Comparative analysis of chromatin accessibility in porcine oocytes from follicles of different sizes

Chromatin accessibility and transcription levels during oocyte growth are important for oocyte maturation and subsequent development. However, chromatin accessibility changes in porcine oocytes during growth are unclear. The present study demonstrated that porcine oocytes derived from large follicles (LFO) exhibited higher developmental capacity than those derived from small follicles (SFO). Assay for transposase-accessible chromatin using sequencing (ATAC-seq) analysis identified 1117 and 1694 uniquely accessible chromatin peaks in LFO and SFO, respectively. Motif analysis of differential peaks revealed the top 10 significantly enriched transcription factor (TF)-binding motifs in LFO versus SFO, with only one increased peak (Spi1 binding site) and nine decreased peaks (NFYA, ATOH1, ZNF549, Foxn1, HAND2, THRB, NHLH2, FoxP1, and FoxP2 binding sites). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified key processes in the regulation of oocyte growth and maturation. Integration of ATAC-seq and RNA sequencing data revealed the top 10 hub genes involved in chromatin remodeling (MYSM1 and EZH2), histone modification (MYSM1, RNF2, USP1, EZH2, and MIER1), and transcription regulation (MYSM1, ASXL3, and MIER1), as well as those involved in metabolic processes and signal transduction (DOCK7, FGGY, DTL, and DNAJC6). All these genes exhibited increased expression levels in LFO versus SFO. In conclusion, the study demonstrated the dynamic nature of chromatin accessibility during porcine oocyte growth and revealed the TFs and genes closely associated with oocyte growth and maturation. These findings provide new insight into porcine oocyte growth and offer a potential strategy to enhance the in vitro developmental ability of SFO.