Effects of cooling on meiotic spindle structure and chromosome alignment within in vitro matured porcine oocytes.
Meiotic spindle structure and chromosome alignment were examined after porcine oocytes were cooled at metaphase II (M II) stage. Cumulus-oocyte complexes (COCs) collected from medium size follicles were cultured in an oocyte maturation medium at 39 degrees C, 5% CO(2) in air for 44 hr. At the end of culture, oocytes were removed from cumulus cells and cooled to 24 or 4 degrees C for 5, 30, or 120 min in a solution with or without 1.5 M dimethyl sulfoxide (DMSO). After being cooled, oocytes were either fixed immediately for examination of the meiotic spindle and chromosome alignment or returned to maturation medium at 39 degrees C for 2 hr for examination of spindle recovery. Most oocytes (65-71%) cooled to 24 degrees C showed partially depolymerized spindles but 81-92% of oocytes cooled at 4 degrees C did not have a spindle after cooling for 120 min. Quicker disassembly of spindles in the oocytes was observed at 4 degrees C than at 24 degrees C. Cooling also induced chromosome abnormality, which was indicated by dispersed chromosomes in the cytoplasm. Limited spindle recovery was observed in the oocytes cooled to both 4 and 24 degrees C regardless of cooling time. The effect of cooling on the spindle organization and chromosome alignment was not influenced by the presence of DMSO. These results indicate that the meiotic spindles in porcine M II oocytes are very sensitive to a drop in the temperature. Both spindle and chromosomes were damaged during cooling, and such damage was not reversible by incubating the oocytes after they had been cooled.
Liu
Rui-Hua
RH
State Key Laboratory of Reproductive Biology, Institute of Zoology, Chinese Academy of Science, Beijing 100080, China.
Sun
Qing-Yuan
QY
Li
Yong-Hai
YH
Jiao
Li-Hong
LH
Wang
Wei-Hua
WH
D000818:Animals; D002875:Chromosomes / Q000502:physiology*; D003080:Cold Temperature; D006358:Hot Temperature; D008540:Meiosis / Q000502:physiology*; D009865:Oocytes / Q000502:physiology*; D008941:Spindle Apparatus / Q000502:physiology*; D013552:Swine / Q000502:physiology