Thesis (Ph.D.) - Cairo University - Faculty of Agriculture - Department of Animal Production

This study was performed to investigate cellular and molecular changes of buffalo cumulus-oocyte complexes (COCs) cultured under oxidative stress, and to assess developmental competence after maturation through, in vitro fertilization and early embryonic development up to the blastocyst stage. Morphologically good quality COCs (n=2672) were screened with brilliant cresy- blue (BCB) staining and then graded into three groups (BCB+, BCB - and control). Oocytes from the different groups were evaluated under low (5%) and high oxygen level (20 %), The progress of the nuclear maturation stage and the rate of cumulus expansion were assessed after 24 hrs of in vitro maturation. Ultra-structure of oocytes have been monitored using transmission electron microscope.The fluorescent intensity of lipid, mitochondria, and reactive oxygen species (ROS) were measured using different molecular probes. Transcript abundance of genes regulating different molecular pathways during oocyte maturation was profiled using Real-time PCR. The cumulus expansion of all oocyte groups under low oxygen tension (5%) was higher (P < 0.05) than those cultured under high oxygen tension (20%). Under high oxygen tension, low-competent oocytes (BCB -) showed the lowest maturation rate (P < 0.05). This was associated with an increase in ROS, which was against the BCB+ oocyte pattern. Ultra-structure examination indicated that under low oxygen tension the competent BCB+ oocytes had a higher rate of migration of cortical granules than BCB -. In parallel, the MAPK14 and CPT2 gene expression profile (P < 0.05) was increased under low compared to high oxygen tension

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