Changes in muscle fiber type and expression of mRNA of myosin heavy chain isoforms in porcine muscle during pre‐ and postnatal development

The purpose of this study is to elucidate developmental changes in muscle fiber type in the pig during pre‐ and postnatal development. For this purpose, we performed a histochemical analysis for myosin adenosine triphosphatase activity to assess muscle fiber type and determined abundances of messenger RNA (mRNA) of myosin heavy chain (MHC) isoforms. Samples of Longissimus dorsi (LD) muscle were taken from fetuses on day 90 of the fetal stage. Further, samples of LD, Rhomboideus and Biceps femoris (B. femoris) muscles were taken from pigs when they were 1, 12, 26, 45 or 75 days old. Expression of MHC 2b mRNA in the LD and the B. femoris muscles rapidly and considerably increased from the late fetal stage to the early postnatal stage and this increase was associated with the development of type 2b fibers at least in the LD muscle. As shown by the rapid and considerable changes in expression of MHC 2b mRNA, it seems that a certain plasticity of muscle fiber type still remains in this developmental stage.     

肌纤维类型及其对猪肉品质影响的研究进展*

 根据肌球蛋白重链的多态性可将猪的肌纤维分为Ⅰ,2a,2b和2x 4种类型，在代谢上分别与慢速氧化型、快速氧化型、快速酵解型和中间类型相对应。从肌纤维的构成、分类及转化等方面介绍肌纤维类型的代谢特点，重点阐述肌纤维类型对猪肉品质的影响，以及影响肌纤维类型的因素。     

Research Progress on Cellular Receptors of Porcine Reproductive and Respiratory Syndrome Virus

Porcine reproductive and respiratory syndrome virus (PRRSV) enters the host cells via a mechanism of receptor-mediated endocytosis. The entry mechanism is mediated by attachment to one or more cellular receptors and/or coreceptor on the cell surface and internalization. This article mainly describes several receptors for PRRSV. As far, it is reported five receptors of PRRSV which are independent and associated, heparin sulphate (HS), sialoadhesin (Sn),vimentin, CD163 and non-muscle myosinⅡA. It plays a significant role for the mechanism of PRRSV infection or disease prevention and treatment by studying the function of cellular receptors of PRRSV.     

Expression of four muscle proteins at different growth stages of Günther's walking catfish Clarias macrocephalus

The complete cDNA sequences of four contractile muscle genes of walking catfish Clarias macrocephalus were characterized by assembling partial EST sequences from a skeletal muscle cDNA library. The four genes were parvalbumin 4 (PV4) (670 bp), troponin C (TnC) (1065 bp), troponin I (TnI) (843 bp) and myosin light chain 3 (MLC3) (953 bp), leading to deduced amino acid sequences of 109, 160, 176 and 150 residues respectively. During the larval stage, TnC mRNA showed the highest levels of expression with a 1.4‐fold increase from day 1 to day 30 post hatch. At 90 days, the relative expression levels of PV4, TnC and MLC3 were the highest, with similar proportions in the skeletal muscle, corresponding to the highest relative growth rate of walking catfish. Expression of the three calcium‐binding proteins remained high in 6‐month‐old fish, with higher levels of PV4. The different proportions of muscle proteins expressed suggested the significance of their contributions to fish growth and appeared to be correlated with the functional properties of muscle cells, which were observed from changes in the swimming activity of the fish.     

cDNA cloning and complete primary structures of myosin heavy chains from brushtooth lizardfish Saurida undosquamis and wanieso lizardfish S. wanieso fast skeletal muscles

ABSTRACT:   The complete cDNA sequences encoding predominant types of myosin heavy chain (MYH) in the fast skeletal muscle were determined for brushtooth lizardfish Saurida undosquamis and wanieso lizardfish S. wanieso , which are used as materials for preparing high-quality surimi-based products. The cDNA consisted of 5973 and 5987 bp, respectively, and both encompassed an open reading frame encoding a polypeptide of 1936 amino acid residues. Brushtooth and wanieso lizardfish MYH showed the amino acid sequence identity of 92–93% to white croaker MYH, which was higher than that of 90% to walleye pollack MYH. The putative binding sites for ATP, actin, and regulatory and essential light chains in the subfragment-1 region of brushtooth lizardfish MYH exhibited a high identity with white croaker counterparts as well as the sequences of subfragment-2 and light meromyosin. In contrast, phylogenetic tree, constructed by the neighbor-joining method based on mitochondrial 16S rRNA gene, revealed that the two lizardfish species formed a cluster with walleye pollack, which was paraphyletic with white croaker. Therefore, a good reputation for lizardfish and white croaker to have a high thermal-gel forming ability seemed to be reflected by MYH rather than biological similarity as revealed by the mitochondrial 16S rRNA gene.     

