Scaling body support in mammals: limb posture and muscle mechanics

The scaling of bone and muscle geometry in mammals suggests that peak stresses (ratio of force to cross-sectional area) acting in these two support elements increase with increasing body size. Observations of stresses acting in the limb bones of different sized mammals during strenuous activity, however, indicate that peak bone stress is independent of size (maintaining a safety factor of between 2 and 4). It appears that similar peak bone stresses and muscle stresses in large and small mammals are achieved primarily by a size-dependent change in locomotor limb posture: small animals run with crouched postures, whereas larger species run more upright. By adopting an upright posture, large animals align their limbs more closely with the ground reaction force, substantially reducing the forces that their muscles must exert (proportional to body mass) and hence, the forces that their bones must resist, to counteract joint moments. This change in limb posture to maintain locomotor stresses within safe limits, however, likely limits the maneuverability and accelerative capability of large animals.     

不同营养水平对民猪和哈白猪影响的研究 Ⅱ.肌肉和骨骼生长发育规律

一、品种间差异 (一)正常饲养组在正常饲养情况下,哈白猪于50公斤体重以后,产肉量占绝对优势,而民猪在四肢骨长度上占优势,其中后肢骨表现最突出.在骨骼重量上两品种间无显著差异. (二)限制饲养组在维持和低维持饲养情况下,民猪不论在肌肉重量上,还是在骨骼重量和长度上都占优势,而且,随营养水平的降低优势程度越明显.由此充分说明,在营养缺乏的情况下,民猪在肌肉重量和骨骼重量与长度方面的抗逆性强于哈白猪. (三)限制饲养组恢复正常饲养总的结果表明:哈白猪和民猪尽管前期遇到营养严重缺乏(维持营养以下),如后期给予正常饲养补偿,两品种的产肉量基本相同,无显著差异,即缩小了两品种生产瘦肉能力的差异;但同时加大了骨骼长度的品种间差异;对骨骼重量的品种间差异无显著影响. 二、营养水平间的差异在70公斤体重阶段,哈白猪和民猪原限制饲养组的肌肉重量、骨骼重量和长度均与其正常饲养组拉平,即两品种限制饲养组都得到补偿.但很难下结论哪个品种的补偿力强. 三、肌肉和骨骼关系民猪股坐夹角比哈白猪小,而坐骨和股骨又比哈白猪长.因此,延长了股后肌群相对髋关节的力臂,相应增大力矩,提高肌肉功率,结果减少了股后肌群的重量.民猪这种肌肉骨骼结构特点有利于生存而不利于肌肉发育.     

Operant conditioning of specific patterns of neural and muscular activity

In awake monkeys we recorded activity of single "motor" cortex cells, four contralateral arm muscles, and elbow position, while operantly reinforcing several patterns of motor activity. With the monkey's arm held semiprone in a cast hinged at the elbow, we reinforced active elbow movements and tested cell responses to passive elbow movements. With the cast immobilized we reinforced isometric contraction of each of the four muscles in isolation, and bursts of cortical cell activity with and without simultaneous suppression of muscle activity. Correlations between a precentral cell and specific arm muscles consistently appeared under several behavioral conditions, but could be dissociated by reinforcing cell activity and muscle suppression.     

Origin of repopulating cells after localized bone marrow depletion

The restoration of marrow in a mechanically depleted segment of rabbit femur is locally determined and apparently initiated by cells normally resident in bone. This conclusion follows from results of two types of radiation experiments: local x-irradiation of the femur shaft immediately before depopulation and x-irradiation of the total body with exception of the femur diaphysis which was depopulated either just before or after irradiation. In contrast to the rapid initiation of marrow restoration in an unirradiated femur, there was little regeneration during the first 3 weeks in an irradiated femur. Recovery of the shielded depopulated femur in the rabbit that otherwise received total-body irradiation was similar to that in the unirradiated animal. Hence, it would appear that the seeding of circulating hemic stem cells is not essential to repopulation and that cells with hematopoietic potential are present in osseous tissue.     

