الفهرس 
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Abstract
Recent study has revealed the role of cathepsin B in cumulus cells on the quality and developmental competence of bovine oocytes. This study was aimed to 1) investigate the role of cathepsin B during IVM and IVC processes, 2) evaluate the effect of its inhibition on the developmental competence and quality as well as providing with cryotolerant embryos. Cathepsin B activity as well as protein and gene expression were evaluated in good and poor quality COCs and embryos. Moreover, the effect of E-64 on the developmental competence of bovine COCs and embryos as well as providing cryotolerant embryos was studied. Furthermore, bovine COCs were exposed to heat stress at 41°C for 16 h and the protective effect of E-64 was investigated. Both cathepsin B avtivity and expression were found to be significantly higher in poor quality bovine oocytes and embryos than good quality ones. Moreover, E-64 was found to have a promising role in improving both developmental rate and quality of produced embryos after its addition either to IVM or IVC medium and had the ability to produce cryotolerant embryos. Furthermore, Addition of E-64 to the IVM medium significantly improved the developmental rate and quality of the produced embryos than heat stress group. from this study we could conclude that cathepsin B activity can be useful as a marker for inferior quality oocytes and embryos. Moreover, inhibition of cathepsin B strongly enhanced the developmental competence of bovine oocytes and embryos.