Cell-cell interactions and the specification of cell fates during C. elegans embryogenesis

During development, cell-cell interactions play an important role in specifying cell fates. Genetic studies in both C. elegans and Drosophila have identified many components of cell signalling pathways, and work in vertebrates indicates that these pathways are highly conserved. In this dissertation I present my work on cell-cell interactions and the specification of cell fates during C. elegans development. First, I have studied a Notchlike signalling pathway, called the GLP signalling pathway. I have found that a ligand for this pathway, APX-1, acts as an inductive signalling ligand at the 4-cell stage of embryogenesis. I demonstrated that APX-1 also plays a role in specifying cell fate in the post-embryonic vulval precursor cells. Secondly, in a screen for mutants which alter APX-1 expression in the embryo, I have identified a new mutant called pin-1 . pin-1 mutant embryos do not express APX-1 and fail to undergo the APX-mediated cell-cell interaction at the 4-cell stage. These embryos also show a defect in the specification of cell fates in the C lineage in the posterior region of the embryo. Lastly, I have shown that a WNT-like signalling pathway, which was known to specify cell fates in the anterior and ventral regions of the embryo, is also required to specify cell fates in the posterior region of the embryo. These studies also indicate that there are potentially two additional cell-cell interactions patterning the posterior region. This work further supports that cell-cell interactions are critical for the specification of cell fates during C. elegans development.