Nucleocytoplasmic ratio of fully grown germinal vesicle oocytes is essential for mouse meiotic chromosome segregation and alignment, spindle shape and early embryonic development.
BACKGROUND
This study examined the effect of nucleocytoplasmic ratio of fully grown germinal vesicle (GV) oocytes on meiotic chromosome segregation and alignment, spindle shape, Ca(2+) oscillations and capacity of early embryonic development in mouse.


METHODS
GV oocytes with reduced volume (equal to 1/5 to 4/5 of an intact oocyte) were made by micromanipulation to remove different amounts of cytoplasm, and then matured and fertilized in vitro.


RESULTS
When >1/2 of GV oocyte cytoplasm was removed, the time-course of GV breakdown (GVBD) was delayed and oocyte maturation rate decreased significantly. Abnormal chromosome segregation rate increased if >1/2 of the cytoplasm was removed from the oocyte. Length and structure of meiotic spindle and chromosome alignment were also impaired by the reduction of cytoplasmic volume. Once matured in vitro, the oocytes could undergo Sr(2+)-induced Ca(2+) oscillations and form pronuclei in a manner independent of nucleocytoplasmic ratio, but their ability to develop to 2-cell embryos was affected if >1/2 of their cytoplasm was removed from the GV oocytes.


CONCLUSIONS
These results suggest that nucleocytoplasmic ratio is essential for normal meiotic chromosome segregation, spindle formation and chromosome alignment over the metaphase spindle, and development to 2-cell stage, for which 1/2 of the volume of the GV oocyte appears to be a threshold.
Cui
Long-Bo
LB
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing.
Huang
Xiu-Ying
XY
Sun
Fang-Zhen
FZ
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D002875:Chromosomes / Q000648:ultrastructure*; D003582:Cytogenetics / Q000379:methods; D003593:Cytoplasm / Q000378:metabolism*; D004622:Embryo, Mammalian / Q000502:physiology*; D047108:Embryonic Development; D005260:Female; D005306:Fertilization; D005307:Fertilization in Vitro; D008540:Meiosis; D051379:Mice; D009865:Oocytes / Q000378:metabolism* / Q000502:physiology*; D009991:Oscillometry; D008941:Spindle Apparatus; D013324:Strontium / Q000378:metabolism; D013997:Time Factors
D002118:Calcium; D013324:Strontium