MicroRNA调控哺乳动物骨骼肌发育

MicroRNA (miRNA)是一类长度大约为22 bp的小分子非编码RNA,广泛存在于哺乳动物中,部分miRNA表达具有时空和组织特异性。哺乳动物中miRNA主要通过与靶基因3° UTR区结合抑制其翻译,调控机体生物学功能。miRNA在哺乳动物骨骼肌发育中发挥重要调节作用。哺乳动物骨骼肌发育是一个复杂的生物学过程,包括骨骼肌干细胞增殖、迁移、分化,成肌细胞增殖、分化、肌管融合,肌纤维肥大,能量代谢,纤维类型转换等。miRNA参与骨骼肌发育的各个环节,通过靶向各个时期的关键因子调控骨骼肌发育。本文对miRNA在骨骼肌发育中的调控作用进行了综述,以期为深入理解骨骼肌发育规律提供参考。     

MiR-206在骨骼肌发育中的功能

微RNA(microRNA,miRNA)是一类在分子进化中十分保守的非编码RNA,长度约22个核苷酸,一般情况下它在转录后水平抑制基因表达。miRNA在细胞增殖、分化、凋亡等诸多生理过程中发挥着重要作用。有些miRNA具有组织特异性表达,其中miR-206是目前发现的唯一在骨骼肌中特异表达的miRNA,它在调节骨骼肌发生过程中扮演重要角色。miR-206表达异常与一些肌肉相关疾病如肌肉营养不良、肌萎缩性侧索硬化症等有关。此外,在Texel羊中,myostatin基因的一个点突变就产生了一个miR-206和miR-1的靶点,抑制了myostain基因的表达,从而产生了双肌表型。因此,miR-206有可能成为治疗肌肉相关疾病和畜禽改良育种的重要候选分子。     

Functional impact of the ryanodine receptor on the skeletal muscle L-type Ca(2+) channel

L-type Ca(2+) channel (L-channel) activity of the skeletal muscle dihydropyridine receptor is markedly enhanced by the skeletal muscle isoform of the ryanodine receptor (RyR1) (Nakai, J., R.T. Dirksen, H. T. Nguyen, I.N. Pessah, K.G. Beam, and P.D. Allen. 1996. Nature. 380:72-75.). However, the dependence of the biophysical and pharmacological properties of skeletal L-current on RyR1 has yet to be fully elucidated. Thus, we have evaluated the influence of RyR1 on the properties of macroscopic L-currents and intracellular charge movements in cultured skeletal myotubes derived from normal and "RyR1-knockout" (dyspedic) mice. Compared with normal myotubes, dyspedic myotubes exhibited a 40% reduction in the amount of maximal immobilization-resistant charge movement (Q(max), 7.5 +/- 0.8 and 4.5 +/- 0.4 nC/muF for normal and dyspedic myotubes, respectively) and an approximately fivefold reduction in the ratio of maximal L-channel conductance to charge movement (G(max)/Q(max)). Thus, RyR1 enhances both the expression level and Ca(2+) conducting activity of the skeletal L-channel. For both normal and dyspedic myotubes, the sum of two exponentials was required to fit L-current activation and resulted in extraction of the amplitudes (A(fast) and A(slow)) and time constants (tau(slow) and tau(fast)) for each component of the macroscopic current. In spite of a >10-fold in difference current density, L-currents in normal and dyspedic myotubes exhibited similar relative contributions of fast and slow components (at +40 mV; A(fast)/[A(fast) + A(slow)] approximately 0.25). However, both tau(fast) and tau(slow) were significantly (P < 0.02) faster for myotubes lacking the RyR1 protein (tau(fast), 8.5 +/- 1.2 and 4.4 +/- 0.5 ms; tau(slow), 79.5 +/- 10.5 and 34.6 +/- 3.7 ms at +40 mV for normal and dyspedic myotubes, respectively). In both normal and dyspedic myotubes, (-) Bay K 8644 (5 microM) caused a hyperpolarizing shift (approximately 10 mV) in the voltage dependence of channel activation and an 80% increase in peak L-current. However, the increase in peak L-current correlated with moderate increases in both A(slow) and A(fast) in normal myotubes, but a large increase in only A(fast) in dyspedic myotubes. Equimolar substitution of Ba(2+) for extracellular Ca(2+) increased both A(fast) and A(slow) in normal myotubes. The identical substitution in dyspedic myotubes failed to significantly alter the magnitude of either A(fast) or A(slow). These results demonstrate that RyR1 influences essential properties of skeletal L-channels (expression level, activation kinetics, modulation by dihydropyridine agonist, and divalent conductance) and supports the notion that RyR1 acts as an important allosteric modulator of the skeletal L-channel, analogous to that of a Ca(2+) channel accessory subunit.     