东北民猪、长白猪和三江白猪的个别肌肉相对生长模式的研究

本文对试验数据分别以半胴重、半胴肌肉重、腿臀部重和腿臀肌肉重做自变量按比量方程(y=ax~b)分别计算了a(截距)及b(生长系数)值,根据方差分析结果计算了R~2(相关指数)和S_y(剩余标准差)。结果表明,在所有四种不同自变量情况下,后腿五块肌肉的早熟性顺位均有各自品种鈞一致性,显示出品种间遗传差异特征:民猪均以半膜肌为最早熟,而长白猪和三江猪均以股薄肌为最早熟。当以半胴重和腿臀部重做自变量,各肌肉的6值:长白猪最高,民猪最低,三江猪居中。当以半胴肌肉重和腿臀部肌肉重做自变量时,三品种猪各肌肉b值具有共同的趋势:半腱肌b值最高,半膜肌R~2值最高。研究证明,民猪的内收肌和长白猪的半膜肌最近似各自品种的半胴肌肉总重和腿臀部肌肉重的生长势模式。     

Myostatin基因及其与动物双肌性状间关系的研究进展

肌肉生长抑制素（myostatin,MSTN）又称生长分化因子8（growth differentiation factor 8,GDF-8）,属于转化生长因子β（transforming growth factor β,TGF-β）超家族成员,由McPherron等在1997年筛选小鼠肌肉cDNA文库时首次发现。目前已研究过的不同哺乳物种间的MSTN基因结构均含３个外显子和２个内含子,且成熟肽氨基酸序列的差异均在3个以内。MSTN在多个组织中表达,包括心肌、脂肪、胎盘、乳腺、子宫、嗅觉神经细胞、肝、脾、肺和肾等,主要在骨骼肌中高水平表达。MSTN的成熟包括由信号肽酶、前蛋白转化酶Furin和金属蛋白酶BMP-1/tolloid家族的酶解和加工,成熟的MSTN为同质二聚体化。MSTN的最显著作用是作为骨骼肌的强有力的负调控因子,可通过自分泌或旁分泌的方式激活TGF-β、p38 MAPK、ERK1/2、和JNK等信号途径及抑制IGF-AKT和Wnt信号途径,协同抑制成肌细胞的增殖和分化。MSTN基因敲除小鼠的肌肉重量显著增加而表现为双肌性状,并可通过增强肌肉再生和降低纤维化的方式提高肌肉愈伤能力;糖的消耗和糖摄入加强,且对胰岛素的敏感性加强;心脏增大且压力应激增强;脂肪重量减轻,脂肪发生受到抑制,且白色脂肪组织的黄化加强而能够促进生热作用;骨密度和骨矿物质含量增强,并可增加骨折骨痂的尺寸和强度而促进骨折的愈合。MSTN还可通过调控胎盘的建立和葡萄糖的摄入、调控子宫平滑肌细胞和内膜上皮细胞的增殖及乳腺的发育,参与雌性哺乳动物的生殖调控。自然发生的MSTN基因功能缺失型纯合突变也能够引起动物表现双肌性状,已知的这些突变包括牛的p.D273RfsX13(也称nt821(del11))、p.C313Y、p.F140X(也称nt419(del7ins10))、p.Q204X、p.E226X和p.E291X突变, 绵羊的c.960delG(也称p.K320NfsX39)和c.120insA（也称p.N40MfsX9）突变,狗的c.939-940delTG突变和人类的c.373+5G＞A突变;此外在绵羊中还存在一个靶向MSTN基因的miRNA功能获得型纯合突变c.2360G＞A(也称g.6223G＞A)也可引起双肌性状。双肌动物在19世纪初就已记载,不仅表现有更多的肌肉,而且有更少的骨骼和脂肪,然而双肌性状也会带来一些缺点,包括产奶率下降、雌性繁殖力下降、难产增加和幼畜死亡率增加,因此运用基因工程技术合理优化MSTN功能的发挥且又降低双肌性状副作用的方法来培育优质肉用家畜品种一直是研究热点。在牛中还存１个保守性错义突变p.F94L,并不会改变MSTN的功能,所以不会发生双肌表型的副作用,但可引起肌肉重量增加,并降低肌内和肌外的脂肪含量,且不会影响肉嫩度,因此目前p.F94L突变已较理想地用于肉牛的分子标记育种。本文综述了哺乳动物MSTN基因的结构、表达、信号转导、生理功能、突变体、双肌表型和在家畜育种中的最新研究进展,旨在为更深入理解哺乳动物MSTN作用机理及为肉用家畜品种的培育提供参考。     

