title: Accelerated modification of the zona pellucida is the primary cause of decreased fertilizability of oocytes in the 129 inbred mouse strain.
abstract: We investigated whether the small litter size in the 129 inbred mouse strain results from a reduction in oocyte fertilizability. Sensitivity of the zona pellucida to α-chymotrypsin was examined for oocytes collected at 14 h (shortly after ovulation), 17 h, and 20 h after hCG injection. Passage of spermatozoa through the zona pellucida (using an in vitro fertilization (IVF) technique) and the density of cortical granules were examined for oocytes collected at 14 and 17 h after hCG injection. The capability of the oolemma to fuse with the sperm plasma membrane was also evaluated by IVF using zona-free eggs. The zona pellucida became markedly resistant to the enzyme 17 h after hCG injection. IVF rates significantly decreased at this time. In addition, there was a significant reduction in the density of cortical granules. When zona-free oocytes were inseminated, high fertilization rates were obtained at both 17 and 14 h after hCG injection. These results indicate that accelerated modification of the zona pellucida primarily causes a decreased fertilizability of oocytes in 129 mice, resulting in the low reproductive performance of this strain.
authors.affiliation: Mitsubishi Kagaku Institute of Life Sciences (MITILS), Tokyo, Japan. hino@asahikawamed.ac.jp
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Hino
authors.forename: Kanako
authors.initials: K
authors.lastname: Oda
authors.forename: Kenji
authors.initials: K
authors.lastname: Nakamura
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tateno
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Toyoda
authors.forename: Minesuke
authors.initials: M
authors.lastname: Yokoyama
mesh_terms: D000818:Animals; D005260:Female; D005306:Fertilization / Q000502:physiology*; D005307:Fertilization in Vitro / Q000379:methods / Q000662:veterinary; D008297:Male; D051379:Mice; D057507:Mice, 129 Strain; D009865:Oocytes / Q000502:physiology*; D013084:Sperm-Ovum Interactions; D015044:Zona Pellucida / Q000378:metabolism*