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. L1 starvation assay was adapted from a previously described protocol (3). Worms strains were grown and maintained at 20 °C as described (29).
- Furthermore, the observed derepression of individual genes by mir-71(lf) seemed too weak to account for the phenotype, consistent with the idea that a prominent phenotype of an miRNA mutation is caused by the collective effect of changing expression in many genes, an important property of miRNA-mediated gene regulation.
- 3′UTRs of genes of interest were cloned into the modified pPD129.57 vector as described previously (18).
- (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).
- 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.
- We further found that this survival rate reduction of ain-1 mutants was overcome by ectopic expression of the AIN-2 protein in the intestine but not in the muscle (Fig. 1A and Fig. S1A).
- The backups are encrypted by the recovery password, which is only known to you and cannot be recovered by Duo.
- 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).
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 tissues where miR-71 is expressed in wild-type worms, but derepressed in the same tissues of mir-71(lf) worms. (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.
Among short-lived miRNA mutants, a mir-71 deletion mutant, mir-71(n4115) (referred to as mir-71(lf) hereafter), displayed a severe reduction in L1 starvation survival rate (Table S1 and Fig. 2A). We found that the reduced survival rate of ain-1 was suppressed by either reduction of age-1 function or loss of unc-31 function (Fig. 1 B and C), suggesting that a significant portion of the overall miRNA functions in L1 diapause is upstream of, or in parallel to, the InsR pathway. In this study, we addressed the questions of whether and how miRNAs impact developmental arrest and the long-term survival of early L1 stage worms in response to food starvation.
