Acta Veterinaria et Zootechnica Sinica ›› 2025, Vol. 56 ›› Issue (9): 4432-4451.doi: 10.11843/j.issn.0366-6964.2025.09.025

• Animal Biotechnology and Reproduction • Previous Articles     Next Articles

Mechanisms of Developmental Competence Differences of Oocytes from Different Grades of Bovine Cumulus-Oocyte Complexes after in Vitro Maturation

WANG Rui(), HENG Nuo, HU Yingfan, WANG Huan, ZHU Ni, HE Wei, XUAN Xiuli, HU Zhihui, XIONG Keng, GONG Jianfei, HAO Haisheng, ZHU Huabin, ZHAO Shanjiang*()   

  1. Key Laboratory of Livestock and Poultry Biological Breeding of the Ministry of Agriculture and Rural Affairs, Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing 100193, China
  • Received:2025-03-11 Online:2025-09-23 Published:2025-09-30
  • Contact: ZHAO Shanjiang E-mail:ruiwang202010@163.com;zhaoshanjiang@caas.cn

Abstract:

This study aimed to investigate the molecular mechanisms underlying the differences in developmental competence of oocytes from different grades of bovine cumulus-oocyte complexes (COCs) after in vitro maturation. Bovine COCs derived from ovaries of bovine from slaughterhouse were classified into two groups (grades Ⅰ-Ⅱ (better)and grades Ⅲ-Ⅳ (poor)) based on cumulus cell layers, compactness, and cytoplasm appearance according to the International Embryo Technology Society manual. The experiment was divided into 3 replicates, each replicate group contained more than 100 COCs. After in vitro maturation, transcriptome analysis of oocytes was performed using Smart-seq2 technology and the differentially expressed genes (DEGs) were validated. Non-targeted metabolomics was employed to analyze differential metabolites in the culture medium of different COC grades. The results showed that: 1) Grade Ⅲ-Ⅳ COCs exhibited significantly lower cleavage rate (60.59%±6.54%) and blastocyst rate (22.11%±2.79%) compared to grade Ⅰ-Ⅱ COCs (78.09%±3.01%, 32.56%±4.33%, P < 0.05); 2) Smart-seq2 analysis identified 541 significant DEGs between grade Ⅰ-Ⅱ and grade Ⅲ-Ⅳ oocytes before maturation, and 860 DEGs after 22-24 h of maturation (after in vitro maturation). GO and KEGG enrichment analyses revealed that these DEGs were primarily associated with glucose metabolism and oxidative phosphorylation pathways; 3) Digital PCR demonstrated significantly lower copy numbers of glycolysis-related gene PKM and electron transport chain complex Ⅰ inhibitor gene NDUFA4L2 in grade Ⅲ-Ⅳ oocytes compared to grade Ⅰ-Ⅱ (P < 0.01). After maturation, grade Ⅲ-Ⅳ oocytes showed significantly lower copy numbers of electron donor generation-related gene IDH3α compared to grade Ⅰ-Ⅱ (P < 0.05). Interestingly, grade Ⅲ-Ⅳ cumulus cells exhibited significantly lower NDUFA4L2 mRNA expression (P < 0.05) but higher PKM and IDH3α mRNA expression than grade Ⅰ-Ⅱ (P < 0.05, P < 0.01); 4) Metabolite analysis identified 69 significantly upregulated and 71 downregulated metabolites in different grades of bovine cumulus-oocyte complexes culture medium. Further functional enrichment analysis showed these metabolites were primarily involved in tricarboxylic acid cycle (TCA), and glycolysis/gluconeogenesis pathways. Relative abundance analysis of key metabolites (α-D-glucose, pyruvate, lactate) revealed significantly higher α-D-glucose content in grade Ⅲ-Ⅳ maturation medium (P < 0.01); 5) Supplementation of sodium pyruvate, a glycolysis product, significantly improved cleavage rate (72.54%±4.79% vs. 61.71%±4.75%) and blastocyst rate (30.63%±4.15% vs. 22.72%±2.39%, P < 0.05) in grade Ⅲ-Ⅳ COCs. This study suggests that the poor developmental competence of grade Ⅲ-Ⅳ COCs after in vitro maturation may result from insufficient glycolytic activity in oocytes coupled with insufficient energy substrate supply from surrounding cumulus cells. The addition of sodium pyruvate significantly improved the developmental competence of grade Ⅲ-Ⅳ COCs, which provide a theoretical basis for enhancing COC utilization and embryo production efficiency.

Key words: bovine, cumulus-oocyte complex, in vitro maturation, glucose metabolism, sodium pyruvate

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