Abstract
MicroRNAs (miRNAs) are non-coding small miRNAs ~22 nucleotides in length and play a vital role in muscle development by binding to messenger RNAs (mRNAs). Large White (LW, a lean type pig) and Meishan pigs (MS, a Chinese indigenous obese breed) have significant postnatal phenotype differences in growth rate, muscle mass and meat quality, and these differences are programmed during prenatal muscle development. Little research shed light directly on the miRNA transcriptome difference in prenatal muscles between these two distinct pig breeds. Myofiber phenotypes of LW and MS were measured at developmental stages of 35, 55 and 90 days post-conception (dpc), which revealed that the myogenesis process is more intense in MS than in LW at 35 dpc. To investigate the role of miRNAs involved in regulating muscle development at earlier stages of myogenesis and decipher the miRNAs transcriptome difference between LW and MS, here, the miRNAomes of longissimus dorsi muscle collected at 35 dpc from female LW and MS were analyzed by deep sequencing. Overall, 1147 unique miRNAs comprising 434 known miRNAs, 239 conserved miRNAs and 474 candidate miRNAs were identified. Expression analysis of the 10 most abundant miRNAs in every library indicated that functional miRNAome may be a small amount and tend to be greater expressed. These sets of miRNA may play house keeping roles that were involved in myogenesis. A total of 87 miRNAs were significantly differentially expressed between LW and MS (reads > 1000, P < 0.05). Gene ontology (GO) and KEGG pathway enrichment analysis revealed that the differentially expressed miRNAs (DE miRNAs) were associated mainly with muscle contraction, WNT, mTOR, and MAPK signaling pathways. Some myogenesis related miRNAs (miR-133, miR-1, miR-206 and miR-148a) are highly abundant in MS, while other miRNAs (let-7 family, miR-214, miR-181) highly expressed in LW. In addition, the expression patterns of miRNAs (miR-1, -133, -206) at three prenatal stages (35, 55 and 90 dpc) were determined using qRT-PCR. Notably, ssc-miR-133 was significantly more highly expressed in LW pigs skeletal muscle at all prenatal stages compared with its expression in LW pigs skeletal muscle. Taken together, the main functional miRNAs during muscle development are different between lean and obese pig breeds. The present study adds new information to existing data on porcine miRNAs and will be helpful to investigate the dominant (main functional) muscle-related miRNAs sets in different pig breeds.
Highlights
Lean pig breeds, such as Large White (LW), have been intensively selected over the past decades for improved growth rate and muscularity, which is believed to have led to deterioration in meat quality [1]
Primary myofiber morphology and transcriptome data To study whether the myogenesis process was different between LW and MS pigs during embryonic period, myofiber density and diameter were determined for porcine embryo in the 35, 55 and 90 dpc, respectively
All these results suggest that the myogenesis process of primary myofiber is more intense in MS than in LW
Summary
Lean pig breeds, such as Large White (LW), have been intensively selected over the past decades for improved growth rate and muscularity, which is believed to have led to deterioration in meat quality [1]. The obese pig breeds, such as Meishan (MS) pigs, exhibit lower growth rate, poor feed efficiency and lower lean meat content, but sensory quality of their meat is superior [2], mainly because of relatively greater intramuscular fat content and reddish meat color [3]. Both total number of fibers (TNF) and fiber types are related to meat quality. High TNF results in increasing muscle fiber size, which influence meat quality negatively in drip loss and tenderness [7, 8]. The above analysis indicate that the differential meat quality between LW and MS pig breeds already starts to develop during early prenatal development
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