SEQUENCE REQUIREMENTS FOR MYOSIN GENE-EXPRESSION AND REGULATION IN CAENORHABDITIS-ELEGANS

Four Caenorhabditis elegans genes encode muscle-type specific myosin h eavy chain isoforms: myo-1 and myo-2 are expressed in the pharyngeal m uscles; unc-54 and myo-3 are expressed in body wall muscles. We have u sed transformation-rescue and lacZ fusion assays to determine sequence requirements for regulated myosin gene expression during development. Multiple tissue-specific activation elements are present for all four genes. For each of the four genes, sequences upstream of the coding r egion are tissue-specific promoters, as shown by their ability to driv e expression of a reporter gene (lacZ) in the appropriate muscle type. Each gene contains at least one additional tissue-specific regulatory element, as defined by the ability to enhance expression of a heterol ogous promoter in the appropriate muscle type. In rescue experiments w ith unc-54, two further requirements apparently independent of tissue specificity were found: sequences within the 3' non-coding region are essential for activity while an intron near the 5' end augments expres sion levels. The general intron stimulation is apparently independent of intron sequence, indicating a mechanistic effect of splicing. To fu rther characterize the myosin gene promoters and to examine the types of enhancer sequences in the genome, we have initiated a screen of C. elegans genomic DNA for fragments capable of enhancing the myo-2 promo ter. The properties of enhancers recovered from this screen suggest th at the promoter is limited to muscle cells in its ability to respond t o enhancers.