Gene expression in the pharyngeal muscles of C. elegans is regulated in part by the NK-2 family homeodomain factor CEH-22, which is structurally and functionally related to Drosophila Tinman and the vertebrate Nkx2-5 factors.
ceh-22 is expressed exclusively in the pharyngeal muscles and is the earliest gene known to be expressed in this tissue. Here we characterize the
ceh-22 promoter region in transgenic C. elegans. A 1.9-kb fragment upstream of
ceh-22 is sufficient to regulate reporter gene expression in a pattern identical to the endogenous gene. Within this promoter we identified two transcriptional enhancers and characterized their cell type and temporal specificity. The distal enhancer becomes active in the pharynx near the time that
ceh-22 expression initiates; however, it becomes active more broadly later in development. The proximal enhancer becomes active after the onset of
ceh-22 expression, but it is active specifically in the
ceh-22-expressing pharyngeal muscles. We suggest these enhancers respond to distinct signals that initiate and maintain
ceh-22 gene expression. Proximal enhancer activity requires a short segment containing a CEH-22 responsive element, suggesting that CEH-22 autoregulates its own expression.