The morphology of porcine oocytes is associated with zona pellucida glycoprotein 3 and integrin beta 2 protein levels

The morphology and quality of oocytes is set during oo- and folliculo-genesis, and is completed during final maturation. Early embryonic development is associated with the morphology of the cumulus-oocyte-complex (COC). However, current knowledge of the possible relationships between oocyte morphology and the level of proteins within the oocyte, which may reflect fertilization ability, is insufficient. Using western-blot analysis and confocal microscopic observation, we determined the levels of integrin beta-2 (integrin p2) and glycoprotein 3 (pZP3) protein levels in the porcine zona pellucida of four morphologically different types of oocytes, graded according to their cytoplasmic composition and cumulus structure. The level of integrin p2 protein was increased in grade I and II oocytes as compared to other grades (P < 0.05). Moreover, the level of pZP3 protein was 3-4 fold higher in grade I oocytes (P < 0.01). We suggest that COC morphology may be associated with oocyte fertilization ability with respect to its sperm-oocyte interaction gene expression, which is the result of increased accumulation of specific proteins prior to fertilization in higher quality oocytes. Higher quality oocytes may also reflect better fertilization ability.