山羊TNNT3基因可变剪切及其对骨骼肌细胞分化的作用

【目的】快速骨骼肌肌钙蛋白T(fast skeletal troponin T3,TNNT3)作为肌钙蛋白(troponin, Tn)家族成员,调节横纹肌收缩、参与骨骼肌的生长发育并影响家畜肉质性状。通过获得山羊TNNT3基因的可变剪切体,分析山羊TNNT3基因可变剪切的表达模式及其在肌细胞分化中的作用,深入解析TNNT3基因在山羊骨骼肌生长发育过程中的作用机制。【方法】基于NCBI已公布山羊TNNT3基因(NM₀01314210.1)和牛TNNT3基因(XM₀10821200)mRNA序列,使用软件Primer Premier6.0设计引物,以简州大耳羊胚胎期和出生后7个阶段骨骼肌为试验材料,克隆测序获得山羊TNNT3基因的CDS区可变剪切体,利用软件ORF Finder、EditSeq、DNAMAN、ClustalW和MEGA_X10.1.8等对序列进行生物信息学分析;进一步设计实时荧光定量(real-time PCR,RT-qPCR)及半定量引物,研究TNNT3基因剪切体在7个不同组织(背最长肌...     

Intracellular acidosis enhances the excitability of working muscle

Intracellular acidification of skeletal muscles is commonly thought to contribute to muscle fatigue. However, intracellular acidosis also acts to preserve muscle excitability when muscles become depolarized, which occurs with working muscles. Here, we show that this process may be mediated by decreased chloride permeability, which enables action potentials to still be propagated along the internal network of tubules in a muscle fiber (the T system) despite muscle depolarization. These results implicate chloride ion channels in muscle function and emphasize that intracellular acidosis of muscle has protective effects during muscle fatigue.     

狮头鹅AR基因克隆和组织表达

本研究旨在克隆鹅雄激素受体基因（Androgen receptor，AR），并了解其在不同组织中的表达情况.以狮头鹅为试验材料，采集下丘脑和睾丸组织样品，提取RNA逆转录后进行AR基因克隆，并用RACE扩增其cDNA全长序列，其它同采用实时荧光定量PCR的方法检测AR基因在各个组织中的表达情况.结果克隆获得AR基因全长cDNA序列，共得到4个转录本.通过氨基酸序列同源进行分析，发现狮头鹅AR基因在禽类和哺乳类动物中同源性较高，说明该基因在禽类和哺乳类进化保守.荧光定量PCR结果显示AR基因在狮头鹅12个组织中均有表达量，其中在腿肌、胸肌和睾丸表达量较高，表明AR基因可能参与调控狮头鹅公鹅的肌肉生长与繁殖.     

Thermoregulation in endothermic insects

On the basis of body weight, most flying insects have higher rates of metabolism, and hence heat production, than other animals. However, rapid rates of cooling because of small body size in most cases precludes appreciable endothermy. The body temperature of small flies in flight is probably close to ambient temperature, and that of flying butterflies and locusts is 5 degrees to 10 degrees C above ambient temperature. Many moths and bumblebees are insulated with scales and hair, and their metabolism during flight can cause the temperature of the flight muscles to increase 20 degrees to 30 degrees C above ambient temperature. Curiously, those insects which (because of size, insulation) retain the most heat in the thorax during flight, also require the highest muscle temperature in order to maintain sufficient power output to continue flight. The minimum muscle temperature for flight varies widely between different species, while the maximum temperature varies over the relatively narrow range of 40 degrees to 45 degrees C. As a consequence, those insects that necessarily generate high muscle temperatures during flight must maintain their thoracic temperature within a relatively narrow range during flight. Active heat loss from the thorax to the abdomen prevents overheating of the flight motor and allows some large moths to be active over a wide range of ambient temperatures. Bumblebees similarly transfer heat from the flight musculature into the abdomen while incubating their brood by abdominal contact. Many of the larger insects would remain grounded if they did not actively increase the temperature of their flight muscles prior to flight. Male tettigoniid grasshoppers elevate their thoracic temperature prior to singing. In addition, some of the social Hymenoptera activate the "flight" muscles specifically to produce heat not only prior to flight but also during nest temperature regulation. During this "shivering" the "flight" muscles are often activated in patterns different from those during flight. The muscles contract primarily against each other rather than on the wings. However, the rate of heat production during shivering and flight is primarily a function of the action potential frequency rather than of the patterns of activation. Thermoregulation is a key factor in the energetics of foraging of some of the flower-visiting insects. The higher their muscle temperature the more flowers they can visit per unit time. When food supplies are ample, bees may invest relatively large amounts of energy for thermoregulation. While shivering to maintain high body temperatures during the short intervals they are perched on flowers (as well as while in the nest), bumblebees often expend energy at rates similar to the rates of energy expenditure in flight. Unlike vertebrates, which usually regulate their body temperature at specific set points, the body temperature of insects is labile. It often appears to be maintained near the lower temperature at which the muscles are able to perform the function at hand. The insects' thermal adaptations may not differ as much from those of vertebrates as previously supposed when size, anatomy, and energy requirements are taken into account.     

