Duckett Susan K, Greene Maslyn A
Department of Animal and Veterinary Sciences, Clemson University, Clemson, SC, United States.
Front Vet Sci. 2022 Apr 15;9:883295. doi: 10.3389/fvets.2022.883295. eCollection 2022.
Intramuscular fat deposition in beef is a major determinant of carcass quality and value in the USA. The objective of this study was to examine changes in microRNA (miRNA) transcriptome that are involved with intramuscular fat deposition with time-on-concentrates (TOC). Yearling steers were individually fed a high concentrate diet and changes in intramuscular fat deposition were monitored by real-time ultrasound at 28 to 33 d intervals. Longissimus muscle biopsies collected on d 0, 92 and 124 TOC to examine changes in miRNA transcriptome that are involved in intramuscular fat deposition.
Steer body weight increased ( < 0.0001) at each weigh day during TOC. Fat thickness increased ( < 0.005) from d 28 to 124. Ribeye area was larger ( < 0.001) on d 124 than d 61, which was larger than d 0 and 28. Ultrasound intramuscular fat content was greater ( < 0.001) on d 92 and 124 compared to d 0, 28 or 61. Sequencing of the muscle biopsy samples identified one miRNA, bta-miR-122, that was up-regulated ( < 0.005) at d 92 and 124 compared to d 0. At d 92 TOC, mRNA expression levels of fatty acid binding protein 4 (FABP4) and elongase 6 (ELOVL6) were up-regulated ( < 0.01) compared to d 0; whereas at d 124, lipogenic genes involved in fatty acid synthesis, fatty acid transport, elongation and desaturation were highly up-regulated compared to d0.
Small RNA sequencing identified bta-miR-122 as a potential miRNA of interest that may be involved in intramuscular fat deposition with increasing TOC. Increased intramuscular fat content, as measured by real-time ultrasound, combined with differential gene expression suggests that preadipocyte differentiation may be stimulated first, which is followed by a global up-regulation of lipogenic genes involved in fatty acid synthesis that provide fatty acids for subsequent hypertrophy.
在美国，牛肉中的肌内脂肪沉积是胴体品质和价值的主要决定因素。本研究的目的是研究随着精料育肥时间（TOC）的变化，与肌内脂肪沉积相关的微小RNA（miRNA）转录组的变化。对周岁公牛单独饲喂高能量精料日粮，并每隔28至33天通过实时超声监测肌内脂肪沉积的变化。在TOC的第0天、第92天和第124天采集背最长肌活检样本，以研究参与肌内脂肪沉积的miRNA转录组的变化。
在TOC期间的每个称重日，公牛体重均增加（P<0.0001）。从第28天到第124天，脂肪厚度增加（P<0.005）。第124天的眼肌面积大于第61天（P<0.001），第61天大于第0天和第28天。与第0天、第28天或第61天相比，第92天和第124天的超声测定的肌内脂肪含量更高（P<0.001）。对肌肉活检样本进行测序，鉴定出一种miRNA，即bta-miR-122，与第0天相比，在第92天和第124天其表达上调（P<0.005）。在TOC第92天时，与第0天相比，脂肪酸结合蛋白4（FABP4）和延长酶6（ELOVL6）的mRNA表达水平上调（P<0.01）；而在第124天时，与第0天相比，参与脂肪酸合成、转运、延长和去饱和的生脂基因高度上调。
小RNA测序鉴定出bta-miR-122是一种潜在的相关miRNA，其可能随着TOC增加参与肌内脂肪沉积。通过实时超声测定的肌内脂肪含量增加，以及基因表达差异表明，可能首先刺激前体脂肪细胞分化，随后参与脂肪酸合成的生脂基因整体上调，为随后的肥大提供脂肪酸。
