MicroRNA-21 Mediated Post-Transcriptional Gene Regulation in Ovarian Function

Abstract

The release of the oocyte from the ovary (ovulation) and terminal differentiation of cells of the preovulatory follicle (luteinization) are initiated by the surge of pituitary luteinizing hormone (LH) and are essential for proper reproductive function. As a result, major research efforts have been dedicated to deciphering the signaling pathways and transcriptional networks that are activated in granulosa cells following the LH surge. Remarkably however, few studies have examined the role post-transcriptional gene regulation plays in mediating LH action within preovulatory granulosa cells. Because cell and tissue function are reliant on the proper splicing, localization, and translation of mRNA to protein (i.e., post-transcriptional gene regulation) understanding this regulatory mechanism is essential for understanding ovarian (granulosa cell) function. MicroRNA (miRNA) mediate changes in post-transcriptional gene expression and have been tightly linked to a number of cell developmental and differentiation events. We identified miRNA-21 (miR-21) as an LH-induced miRNA in murine granulosa cells. The goal of this dissertation was to determine the function of miR-21 in granulosa cells of the periovulatory follicle. We found that in vitro knockdown of miR-21 in granulosa cells using antisense locked nucleic acid oligonucleotides (LNA) increased apoptotic death and decreased global translation, and these cellular events could be separated pharmacologically. Exogenous miR-21 increased global translation and our current evidence implicates changes in the activity of the Akt/mTOR pathways upstream of the critically important elongation factor-2 as the cause for this increase in protein synthesis. In vivo knockdown of miR-21 blocked ovulation and increased granulosa cell apoptosis. Therefore, miR-21 functions in periovulatory granulosa cells to inhibit apoptosis and to promote global translation, thus likely promoting the formation of a functional corpus luteum and allowing for the establishment and maintenance of pregnancy.