Running title: ROCK INHIBITION IN VITRIFIED-WARMED BOVINE OOCYTES

Cryotolerance of bovine matured oocytes is not fully practical even though promising vitrification procedure with ultra-rapid cooling rate was applied. The present study was conducted to investigate whether recovery culture of vitrified-warmed bovine oocytes with an inhibitor (Y-27632) of Rho-associated coiled-coil kinase (ROCK) can improve the developmental potential after in vitro fertilization (IVF) and in vitro culture. Immediately after warming, almost oocytes appeared morphological normal. Treatment of the post-warm oocytes with 10 µM Y-27632 for 2 h resulted in the significantly higher oocyte survival rate prior to the IVF, cleavage rate and blastocyst formation rate. Quality analysis of the resultant blastocysts in terms of total cell number and apoptotic cell ratio also showed the positive effect of the Y-27632 treatment. Time-dependent change in mitochondrial activity of the vitrified-warmed oocytes was not influenced by ROCK inhibition during the period of recovery culture. However, the ability of ooplasm to support single-aster formation was improved by the ROCK inhibition. Thus, inhibition of ROCK activity in vitrified-warmed bovine oocytes during a short-term recovery culture can lead to the higher developmental competence, probably due to decreased apoptosis and normalized function of microtubule-organizing center.