Meat Science and Muscle Biology Symposium: extracellular matrix regulation of skeletal muscle formation

Skeletal muscle development and growth is a complex process that involves the interaction of muscle cells with their extracellular environment. Because muscle development involves the interaction of the cell surface and extracellular matrix molecules, research focus has been placed on the proteoglycans. Proteoglycans are macromolecules containing a central core protein with attached carbohydrates, called glycosaminoglycans, that are located at both the cell surface and the extracellular matrix. Research focus has been placed on understanding the mechanisms of the membrane-associated heparan sulfate proteoglycans, syndecan-4 and glypican-1, which are both capable of regulating cellular responsiveness to fibroblast growth factor 2 (FGF2). Fibroblast growth factor 2 is a potent stimulator of muscle cell proliferation and a strong inhibitor of differentiation. Studies on syndecan-4 and glypican-1 show that these proteoglycans differentially regulate muscle cell proliferation, differentiation, and cellular responsiveness to FGF2 with syndecan-4 predominantly modulating muscle cell proliferation and glypican-1 modulating differentiation. Site-directed mutagenesis approaches were used to define the effect of the syndecan-4 and glypican-1 covalently attached side chains on their activity. In general, a functional association was found between the glycosaminoglycan and N-glycosylated chains attached to the central core proteins of syndecan-4 and glypican-1 affecting their regulation of muscle cell proliferation, differentiation, and FGF2 responsiveness. Current research efforts are directed at identifying the cellular signaling pathways modulated by syndecan-4 and glypican-1.     

Meat Science and Muscle Biology Symposium: manipulating meat tenderness by increasing the turnover of intramuscular connective tissue

Controlled reduction of the connective tissue contribution to cooked meat toughness is an objective that would have considerable financial impact in terms of added product value. The amount of intramuscular connective tissue in a muscle appears connected to its in vivo function, so reduction of the overall connective tissue content is not thought to be a viable target. However, manipulation of the state of maturity of the collagenous component is a biologically viable target; by increasing connective tissue turnover, less mature structures can be produced that are functional in vivo but more easily broken down on cooking at temperatures above 60°C, thus improving cooked meat tenderness. Recent work using cell culture models of fibroblasts derived from muscle and myoblasts has identified a range of factors that alter the activity of the principal enzymes responsible for connective tissue turnover, the matrix metalloproteinases (MMP). Fibroblasts cultured from 3 different skeletal muscles from the same animal show different cell proliferation and MMP activity, which may relate to the different connective tissue content and architecture in functionally different muscles. Expression of MMP by fibroblasts is increased by vitamins that can counter the negative effects of oxidative stress on new collagen synthesis. Preliminary work using in situ zymography of myotubes in culture also indicates increased MMP activity in the presence of epinephrine and reactive oxidative species. Comparison of the relative changes in MMP expression from muscle cells vs. fibroblasts shows that myoblasts are more responsive to a range of stimuli. Muscle cells are likely to produce more of the total MMP in muscle tissue as a whole, and the expression of latent forms of the enzymes (i.e., pro-MMP) may vary between oxidative and glycolytic muscle fibers within the same muscle. The implication is that the different muscle fiber composition of different muscles eaten as meat may influence the potential for manipulation of their connective tissue turnover.     

Meat Science and Muscle Biology Symposium: stem cell niche and postnatal muscle growth

Stem cell niche plays a critical role in regulating the behavior and function of adult stem cells that underlie tissue growth, maintenance, and regeneration. In the skeletal muscle, stem cells, called satellite cells, contribute to postnatal muscle growth and hypertrophy, and thus, meat production in agricultural animals. Satellite cells are located adjacent to mature muscle fibers underneath a sheath of basal lamina. Microenvironmental signals from extracellular matrix mediated by the basal lamina and from the host myofiber both impinge on satellite cells to regulate their activity. Furthermore, several types of muscle interstitial cells, including intramuscular preadipocytes and connective tissue fibroblasts, have recently been shown to interact with satellite cells and actively regulate the growth and regeneration of postnatal skeletal muscles. From this regard, interstitial adipogenic cells are not only important for marbling and meat quality, but also represent an additional cellular component of the satellite cell niche. At the molecular level, these interstitial cells may interact with satellite cells through cell surface ligands, such as delta-like 1 homolog (Dlk1) protein whose overexpression is thought to be responsible for muscle hypertrophy in callipyge sheep. In fact, extracellular Dlk1 protein has been shown to promote the myogenic differentiation of satellite cells. Understanding the cellular and molecular mechanisms within the stem cell niche that regulate satellite cell differentiation and maintain muscle homeostasis may lead to promising approaches to optimizing muscle growth and composition, thus improving meat production and quality.     

