In animals, microRNAs (miRNAs), typically, pair to sites of partial complementarity in the 3′-untranslated regions (3′UTRs) of target genes. Regulation by miRNAs often results in down-regulation of target mRNA and protein expression by mechanisms that are yet to be fully elucidated. Additionally, changes in environmental conditions have been shown to influence miRNA function in some cell culture systems. Here, we report the effect of nutrient deprivation on regulation of an endogenous miRNA target in developing worms. In Caenorhabditis elegans, the lin-4 miRNA recognizes multiple sites in the lin-14 3′UTR and directs mRNA degradation and translational repression, but it is unclear how these processes are coupled. In this study, we demonstrate that nutrient deprivation results in loss of lin-14 mRNA, but not protein, repression. In worms removed from feeding conditions, lin-14 mRNA reaccumulates despite the continued expression of lin-4 miRNA. The relative increase in lin-14 mRNA levels during nutrient deprivation is less pronounced in genetic mutants lacking lin-4 miRNA or the lin-14 3′UTR target sites. In conclusion, regulation of lin-14 at the mRNA and protein levels can be uncoupled by changes in culture conditions, indicating that miRNA function can be modulated by environment in multicellular organisms. The awareness that endogenous miRNA pathways can be sensitive to environment is an important consideration for elucidating the mechanism used by miRNAs to regulate target mRNA and protein expression
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