| The C. elegans heterochronic genes program stage-specific temporal identities in multiple tissues during larval development. These genes include the first two miRNA-encoding genes discovered, lin-4 and let-7. I show that lin-58 alleles, identified as lin-4 suppressors, define another miRNA that controls developmental time. These alleles are unique in that they contain point mutations in a gene-regulatory element of mir-48, a let-7 family member. mir-48 is expressed prematurely in lin-58 mutants, whereas expression of mir-241, another let-7 family member residing immediately upstream of mir-48 , appears unaffected. A mir-48 transgene bearing a lin-58 point mutation causes strong precocious phenotypes in the hypodermis and vulva when expressed from multicopy arrays. mir-48::gfp fusions reveal expression in these tissues, and inclusion of a lin-58 mutation causes precocious and enhanced gfp expression. These results suggest that lin-58 alleles disrupt a negative regulatory element that restricts the time of miR-48 action in wild-type animals.; hbl-1, a heterochronic gene whose 3'UTR contains multiple binding sites for the let-7 family microRNAs, has been shown to be a target of miR-48. I attempted to identify additional miR-48 targets using a combination of bioinformatics and experimental approaches. Putative miR-48 targets include genes in the heterochronic pathway and dauer formation pathway. Experiments that can be used to validate these potential miR-48 targets are discussed. |
