Are the levels of Cdk4 and Cx43 proteins of porcine oocytes associated with follicular size?

Abstract

Abstract Gap junction connections are formed by proteins which play an important role in oocyte developmental competency but there is little information on the relationship between follicle size and the expression of genes encoding these proteins. The aim of this study was to investigate the potential association between follicle size and the levels of Cdk4 and Cx43 proteins using western blot analysis and confocal microscopic observations. Cumulus-oocyte complexes (COCs) were collected from puberal gilts (n = 20) of large (>5 mm), medium (3-5 mm), and small (<3 mm) follicles, and stained with BCB. BCB+ COCs, which had finished their growth phase, were cultured in TCM 199 for 44 h. Western blot analysis revealed an increased level of Cdk4 protein in oocytes isolated from large follicles as compared to medium (P < 0.05) and small (P < 0.01) ones. We did not detect differences in Cx43 protein levels in oocytes collected from any follicle class. Confocal microscopic observation revealed a specific membrane and zona pellucida localization of Cdk4 protein in oocytes isolated from large follicles, but an exclusively cytoplasmatic distribution of Cdk4 in oocytes from smaller follicle categories. The effect of follicular size on Cdk4 is indicated by the higher level of Cdk4 protein in oocytes isolated from large follicles and its variable distribution – perhaps resulting from a specific translocation mechanism – in the membrane, zona pellucida, and cytoplasm. IVM may also have a significant effect on Cdk4, as seen from the considerable difference in the expression and localization of Cdk4 protein in oocytes after IVM.