Bone marrow stromal cells generate muscle cells and repair muscle degeneration

Bone marrow stromal cells (MSCs) have great potential as therapeutic agents. We report a method for inducing skeletal muscle lineage cells from human and rat general adherent MSCs with an efficiency of 89%. Induced cells differentiated into muscle fibers upon transplantation into degenerated muscles of rats and mdx-nude mice. The induced population contained Pax7-positive cells that contributed to subsequent regeneration of muscle upon repetitive damage without additional transplantation of cells. These MSCs represent a more ready supply of myogenic cells than do the rare myogenic stem cells normally found in muscle and bone marrow.     

Specification of jaw muscle identity in zebrafish: correlation with engrailed-homeoprotein expression

Molecules that determine the specific features of individual muscles in vertebrates are unknown. Antibody labeling studies described here revealed a molecular difference among muscles in the zebrafish head, in that two functionally related jaw muscles (the levator arcus palatini and the dilator operculi), and not other head muscles, expressed engrailed-homeodomain proteins. Expression began in mesoderm-derived muscle-precursor cells in the paraxial mesenchyme and continued during muscle morphogenesis and differentiation. Growth cones of trigeminal motoneurons that innervate these muscles associated with the precursors within a few hours of the time they began to express engrailed. It is proposed that the engrailed proteins in these cells establish muscle identity and neuromuscular target recognition.     

Muscle contraction and free energy transduction in biological systems

Muscle contraction occurs when the actin and myosin filaments in muscle are driven past each other by a cyclic interaction of adenosine triphosphate (ATP) and actin with cross-bridges that extend from myosin. Current biochemical studies suggest that, during each adenosine triphosphatase cycle, the myosin cross-bridge alternates between two main conformations, which differ markedly in their strength of binding to actin and in their overall structure. Binding of ATP to the cross-bridge induces the weak-binding conformation, whereas inorganic phosphate release returns the cross-bridge to the strong-binding conformation. This cross-bridge cycle is similar to the kinetic cycle that drives active transport and illustrates the general principles of free energy transduction by adenosine triphosphatase systems.     

鸭MyoG基因启动子的生物信息学分析及其甲基化频率对基因表达的影响

采用RT–PCR技术扩增和克隆鸭Myo G基因启动子,并对其启动子序列进行生物信息学分析,采用Sequenom Mass Array技术检测Cp G岛在鸭肌肉组织中的甲基化水平,用q RT–PCR检测Myo G基因的表达量。结果表明,扩增得到鸭Myo G基因启动子序列2 730 bp,对启动子序列预测后,发现存在2个Cp G岛,其中Cp G岛(–2 536~–1 997 bp)存在5个转录因子结合位点和多个真核生物结构元件。甲基化检测结果表明:在鸭的个体和组织水平上,启动子甲基化率均未聚类在一起;Cp G位点甲基化频率存在个体差异,22%Cp G位点的甲基化频率与Myo G的m RNA表达量呈负相关(P0.05),78%Cp G位点的甲基化频率呈正相关(P0.05),其中,腿肌甲基化位点Cp G_1、Cp G_26.27.28.29的甲基化频率与Myo G基因表达水平均呈显著相关(P0.05)。Myo G基因在鸭与在哺乳动物中的转录调控机制存在差异。试验中发现多个影响鸭Myo G基因转录的潜在甲基化位点,其中Cp G_1与Cp G_26.27.28.29能通过DNA甲基化修饰影响Myo G基因在鸭腿肌中的转录。本研究结果可为鸭Myo G基因转录调控提供参考依据。     

Fuel-powered artificial muscles

Artificial muscles and electric motors found in autonomous robots and prosthetic limbs are typically battery-powered, which severely restricts the duration of their performance and can necessitate long inactivity during battery recharge. To help solve these problems, we demonstrated two types of artificial muscles that convert the chemical energy of high-energy-density fuels to mechanical energy. The first type stores electrical charge and uses changes in stored charge for mechanical actuation. In contrast with electrically powered electrochemical muscles, only half of the actuator cycle is electrochemical. The second type of fuel-powered muscle provides a demonstrated actuator stroke and power density comparable to those of natural skeletal muscle and generated stresses that are over a hundred times higher.     