MicroRNA调控猪骨骼肌发育的研究进展

骨骼肌的生长发育是影响猪肉产量和品质的重要因素,其受遗传和营养等众多因素的精细调控。MicroRNA (miRNA)是一种长度约为22 nt的非编码RNA,通过与靶基因的mRNA 3′UTR序列结合,调控其转录后的表达发挥作用。近年来,大量的研究表明miRNA参与机体的生长发育、生殖、疾病等多种生命过程。本文对miRNA在猪骨骼肌发育调控中的作用进行了综述,以期为猪的遗传改良提供参考和借鉴。     

Cellular heterogeneity during vertebrate skeletal muscle development

Although skeletal muscles appear superficially alike at different anatomical locations, in reality there is considerably more diversity than previously anticipated. Heterogeneity is not only restricted to completely developed fibers, but is clearly apparent during development at the molecular, cellular and anatomical level. Multiple waves of muscle precursors with different features appear before birth and contribute to muscular diversification. Recent cell lineage and gene expression studies have expanded our knowledge on how skeletal muscle is formed and how its heterogeneity is generated. This review will present a comprehensive view of relevant findings in this field.     

虾红素对小鼠肌肉组织和骨骼肌细胞中能量代谢相关基因mRNA表达的影响

本试验用高、低浓度虾红素日粮饲喂昆白系小鼠和处理原代培养小鼠骨骼肌细胞,提取总RNA,检测各时段UCP3、LXRα基因mRNA表达量,探讨虾红素对小鼠个体发育、肌肉能量代谢相关基因表达变化规律的影响。结果表明:高浓度组与对照组相比,小鼠体重增长明显减慢,肌肉组织第10天、30天以及骨骼肌细胞作用24h时UCP3mRNA表达量均显著下降(P<0.05),LXRα基因mRNA表达量均显著上升(P<0.05),72h达到极显著水平(P<0.01)。低浓度组与对照组相比,肌肉组织中UCP3、LXRα基因mRNA表达差异均不显著(P>0.05);虾红素作用骨骼肌细胞24hUCP3基因mRNA表达量显著下降(P<0.05),LXRα基因mRNA表达量显著上升(P<0.05)。结果提示虾红素对小鼠肌肉的能量利用有一定的调控作用。     

猪的骨骼肌生长发育研究进展

瘦肉率对生猪产业来说是一个极其重要的经济指标,而这一指标完全取决于骨骼肌的生长发育。因此,猪骨骼肌生长发育机理的研究是十分必要的。然而,在早期由于各种因素的限制,猪骨骼肌单个基因的研究一直进展缓慢;相反,以小鼠为模型,其骨骼肌单基因的功能研究却取得了较大进展。在这一时期,影响肌决定和肌分化的基因,如MRFs家族和MEF2家族相继被发现,这些基因在猪的肌肉发育中也发挥着同样的作用。然而,这些结果并不能很好地揭示骨骼肌发育过程中复杂的基因间互作关系。随着近年来芯片和测序技术的不断发展,更多人试图从整个转录谱的水平来阐述猪肌肉发育的分子机理,并且也取得了较大的进展。为了对猪骨骼肌生长发育有一个更为清晰的认识,该文将以目前猪骨骼肌生长发育研究结果为基础,同时结合模式动物小鼠骨骼肌单基因的研究成果,对猪的骨骼肌生长发育分子调控机理进行详细的阐述。     

The innervation pattern of crustacean skeletal muscle

Summary The innervation pattern of distal muscle fibers of the opener muscle of walking legs of crayfish (Astacus leptodactylus) was investigated using methylene-blue staining, cobalt infiltration, and electron microscopy. A quantitative analysis of the entire innervation of single muscle fibers was attempted.It was found that instead of the generally assumed parallel array of numerous excitatory and inhibitory terminals, innervation consists of only a few branched terminals. The branches of excitatory and inhibitory terminals lie side-by-side. Both types are characterized by numerous varicosities (see Fig. 9B). The aggregate length of excitatory as well as inhibitory terminals on one muscle fiber is, on the average, about 1,500 m with a total of 152 varicosities spaced about 10 m apart. The average diameter of the varicosities is 4.26 m, that of the connecting thin segments about 0.5 m. Total terminal surface of motor or inhibitory terminals amounts to about 10,000 m² per muscle fiber. There are approximately 2,000 motor synapses on each muscle fiber, but their average total area is only about 6% of the terminal membrane area, or 0.06% of the (idealized) muscle fiber surface.There are conspicuous differences in the postsynaptic specializations associated with excitatory and inhibitory terminals; these are described in detail.The results are discussed in a functional context and with regard to design and results of electrophysiological experiments.Supported by Sonderforschungsbereich 138 of the Deutsche Forschungsgemeinschaft     

