(B) Survival rate of single and double mutants to indicate the functional relationship between ain-1 and age-1. The two ain-1 loss-of-function alleles displayed significant reductions in L1 starvation survival rate. We further found that this survival rate reduction of ain-1 mutants was overcome by ectopic expression of the AIN-2 protein in the intestine but not in the muscle (Fig. 1A and Fig. S1A). We found that ain-1 but not ain-2 mutants displayed a significant reduction in L1 starvation survival rate compared with that of wild type (Fig. 1 A and D).
MiR-71 regulates vulval cell division during recovery of starved L1 worms. These results indicate that miR-71 is not essential for arresting seam cell or M-cell divisions during L1 diapause, suggesting that miR-71 function is distinct from DAF-16 function. DAF-16 (the FOXO homolog in C. elegans) has been shown to play an important role in cell cycle arrest and developmental progression partly by promoting cki-1 expression in some somatic cells during L1 arrest (2).
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Furthermore, a recent study suggests that the expression of certain miRNAs is differentially regulated by starvation-induced dauer diapause (15). Consistent with these ideas, several recent lines of evidence suggest that miRNA let-7 and the heterochronic genes lin-42 and hbl-1 are required to regulate the starvation-induced dauer diapause (10–12) and that a number of miRNAs including lin-4 and mir-71 are involved in regulating life span (13, 14). Furthermore, worms that are long-lived due to dietary restriction or decreased mitochondrial respiratory rates are short-lived during L1 diapause, suggesting that the mechanisms controlling L1 starvation survival are different at least in some aspects from those controlling aging (3).
These results suggest that miRNAs act in the intestine, and possibly in other tissues, to promote L1 starvation survival. MicroRNAs (miRNAs) are well known for their functions in controlling developmental timing in the nematode (5, 6). Upon entering L1 diapause, RNA polymerase II quickly accumulates and pauses at promoter regions, and this accumulation was speculated to stop transcription and facilitate the immediate reinitiation of gene expression when food becomes available (2).
