Stepicheva, Nadezda2017-02-102017-02-102016http://udspace.udel.edu/handle/19716/20511microRNAs (miRNAs) are small endogenous RNAs that regulate the translation and stability of their target mRNAs. They play an important role in many biological processes, including growth and development; however, studying the functional role of a single miRNA can be challenging. We take advantage of a small number of miRNAs and the rich knowledge on gene regulatory network (GRN), signaling pathways, and the cell fate specification of the sea urchin, Strongylocentrotus purpuratus. The overarching goal of this research project is to identify the functions of miRNAs in the early embryo. Previously, we demonstrated that the depletion of the total pool of miRNAs by knocking down the key miRNA biogenesis enzymes resulted in severe endomesodermal defects that could be rescued by the addition of four most abundantly sequenced miRNAs (miR-1, miR-31, miR-71 and miR-2012). We have demonstrated that a highly evolutionarily conserved Wnt/β-catenin pathway that is responsible for endomesodermal specification, is regulated by miRNAs. Removal of miRNA regulation of β-catenin resulted in defects in endoderm and mesoderm. Moreover, our data indicate that skeletogenesis GRN that is activated by the canonical Wnt/β-catenin pathway is tightly regulated by the two highly conserved miRNAs, miR-31 and miR-1. Further, we demonstrate that the proper formation of endomesoderm in the developing sea urchin embryo is dependent on the small GTPase Arf6 that may also be regulated by miR-31. Taken together, we demonstrated that miRNAs regulate the proper endomesoderm formation in the sea urchin embryo. This study contributes to the mechanistic understanding of how a developing embryo utilizes miRNAs to regulate GRNs and signaling pathways to ensure proper development.MicroRNA.Gene regulatory networks.Strongylocentrotus purpuratus -- Embryos.Strongylocentrotus purpuratus -- Development.Catenins.Mesoderm.Guanosine triphosphatase.Thesis972092160https://doi.org/10.58088/apje-7q53