骨骼肌生长调控信号通路

骨骼肌能够根据环境刺激的变化改变其质量,可以通过细胞融合或提高蛋白质水平来增加它的大小。介绍了参与骨骼肌生长发育调控的两个关键性信号通路——胰岛素样生长因子1和肌肉生长抑制素信号通路中新的且重要的研究结果,这对于了解肌肉的发育和成年期肌肉稳态的维持,并寻找肌肉相关疾病潜在的治疗靶点非常有意义。     

Role of FGFs in skeletal muscle and limb development

Fibroblast growth factors (FGFs) are a family of nine proteins that bind to three distinct types of cell surface molecules: (i) FGF receptor tyrosine kinases (FGFR-1 through FGFR-4); (ii) a cysteine-rich FGF receptor (CFR); and (iii) heparan sulfate proteoglycans (HSPGs). Signaling by FGFs requires participation of at least two of these receptors: the FGFRs and HSPGs form a signaling complex. The length and sulfation pattern of the heparan sulfate chain determines both the activity of the signaling complex and, in part, the ligand specificity for FGFR-1. Thus, the heparan sulfate proteoglycans are likely to play an essential role in signaling. We have recently identified a role for FGF in limb bud development in vivo. In the chick limb bud, ectopic expression of the 18 kDa form of FGF-2 or FGF-2 fused to an artificial signal peptide at its amino terminus causes skeletal duplications. These data, and the observations that FGF-2 is localized to the subjacent mesoderm and the apical ectodermal ridge in the early developing limb, suggest that FGF-2 plays an important role in limb outgrowth. We propose that FGF-2 is an apical ectodermal ridgederived factor that participates in limb outgrowth and patterning. © 1994 Wiley-Liss, Inc.     

miRNAS in normal and diseased skeletal muscle

The last 20 years have witnessed major advances in the understanding of muscle diseases and significant inroads are being made to treat muscular dystrophy. However, no curative therapy is currently available for any of the muscular dystrophies, despite the immense progress made using several approaches and only palliative and symptomatic treatment is available for patients. The discovery of miRNAs as new and important regulators of gene expression is expected to broaden our biological understanding of the regulatory mechanism in muscle by adding another dimension of regulation to the diversity and complexity of gene-regulatory networks. As important regulators of muscle development, unravelling the regulatory circuits involved may be challenging, given that a single miRNA can regulate the expression of many mRNA targets. Although the identification of the regulatory targets of miRNAs in muscle is a challenge, it will be critical for placing them in genetic pathways and biological contexts. Therefore, combining informatics, biochemical and genetic approaches will not only expected to reveal the elucidation of the miRNA regulatory network in skeletal muscle and to bring a better knowledge on muscle tissue regulation but will also raise new opportunities for therapeutic intervention in muscular dystrophies by identifying candidate miRNAs as potential targets for clinical application.     

骨骼肌的内分泌功能

长期以来,骨骼肌被认为是一种效应器官,接受神经和体液的调节。近年大量实验研究资料发现骨骼肌也具有分泌活性物质的功能,能表达、合成和分泌多种生物信号分子,包括调节肽、细胞因子和生长因子等,也是一种重要的内分泌器官。骨骼肌分泌的活性物质以旁分泌和／或自分泌方式调节骨骼肌的生长、代谢和运动功能;甚至以血液循环内分泌的方式调节机体远隔器官组织的功能。骨骼肌生成和分泌的活性物质在运动系统疾病和某些全身性疾病的发病中具有重要的作用。本文将对骨骼肌分泌的主要活性物质及其生理和病理生理学意义进行综述。     

Cooperative mechanisms in the activation dependence of the rate of force development in rabbit skinned skeletal muscle fibers

Regulation of contraction in skeletal muscle is a highly cooperative process involving Ca(2+) binding to troponin C (TnC) and strong binding of myosin cross-bridges to actin. To further investigate the role(s) of cooperation in activating the kinetics of cross-bridge cycling, we measured the Ca(2+) dependence of the rate constant of force redevelopment (k(tr)) in skinned single fibers in which cross-bridge and Ca(2+) binding were also perturbed. Ca(2+) sensitivity of tension, the steepness of the force-pCa relationship, and Ca(2+) dependence of k(tr) were measured in skinned fibers that were (1) treated with NEM-S1, a strong-binding, non-force-generating derivative of myosin subfragment 1, to promote cooperative strong binding of endogenous cross-bridges to actin; (2) subjected to partial extraction of TnC to disrupt the spread of activation along the thin filament; or (3) both, partial extraction of TnC and treatment with NEM-S1. The steepness of the force-pCa relationship was consistently reduced by treatment with NEM-S1, by partial extraction of TnC, or by a combination of TnC extraction and NEM-S1, indicating a decrease in the apparent cooperativity of activation. Partial extraction of TnC or NEM-S1 treatment accelerated the rate of force redevelopment at each submaximal force, but had no effect on kinetics of force development in maximally activated preparations. At low levels of Ca(2+), 3 microM NEM-S1 increased k(tr) to maximal values, and higher concentrations of NEM-S1 (6 or 10 microM) increased k(tr) to greater than maximal values. NEM-S1 also accelerated k(tr) at intermediate levels of activation, but to values that were submaximal. However, the combination of partial TnC extraction and 6 microM NEM-S1 increased k(tr) to virtually identical supramaximal values at all levels of activation, thus, completely eliminating the activation dependence of k(tr). These results show that k(tr) is not maximal in control fibers, even at saturating [Ca(2+)], and suggest that activation dependence of k(tr) is due to the combined activating effects of Ca(2+) binding to TnC and cross-bridge binding to actin.     

