Worm Breeder's Gazette 13(3): 30 (June 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.
The maternal gene skn-1 encodes a putative transcription factor that is localized to the nuclei of posterior blastomeres between the 2-cell and 8-cell stages of embryogenesis (Bowerman et al, Cell 74, 443-452). For example, at the 4-cell stage the two anterior sister blastomeres contain little or no detectable SKN-1 protein, but the two posterior sister blastomeres, P2 and EMS, stain brightly with antibodies that recognize SKN-1 . skn-1 function appears to be required only in EMS: no SKN-1 protein is detectable in skn-1 mutant embryos, yet P2 develops normally. In contrast, the fate of EMS is severely affected in skn-1 mutants. Instead of producing intestinal and pharyngeal cells, as in wild-type embryos, EMS instead adopts a fate more similar to that of P2 ,producing both hypodermal cells and body wall muscles. Thus skn-1 (+) functions in a process that specifies blastomere fate and is in part responsible for distinguishing EMS from P2 .
We want to understand the molecular basis for the restriction of SKN-1 protein to posterior blastomeres in the early embryo. Because in situ hybridization studies have shown that the maternal skn-1 mRNA is evenly distributed at low levels throughout all early blastomeres (G. Seydoux and A. Fire, personal communication), it is possible that the unequal distribution of SKN-1 protein is due to translational regulation of the maternal message. Therefore we have begun to test the ability of skn-1 mRNA sequences to act in cis to confer a SKN-1 pattern of expression when fused to coding sequences for ß-galactosidase or GFP (Green Fluorescent Protein). We have made plasmid constructs in which sequences from a skn-1 cDNA, including the 3' untranslated region, have been fused to reporter gene coding sequences, using the vector pJK350 ,kindly provided by T. Evans (Cell 77, 183-194). Chimaeric mRNAs transcribed in vitro from linearized plasmid templates will be microinjected into the syncitial gonads of adult hermaphrodites. Embryos from the injected mothers will be analyzed for lacZ or GFP expression patterns. We also are microinjecting full-length skn-1 transcripts made in vitro into the gonads of homozygous skn-1 mothers to determine if we can rescue mutant embryos by microinjection of wild-type mRNA. Finally, we plan to examine the phenotypic consequences of mislocalizing SKN-1 expression in early embryos by microinjecting chimaeric mRNAs in which the coding sequences from skn-1 are fused to the 3' untranslated region from glp-1 ,which has been shown to restrict translation of a heterologous message to anterior blastomeres (see Evans et al., Cell 77, 183-194).