Cell interactions at the 4 and 12 cell-stages of C. elegans embryogenesis are involved in determining appropriate cell fates. We are interested in determining how such inductive interactions occur at the molecular level. Although these two interactions occur at different times, involve different blastomeres (P2 ABp and MS ABara, ABalp), and have distinct developmental outcomes, they appear to share some of the same molecular components. Both interactions require the
glp-1 transmembrane protein.
glp-1 is supplied maternally to the embryo, and has been shown to be localized to the cellular membranes of the AB blastomere and its descendants (Evans et al., 1994). Most likely,
glp-1 functions as a receptor for signals from the P2 blastomere, and later from the MS blastomere. This role for
glp-1 would be analagous to its later role in the development of the germline, and the role of its homologue,
lin-12, in the development of the vulva. We have identified two new genes,
aph-1 and
aph-2, whose products appear to be required for both the 4-cell and the 12-cell stage interactions. Maternal-effect-lethal mutations in these genes result in a phenotype similar to that of
glp-1 mutants. Although
aph-1 and
aph-2 are essential for interactions mediated by
glp-1 in the embryo, they do not appear to be required in the later developmental events mediated by
glp-1. We have cloned the
aph-2 gene and found that it encodes a novel protein of 722 aa with a well-defined signal sequence at its N-terminus. To examine the spatial distribution of the
aph-2 gene product in embryos we generated antisera against the
aph-2 protein. We find that the
aph-2 protein is localized to the cellular membranes of all blastomeres in the early embryo. These observations suggest that the role of
aph-2 in mediating cell interactions occurs at the cell surface, perhaps contributing to cell-cell contacts, or perhaps interacting directly with
glp-1. In order to elucidate the specific function of
aph-2, we are currently testing weather
aph-2 is required on both, or only one side, of the cell interactions it mediates.