The numbers on each image indicate how many worms of the examined ones displayed the indicated phenotype. (Right panels) The gonad of the same animals in the Left panels to indicate the similar developmental stage. (A) Differential interference contrast (DIC) images showing L4 worms recovered from 4-d–starved L1 worms.
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). 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.
These results compelled us to examine specific interactions between individual miRNAs and their targets to gain mechanistic insights. This result suggests that miR-71 likely functions upstream of, or in parallel to, HBL-1 in regulating VPC timing. Moreover, the expression of hbl-1 is repressed by let-7 family miRNAs at L3 during normal development, and the hyperactivity of hbl-1 caused by failure of miRNA regulation leads to retarded development (26).
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.
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(E) DIC images showing that hbl-1(RNAi) caused precocious VPC divisions in late L2/early L3 in both wild-type and mir-71(lf) worms recovered from 4 d of L1 starvation. 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. (C) Bar graph showing that the delayed VPC timing defects of mir-71(lf) worms was suppressed by an unc-31(lf) mutation and partially suppressed by an age-1(rf) mutation. 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.
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The reporter construct, the control plasmid, and a transformation marker plasmid were coinjected into worms to generate the extrachromosomal arrays for analysis. Elegans and Caenorhabditis briggsae, leading us to focus further analyses on these two genes. We further examined the functional relationship between miR-71 and DAF-16, a FOXO transcription factor acting critically and negatively downstream of AGE-1/PI3K in the InsR pathway. Because the InsR pathway was previously shown to play a prominent role in L1 diapause (2, 3), we examined genetic interactions between miR-71 and different components of the InsR pathway.
- 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.
- Moreover, the expression of hbl-1 is repressed by let-7 family miRNAs at L3 during normal development, and the hyperactivity of hbl-1 caused by failure of miRNA regulation leads to retarded development (26).
- 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.
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Individual GFP reporter constructs for candidate genes (4 ng/μL) and the mCherry internal control plasmid (4 ng/μL) were mixed with unc-119 rescuing plasmid (20 ng/μL) and pBluescript KS+ (72 ng/μL) and coinjected into unc-119(ed3) and mir-71(n4115); unc-119(ed3) worms following standard protocols (32). Knocking down lit-1 by RNAi in mir-71(lf); lin-42(lf) double mutants caused no significant suppression of the VPC timing defects of mir-71(lf) worms. To determine the functional relationship of miR-71 with LIN-42 and LIT-1, mir-71(lf); lin-42(lf) L1 worms were starved for 4 d and recovered on lit-1(RNAi) plates.
miR-71 Is Not Required for Arresting Seam Cell or M-Cell Divisions During L1 Diapause.
Elegans Genetic Center (reference 257) and an N2 strain from the laboratory stock, respectively. Wild-type strains A and B are an N2 strain recently obtained from the C. (A) Survival rate curves of wild-type and mutant strains, as indicated. This is consistent with the previous reports that AIN-1 and AIN-2 are functional homologs with overlapping biochemical roles (16, 17). The roles of InsRs have also been implicated in arresting the cell cycle in germ cells and a portion of somatic cells during L1 diapause (2, 4). Contributed new reagents/analytic tools; X.Z., R.Z., and M.H.
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.
RRF Regulation
- (B) The severely reduced survival rate of the mir-71(lf) mutant was suppressed by a null allele of unc-31(e928).
- Previous studies showed that the release of postdocking calcium-regulated dense-core vesicles, the insulin receptor (InsR) pathway, the AMPK pathway, and protein chaperones are required for the long-term survival of starved L1 worms (2–4).
- MiR-71 regulates vulval cell division during recovery of starved L1 worms.
- 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).
- These results suggest that miRNAs act in the intestine, and possibly in other tissues, to promote L1 starvation survival.
- (C) Bar graph showing that the delayed VPC timing defects of mir-71(lf) worms was suppressed by an unc-31(lf) mutation and partially suppressed by an age-1(rf) mutation.
It is also worth mentioning that multiple components of the InsR pathway, including age-1, pdk-1, akt-2, and daf-16, are predicted to be targets of the let-7 family miRNAs. Our data provide the experimental evidence that two components of the InsR pathway are likely direct targets of miR-71 in its role in a specific physiological process, L1 diapause (see a model in Fig. S5). Components of the InsR pathway, including age-1, have recently been predicted to be targets of miR-71 in its role in aging (14).
Through the Facility, the Commission raises funds by borrowing on the capital markets (issuing bonds on behalf of the EU). Anyone can set up two-step login on their individual account by visiting the web app and choosing Settings → Security → Two-step login. What’s important is that any form of two-step login is active to be sure your account is protected. After entering your Bitwarden master password, you will be prompted to enter a one-time verification code sent to your account email.
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