Isolation and characterization of mammalian homologues of Caenorhabditis elegans lin-7: localization at cell-cell junctions

In Caenorhabditis elegans, the vulval induction is mediated by the let-23 r eceptor tyrosine kinase (RTK)/ Ras signaling pathway. The precise localizat ion of the let-23 RTK at the epithelial junctions is essential for the vulv al induction, and requires three genes including lin-2, -7, and -10. The ma mmalian homologue of lin-2 has been identified as a protein interacting wit h a neuronal adhesion molecule, neurexin, and named CASK. CASK has recently been reported to interact with syndecans and an actin-binding protein, ban d 4.1, at epithelial and synaptic junctions, and to play central roles in t he formation of cell-cell junctions. The product of C. elegans lin-7 direct ly interacts with let-23 RTK and localize it at epithelial junctions. Here, we report three rat homologues of lin-7 ubiquitously expressed in various tissues, These homologues are accumulated at the junctional complex region in cultured Madin-Darby canine kidney cells, and are also localized at the synaptic junctions in neurons. The mammalian homologues of lin-7 may be imp licated in the formation of cell-cell junctions.