冻融对早胜牛肉品质及微细结构的影响

为探讨反复冻融对早胜牛肉品质的影响,选取2.0～2.5岁阉割牛背最长肌,随机分成6组,称重,真空包装,进行不同次数的反复冷冻—解冻试验,分别检测原料肉解冻损失、煮制损失、失水率、熟肉剪切力及pH,并观察原料肉显微超微结构的变化。结果显示,随着反复冻融次数的增加,原料肉解冻损失和煮制损失极显著增加,失水率只在第1次冻融后显著增加,剪切力先显著增加后再降低,pH随着冻融次数增加而显著降低,肌纤维结构混乱,肌束及肌原纤维间隙增加,肌节略微缩短,线粒体肿胀、空泡样变,Z线错位排列,甚至溶解、消失。结果表明,反复冻融严重破坏了早胜牛肉的组织结构,显著降低了肉品质。     

禽肉组织学性状及其与肉质的关系

肌肉的组织学特性与肉质具有一定的相关性,本文综述了禽类骨骼肌肌纤维类型、肌纤维直径、肌纤维密度、肌纤维面积比例、结缔组织面积比例、脂肪组织面积比例以及肌节长度等组织学特性与肉品品质的关系。     

肌红蛋白影响畜禽活体肌肉和宰后鲜肉肉色的研究进展

肉色是影响消费者购买肉产品的最主要因素,因为消费者通过肉色对肉产品新鲜度和卫生状况产生第一印象。肉色的化学本质是肌红蛋白分子,本文综述了4个肌红蛋白分子(脱氧肌红蛋白、氧合肌红蛋白、高铁肌红蛋白、碳氧肌红蛋白)的结构及其相互转化反应和对畜禽活体肌肉和宰后鲜肉肉色的影响。     

含不同比例梅山猪血缘杂交肉猪肉质及肌纤维组织学特性研究

选不同比例梅山猪血缘（梅山猪血缘比例为0,1/8,1/4,3/8,1/2,1)的杂种仔猪68头，采用单因子试验设计，在同一营养水平（DE：前期14.21MJ/kg，后期13.79MJ/kg；CP：15％，13％；Lys:0.75%,0.65%)下，研究不同比例梅山猪血缘对不同体重阶段生长肥育猪肉质及肌纤维组织学特性的影响。结果表明，梅山及其杂种猪与杜大猪相比，肉色好（P＜0.05)，pH正常（P＜0.01)，肌内脂肪含量高（P＜0.01)，分布均匀，系水力高（P＜0.05)，无异常肉发生，其它常规化学成分分析差异不显著（P＞0.05)；肌纤维直径随梅山猪血缘比例增加逐渐变细，而随体重增加逐渐增大。     

Lactation Biology Symposium: circadian clocks as mediators of the homeorhetic response to lactation

The transition from pregnancy to lactation is the most stressful period in the life of a cow. During this transition, homeorhetic adaptations are coordinated across almost every organ and are marked by changes in hormones and metabolism to accommodate the increased energetic demands of lactation. Recent data from our laboratory showed that changes in circadian clocks occur in multiple tissues during the transition period in rats and indicate that the circadian system coordinates changes in the physiology of the dam needed to support lactation. Circadian rhythms coordinate the timing of physiological processes and synchronize these processes with the environment of the animal. Circadian rhythms are generated by molecular circadian clocks located in the hypothalamus (the master clock) and peripherally in every organ of the body. The master clock receives environmental and physiological cues and, in turn, synchronizes internal physiology by coordinating endocrine rhythms and metabolism through peripheral clocks. The effect of the circadian clock on lactation may be inferred by the photoperiod effect on milk production, which is accompanied by coordinated changes in the endocrine system and metabolic capacity of the dam to respond to changes in day length. We have shown that bovine mammary epithelial cells possess a functional clock that can be synchronized by external stimuli, and the expression of the aryl hydrocarbon receptor nuclear translocator-like gene, a positive limb of the core clock, is responsive to prolactin in bovine mammary explants. Others showed that 7% of genes expressed in breasts of lactating women had circadian patterns of expression, and we report that the diurnal variation of composition of bovine milk is associated with changes in expression of mammary core clock genes. Together these studies indicate that the circadian system coordinates the metabolic and hormonal changes needed to initiate and sustain lactation, and we believe that the capacity of the dam to produce milk and cope with metabolic stresses in early lactation is related to her ability to set circadian rhythms during the transition period.     

肌注PHA对犬血清中补体C3、C4的影响

对各犬只肌注PHA,通过测定不同时期血清中补体C3,C4的浓度,以判定PHA对补体的影响作用。把PHA分成4个剂量组:低剂量组(0.05 mg/kg)、中剂量组(0.10 mg/kg)、高剂量组(0.20 mg/kg)和对照组(相同剂量的生理盐水)。在注射前和注射后的7 d、14 d对各组实验犬只进行采血分析,测定其血清中补体的含量,并进行统计学分析。结果显示,不同剂量的PHA对犬只的补体系统刺激作用不同,其中中剂量组可以极大地提高机体的补体水平,并保持一定时间的高水平,而低剂量组和高剂量组的差异不显著。     

The influence of ultimate pH and intramuscular fat content on pork tenderness and tenderization

