Caspr proteins are members of the Neurexin superfamily, a group of transmembrane molecules implicated in mediating cell-cell contacts and in the formation of specialized membranous domains in polarized epithelial and nerves cells. Our study focuses on the two Caspr orthologues found in the Caenorhabditis elegans genome encoded by
itx-1 and
nlr-1. Transgenic line expressing
itx-1 promoter fused to GFP reporter revealed that this gene is expressed in intestinal cells epithelia in embryonic and post-embryonic development all through adulthood, as well as in socket cells of the inner and outer labial sensilla. Furthermore, GFP is detected rectal epithelia, spermathica and vulva muscle cells. Whole mount immunofluorescence confined ITX-1 protein t o the baso-lateral membranes of intestinal epithelia. In the apical region it is situated as a wider belt than AJM-1/DLG-1 unit, suggesting that it may delineate a distinct type of domain or sub-junctional region yet to be characterized molecularly. Co-labeling with anti b-Spectrin (BGS-1/UNC-70) show similar localization with ITX-1 along the entire lateral membrane of gut epithelia. Immuno-electron microscopy experiment established the presence of ITX-1 adjacent to the electron dense zonula adherens as well as along the entire lateral membrane. Induction of ITX-1 loss of function by RNA mediated interference (RNAi) did not disrupt organogenesis integrity, polarity or proper function of the intestine at any developmental stage. Nevertheless,
itx-1 RNAi affect in AJM-1::GFP (JcIs1) strain abolished GFP expression of intestinal AJM-1. These results suggest that ITX-1 may participate in delineating the lateral domain of gut epithelia thus facilitating the correct positioning or maintenance of C. elegans apical junctions. We are further trying to elucidate the role of ITX-1 in junction assembly and in maintaining epithelial integrity by searching for its molecular partners. We have also begun analyzing the expression of
nlr-1, the second Caspr protein in C. elegance. In contrast to ITX-1, NLR-1 is expressed in a large variety of cell types such as pharyngeal gland and muscle cells, DB ventral cord motor neurons, and in several interneurons of head ganglia. We are currently engaged in studying the role of this gene utilizing RNAi techniques and ectopic expression of the protein fused to GFP reporter.