Analysis of lin-42/period through characterization of a null allele reveals the implications of all three isoforms

Abstract

The timing of post-embryonic development is regulated by the heterochronic gene pathway in C. elegans. An important member of this pathway is lin-42, the worm homolog of the circadian clock gene period. Existing lin-42 alleles have implicated this gene in developmental timing, molting, and the decision to enter the alternative dauer state. lin-42 is a complex locus, encoding overlapping and non-overlapping isoforms, and as a result hypomorphic alleles leave at least one isoform intact. A null allele is needed to understand all of the roles of lin-42 and its individual isoforms. To remedy this problem, and discover the null phenotype, we engineered an allele that deletes the entire lin-42 protein coding region. lin-42 null mutants are homozygous viable, but have more severe phenotypes than observed in previously characterized hypomorphic alleles. Additional evidence is also provided for this conclusion by using the null allele as a base for reintroducing different isoforms, showing that each isoform can provide heterochronic and molting pathway activities. lin-42 functions in the heterochronic pathway to regulate transcription of primary miRNAs, including the let-7 miRNA family. One member of the let-7 family is mir-48. To better understand how mir-48 fits in the pathway a mir-48 gain-of-function suppressor screen was performed. This screen yielded multiple candidates that could function with mir-48 in the heterochronic gene pathway, as miR-48 target genes, or as regulators of miRNA biogenesis and function. Analysis of these mutants should provide insights into control of developmental time.