Influence of Morphology, Follicle Size and Bcl‐2 and Bax Transcripts on the Developmental Competence of Bovine Oocytes

• Published in: Reproduction in domestic animals 2014-08, Vol.49 (4), p.576-583
• Main Authors: De Bem, THC, Adona, PR, Bressan, FF, Mesquita, LG, Chiaratti, MR, Meirelles, FV, Leal, CLV
• Format: Article
• Language: English
• Subjects: abnormal development; Animal reproduction; Animals; Apoptosis; Apoptosis - genetics; bcl-2-Associated X Protein - genetics; blastocyst; Cattle; Cumulus Cells - physiology; Cytoplasm; DNA Fragmentation; Embryo Culture Techniques - veterinary; embryogenesis; Embryonic Development; Female; Fertilization in Vitro - veterinary; Gene Expression; genes; Genes, bcl-2; In Situ Nick-End Labeling; Morphology; oocytes; Oocytes - chemistry; Oocytes - cytology; Oocytes - growth & development; Ovarian Follicle - anatomy & histology; RNA, Messenger - analysis; selection methods
• ISSN: 0936-6768; 1439-0531
• DOI: 10.1111/rda.12325

This study analysed two non‐invasive oocyte selection methods in relation to in vitro embryo development capacity and expression of apoptosis‐related genes. Selection was based on morphological quality of oocytes or follicle diameter. Oocytes were classified as grade I (GI ≥3 layers compact cumulus cells and homogeneous cytoplasm; grade II (GII ≤3 layers compact cells and homogeneous cytoplasm;, and grade III (GIII ≥3 layers, but cells with slight expansion and slightly granulated cytoplasm). Blastocyst development was lower for GII (28.5%) than for GIII (47.7%, p < 0.05), and GI was similar to both (36.9%, p > 0.05). Relative expression of Bcl‐2 gene was lower in the GI (1.0, p < 0.05) than in the GII (1.8) and GIII (2.2), which were not different (p > 0.05). There was no difference (p > 0.05) between GI (1.0), GII (0.92) and GIII (0.93) regarding the Bax transcript. However, the Bax and Bcl‐2 transcript ratios in GII (Bax; 0.92 and Bcl‐2; 1.8) and GIII (Bax; 0.93 and Bcl‐2; 2.2) were different (p < 0.05). Regarding oocytes from follicles of different sizes, cleavage and blastocyst rates for 1–3 mm (82.5; 23.7%) were lower (p < 0.05) than for 6–9 mm (95.6; 41.1%), but similar (p > 0.05) to 3–6 mm (93.7; 35.4%), which were not different (p > 0.05). Regarding Bax and Bcl‐2 expression, the oocytes were similar (p > 0.05) for 1–3 mm (Bax; 1.0 and Bcl‐2; 1.0), 3–6 mm (Bax; 1.0 and Bcl‐2; 0.93) and 6–9 mm (Bax; 0.92 and Bcl‐2; 0.91). In conclusion, oocyte selection based on morphological appearance does not guarantee the success of embryonic development. Additionally, the absence of apoptosis is not necessarily a benefit for the development of oocytes. Bovine COCs with initial signs of atresia may be used for the in vitro production of embryos, and COCs taken from follicles >3 mm in diameter are better suited to in vitro embryo development.