The effect of VEGF on the temporal–spatial change of α-tubulin and cortical granules of ovine oocytes matured in vitro

The effects of vascular endothelial growth factor (VEGF) on the temporal–spatial change of α-tubulin and cortical granules (CGs) in ovine oocytes matured in vitro were studied using human recombinant VEGF165 at 5ng/ml in maturation media. Immunofluorescence, confocal microscopy and orcein staining were used to evaluate cell cycle-dependent modifications in nuclear configuration, quality of the metaphase II oocytes, microtubule organizing centers (MTOCs) translocation, temporal and spatial redistribution of α-tubulin and CGs in ovine oocytes undergoing in vitro maturation. The percentage of oocytes that reached metaphase II (M-II) in the VEGF-treated and the control groups were 87.08% and 80.03% (P=0.077) at 18h and 87.42% and 83.89% (P=0.28) at 24h, respectively. The percentages of oocytes displaying a normal distribution of α-tubulin and chromosomes in M-II increased significantly (P=0.015) in the VEGF group (77.50%) compared to the control (62.60%). The percentage of oocytes with CGs transfering completely in cortex was significantly higher (P=0.002) in the VEGF group (79.24%) than in the control group (60.97%). VEGF promoted the MTOCs domains to disappear from the cortex and stimulated assembly of α-tubulin around chromosome domains when germinal vesicle breakdown (GVBD) was commencing. In conclusion, VEGF may improve the quality of nuclear and cytoplasmic maturation of ovine oocytes in vitro by its effect on temporal and spatial translocation or redistribution of α-tubulin and CGs and on the normal distribution of nuclear configuration.