撤销学位论文学术影响力研究

[目的/意义]分析被撤销学位的博硕士学位论文分布情况,揭示其在学术系统的不良影响,为管理部门制订相关政策提供建议和参考,为具体实践提供方法和策略.[方法/过程]通过媒体的公开报道获得撤销学位案例,在学位论文数据库和网络阅读分享平台中获得撤销学位论文的分布数据、引用数据和Altmetrics数据,分析撤销学位论文的学术影...     

边鸡在右玉县的性能测定及其选育

边鸡在山西境内,主要产于右玉县长城一带,遍及全县,以杀虎口、李达窑、破虎堡、丁家窑一带品质较好。该鸡种以体大、蛋重而驰名,特别是蛋大、壳厚而红、色泽美观、蛋肉品质均优,属蛋肉兼用品种。且具耐粗抗病、觅食力强,适应性能好等优良特性,博得人们的喜爱。边鸡在当地条件下,平均年产蛋120枚,平均蛋重58.82克,最大蛋重83.6克;大蛋12-14个一公斤。边鸡肉质优良,胸、腿肉发达丰满、充实,煮熟后骨肉比为32.27％,腿部肌肉占整体肉重的32.49％,胸部肌肉占整体肉重的23.94％。当地饲养条件下的成年边鸡,经屠宰测定,公鸡全净膛屠宰率为71.5％,其胸角为72.2°,母鸡全净膛屠宰率为66.5％,其胸角为74.1°。边鸡加工成熏(烧)鸡味美酥软,别具风味,早在满清时期宫廷民间已广泛流传,迄今仍享有盛名,可作为盛宴的佳肴之一。边鸡的进一步选育,可为培育现代化养鸡的肉用型鸡和蛋用型的褐壳蛋系鸡种,投放国内和国际市场提供鸡源和蛋源。     

犬的全身骨骼标本制作技术探讨

为探究犬的全身骨骼标本的制作技术,以犬为材料,在传统制作方法的基础上,采用开水适度烫煮剔除骨骼上肌肉,充分利用韧带保持骨骼间连接,用热烧碱水对骨骼浸泡脱脂,用双氧水刷拭骨骼表面对骨骼进行漂白等新方法制作犬的整体骨骼标本。结果表明,该方法简便、环保安全,制作的标本肋软骨不变形,碎骨不丢失,骨骼间各部位连接完整,骨骼齐全,骨质不损伤,经久耐用,能够保持骨骼结构的原有状态。     

肌纤维类型组成对猪肌肉品质与能量代谢的影响研究进展

肌纤维是肌肉组织的基本结构单位,通过改变肌纤维类型组成提高肌肉品质是当前的研究热点之一.成年哺乳动物骨骼肌肌纤维类型按肌球蛋白重链基因(MyHC)的多态性表达可分为Ⅰ、2a、2x、2b型4种类型,Ⅰ、2a型属偏氧化型肌纤维,2x、2b型属偏酵解型肌纤维.动物出生前,肌纤维MyHC异构体一般表达为胚胎型、胎儿型、Ⅰ和2a...     

All members of the MHC multigene family respond to thyroid hormone in a highly tissue-specific manner

In mammals different isoforms of myosin heavy chain are encoded by the members of a multigene family. The expression of each gene of this family is regulated in a tissue- and developmental stage-specific manner as well as by hormonal and various pathological stimuli. In this study the molecular basis of isoform switches induced in myosin heavy chain by thyroid hormone was investigated. The expression of the myosin heavy chain gene family was analyzed in seven different muscles of adult rats subjected to hypo- or hyperthyroidism with complementary DNA probes specific for six different myosin heavy chain genes. The results demonstrate that all six genes are responsive to thyroid hormone. More interestingly, the same myosin heavy chain gene can be regulated by thyroid hormone in highly different modes, even in opposite directions, depending on the tissue in which it is expressed. Furthermore, the skeletal embryonic and neonatal myosin heavy chain genes, so far considered specific to these two developmental stages, can be reinduced by hypothyroidism in specific adult muscles.