The C. elegans pharynx is a distinct neuromuscular organ consisting of five cell types: muscles, glands, epithelial cells, neurons, and structural cells termed marginal cells. We are interested in how these cells are produced during embryonic development. To address this question, we are examining how gene expression is regulated in one pharyngeal cell type, the muscles. The pharyngeal muscle myosin gene
myo-2 is regulated in part by organ-specific signals that target a site in the
myo-2 enhancer termed the C subelement. Activity of the C subelement requires the organ specification factor PHA-4. However, PHA-4 must cooperate with other factors binding C, because mutations both within and outside the PHA-4 binding site eliminate C subelement enhancer activity. Here we describe the novel transcription factor PEB-1, which binds a site overlapping the PHA-4 site in the C subelement and cooperates with PHA-4 to activate C subelement enhancer activity. We have examined
peb-1 mRNA and protein expression using a variety of techniques.
peb-1 mRNA is abundantly expressed in embryos, where it accumulates in the developing pharynx. Expression decreases during larval development, although
peb-1 mRNA is detectable through the remainder of the life cycle. In adults, a substantial amount of
peb-1 mRNA appears to be expressed in the germline. PEB-1 protein accumulates in pharyngeal nuclei beginning about the comma stage of embryogenesis, and it remains detectable in the pharynx until mid larval development. PEB-1 is expressed in most pharyngeal cells including the muscles, marginal cells, epithelial and gland cells, but, in contrast to PHA-4, it is undetectable in the pharyngeal neurons. PEB-1 protein is also detectable in a small number of tissues outside the pharynx including the pharyngeal-intestinal valve cells, cells near the rectum and vulva, and hypodermal cells in the head and tail. We are currently examining the effect of ectopically expressing
peb-1 either alone or in combination with PHA-4 and other pharyngeal transcription factors. While we have not observed ectopic expression of
myo-2 in these experiments, we have found that expression of
peb-1 using a heat-shock promoter results in heat inducible lethality, and using a body wall muscle promoter results in an Unc (uncoordinated) phenotype.