Modifications of the human oocyte plasma membrane protein pattern during preovulatory maturation.

Abstract

The plasma membrane protein pattern of human oocytes was established using a highly sensitive nonisotopic technique. Unfertilized, 2-day-old metaphase II (MII) and immature oocytes were biotinylated at 4 degrees C and zona pellucida were mechanically removed. Proteins were resolved by 7% SDS PAGE, and electrotransferred to PVDF membranes. Plasma membrane proteins were selectively detected by streptavidin-horseradish peroxidase (HRP) and enhanced chemoluminescence (ECL). Thirteen biotinylated polypeptide bands were identified in MII oocyte plasma membrane (126, 110, 98, 90, 77, 71, 64, 61, 58, 54, 50, 48, 44 kD). During maturation, the total amount of membrane proteins decreased dramatically from the germinal vesicle (GV) to the MII stage oocytes, while the relative proportion of the 71 kD band increased from 9.9% to 13.1% and 27.4% in GV, metaphase I, and MII stage oocytes, respectively. Improvement of the detection technique permitted to establish the protein profile of a single oocyte loaded per lane (n = 12). Five to ten polypeptides were identified, indicating a great polymorphism of the plasma protein pattern, even for oocytes from the same cohort. Hamster and mouse oocyte plasma membrane protein patterns were also investigated with the same technique. Both presented 15 bands, 12 of which had a molecular weight similar to those from the human oocytes. In conclusion, the protein pattern in the human plasma membrane appears qualitatively limited to 13 species, and quantitatively, their amount decreases during oocyte preovulatory maturation. A great polymorphism from one oocyte to another was detected. The protein pattern is highly conserved between human, hamster, and mouse oocytes. This very sensitive technique will allow further studies on the functional significance of this protein pattern.