Extended In Vitro Maturation Reveals a Prolonged Nuclear Maturation Window and Dynamic BAX/BCL-2 Regulation in...

Temporal changes in nuclear maturation, BAX/BCL-2 transcriptional dynamics, and functional competence during extended in vitro maturation (IVM) remain poorly characterized in dromedary camel oocytes. This study investigated nuclear maturation dynamics, BAX and BCL-2 expressions, and early cleavage competence during extended IVM. Oocytes were evaluated at 0, 24, 30, 36, and 48 h for nuclear maturation, while transcript abundance was analyzed by reverse-transcription quantitative PCR (RT-qPCR) using three independent biological replicates per time point. Early cleavage following artificial activation was compared between 36 and 48 h. The proportion of metaphase II (MII) oocytes increased from 36.36% at 30 h to 69.36% at 36 h and 84.27% at 48 h, with no significant difference between 36 and 48 h. At 24 h, both BAX and BCL-2 were markedly reduced, but the greater reduction in BCL-2 produced the highest relative BAX/BCL-2 balance. Between 24 and 30 h, BCL-2 increased markedly and the relative BAX/BCL-2 balance declined sharply, remaining low at 36 and 48 h. Cleavage rates were 10.05 ± 0.92% and 12.81 ± 3.45% at 36 and 48 h, respectively, with no significant difference (p = 0.299). These findings identify an extended nuclear-maturation window spanning 36-48 h, accompanied by distinct changes in BAX/BCL-2 transcriptional balance without a detectable reduction in early cleavage competence.