Biogenesis of microRNAs (miRNAs) is essential in animals, as disruption of this pathway leads to developmental arrest in multiple species. Interestingly, in most studied animals, developmental arrest during embryogenesis is mainly caused by the absence of functionally redundant groups of miRNAs, called miRNA families. In the case of C. elegans, embryonic arrest in the absence of miRNAs seems to be primarily due to loss of two miRNA families, both highly expressed in the embryo: the miR-35 and miR-51 families. Here, we set out to investigate the function of the miR-51 family, evolutionarily related to miR-100 (the most conserved animal miRNA). The members of this family, miR-51 through 56, share the same seed sequence, but differ in their remaining sequence. Only simultaneous deletion of the six members leads to arrest during embryogenesis, while presence of at least one of them is sufficient to allow for completion of the process. However, the contributions of the different family members to larval development differ and it is unclear whether this is due to their differences in sequence, in expression pattern or in dose. Moreover, despite the importance of this miRNA family, we have no knowledge about its functionally-relevant targets or its cellular impact on embryogenesis. Using the extensive genetic toolbox available in C. elegans, we have shown that, unlike what happens with other miRNA families in the worm (e.g. the
let-7 family), the sequence beyond the seed is not responsible for the differences observed during larval development. However, using a quantitative assay to explore dose-dependency in the miR-51 family function, we found quantifiable differences upon changes in miR-51 family concentration. Our results suggest that the miR-51 family regulates, as a whole, a common target or set of targets in a dose-dependent manner. To find the target/s of the family, we performed RNAseq in wild type and miR-51 family deficient embryos, at different timepoints of embryogenesis. Our data show that several genes seem to be regulated by this family -including the homolog of the NOTCH receptor,
lin-12. We are currently validating our hits by generating endogenous reporters of gene expression,and will report our updated efforts in the search for functional targets of this miRNA family.