Abstract
The dynamic process involving the selection and maturation of follicles is regulated and controlled by a highly synchronized and exquisitely timed cascade of gene expression. Studies have shown that long non-coding RNA (lncRNA) is essential for the normal maintenance of animal reproductive function and has an important regulatory function in ovarian development and hormone secretion. In this study, a total of 2076 lncRNAs (1362 known lncRNAs and 714 new lncRNAs) and 25,491 mRNAs were identified in libraries constructed from Duroc ovaries on days 0, 2 and 4 of follicle development. lncRNAs were shorter, had fewer exons, exhibited a shorter ORF (Open Reading Frame) length and lower expression levels, and were less conserved than mRNAs. Furthermore, 1694 transcripts (140 lncRNAs and 1554 mRNAs) were found to be differentially expressed in pairwise comparisons. A total of 6945 co-localized mRNAs were detected in cis in 2076 lncRNAs. The most enriched GO (Gene Ontology) terms were related to developmental processes. KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway analysis revealed that the differentially expressed lncRNAs targeted mRNAs, and the differentially expressed mRNAs were related to the TGF-β signaling pathway, the PI3K-Akt signaling pathway, the Retinol metabolic pathway and the Wnt signaling pathway. This study deepened our understanding of the genetic basis and molecular mechanisms of follicular development in pigs.
Highlights
Fecundity is a major factor to be addressed in increasing the efficiency of the pig industry, and litter size is one of the main objective traits for improving pig breeding
We described the characteristics of 2076 long non-coding RNA (lncRNA) and 25,491 mRNAs
Our results indicated that the previously known and novel lncRNAs were shorter than mRNAs (Figure 2A); their expressions levels were lower than those of mRNAs (Figure 2E); and their genes tended to contain fewer exons (Figure 2B)
Summary
Fecundity is a major factor to be addressed in increasing the efficiency of the pig industry, and litter size is one of the main objective traits for improving pig breeding. Ovulation is the first determinant factor for litter size, and some studies have shown that selection according to ovulation numbers can increase litter size in sows [1]. The ovulation rate of Duroc pigs in each estrous cycle is only 12.3 on average, and because of the decreased follicular phase selection period of this breed, it cannot be treated in the same way as high-yield sows to maintain a larger medium-follicular library [2]. Each stage in the normal ovarian life cycle involves a highly synchronized and elaborate cascade of gene expression. The regulation of follicular and oocyte maturation is not a simple cascade but rather a complex multifactorial regulatory process that requires specific genes to be accurately expressed at particular times [3]
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