Due to the increasing demand for producing chickens with high meat quality, there is a need to determine its mode of action on chicken meat quality traits across a wider age spectrum. In this study, five groups of 200 male Da-Heng meat type birds were reared until slaughter age of 60, 90, 120, 150, 180 days old and breast muscle performance, meat quality traits, and myofiber characteristics were evaluated. The larger body weight and breast weight of chicken are based on larger myofiber diameter and area, less myofiber density for the older birds than younger birds. There was an age effect on all meat quality traits of chicken breast muscle (p < 0.05). Older chickens often presented a higher pH, lower drip loss, higher shear force, darker, and redder breast meat. The correlation coefficients showed that myofiber characteristics played an important role in breast pH values, drip loss, and meat color (p < 0.05). Besides, significant correlations were also found between meat quality traits (p < 0.05). Further studies are needed to explore the biochemical character and potential molecular mechanism of chicken breast muscle to determine the factors that causes these age-related differences in meat quality in the current study.

The proliferation and differentiation of skeletal muscle satellite cells (SMSCs) play an important role in the development of skeletal muscle. Our previous sequencing data showed that miR-21-5p is one of the most abundant miRNAs in chicken skeletal muscle. Therefore, in this study, the spatiotemporal expression of miR-21-5p and its effects on skeletal muscle development of chickens were explored using in vitro cultured SMSCs as a model. The results in this study showed that miR-21-5p was highly expressed in the skeletal muscle of chickens. The overexpression of miR-21-5p promoted the proliferation of SMSCs as evidenced by increased cell viability, increased cell number in the proliferative phase, and increased mRNA and protein expression of proliferation markers including PCNA, CDK2, and CCND1. Moreover, it was revealed that miR-21-5p promotes the formation of myotubes by modulating the expression of myogenic markers including MyoG, MyoD, and MyHC, whereas knockdown of miR-21-5p showed the opposite result. Gene prediction and dual fluorescence analysis confirmed that KLF3 was one of the direct target genes of miR-21-5p. We confirmed that, contrary to the function of miR-21-5p, KLF3 plays a negative role in the proliferation and differentiation of SMSCs. Si-KLF3 promotes cell number and proliferation activity, as well as the cell differentiation processes. Our results demonstrated that miR-21-5p promotes the proliferation and differentiation of SMSCs by targeting KLF3. Collectively, the results obtained in this study laid a foundation for exploring the mechanism through which miR-21-5p regulates SMSCs.

Intramuscular fat (IMF) is one of the crucial factors determining meat quality. IMF deposition depends on the hyperplasia and hypertrophy of intramuscular preadipocytes, in which genes and noncoding RNAs play an important regulatory role. According to previous transcriptome analysis, ANXA6 and miR-24-3p were identified as involved in lipid metabolism in breast muscle. In this study, we further investigated their function in the proliferation and differentiation of chicken intramuscular preadipocytes. The results indicated that overexpression of ANXA6 inhibited proliferation and promoted differentiation of intramuscular preadipocytes, while knockdown of ANXA6 promoted cell proliferation and inhibited adipogenic differentiation. miR-24-3p was proved to directly bind to the 3′ untranslated region (3′UTR) of ANXA6 by dual-luciferase reporter assay. The regulatory effect of miR-24-3p on the proliferation and differentiation of intramuscular preadipocytes was opposite to that of ANXA6. Besides, the overexpression vector of ANXA6 eliminated the impact of miR-24-3p mimics on intramuscular preadipocytes. In brief, we revealed that miR-24-3p promoted proliferation but inhibited differentiation of intramuscular preadipocytes by blocking ANXA6 expression, thus dominating IMF deposition in broilers. These findings may provide a novel target for improving chicken meat quality.

Recent studies in mice suggested that KLF5 (Kruppel like factor 5), a zinc-finger transcription factor, plays an important role in skeletal muscle development and regeneration. As an important factor in the process of muscle development, KLF5 participates in the regulation of the cell cycle, cell survival, and cell dryness under different environmental conditions, but it is not clear whether KLF5 participates in muscle atrophy. Therefore, we investigated whether KLF5 can regulate the atrophy of chicken satellite cells in vitro and examined its mechanism of action. qPCR showed that KLF5 gene knockdown promoted the expression of key genes in muscle atrophy. Subsequently, we sequenced and analyzed the transcriptomes of KLF5 silenced and control cells, and we showed that the differentially expressed genes were mainly enriched in 10 signaling pathways (P<0.05),with differential gene and enrichment analyses indicating that the Wnt signaling pathways are extremely important. In conclusion, our results indicate that KLF5 may regulate the atrophy of chicken skeletal muscle through the Wnt/β-catenin signaling pathway.

Reducing abdominal fat (AF) accumulation and increasing the level of intramuscular fat (IMF) simultaneously is a major breeding goal in the poultry industry. To explore the different molecular mechanisms underlying AF and IMF, gene expression profiles in the breast muscle (BM) and AF from three chicken breeds were analyzed. A total of 4737 shared DEGs were identified between BM and AF, of which 2602 DEGs were upregulated and 2135 DEGs were downregulated in the BM groups compared with the AF groups. DEGs involved in glycerophospholipid metabolism and glycerolipid metabolism were potential regulators, resulting in the difference in lipid metabolite accumulation between IMF and AF. The PPAR signaling pathway was the most important pathway involved in tissue-specific lipid deposition. Correlation analysis showed that most representative DEGs enriched in the PPAR signaling pathway, such as FABP5, PPARG, ACOX1, and GK2, were negatively correlated with PUFA-enriched glycerophospholipid molecules. Most DEGs related to glycerophospholipid metabolism, such as GPD2, GPD1, PEMT, CRLS1, and GBGT1, were positively correlated with glycerophospholipid molecules, especially DHA- and arachidonic acid (ARA)-containing glycerophospholipid molecules. This study elucidated the molecular mechanism underlying tissue-specific lipid deposition and poultry meat quality.