(A) The mir-71(n4115, lf) mutant displayed severe reduction in L1 starvation survival rate, and the reduced survival rate of mir-71(lf) was suppressed by a reduction-of-function allele of age-1(hx546). (C) The reduced L1 starvation survival rate of ain-1(lf) mutants was significantly suppressed by a null allele of unc-31. Compromising overall miRNA function dramatically reduces the survival rate of L1 worms in starvation-induced diapause, and the effect can be significantly suppressed by an age-1/PI3K mutation.
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- A recent study showed that the expression of miR-71 was significantly increased relative to other miRNAs in starved L1 worms (15).
- We then compared the expression of a hbl-1 3′UTR reporter (18) in the mir-71(lf) mutants with that in wild type and found that the expression of this reporter was slightly derepressed at L3 in the mir-71 mutant (Fig. 4 F and G).
- To test the hypothesis that these developmental timing genes mediate the regulatory role of miR-71 in larval development during recovery from starvation-induced L1 diapause, we examined whether knocking down HBL-1 function can suppress the retarded VPC timing defect of mir-71(lf).
- To understand how miR-71 affects VPC division, we searched its predicted targets for potential genes involved in regulating developmental timing.
- This result is consistent with the observation that miR-71 is specifically required for the starvation-induced stress response (Fig. S5).
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For examining the age-1 3′UTR reporter, the rol-6(d) marker (100 ng/μl pRF4) was used instead of the unc-119(+) plasmid. Non-Unc stable transgenic lines were maintained, and the expression of GFP and mCherry were observed under a Zeiss Axiovision II microscope. Three days later, the number of worms that were L2 or older was recorded as number of survived worms (Ns), and the survival rate was calculated as Ns/Np, which is an estimation of survived worms in the whole population.
MT12993 mir-71(n4115) worms were outcrossed with N2 for four generations before any test except the initial screen. A recent study showed that the expression of miR-71 was significantly increased relative to other miRNAs in starved L1 worms (15). However, miR-71 does not appear to regulate all postembryonic development during L1 diapause recovery. Unlike classical heterochronic miRNAs such as lin-4 and let-7, the role of miR-71 in vulval cell division is essential in animals recovering from starvation-induced L1 diapause, but not in animals hatched on plates with food. As pointed out above, multiple miRNAs in addition to miR-71 and the let-7 family miRNAs have roles in L1 diapause, and they may regulate the expression of many diverse targets that may include, but are not limited to, factors involved in UNC-31–InsR-signaling activities.
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.
- The two ain-1 loss-of-function alleles displayed significant reductions in L1 starvation survival rate.
- We speculate that the expression of heterochronic genes controlling the L2/L3 programs, including that of hbl-1 and lin-42, are increased during L1 diapause to arrest the developmental progression, and miR-71 is probably required to suppress these “excess” signals during the recovery phase (Fig. S5).
- We further examined worms recovering from 4 d of L1 starvation and found that around 90% of the mir-71(lf) mutants displayed retarded vulval precursor cell (VPC) division, compared with less than 5% in wild type (Fig. 4A).
- 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.
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- 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).
Duo Mobile cannot recover access to those accounts without a backup. Be sure to enable third-party account backup and restore if you use Duo Mobile to generate passcodes for logging into applications like Instagram, Facebook, Snapchat, or other web services. To compare the survival rates between strains, we simulated the survival rate of each genotype to 100 arbitrary “individual worms” and performed the log-rank test in Graphpad Prism 4. This result suggests that the high expression of miR-71 during L1 diapause is induced or maintained by other signaling pathways. We asked whether the expression of miR-71 was regulated by DAF-16, which is required during L1 diapause for long-term survival (2).
miR-71 Is Not Required for Arresting Seam Cell or M-Cell Divisions During L1 Diapause.
{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).}
