Expression of the pharyngeal muscle-specific myosin gene
myo-2 is regulated by cell type-specific signals that target a site in the
myo-2 enhancer called the B subelement. This regulatory sequence can enhance reporter gene expression specifically in the pharyngeal muscles. We have previously shown that activity of the B subelement requires binding of the NK-2 family homeodomain factor CEH-22, and that CEH-22 is a key regulator of B subelement cell type specificity. However, mutational analyses of the B subelement indicate additional factors are likely to be necessary for its enhancer function. To identify these factors we have continued our screen of a C. elegans cDNA expression library for proteins binding the B subelement and have identified one new factor that binds a site distinct from CEH-22. This factor, which we call ZIP-1, shares weak similarity to basic-leucine zipper family transcription factors.
zip-1 maps on chromosome III near
pie-1 , and its genomic structure predicted by Genefinder is designated Y75B8A.35. We are currently examining the expression pattern and function of
zip-1 during C. elegans development.
zip-1 mRNA is detectable by Northern blot in all C. elegans developmental stages. To determine the activity pattern of the
zip-1 promoter, we have examined expression of a
zip-1::lacZ fusion in transgenic C. elegans .
zip-1::lacZ is expressed strongly in the pharynx and a limited set of non-pharyngeal tissues, which we have provisionally identified as the seam cells, vulval muscles, and a number of cells near the rectum. We are now generating antibodies against ZIP-1 to verify this expression pattern and to examine the subcellular localization of ZIP-1. As a preliminary characterization of its function we have attempted RNAi with
zip-1 ; however we have not yet observed an informative phenotype. We are planning to continue our analysis of
zip-1 by isolating a mutant as well as by examining the effect of ectopic
zip-1 expression.