Basigin maintains glial wrapping of axons. Lindsay Petley-Ragan. Zoology, University of British Columbia, Vancouver, BC, BC, Canada.

   Drosophila axons are ensheathed by multiple layers of insulating glial cells and an outer layer of extracellular matrix (ECM). Glial-ECM, glial-glial and glial-axonal adhesion are crucial for maintaining the structure and function of nerves. We are investigating a novel role for basigin, a transmembrane protein containing two Ig domains, in glial-axonal adhesion. In vertebrates, basigin is known to be highly expressed on the surface of tumours where it induces the expression of matrix metalloproteinases to mediate tumour metastasis. However, basigin has also been suggested to bring monocarboxylate transporters to the membrane, mediate neuronal adhesion, and genetically interact with integrin. The function of basigin in glia has not yet been investigated. We have demonstrated that in 3rd instar larvae, basigin is expressed by both neurons and glia in the central and peripheral nervous systems (CNS and PNS). Of particular interest is the high concentration of basigin in axons in the CNS at the CNS/PNS transition zone and apparent lack of basigin in PNS axons. Basigin is uniformly expressed in the insulating CNS and PNS glial layers. Knockdown of basigin in glia is lethal and resulted in death and fragmentation of the innermost wrapping glial layer as well as larval locomotion defects. Larvae homozygous for basigin mutations demonstrate similar phenotypes in addition to disrupted CNS glial morphology. We hypothesize that basigin is involved in maintaining adhesion between glia and axons in the central and peripheral nervous systems.