(B) Bar graph showing the correlation between the severity of the retarded vulval precursor cell (VPC) timing defect of mir-71(lf) mutants and the duration of L1 starvation. Whereas the vulva of wild-type worms developed into the pyramidal stage (81 of 82 worms), the P6.p of mir-71(n4115, lf) mutant worms divided only once (83 of 89 worms). The computation-based prediction that age-1 and pdk-1 are potential targets of miR-71 was also reported in a recent study focusing on miRNA functions in aging where the mRNA level of pdk-1 was shown to be up-regulated in mir-71 worms (14). We found that the 3′UTRs of several genes of the InsR pathway, including unc-31, age-1, pdk-1, akt-2, and sgk-1, contain predicted miR-71 targeting sites (as predicted by TargetScan and mirWIP). (C) Fluorescence and differential interference contrast (DIC) images showing that the age-1 3′UTR reporter was repressed in mir-71(+) worms (3/4 transgenic lines) but not in mir-71(lf) worms (4/4 transgenic lines).
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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. Food deprivation is a life-threatening challenge that animals frequently face as individuals and as species. Numerous animal species across multiple phyla enter developmental arrest for long-term survival in unfavorable environments and resume development upon stress removal. Contributed new reagents/analytic tools; X.Z., R.Z., and M.H.
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Reduction-of-function mutation (rf) in the age-1/PI3 kinase gene, age-1(hx546), made worms long-lived in the L1 starvation assay and was able to suppress the reduced L1 survival rate of mir-71(lf); the rate of the double mutants was comparable to that of wild type (Fig. 2A). In worms that recovered from 4 d of L1 starvation, we also found that a significant portion of the mir-71(lf) mutants displayed egg-laying defects and overproliferating or precociously reflexed gonads. (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). 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). 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). Note that the daf-16(lf) worms recovering from 3 d of L1 starvation displayed a ∼12-h delay in overall development and that the mir-71(lf); daf-16(lf) double mutants displayed an ∼24-h delay.
