MEGF9: a novel transmembrane protein with a strong and developmentally regulated expression in the nervous system.

MEGF9 [multiple EGF (epidermal growth factor)-like-domains 9], a novel transmembrane protein with multiple EGF-like repeats, is predominantly expressed in the developing and adult CNS (central nervous system) and PNS (peripheral nervous system). The domain structure of MEGF9 consists of an N-terminal region with several potential O-glycosylation sites followed by five EGF-like domains, which are highly homologous with the short arms of laminins. Following one single pass transmembrane domain, a highly conserved short intracellular domain with potential phosphorylation sites is present. The protein was recombinantly expressed and characterized as a tissue component. To study the expression pattern further, immunohistochemistry was performed and staining was detected in Purkinje cells of the cerebellum and in glial cells of the PNS. Additional expression was observed in the epidermal layer of skin, papillae of the tongue and the epithelium of the gastrointestinal tract. By immunoelectron microscopy, MEGF9 was detected in glial cells of the sciatic nerve facing the basement membrane. MEGF9 represents a novel putative receptor, expressed in neuronal and non-neuronal tissues, that is regulated during development and could function as a guidance or signalling molecule.