The vulval cells vulF and vulE are each formed by fusion of a subset of the cells of the primary vulval lineage.
egl-26 mutants have no functional connection between the vulval and uterine lumens because the most dorsal vulval cell, vulF, becomes restricted at the dorsal side and no passageway for eggs is opened. In
egl-26 mutants, vulF adopts a morphology similar to its neighbor vulE. However, by examining the expression of several vulE-specific GFP markers in an
egl-26 mutant background, we determined that a vulF to vulE fate transformation could not account for the abnormal vulF morphology. EGL-26 encodes a novel protein with a conserved domain of unknown function, the H-box/NC domain. H-box/NC proteins are a large family of proteins which includes the human H-REV107 class II tumor suppressor. The H-box/NC motif is most often associated with a C-terminal transmembrane domain. Although EGL-26 has no such predicted transmembrane domain, it is localized to the apical membrane of cells where it is expressed. Specifically, it is expressed around the apical edge of the vulE cell. Thus, we hypothesize that EGL-26 acts non cell-autonomously in vulE to control vulF cell morphology, and we are currently testing this model. In order to understand how EGL-26 is associated with the membrane and the molecular function of the novel protein and the conserved H-box/NC motif, we are searching for proteins that interact with EGL-26. We have generated transgenic animals that express a functional FLAG-tagged version of EGL-26 in order to search for binding proteins by co-immunoprecipitation. We are also performing a yeast two hybrid screen and expect to report on putative interactors at the meeting.