A microRNA controls developmental timing

Normally, C. elegans develops into an adult after four larval stages, and hypodermal cell lineages conclude their development at L4 (hatched lines at ends of V1-V4 lineages). (a) In let-7 mutants, the transition from the L4 larval stage to adult is delayed and the cell lineages of lateral hypodermal cells (V) are reiterated. (b) let-7 encodes an miRNA that is complementary to sequences in the 3′ UTR of lin-41 mRNA.