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 beta 2) 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 beta 2 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.