Vitrificazione di oociti immaturi di ovino

Studies were conducted to test the meiotic competence of immature ovine oocytes vitrified by the Minimal Essential Volume Technique (MEMT) using cryotops. Oocytes from slaughterhouse ovaries were vitrified immediately after collection with (A) or without (B) curnulus cells. After thawing oocytes from group A were matured in vitro for 24h in TCM 199 + l 0% FCS+ LH, FSH+ cysteamine and oocytes from group B in the same medium with additional fresh cumulus cells. At the end of the culture all the oocytes were fixed and stained with glycerolHoechst 33342 to evaluate nuclear maturation and chromosome organisation. Moreover, cumulusoocyte communications before and after vitrification and meiotic spindle morphology were evaluated using specific fluorescent probes. The results indicate that oocytes vitrified without cumulus cells exhibited a significantly higher survival rate (20.3% vs 1.5%) and superior capability to mature to MII stage (62.1% vs 31.2%) compared with oocytes vitrified with cumulus cells. However, when distribution of chromosomes and microtubule were evaluated, 43.9% of MII oocytes from group B showed chromosome disorganisation associate with abnormal spindles morphology.