Three slow skeletal muscle troponin genes in small-tailed Han sheep (Ovis aries): molecular cloning, characterization and expression analysis

Effects of feeding restriction on skeletal muscle development and functional analysis of TNNI1 in New Zealand white rabbits

While restricting nutrition can improve diseases related to the digestive tract, excessive restriction of food intake can also lead to malnutrition and delayed physical growth. Therefore, this brings the demand to study the effect and potential mechanism of restricted feeding on skeletal muscle development in rabbits. This study utilized hematoxylin-eosin (HE) staining to detect muscle fiber area which depicted significant reduction in skeletal muscle fiber upon 30% feed restriction (p < 0.05). The control group and 30% feed restricted group showed 615 deferentially expressed genes (DEGs). Through the GO and KEGG functional enrichment analysis demonstrated 28 DEGs related to muscle development. KEGG analysis showed enrichment of pathways including PI3K/Akt signaling pathway, MAPK signaling pathway, and Hedgehog signaling pathway. Further, the full length of troponin I1, slow skeletal type (TNNI1) was cloned. We studied the expression of skeletal muscle differentiation-related genes such as MyoD, Myf5 gene and Desmin. Specifically, the TNNI1 gene overexpression and knockdown studies were conducted. The over-expression of TNNI1 significantly enhanced the expression of the skeletal muscle development-related genes. Contrastingly, the silencing of TNNI1 gene reduced the expression significantly. These findings showed that TNNI1 may be a regulator for regulating the expression of muscle development-related genes.

Naringin induces skeletal muscle fiber type transformation via AMPK/PGC-1α signaling pathway in mice and C2C12 myotubes

A large number of studies have shown that polyphenols can regulate skeletal muscle fiber type transformation through AMPK signal. However, the effects and mechanism of naringin (a natural polyphenol) on muscle fiber type transformation still remains unclear. Thus, we hypothesized that naringin would induce the transformation of skeletal muscle fibers from type II to type I by AMPK signaling. C2C12 myotubes and BALB/c mice models were used to test this hypothesis. We found that naringin significantly increased the protein expression of slow myosin heavy chain (MyHC), myoglobin and troponin I type I slow skeletal (Troponin I-SS) and the activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH), and significantly decreased fast MyHC protein expression and lactate dehydrogenase (LDH) activity, accompanied by the activation of AMPK and the activity of peroxisome proliferator activated receptor-γ coactivator-1α (PGC-1α) in mice and C2C12 myotubes. Further inhibition of AMPK activity by compound C showed that the above effects were significantly inhibited in C2C12 myotubes. In conclusion, naringin promotes the transformation of skeletal muscle fibers from type II to type I through AMPK/PGC-1α signaling pathway, which not only enriches the nutritional and physiological functions of naringin, but also provides a theoretical basis for the regulation of muscle fiber type transformation by nutritional approaches.

MicroRNA‑23a‑5p mediates the proliferation and differentiation of C2C12 myoblasts

Skeletal myogenesis is a highly ordered and complex biological process that is mediated by numerous regulatory factors. In previous studies, it has been demonstrated that microRNAs (miRs) and long non-coding RNAs (lncRNAs) serve key roles in skeletal myogenesis. The present study showed that the expression levels of miR-23a-5p showed a dynamic change from decrease to increase during C2C12 myoblast proliferation and differentiation. Functional analysis using 5-ethynyl-2′-deoxyuridine proliferation and Cell Counting Kit-8 detection assays indicated that overexpression of miR-23a-5p significantly promoted C2C12 myoblast proliferation compared with the negative control. In addition, in C2C12 myoblasts transfected with miR-23a-5p mimics, increased expression levels of regulators associated with cell proliferation (Cyclin E, CCND1 and Cyclin B) were observed compared with the negative control. By contrast, overexpression of miR-23a-5p decreased the expression levels of specific-myogenesis factors (MyoD, MyoG and Myf5) and decreased C2C12 myoblast differentiation. Luciferase activity assays indicated that miR-23a-5p suppressed the luciferase activity of lncDum. Further analysis demonstrated that miR-23a-5p not only showed an opposite expression level pattern compared with lncDum, which was first increased and then decreased, but also had an opposite effect on the proliferation and differentiation of C2C12 myoblasts compared with lncDum which inhibited cell proliferation and promoted cell differentiation. Taken together, these results indicated that miR-23a-5p may mediate the proliferation and differentiation of C2C12 myoblasts, which may be involved in lncDum regulation.

