Sperm binding capacity of human zona pellucida derived from oocytes obtained from different sources
The important contributions of sperm-oocyte interaction to infertility diagnostics is well established. Scientists are urged to search for methods to improve the assessment of gamete interaction. Sperm binding and penetration assays have frequented the literature, reporting on various aspects of sperm-oocyte interaction using either microbisected or whole human oocytes during the assay procedure. The objective of the study was to evaluate additional zona pellucida sources which can be used during zona binding studies. Hemizonae were obtained from the following oocytes: 1) experiment 1, prophase I oocytes from post-mortem ovarian tissue from different age groups namely, 7 months, 5 years, 7 years, 12 years and 30 years; 2) experiment 2 used donated immature Prophase I oocytes from the IVF treatment program and 3) experiment 3 evaluated zona binding for hemizonae which were previously used in hemizona assays. Results indicated that, in experiment 1, ovarian age does not have any influence on the zona pellucida's capacity to bind spermatozoa. The mean number of bound sperm among the different age groups did not differ significantly, namely 38.9 ± 17 (7 months), 31.0 ± 27 (5 years), 49.3 ± 21 (7 years), 32.8 ± 18 (12 years) and 39.5 ± 17 (30 years). The pooled mean ± SD binding for all the age groups in experiment 1 was 37.7 ± 7. Likewise, the mean number of sperm bound (experiment 2) to zonae collected from oocytes using different ovulation induction regimes were 31.1 ± 20 (unstimulated), 54.4 ± 12 (HMG/HCG) and 15.3 ± 9 (HMG alone). The pooled binding data for experiment 2 were 33.0 ± 20. Results of experiment 3 indicated metaphase II oocytes with previous exposure to sperm retained its binding capacity indicating that hemizonae can be recycled for at least a second binding experiment. Zonae that had been exposed to sperm and that were subsequently stripped from bound sperm, revealed a mean number of bound sperm after re-insemination that were significantly higher than the prophase I oocytes namely, 115.0 ± 2.8 versus 35.6 ± 12 (P = 0.0001). In conclusion, the data highlights (i) new sources of human oocytes needed for sperm-oocyte interaction studies; (ii) the capability of the human zona pellucida to bind sperm after previous exposure and (iii) the importance of nuclear competence to obtain increased zona pellucida binding.