title: Cytoplasmic maturation for activation of pig follicular oocytes cultured and arrested at metaphase I.
abstract: A large population (62-90%) of pig follicular oocytes can mature to metaphase II after culture for 48 h. However, a proportion (6-22%) remain in an immature stage at metaphase I (metaphase I-arrested). The main objective of this study was to determine whether the cytoplasm of metaphase I-arrested pig oocytes is capable of being activated by sperm penetration or parthenogenetic stimulation. After culture for 48 h, oocytes without a polar body (73% were shown to be at metaphase I after staining) and those with a polar body (94% were at metaphase II) were fertilized in vitro. A total of 69% and 62% of the oocytes were activated to form a female pronucleus, respectively, and the rate of polar body extrusion induced by fertilization in the activated oocytes was 90% (the first polar body) and 95% (the second polar body), respectively. When oocytes without and with a polar body were stimulated with an electric pulse, 53% and 81% of the oocytes were activated, respectively. The rate of polar body extrusion in the activated oocytes was 73% (the first polar body) and 79% (the second polar body), respectively. In contrast, young metaphase I oocytes cultured for 24 h had low (6%) or zero activation rate after in vitro fertilization or electric pulse stimulation. However, about one-third of the young metaphase I oocytes penetrated by spermatozoa after in vitro fertilization responded to electric pulse 12 h after insemination, and almost all (93%) were activated when they were stimulated 24 h after insemination. Patterns of polypeptide synthesis and histone H1 kinase activity were similar in metaphase I-arrested and metaphase II oocytes, and were characterized by increase in a 25 kDa polypeptide and by decrease in kinase activity. Although the first step of meiotic division is impaired, these results indicate that metaphase I-arrested oocytes are mature cytoplasmically.
authors.affiliation: Department of Genetic Resources II, National Institute of Agrobiological Resources, Ibaraki, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kikuchi
authors.forename: T
authors.initials: T
authors.lastname: Nagai
authors.forename: J
authors.initials: J
authors.lastname: Ding
authors.forename: N
authors.initials: N
authors.lastname: Yamauchi
authors.forename: J
authors.initials: J
authors.lastname: Noguchi
authors.forename: Y
authors.initials: Y
authors.lastname: Izaike
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003593:Cytoplasm / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D005307:Fertilization in Vitro; D008297:Male; D016200:Maturation-Promoting Factor / Q000378:metabolism; D008677:Metaphase; D008858:Microscopy, Phase-Contrast; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D009866:Oogenesis / Q000502:physiology*; D010452:Peptide Biosynthesis; D013084:Sperm-Ovum Interactions; D013552:Swine / Q000502:physiology*
chemical_list: D016200:Maturation-Promoting Factor