Transcriptome analysis of miRNAs and mRNAs of medium-sized ovarian follicles of Duroc and Meishan sows

Litter size is an economically important trait in the swine industry. A high ovulation rate is a prerequisite for a large litter size. It differs among pig breeds with different genetic backgrounds. During the middle-late follicular stage, the medium-sized follicles (3-6.9 mm) of sows with a high ovulation rate can maintain their potential for development into ovulatory follicles. In this study, Meishan and Duroc sows were utilized as model animals due to their extreme litter size phenotypes. M2 follicles (5-6.9 mm) were collected on Day 4 of the follicular phase for high-throughput sequencing of small RNAs and mRNAs. Differentially expressed miRNAs (DEMs) and differentially expressed genes (DEGs) were analyzed. KEGG pathway and GO enrichment analyses were conducted to analyze the DEGs and the target genes of DEMs, resulting in the construction of a regulatory network of DEMsDEGs. A total of 402 miRNAs were identified, with 8 upregulated and 3 downregulated miRNAs in the Meishan group. KEGG pathway analysis revealed significant enrichment of target genes of DEMs in pathway such as Apoptosis, GnRH signaling pathway, MAPK signaling pathway, and PI3K-Akt signaling pathway. GO enrichment analysis revealed 1930 significantly enriched GO terms. KEGG pathway analysis of the DEGs revealed 13 significantly enriched pathways, including those involved in complement and coagulation cascades, ECMreceptor interactions, and PI3K-Akt signaling pathway. A total of 642 GO terms were significantly enriched. Through Pearson correlation analysis, 67 DEM-DEG pairs were identified, and 62 DEGs were found to be regulated by 9 DEMs. This study provides valuable insights into the function of miRNAs and mRNAs in regulating the growth and development of follicles.