The C. elegans heterochronic gene
lin-42 and the period family of circadian rhythm genes from flies and vertebrates provide an intriguing example of gene conservation paralleled by functional conservation; all are involved in biological timing mechanisms. LIN-42 times stage-specific developmental programs and molting cycles during larval development, while Per proteins synchronize various processes with the 24-hr clock. Remarkably, LIN-42, like its Period homologs, exhibits a dynamic, oscillatory expression pattern with levels peaking once in each larval stage. LIN-42 and Period proteins share multiple regions of homology, notably a PAS domain that mediates protein-protein interactions and smaller SYQ and LT domains of unknown function.
lin-42 encodes four isoforms, two of which do not overlap. One of these non-overlapping isoforms contains the PAS domain, while the other contains the SYQ and LT domains; the remaining two isoforms contain all of these homology domains. Previously described
lin-42 mutations leave at least one isoform intact, complicating genetic and phenotypic analyses. We generated a null allele using mosDEL technology to delete the entire
lin-42 coding region.
lin-42(0) mutants display a strong precocious heterochronic phenotype similar to
lin-42(lf) alleles. In addition,
lin-42(0) mutants have severe molting defects, similar to those seen in
lin-42(
ok2385), a deletion that spans the SYQ and LT domains. The majority of
lin-42(0) animals arrest during early larval development, a phenotype present in
lin-42(
ok2385) mutants and likely to be a result of failed ecdysis. However, the larval arrest phenotype is statistically more penetrant in the null, suggesting that the PAS-containing isoform still present in
lin-42(
ok2385) mutants contributes to regulation of molting. The SYQ-LT containing isoform can rescue the null when over-expressed, indicating it is key to LIN-42 function, while the other isoforms may play more regulatory role(s). A null allele now allows epistasis analysis and will facilitate placement of
lin-42 in the heterochronic and molting pathways.