The generation and maintenance of epithelial polarity relies on the correct reception of signals and cues from apical and baso-lateral sources (1). Thus, in Drosophila the Crumbs protein (2, 3) is localized apically to the zonula adherens (ZA; 4) and plays a key role in maintaining the polarized phenotype of the ectoderm and its derivatives (5). We have started to investigate epithelial polarization in the embryonic gut of C. elegans, a simple tube of 20 cells, arranged in a series of nine rings (6). Using the sequence of the Drosophila Crumbs cytoplasmic domain, we identified two C.e. homologues of CRB. We applied RNA interference technique (cDNA clones kindly provided by Dr. Kohara), in order to disturb normal development, but no visible phenotypes could be detected so far. Immuno-staining during morphogenesis of C.e. demonstrates expression of CeCRB1 in the gut and later in the pharynx, while at the same time intestinal staining is reduced. Double-labelling against phosphotyrosine reveals localization of CeCRB1 apical to the ZA in the embryonic gut of C.e. We are now concentrating on basal cues necessary for polarization of the gut epithelium and have begun to study C.e. mutants with defects in major constituents of basement membranes (e.g.
let-2,
emb-9,
unc-52), beta-integrin (
pat-3) or vinculin (
deb-1). The phenotype of ZA organization in the above mutants was analyzed by confocal microscopy. It ranges from fragmentation to complete absence of the ZA. While elements of the Wnt/pop-1 signalling pathway have been postulated to act autonomously within the E-lineage for anterior-posterior patterning (7), we suggest that processing of extracellular matrix information is a prerequisite for establishing correct apico-basal polarity in the embryonic gut of C.elegans. (1) Eaton and Simons, (1995). Cell 82: 5-8; (2) Tepass et al., (1990). Cell 61: 787-799; (3) Wodarz et al., (1995). Cell: 82, 67-76; (4) Tepass, (1996). Dev. Biol. 177: 217-225; (5) Tepass and Knust, (1990). Roux´s Arch. Dev. Biol. 199: 189-206; (6) Sulston et al., (1983). Dev. Biol. 100: 64-119; (7) Schroeder and McGhee, (1998). Development 125: 4877-4887.