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Previous studies showed that the release of postdocking calcium-regulated dense-core vesicles, the insulin receptor (InsR) pathway, the AMPK pathway, and protein chaperones are required for the long-term survival of starved L1 worms (2–4). Unlike dauer diapause, L1 diapause is not accompanied by life cycle changes and has not been shown to require certain signaling pathways that control the formation of dauer diapause such as TGF-β signaling (daf-1, daf-7) and nuclear hormone receptor (daf-12) (2, 3). The coordinated entrance into developmental arrest, long-term survival, and the reinitiation of development upon food availability are important biological processes to investigate. Different organisms have developed versatile growth arrest strategies to overcome starvation-induced metabolic and developmental problems. The presented results indicate that interactions between multiple miRNAs and likely a large number of their mRNA targets in multiple pathways regulate the response to starvation-induced L1 diapause.

Although the complete removal of miRNA functions causes embryonic lethality or infertility in worms, a partial disruption of overall miRNA functions by mutating either ain-1 or ain-2 provides an effective way to investigate miRNA functions (16, 17). However, we found that the reporter transgene with the lin-42 3′UTR was significantly repressed in wild-type worms, but derepressed in the mir-71(lf) worms (Fig. 4 H and I). This is consistent with hbl-1 being one of the downstream targets of miR-71, although this modest effect alone is not expected to account for the vulval developmental phenotype in mir-71 mutant. In starved L1 worms, we detected only a slight increase in the mRNA level of hbl-1 in mir-71 mutants compared with that in wild type (∼10%), which may not be biologically significant. In contrast, the mir-71(lf) mutant worms recovering on hbl-1(RNAi) displayed precocious VPC divisions similar to that seen in wild type (Fig. 4E).