Comparative transcriptome analysis identifies important maternal molecules and associated biological pathways for pig and human mature oocytes

Recent researches reveal that during oocyte maturation, species-specific molecular profile exists and has important functional roles. However, molecular differences between pig (a larger animal model for human reproduction) and human mature oocytes remain unknown. Here, by comparative transcriptome analyses of single-cell RNA-seq data, we aimed to identify the common and unique maternal factors and associated biological processes between in vivo and in vitro matured pig oocytes, and between in vitro matured human and pig oocytes. Annotated protein-coding mRNAs were identified in pig in vivo (11,147) and in vitro (11,997), and human in vitro (14,491) MII oocytes, respectively. For in vivo and in vitro derived pig MII oocytes, 10,551 annotated maternal mRNAs were common, mainly enriched in signalling pathways such as cell cycle, oocyte meiosis, microtubule cytoskeleton, MAPK, RNA processing/binding. Besides, in vivo (596) and in vitro (1446) pig MII-specific mRNAs and their involved signalling pathways (in vivo: Bmp, calcium-mediated signalling, PI3K-Akt; in vitro: growth factor activity, JAK-STAT, cytokine-cytokine receptor interaction, calcium signalling pathway) were also found. As for in vitro derived human and pig MII oocytes, 10,285 annotated mRNAs were common, enriched in a variety of signalling pathways (cell cycle, oocyte meiosis, microtubule, AMPK, RNA splicing, protein serine/threonine kinase activity, etc). In vitro MII-specific mRNAs were found for humans (4206) and pigs (1712), which were also enriched in species-specific signalling pathways (humans: golgi-related terms, transcription repressor and hormone activity; pigs: ATP biosynthetic process, G protein-coupled peptide receptor activity, animoacyl-tRNA biosynthesis), respectively. These findings improve our understanding on oocyte maturation, and also the limitations of pig model for human oocyte maturation and fertilization.