Development to the blastocyst stage of immature pig oocytes arrested before the metaphase-II stage and fertilized in vitro

• Published in: Animal reproduction science Vol. 90; no. 3; pp. 307 - 328
• Main Authors: Somfai, Tamás, Kikuchi, Kazuhiro, Medvedev, Sergey, Onishi, Akira, Iwamoto, Masaki, Fuchimoto, Dai-ichiro, Ozawa, Manabu, Noguchi, Junko, Kaneko, Hiroyuki, Ohnuma, Katsuhiko, Sato, Eimei, Nagai, Takashi
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2005
• Subjects: Animals; blastocyst; Blastocyst - physiology; Cells, Cultured; chromosome number; cumulus oophorus; cytoplasm; diploidy; embryogenesis; Embryonic Development; Female; Fertilization in Vitro; food animals; In vitro fertilization; meiosis; Metaphase; Oocytes; Oocytes - cytology; Oocytes - growth & development; Pig blastocysts; sows; Swine; triploidy; In vitro fertilization; Pig blastocysts; Oocytes
• ISSN: 0378-4320; 1873-2232
• DOI: 10.1016/j.anireprosci.2005.03.018

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.