Effects of follicle size and stages of maturation on mRNA expression in bovine in vitro matured oocytes

Transcription in bovine oocytes: The goal of this study was to unravel the dynamics of transcripts thought to be critically involved in oocyte maturation. The relative abundance (RA) of DYNLL1 (cytoplasmic dynein light chain LC8), DYNC1I1 (cytoplasmic dynein 1 intermediate chain), DCTN1 (dynactin 1; pGlued homolog, the activator of the cytoplasmic dynein complex 1), PMSB1 (proteasome beta subunit 1), PMSA4 (proteasome alfa subunit 4), PAP (poly-A polymerase) and Cx43 (connexin 43) were determined by semi-quantitative endpoint RTPCR at different stages of lVM, that is, GV, GVBD, MI and Mll in oocytes collected from follicles of two different size categories, that is, <2 mm and 2-8 mm. The RA of DYNLL1 and DYNC1I1 were significantly higher in immature oocytes from bigger follicles than in oocytes from small follicles. Messenger RNA expression levels were similar for DCTN1, PMSB1, PMSA4, PAP, and Cx43 in the two groups during the maturation process. RA of DYNLL1, DYNC1I1 and PMSB1 decreased significantly during lVM in oocytes from follicles 2 to 8 mm. The RA for DYNLL1 was significantly higher in GVBD and MI in the oocytes from follicles 2 to 8 mm in size compared to the other group. The higher mRNA expression of DYNLL1 and DYNC1I1 and the diverging dynamics of DYNLL1, DYNC1I1, and PMSB1 mRNA expression during lVM in oocytes from the different follicle categories could be related to the developmental capacity, that is, development to blastocysts after IVF. The differences found between groups of oocytes could serve as a marker to assess the developmental capacity of bovine oocytes.