We previously identified two genes involved in embryonic elongation.
let-502 encodes a protein with similarity to Rho-binding ser/thr kinases and
mel-11 encodes the regulatory subunit of myosin protein phosphatase (PP-1M).
mel-11 and
let-502 suppress each other, suggesting they play antagonistic roles during elongation (Wissman et al., 1997). The
let-502(
ca201) allele was initially identified as a zygotic lethal mutation, and five others had been previously isolated from a saturation screen of LGI (Howell and Rose, 1990). These alleles are separated into two classes based on their phenotypes. The first class show a variety of phenotypes, the most severe resulting in arrest during early elongation. These alleles have missense mutations in the kinase domain. The second class of alleles display a range of weaker phenotypes, such as adult sterility. These alleles are predicted to result in truncated protein products. These two classes of
let-502 alleles were isolated based on larval lethality or adult sterility; if the
let-502 null phenotype is wild type, it would not have been found. Indeed, genetic evidence suggests all of the previous alleles have gain-of-function properties. A deficiency of the
let-502 region dominantly suppresses
mel-11. This interaction provided us with a method for isolating novel
let-502 alleles that would be either loss-of-function or null mutations. We now have identified an additional eight
let-502 alleles as suppressors of the temperature sensitive
mel-11 allele
it26, as well as several mutations in other genes. These new
let-502 alleles all have missense mutations in or just prior to the region encoding the kinase domain. Most of these
let-502 alleles are hypomorphs, and display a variety of phenotypes such as an incomplete penetrant Roll. This is consistent with
let-502 antisense experiments, which resulted in a similar variation of phenotypes. The
let-502(hypomorph);
mel-11(
it26) strains also display near wild type phenotypes. This suggests that the
let-502 and
mel-11 pathway may be redundant, and alternate pathways could function to regulate elongation. Previous studies with GFP fusion constructs showed
let-502 expression in the hypodermal cells of developing embryos during early elongation. However,
let-502 is also maternally expressed, and so LET-502 protein expression is being characterized through the use of antibodies, in both Western blotting and immunostaining. Antibodies are currently being made to MEL-11 to further characterize patterns of protein expression. This will also allow us to discern any possible protein-protein interactions between proposed components of the pathway(s) involved in the process of elongation, for example to test for interactions between MEL-11 and LET-502. Howell, A.M. and Rose, A.M. 1990. Genetics 126: 583-592. Wissmann, A., Ingles, J., McGhee, J.D. and Mains, P.E. 1997. Genes and Development 11: 409-422.