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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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.
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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).
The transcript level of unc-31 was increased in mir-71(lf) worms, compared with that of wild-type controls that were normalized to the value of 1. MiR-71 represses the expression of age-1 and unc-31 through the actions on their 3′UTR, but miR-71 is not required for arresting M cell division during L1 diapause. (B) The severely reduced survival rate of the mir-71(lf) mutant was suppressed by a null allele of unc-31(e928). The effect observed in ain-1(lf) mutants is likely the consequence of the combined effects of attenuating functions of these individual miRNAs. Previous studies indicate that the InsR pathway plays a dominant role in regulating L1 starvation survival and that reducing the activity of the insulin receptor daf-2, the PI3Kinase age-1, or the upstream regulator unc-31 results in increased L1 starvation survival rate (2, 3).
Intestinal miRNAs Play Critical Roles in L1 Starvation Survival.
- Numerous animal species across multiple phyla enter developmental arrest for long-term survival in unfavorable environments and resume development upon stress removal.
- Different organisms have developed versatile growth arrest strategies to overcome starvation-induced metabolic and developmental problems.
- Non-Unc stable transgenic lines were maintained, and the expression of GFP and mCherry were observed under a Zeiss Axiovision II microscope.
- The RRF is also crucial for implementing the REPowerEU plan – the Commission’s response to the socio-economic hardships and global energy market disruption caused by Russia’s invasion of Ukraine.
- The reporter is strongly expressed in H and V cells in both wild-type and mir-71(lf) worms.
{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). The strong suppression of the mir-71(lf) defect by hbl-1(RNAi), and the relatively weak effect of miR-71 on hbl-1 expression, are consistent with the idea that miR-71 exerts its role by modulating activities of multiple genes related to hbl-1 function in developmental timing. In contrast, the nuclear-localized GFP expression under the control of the 3′UTR of age-1(Fig. 3 C and D) or unc-31 (Fig. 3 E and F) was strongly repressed in the control worms, but prominently derepressed in mir-71(lf) mutant worms. If the 3′UTR of age-1 or unc-31 is repressed by miR-71, the GFP expression will be repressed in revery play login tissues where miR-71 is expressed in wild-type worms, but derepressed in the same tissues of mir-71(lf) worms.}
