title: Development to the blastocyst stage of immature pig oocytes arrested before the metaphase-II stage and fertilized in vitro.
abstract: In vitro fertilization (IVF) and embryonic development of mature and meiotically arrested porcine oocytes were compared in the present study. After in vitro maturation (IVM) of cumulus-oocyte complexes for 48 h, 75.4% of them extruded a visible polar body (PB). Most of the oocytes with a first polar body (PB+ group) were at the metaphase-II (M-II) stage (91.4%). Most of the oocytes without a visible polar body (PB- group) appeared to be arrested at the germinal vesicle (GV) (41.6%) and metaphase-I (M-I) (34.0%) stages. After IVF of oocytes (day of IVF=Day 0), there was no difference between PB+ and PB- groups in rates of sperm penetration, mono-spermy, however oocyte activation rate after penetration was greater in the PB+ than in the PB- group (P<0.05). On Day 2, there was no difference between rates of embryos cleaved at the 2-4 cell stages in PB+ and PB- groups (42.1+/-48.8% and 33.6+/-2.1%, respectively). On Day 4, the rate of PB+ embryos developing beyond the 4-cell stage was greater than that of PB- embryos (P<0.05, 31.7+/-3.9% and 14.1+/-1.5%, respectively), and PB+ embryos had more cells than the PB- embryos (P<0.05, 8.3+/-0.4 and 6.0+/-0.8 cells, respectively). On Day 6, a greater proportion of PB+ embryos developed to the blastocyst stage than did PB- embryos (P<0.05, 34.6+/-2.4% and 20.7+/-2.8%, respectively). However, when the GV oocytes of the PB- group were not included in recalculations, there was no difference in blastocyst rates between M-I arrested and M-II oocytes (35.3 and 34.6%, respectively). The number of blastomere nuclei in embryos obtained from the PB+ group (52.0+/-2.5) was greater than that from the PB- group (P<0.05, 29.1+/-2.8). The proportion of degenerated parts in the blastocysts, as determined by morphological appearance, was the same in the PB+ and PB- groups. Although the quality of PB+ embryos was enhanced as compared with that of the PB- group, the proportion of inner cell mass and trophectoderm cells in PB+ and PB- blastocysts did not differ (1:1.9 and 1:2.2, respectively). Chromosome analysis revealed that PB+ blastocysts had more diploidy (P<0.05, 69.7%) than did PB- blastocysts (44.0%), whereas PB- blastocysts had more triploid cells (P<0.05, 34.0%) than did PB+ oocytes (8.4%). These results indicate that pig oocytes arrested before the M-II stage (M-I oocytes) undergo cytoplasmic maturation during maturation culture and have the same ability to develop to blastocysts after IVF as M-II oocytes, but some of them resulted in degeneration or delayed development with poor embryo quality.
authors.affiliation: Developmental Biology Department, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan.
authors.forename: Tamás
authors.initials: T
authors.lastname: Somfai
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Sergey
authors.initials: S
authors.lastname: Medvedev
authors.forename: Akira
authors.initials: A
authors.lastname: Onishi
authors.forename: Masaki
authors.initials: M
authors.lastname: Iwamoto
authors.forename: Dai-Ichiro
authors.initials: D
authors.lastname: Fuchimoto
authors.forename: Manabu
authors.initials: M
authors.lastname: Ozawa
authors.forename: Junko
authors.initials: J
authors.lastname: Noguchi
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kaneko
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Ohnuma
authors.forename: Eimei
authors.initials: E
authors.lastname: Sato
authors.forename: Takashi
authors.initials: T
authors.lastname: Nagai
mesh_terms: D000818:Animals; D001755:Blastocyst / Q000502:physiology*; D002478:Cells, Cultured; D047108:Embryonic Development; D005260:Female; D005307:Fertilization in Vitro; D008677:Metaphase; D009865:Oocytes / Q000166:cytology / Q000254:growth & development*; D013552:Swine