We thus asked whether miR-71 was required for the reinitiation of developmental programs during the recovery phase after L1 starvation. These results suggest that miR-71 regulates the expression of unc-31 and age-1 through their 3′UTRs. Note that there are extra GFP-positive cells (red arrows) in mir-71(lf) mutants.
It is possible that other miRNAs, including those in the let-7 family, control developmental timing in other tissues during the recovery phase after L1 starvation. 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).

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To test whether the activity of the InsR pathway was down-regulated by miR-71, we first examined the endogenous expression of components of the InsR pathway in mir-71(lf). (C) The poor survival rate of daf-16(mu86, null) was enhanced by mir-71(lf). To identify individual miRNAs that play prominent roles in L1 diapause, we screened 72 available mutant strains of individual miRNAs and miRNA families (87 miRNAs in total) using the L1 starvation assay. (D) A representative chart of the L1 starvation survival rates of different miRNA mutants.

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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). Consistent with the observation described above, the 4-d–starved mir-71(lf) mutants recovering on the RNAi control plates displayed the highly penetrant retarded defect in VPC division. If this were true, the starved mir-71(lf); daf-16(lf) double-mutant worms should show a slow growth phenotype similar to that of daf-16(lf) worms, but no specific VPC timing defect. (H) Fluorescence and DIC images showing that a lin-42 3′UTR reporter was repressed in mir-71(+) worms (2/2 transgenic lines) and prominently derepressed in mir-71(−) worms (2/2 transgenic lines).

• MT12993 mir-71(n4115) worms were outcrossed with N2 for four generations before any test except the initial screen.
• Our data provide the experimental evidence that two components of the InsR pathway are likely direct targets of miR-71 in its role in a specific physiological process, L1 diapause (see a model in Fig. S5).
• To investigate the roles of miRNAs in animal survival during starvation-induced L1 diapause, we impaired the overall miRISC function with loss-of-function (lf) mutants of ain-1 (ku322, ku425, and tm3681) and ain-2(tm2432) and examined their L1 starvation survival rate (Materials and Methods).
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• (F) Fluorescence and DIC images showing that an hbl-1 3′UTR reporter was repressed in mir-71(+) worms and slightly derepressed in mir-71(lf) mutants.
• We further examined the functional relationship between miR-71 and DAF-16, a FOXO transcription factor acting critically and negatively downstream of AGE-1/PI3K in the InsR pathway.
• 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).

S1A indicated a dominant role of intestinal miRNAs in regulating L1 starvation survival. We used a dual-color 3′UTR reporter system (18) to test the computational, prediction-based hypothesis that the 3′UTRs of age-1 and unc-31 are directly regulated by miR-71 (Fig. 3B and Materials and Methods). Among these potential miRNA targets, the predicted miR-71–targeting sites in the 3′UTRs of age-1 and unc-31 are conserved between C.
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).
However, it remains unclear how, and to what extent, miRNAs coordinate animal survival and development in response to stresses. However, the mechanisms that coordinate the long-term survival, overall developmental arrest, and reinitiation remain to be investigated. However, when newly hatched L1 worms encounter an environment with no food, developmental programs arrest and the worm enters L1 diapause. When late, first larval stage (L1) worms sense unfavorable conditions, they enter an alternative and long-lived larval stage called dauer larvae (or dauer diapause). The nematode Caenorhabditis elegans responds to starvation by entering developmental arrest at multiple stages of its life cycle (1). Extreme climate events such as droughts and heatwaves are intensifying under climate change, yet their combined effects on plant recovery remain unclear.

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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. Numerous animal species across multiple phyla enter developmental arrest for long-term survival in unfavorable environments and resume development upon stress removal. Such lagged trait recovery, combined with rapid invasive recovery, suggests potential for longer-term shifts in grassland composition and function.