Worm Breeder's Gazette 13(2): 54 (February 1, 1994)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
We have been characterizing factors regulating expression of the pharyngeal muscle-specific myosin gene, myo-2 .We previously described an element of the myo-2 enhancer that is highly active in a subset of pharyngeal muscles ( m3 , m4 , m5 ,and m7 )and the protein, CEH-22 ,that binds to this element (WBG 12#4). We have characterized the ceh-22 expression pattern by immuno-staining with antibodies raised against CEH-22 protein, by in situ hybridization to ceh-22 RNA, and by examining the expression pattern of a ceh-22 ::1acZfusion. Each of this analyses indicates ceh-22 expression is limited to pharyngeal muscles m3 , m4 , m5 , m6 ,and m7 (and probably also to m1 ).Thus, CEH-22 appears to be a key regulator of myo-2 enhancer activity. The predicted CEH-22 protein contains a homeodomain DNA binding motif belonging to the phylogenetically conserved NK-2 family (see Figure). The CEH-22 homeodomain shares 63-87% identity with members of this family. By contrast, CEH-22 shares only 27-50% identity with published C. elegans homeodomain sequences.
The NK-2 class homeodomains most similar to that of CEH-22 (77-87% identical) are preferentially expressed in the central nervous system. Because we have seen no CEH-22 expression in nerve cells in C. elegans, we do not believe that these highly related homeoproteins are functional homologs of CEH-22 .In contrast, three homeodomains that are somewhat less similar to that of CEH-22 (60-67% identical) are expressed in mesodermal tissues similarly to CEH-22 .The mouse gene Nkx-2 .5/Csx,as well as the Drosophila genes tinman (tin) and bagpipe (bag), are expressed in the developing heart prior to myogenic differentiation. The similar expression patterns of CEH-22 , Nkx-2 .5/Csx,tin, and bag suggest that the developmental function of these genes may be conserved. An attractive hypothesis based on these analyses is that nematode pharyngeal muscle is related to cardiac muscle in vertebrates and Drosophila.