Canine oocyte diameter in relation to meiotic competence and sperm penetration

摘要

This study was conducted to determine the diameter of canine oocytes that are able to attain full meiotic competence and sperm penetration. Oocytes were collected from ovaries of bitches at various stages of the estrous cycle. Only healthy-looking cumulus-oocyte complexes were used for in vitro maturation, and were divided into four groups based on diameter: =120 #mu#m. Following in vitro maturation or fertilization, oocytes were stained to assess nuclear maturation and penetration rates. The mean oocyte diameter was 108.5 +- 0.4 #mu#m; The oocytes displayed size-related ability to undergo meiotic maturation. After culture for 72 h, the rates of oocytes that remained at the germinal vesicle stage in the <110 #mu#m groups were significantly higher (P<0.01) than in the >=110 #mu#m groups. None of the oocytes <110 #mu#m reached metaphase 11 (ME), but 4.9 and 21.5% of the oocytes that were greater than 110 and 120 #mu#m, respectively, progressed to Mil. After in vitro fertilization for 20 h, 10 to 25% of oocytes were penetrated by spermatozoa, but there were no clear relationships between oocyte diameter and penetration rates of the oocyte by sperm. In the <120 #mu#m groups, sperm penetration was mostly found in oocytes arrested at the germinal vesicle stage. However, a total of eight oocytes >=120 #mu#m in diameter were penetrated by spermatozoa, of which five oocytes reached MI1. These results , suggest that there is a clear relationship between oocyte diameter and meiotic competence, but no relationship between oocyte diameter and sperm penetration: Canine oocytes may have acquired meiotic competence once they reach at a diameter of 120 #mu#m, but the oocytes may allow the entry of spermatozoa into the ooplasm irrespective of oocyte diameter.