the polarized deposition of laminin and the correct ensheathment of peripheral nerve axons.