Intramuscular fat (IMF) and ultimate pH (pHu) influence tenderness, but their roles have not been conclusively determined. Length of storage also affects tenderness and may interact with IMF and pHu. We evaluated the effects of pHu, IMF, and storage time on the tenderness of pork longissimus muscle and determined whether the contribution of the various factors was dependent on genetic line. To obtain variation in IMF, Berkshire (B), Duroc (D) and Hampshire (H) boars were crossed with Yorkshire-Landrace sows. In four trials, a total of 176 pigs were used. To obtain a range in pHu, half of the pigs were deprived of feed before slaughter. Warner-Bratzler shear force (WBS) of each loin was assessed after 2, 7, and 14 d of storage at 0 to 2 degrees C. Warner-Bratzler shear force decreased (P < 0.05) from 4.89 kg at d 2 to 4.16 kg at d 7 to 3.52 kg at d 14. The H pork (n = 62) had a lower (P < 0.05) WBS than the other pork at d 2. After 7 d of storage, this difference had disappeared. Based on glycolytic potential, 30 of the H pigs were carriers of the Rendement Napole (RN) gene. When these pigs were excluded from the analysis, there was no difference in tenderness or tenderization of H, D, and B pork. The correlation between IMF and WBS was -0.11 at d 2, -0.21 at d 7, and -0.19 at d 14. In D pork, the relationship between IMF and WBS was linear, and IMF accounted for 47% of the differences in WBS. In H and B pork, the relationship between IMF and WBS was not significant. For each cross, the relationship between pHu and WBS was different; in D pork it was quadratic, in H pork WBS increased linearly, and in B pork there was no significant relationship between WBS and pHu. The 30 kDa/actin ratio, a measure of myofibrillar degradation, increased (P < 0.05) during storage. Differences in 30 kDa/actin ratio did not explain differences in pork tenderness or tenderization. Further research on determinants and mechanisms of pork tenderness and pork tenderization is needed before production of consistently tender pork will be possible.     

性成熟对广西三黄鸡胸肌肌肉品质的影响

以广西三黄鸡母鸡为研究对象,分析鸡冠发育与性成熟之间的关系,同时对性成熟与胸肌肌肉品质之间的关系进行了研究.结果表明:早期的鸡冠高度与性成熟之间存在相关性,但是到了后期,特别是98日龄之后的鸡冠高度与性成熟之间不相关;鸡冠的发育以及性成熟与否,至少与以下这些肉质指标之间没有关系,包括系水力、胸肌含水率以及肌内脂肪含量,甚至鸡冠较高也不意味着就会沉积较多的腹脂.由于性威熟与鸡食用品质之间的相关性,研究结果提示性成熟可能通过其它的肉质指标影响优质鸡的肌肉品质.     

大豆异黄酮对骨骼肌发育的影响及其对动物肉品质的调控作用

大豆异黄酮是一类植物雌激素,对动物机体的调控作用非常广泛。近年来研究发现,大豆异黄酮对动物的骨骼肌发育有很重要的调控作用。本文综述了大豆异黄酮对肌肉能量与蛋白代谢、肌细胞的增殖与分化以及肌纤维类型转化的影响,并进一步探讨了大豆异黄酮对动物肌肉品质的调控作用。     

营养调控影响猪肌内脂肪沉积的研究进展

<正>猪肉是我国城乡居民消费量最大的肉食品,随着人们生活水平的不断提高,猪肉品质已越来越受到消费者和生产者的重视。如何提高猪肉品质已成为现代养猪业的重要课题。我们通常说的猪肉品质主要包括pH、肉色、嫩度、肌肉系水力、     

莱芜猪和鲁菜黑猪肌纤维发育规律及其对肉质特性的影响

本研究以40～90kg6个体重阶段的莱芜猪和鲁莱黑猪为试验对象,每个阶段每组各6头猪,采用组织化学切片染色技术进行组织学观察,探讨猪肌纤维的发育规律及其对肉质特性的影响。结果表明：①随着体重的增加,莱芜猪与鲁莱黑猪肌纤维的发育较为明显,但发育特点明显不同,莱芜猪40～70kg体重时肌纤维生长较慢,直径和面积变化不明显,70kg后肌纤维生长发育明显加快（P〈0．05）;而鲁莱黑猪则是40～60kg体重时肌纤维生长较快,60奴后肌纤维生长发育变慢（P〈0．05）。（爹琥珀酸脱氢酶（sDH）组织化学处理显示,肌肉肌纤维是由红肌纤维、中间型肌纤维和白肌纤维这3种类型肌纤维构成,并以白肌纤维占优势。莱芜猪与鲁莱黑猪在肌纤维类型的组成和不同类型肌纤维直径上具有不同的发育性变化模式,总体上莱芜猪红肌纤维含量有高于鲁莱黑猪的变化趋势。在不同类型肌纤维直径方面,莱芜猪与鲁莱黑猪具有基本相同的发育性变化模式。③相关性分析表明,肌肉的肌纤维尤其是红肌纤维的生长发育,对肌肉的干物质、肌内脂肪及系水力等肉质性状具有有利的影响,但白肌纤维的生长发育对肌肉的系水力具有不利的影响。研究结果提示：在肌肉组织中肌纤维的发育方面,莱芜猪比鲁莱黑猪较为晚熟;在肌纤维类型的组成方面。红肌纤维更有利于优良肉质特性的形成。