Abstract / Description of output
Several different miRNAs have been proposed to regulate ovarian follicle function, however, very limited information exists on the spatiotemporal patterns of miRNA expression during follicle development. The objective of this study was to identify, using microarray, miRNA profiles associated with growth and regression of dominant-size follicles in the bovine monovular ovary, and to characterize their spatiotemporal distribution during development. Follicles were collected from abattoir ovaries and classified as Small (4-8 mm) or Large (12-17 mm); these were further classified as Healthy or Atretic based on estradiol and CYP19A1 levels. Six pools of Small follicles and individual Large Healthy (n=6) and Large Atretic (n=5) follicles were analyzed using Exiqon's miRCURY LNA™ microRNA Array 6th gen, followed by qPCR validation. A total of 17 and 57 sequences were differentially expressed (≥2 fold; P<0.05) between Large Healthy and each of Small and Large Atretic follicles, respectively. Bovine miRNAs confirmed to be upregulated in Large Healthy relative to Small follicles (bta-miR-144, bta-miR-202, bta-miR-451, bta-miR-652 and bta-miR-873) were further characterized. Three of these miRNAs (bta-miR-144, bta-miR-202 and bta-miR-873) were also downregulated in Large Atretic relative to Large Healthy follicles. Within the follicle, these miRNAs were predominantly expressed in mural granulosa cells. Further, body-wide screening revealed that bta-miR-202, but not other miRNAs, was expressed exclusively in the gonads. Finally, a total of 1359 predicted targets of the 5 miRNAs enriched in Large Healthy follicles were identified which mapped to signaling pathways involved in follicular cell proliferation, steroidogenesis, prevention of premature luteinization and oocyte maturation.