Identification of circRNA-associated ceRNA networks using longissimus thoracis of pigs of different breeds and growth stages.
BACKGROUND
Long-term artificial selection for growth rate and lean meat rate has eventually led to meat quality deterioration. Muscle fiber type is a key factor that markedly affects meat quality. circRNAs have been reported to participate in diverse biological activities, including myofiber growth and development; thus, we herein compared porcine circRNA transcriptome between oxidative and glycolytic muscle tissues.


RESULTS
Longissimus thoracis muscle tissues were obtained from Lantang and Landrace pigs at birth (LT1D and LW1D, respectively) and 90 postnatal days (LT90D and LW90D, respectively). Hematoxylin and eosin staining and quantitative real-time PCR revealed that all structural traits of the muscle showed large variations between different breeds and growth stages. In total, 329 known miRNAs and 42,081 transcript candidates were identified; 6,962 differentially expressed transcripts were found to play a key role in myogenesis by gene ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses. In addition, 3,352 circRNAs were identified using five predicting algorithms, and 104 circRNA candidates were differentially expressed. Integrated analysis of differentially expressed miRNAs, mRNAs, and circRNAs led to the identification of 777, 855, and 22 convincing ceRNA interactions in LT1D vs. LT90D, LW1D vs. LW90D, and LT90D vs. LW90D, respectively. Finally, we identified a circRNA candidate circKANSL1L, which showed high homology between mice and pigs, and it was found to inhibit the proliferation of C2C12 cells but promote their differentiation.


CONCLUSIONS
We identified genome-wide circRNAs in 0- and 90-day-old Lantang and Landrace pigs by RNA-seq and found that circRNAs were abundant, differentially expressed, and associated with myogenesis. Our results should serve as a reference for future studies on pork quality.