| MicroRNAs (miRNAs) are small (∼22 nucleotides) regulatory molecules that silence specific mRNAs through translational inhibition and/or targeted degradation. The main focus of this thesis is to study miRNA function in a developmental context. We investigated composition of miRNA-containing ribonucleoprotein complexes (miRNPs) from Caenorhabditis elegans. The endogenous miRNAs were found in two distinct miRNP species, each containing either Tudor Staphylococcal nuclease (TSN-1), or threonyl-tRNA synthetase (TRS-1) as the core protein component. The observed mi RNP compositions suggest that several proposed modes of miRNP-mediated repression including mRNA destabilization and translational arrest may operate simultaneously to control developmental processes. We also demonstrated that miRNP-associated endonuclease activity is capable of targeting either partially or fully complementary target RNAs, cleaving adjacent to (but not within) miRNP-docking sites. In the last chapter, we measured the temporal expression profiles for all the known miRNAs in hermaphrodite C. elegans. The results show that the developmentally regulated miRNAs are predominantly clustered in two groups---embryonic or larval expression patterns, suggesting these miRNAs regulate gene expression events at the corresponding stage(s). miRNAs that potentially target similar RNA sequences tend to have similar expression pattern suggesting certain miRNAs might be redundant in their function. |
