Developmental competence and expression of the MATER and ZAR1 genes in immature bovine oocytes selected by brilliant cresyl blue.

The objective of this work was to evaluate the selection of immature bovine oocytes by brilliant cresyl blue dye (BCB) and expression of transcripts MATER and ZAR1. Cumulus-oocyte complexes (COCs) from slaughterhouse ovaries were exposed to BCB diluted in mDPBS and incubated for 60 min at 38.5 degrees C in humidified air. After exposure those COCs were distributed in two groups, according to their cytoplasm colour: BCB+ (coloured cytoplasm) or BCB- (colourless cytoplasm). The control group was submitted to in vitro maturation (IVM) immediately after morphological selection and holding control group COCs were exposed to mDPBS without BCB but in the same incubation conditions of BCB+ and BCB- group. The COCs of all groups were submitted to IVM, in vitro fertilization (IVF) and in vitro culture (IVC). Cleavage rate (72 h post-insemination) was similar between control (65.3%) and BCB+ (64.4%) groups, but greater than (p < 0.05) holding control (49.8%) and BCB- (51.3%) groups. Blastocyst rate (192 h post-insemination) was not different between BCB+ (18.5%) and control (16.3%) groups, but greater (p < 0.05) than BCB- (8.4%) group. No difference was found for blastocyst rate between holding control group (14.2%), control and BCB+ groups. The relative expression of MATER and ZAR1 genes was evaluated by real-time PCR in immature oocytes collected from the control, holding control, BCB+ and BCB- groups. Despite the relative expression of MATER in holding control, BCB+ and BCB- were down regulated in comparison to control group there was no statistical difference (p > 0.05) in the relative expression of MATER and ZAR1 transcripts among groups. The results indicate that the BCB dye detects immature oocyte populations with different developmental competence, although no improvement in in vitro embryo production using oocytes exposed or not to BCB was observed. Development competence of immature oocytes exposed to BCB does not seem to be associated with variations in the expression of MATER and ZAR1 transcripts.