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). 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). Our genetic analysis indicated that for both L1 diapause survival and developmental recovery functions, miR-71 regulates expressions of genes in both the insulin receptor-dependent and -independent pathways.
To determine viability, 20-μL aliquots (60–100 worms) were placed every 3 d onto two 6-cm nematode growth medium (NGM) plates seeded with OP50, and the numbers of L1 worms were recorded as number of plated worms (Np). A total of 16–24 h later, the density of newly hatched L1 worms was adjusted to three to five worms per microliter S-basal. The eggs were transferred to plates seeded with HB101 and bleached again 3 d later. Briefly, worms were well fed for at least two generations, and gravid adults were bleached with hypochlorite and sodium hydroxide.
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.
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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.}
