The Role of miRNAs in Cell Fate Decisions During Osteogenesis
Bone is a complex mineralized tissue that functions as a structural support for the body, as well as in mineral storage and homeostasis. Its development is as complex as it’s function, with multiple molecular cues governing several aspects of its development and maintenance. Multiple previous studies over several decades have shown that failure to maintain tight regulation of these cues results in varying degrees of bone malformation, most frequently of the craniofacial variety. Various reports have cited a fundamental importance of both non-canonical and canonical Wnt signaling in regulating osteogenesis. Multiple studies have also revealed the importance of temporal-spatial regulation of their expression in promoting proper bone development.
MicroRNAs (miRNAs) are small non-coding RNAs that are able to negatively regulate protein expression, serving as a regulatory mechanism in a variety of developmental processes and diseases. They function by binding to the 3’ Untranslated Region of target mRNAs to induce mRNA degradation or translational inhibition. They are crucial for early embryonic differentiation, as studies have shown that embryonic stem cells that cannot generate miRNA exhibit impaired differentiation.
The work presented in this dissertation focuses on two miRNAs that have not been previously characterized in osteogenesis: miR-690 and miR-361. These miRNAs were selected from a screen based on their differential patterns of accumulation in response to osteogenic factors, and their ability to positively regulate osteogenesis. Using embryonic stem cells as a model for early embryonic development, we observed that both miRNAs were capable of affecting Wnt signaling. We also noted a correlation of miRNA expression with accelerated and/or sustained expression of genes that are associated with neural crest specification or differentiation. These studies have established (i) that miR-690 supports osteogenesis by directly regulating Ctnnb1 during differentiation from the mesenchyme; and (ii) that miR-361 promotes osteogenesis by directly regulating the non- canonical Wnt inhibitor Prickle during mesenchymal commitment. This research presents novel possibilities in miRNA-mediated regulation of early osteogenic development, specifically with regard to regulation of Ctnnb1.