Worm Breeder's Gazette 14(3): 51 (June 1, 1996)
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.
|1||Department of Biological Sciences, University of Illinois at Chicago|
|2||Department of Embryology, Carnegie Institution of Washington|
Pharyngeal muscle gene expression is activated by a combination of cell type- and organ-specific signals (1). In the myo-2 enhancer these distinct developmental pathways cooperate to activate transcription through discrete pharyngeal muscle-specific and organ-specific sub-elements which we refer to as B and C, respectively. The gene ceh-22 appears to be a key component of the pharyngeal muscle-specific pathway for activating gene expression (1). CEH-22 protein binds a site essential for B sub-element function and ectopic ceh-22 expression can activate expression of the endogenous myo-2 gene (1,2). We have previously described the mutant ceh-22(cc8266) that results in a partially penetrant L1 arrest phenotype (2). Although these mutants have pharyngeal muscle defects, expression of both myo-2 and an antigen recognized by MAb 3NB12 appear normal. We do not know if ceh-22(cc8266) is a null allele. The pha-1 gene is also required for normal differentiation of pharyngeal muscle, as well as differentiation of all other pharyngeal cell types (3). This organ-specific phenotype suggests pha-1 could function in parallel to ceh-22 as a direct activator of gene expression via the C sub-element. To explore the relationship between pha-1 and ceh-22 we have: 1) examined ceh-22 expression in a pha-1 mutant; 2) characterized pharyngeal muscle differentiation in a pha-1; ceh-22 double mutant; and 3) examined transcriptional activity of the C sub-element in a pha-1 mutant. The results of these experiments suggest that ceh-22 and pha-1 affect related processes required for pharyngeal muscle differentiation, but it is unlikely that pha-1 functions directly through C. ceh-22 is expressed normally in pha-1 mutant embryos: pha-1(e2123ts) animals raised at the non-permissive temperature (25C) were stained with anti-CEH-22 antibodies. In these mutants, both the temporal and spatial pattern of CEH-22 expression appeared normal indicating that pha-1 is not required upstream to activate ceh-22 expression. Synthetic interactions between ceh-22 and pha-1 mutations: The pharyngeal muscles of pha-1 null mutants and pha-1(e2123ts) mutants grown at 25! stain very well with the antibody 3NB123. Likewise, ceh-22(cc8266) mutants stain normally with this antibody. In contrast, pha-1(e2123ts); ceh-22(cc8266) double mutants raised at 25C show almost no 3NB12 staining. myo-2 expression also appears to be reduced in pha-1(e2123ts); ceh-22(cc8266) at 25C, however this reduction has been more difficult to characterize because myo-2 expression is already partially inhibited in the pha-1 single mutant. A similar synthetic interaction is also observed at the permissive temperature where pha-1(e2123ts) enhances the lethal phenotype of ceh-22(cc8266). This synergism between mutations in pha-1 and ceh-22 indicates the functions of these genes are closely related. pha-1 is not required for C sub-element function: To test whether the C sub-element requires wild-type pha-1, we assayed function of an enhancer consisting of four copies of C in wild type animals and in pha-1(e2123ts) grown at the non-permissive temperature. This enhancer activates expression of a linked lacZ reporter in pharyngeal muscle and non-muscle cells in both wild-type and pha-1 mutants. Thus, C sub-element function does not depend on wild-type pha-1. 1 Okkema, P.G. and A. Fire (1994) Development 120, 2175-2186. 2 Okkema et al., (1994) WBG 13 #4, pg. 90. 3 Schnabel, H. and R. Schnabel (1990) Science 250, 686-688.