Ovine congenital progressive muscular dystrophy (OCPMD) is a model of TNNT1 congenital myopathy

Ovine congenital progressive muscular dystrophy (OCPMD) was first described in Merino sheep flocks in Queensland and Western Australia in the 1960s and 1970s. The most prominent feature of the disease is a distinctive gait with stiffness of the hind limbs that can be seen as early as 3 weeks after birth. The disease is progressive. Histopathological examination had revealed dystrophic changes specifically in type I (slow) myofibres, while electron microscopy had demonstrated abundant nemaline bodies. Therefore, it was never certain whether the disease was a dystrophy or a congenital myopathy with dystrophic features. In this study, we performed whole genome sequencing of OCPMD sheep and identified a single base deletion at the splice donor site (+ 1) of intron 13 in the type I myofibre-specific TNNT1 gene (KT218690 c.614 + 1delG). All affected sheep were homozygous for this variant. Examination of TNNT1 splicing by RT-PCR showed intron retention and premature termination, which disrupts the highly conserved 14 amino acid C-terminus. The variant did not reduce TNNT1 protein levels or affect its localization but impaired its ability to modulate muscle contraction in response to Ca²⁺ levels. Identification of the causative variant in TNNT1 finally clarifies that the OCPMD sheep is in fact a large animal model of TNNT1 congenital myopathy. This model could now be used for testing molecular or gene therapies.

The specificity protein 3 (SP3) gene in ducks (Anas platyrhynchos): cloning, characterization and expression during viral infection

Specificity Protein 3 (SP3) is a newly identified regulator of tumor growth and invasiveness in humans. In this study, we identified and characterized the function of duck SP3 (duSP3). The full-length cDNA sequence of the duSP3 gene was cloned via rapid amplification of cDNA ends. It contained 2468 nucleotides, including a 111 base pair (bp) 5'-untranslated region (UTR), 215 bp 3'-UTR, and 2142 bp open reading frame (ORF), which encoded a 713 amino acid (AA) strongly conserved with Avian SP3. Tissue specificity analysis demonstrated that duSP3 was constitutively expressed in the eight tissues tested: liver, spleen, lung, heart, kidney, thymus, breast, and leg; and low expression levels were observed in all tissues, except the spleen and thymus. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis revealed that duSP3 expression rapidly increased in vitro after stimulation with both the hepatitis virus (DHV-1) and polyriboinosinic polyribocytidylic acid (poly(I:C)). However, the expression under these treatments varied in kidney and liver tissues; in the liver, duSP3 increased significantly at 36 h after the DHV-1 treatment and peaked at 72 h after poly(I:C) stimulation. These results suggested that SP3 may play a positive role in immune responses against viral infections in ducks.

Sheep skeletal muscle transcriptome analysis reveals muscle growth regulatory lncRNAs

As widely distributed domestic animals, sheep are an important species and the source of mutton. In this study, we aimed to evaluate the regulatory lncRNAs associated with muscle growth and development between high production mutton sheep (Dorper sheep and Qianhua Mutton Merino sheep) and low production mutton sheep (Small-tailed Han sheep). In total, 39 lncRNAs were found to be differentially expressed. Using co-expression analysis and functional annotation, 1,206 co-expression interactions were found between 32 lncRNAs and 369 genes, and 29 of these lncRNAs were found to be associated with muscle development, metabolism, cell proliferation and apoptosis. lncRNA–mRNA interactions revealed 6 lncRNAs as hub lncRNAs. Moreover, three lncRNAs and their associated co-expressed genes were demonstrated by cis-regulatory gene analyses, and we also found a potential regulatory relationship between the pseudogene lncRNA LOC101121401 and its parent gene FTH1. This study provides a genome-wide resolution of lncRNA and mRNA regulation in muscles from mutton sheep.