Role of fatty acids in the transition from anaerobic to aerobic metabolism in skeletal muscle during exercise

In moderate physical exercise, the transition from predominantly anaerobic towards predominantly aerobic metabolism is a key step to improve performance. Increase in the supply of oxygen and nutrients, such as free fatty acids (FFA) and glucose, which accompanies high blood flow, is required for this transition. The mechanisms involved in the vasodilation in skeletal muscle during physical activity are not completely known yet. In this article, we postulate a role of FFA and heat production in this process. The presence of uncoupling protein-2 and -3 (UCP-2 and -3) in skeletal muscle, whose activity is dependent on FFA, suggests that these metabolites can act as mitochondrial uncouplers in this tissue. Evidence indicates however that UCPs act as uncouplers only when coenzyme Q is predominantly in the reduced state (i.e. under nonphosphorylation conditions or state 4 respiration) as is observed in resting muscles and in the beginning of physical activity (predominantly anaerobic metabolism). The increase in the lipolytic activity in adipose tissue in the beginning of physical activity results in elevated plasma FFA levels. The FFA can then act on the UCPs, increasing the local heat production. We propose that this calorigenic effect of FFA is important to activate nitric oxide synthase, resulting in nitric oxide production and consequent vasodilation. Therefore, FFA would be important mediators for the changes that occur in muscle metabolism during prolonged physical activity, ensuring the appropriate supply of oxygen and nutrients by increasing blood flow at the beginning of exercise in the contracting skeletal muscles.     

Regulation of RNA N6-methyladenosine modification and its emerging roles in skeletal muscle development

N⁶-methyladenosine (m⁶A) is one of the most widespread and highly conserved chemical modifications in cellular RNAs of eukaryotic genomes. Owing to the development of high-throughput m⁶A sequencing, the functions and mechanisms of m⁶A modification in development and diseases have been revealed. Recent studies have shown that RNA m⁶A methylation plays a critical role in skeletal muscle development, which regulates myoblast proliferation and differentiation, and muscle regeneration. Exploration of the functions of m⁶A modification and its regulators provides a deeper understanding of the regulatory mechanisms underlying skeletal muscle development. In the present review, we aim to summarize recent breakthroughs concerning the global landscape of m⁶A modification in mammals and examine the biological functions and mechanisms of enzymes regulating m⁶A RNA methylation. We describe the interplay between m⁶A and other epigenetic modifications and highlight the regulatory roles of m⁶A in development, especially that of skeletal muscle. m⁶A and its regulators are expected to be targets for the treatment of human muscle-related diseases and novel epigenetic markers for animal breeding in meat production.     

Morphometric properties and innervation of muscle compartments in rat medial gastrocnemius

The rat medial gastrocnemius (MG) muscle is composed of the proximal and distal compartments. In this study, morphometric properties of the compartments and their muscle fibres at five levels of the muscle length and the innervation pattern of these compartments from lumbar segments were investigated. The size and number of muscle fibres in the compartments were different. The proximal compartment at the largest cross section (25% of the muscle length) had 34% smaller cross-sectional area but contained a slightly higher number of muscle fibres (max. 5521 vs. 5360) in comparison to data for the distal compartment which had the largest cross-sectional area at 40% of the muscle length. The muscle fibre diameters revealed a clear tendency within both compartments to increase along the muscle (from the knee to the Achilles tendon) up to 46.9?μm in the proximal compartment and 58.4?μm in the distal one. The maximal tetanic and single twitch force evoked by stimulation of L4, L5, and L6 ventral roots in whole muscle and compartments were measured. The MG was innervated from L4 and L5, only L5, or L5 and L6 segments. The proximal compartment was innervated by axons from L5 or L5 and L4, and the distal one from L5, L5 and L6, or L5 and L4 segments. The forces produced by the compartments summed non-linearly. The tetanic forces of the proximal and distal compartments amounted to 2.24 and 4.86?N, respectively, and their algebraic sums were 11% higher than the whole muscle force (6.37?N).