蛋白质磷酸化对肌动球蛋白解离及其乙酰化水平的影响

【目的】研究肌球蛋白重链和肌动蛋白磷酸化对其乙酰化水平、肌动球蛋白解离及ATP酶活性的影响,为通过调控磷酸化水平改善肉品嫩度提供理论依据。【方法】以羊背最长肌为材料制备肌肉匀浆液,采用碱性磷酸酶抑制剂（抑制去磷酸化）和蛋白激酶抑制剂（抑制磷酸化）调控其磷酸化水平,在4℃分别孵育0、0.5、4、12、24、48和72 h,利用SDS-PAGE电泳和荧光染色、蛋白质免疫印迹、ATP酶活性测定试剂盒分析蛋白质磷酸化水平、乙酰化水平、肌动球蛋白解离程度和ATP酶活性随孵育时间的变化;利用分子动力学模拟分析肌球蛋白重链和肌动蛋白磷酸化对肌动球蛋白结构的影响。【结果】碱性磷酸酶抑制剂处理组中肌球蛋白重链磷酸化水平在孵育4、12和72 h时显著高于对照组和蛋白激酶抑制处理组（P<0.05）,肌动蛋白磷酸化水平在孵育4、12、24、48和72 h时显著高于对照组和蛋白激酶抑制处理组（P<0.05）,表明肌球蛋白重链和肌动蛋白发生去磷酸化反应被碱性磷酸酶抑制剂所抑制。碱性磷酸酶抑制剂处理组中肌动蛋白乙酰化水平在孵育4、12、24、48和72 h时显著低于蛋白激酶抑制组（P<0.05）,肌球蛋白重链乙酰化水平呈无规律变化,表明肌动蛋白磷酸化抑制其乙酰化,肌球蛋白重链磷酸化对其乙酰化影响无明显规律。分子动力学结果表明,肌球蛋白重链第2、3、54位丝氨酸等位点和肌动蛋白第54位丝氨酸、第55位酪氨酸等位点磷酸化增加了肌动球蛋白结构的总能量、势能和动能,降低了键能,导致肌动球蛋白结构变得不稳定。在0—72 h孵育过程中,碱性磷酸酶抑制剂处理组的肌动球蛋白解离程度始终高于蛋白激酶抑制处理组,ATP酶活性低于蛋白激酶抑制处理组（P<0.05）,表明肌球蛋白重链和肌动蛋白磷酸化促进肌动球蛋白解离。【结论】肌球蛋白重链磷酸化直接促进肌动球蛋白解离,肌动蛋白磷酸化通过抑制其自身乙酰化促进肌动球蛋白解离。     

Spawning induces a shift in energy metabolism from glucose to lipid in rainbow trout white muscle

Enzymatic changes that occur in the white somatic muscle of rainbow trout (Oncorhynchus mykiss) in response to spawning were investigated, and the evenness of their distribution across the ventral-dorsal plane of this muscle was assessed. Four enzymes that are involved in energy metabolism were measured (phosphofructokinase: glycolytic capacity, 3-hydroxyacyl-CoA dehydrogenase: -oxidation, citrate synthase: citric acid cycle, cytochrome oxidase: oxidative capacity). The enzyme activities were followed in different parts of the white muscle of non-spawning female rainbow trout from May, four months after their first spawning, until December, at second spawning. Samples were taken from white epaxial muscle along the lateral line, on the dorsum, and in between. Samples were also taken from red muscle of non-spawning fish. The isoforms of myosin heavy chains (MyHC) were electrophoretically identified on 6% SDS-PAGE gel to study possible changes in contractile properties of the muscle.Transformation from the non-spawning to spawning phase was associated with dramatic changes in the activity of the enzymes studied in white muscle: glycolytic capacity decreased to less than half, whereas oxidative metabolism increased about two- to four-fold in all areas. Significant quantitative differences in enzyme activities were found between the three epaxial muscle areas: in the non-spawning fish lateral line samples differed from those taken in the other two areas, whereas in spawning fish the dorsal sample difered from the other two. No difference in the expression of MyHC-isoforms was found between spawning and non-spawning fish. Co-expression of both slow and fast isoforms was found in single fibres isolated from red muscle.The results show that the energy metabolism in white muscle of domestic rainbow trout is altered during spawning; i.e., the metabolism becomes increasingly aerobic, with an increased capacity for fatty acid utilization, concomitant with phenotypic changes associated with sexual maturation. These changes are especially pronounced in ventral, superficially located fibres.     

Comparative study on thermal denaturation modes of myosin in walleye pollack and carp myofibrils as affected by salt concentration

ABSTRACT:   The effect of salt concentration on the thermal denaturation profile of myosin in walleye pollack and carp myofibrils was compared by studying the subfragment-1 (S-1) and rod denaturation rates upon heating. Species-specific denaturation mode observed at 0.1 M KCl was no longer detected when samples were heated above 0.5 M KCl, where S-1 and rod denaturation rates were identical to each other. As the heating of the chymotryptic digest of myofibril formed practically no rod aggregates, S-1 denaturation in a form of myosin was the rate limiting step for rod aggregate formation. As the aggregate formation by rod was remarkably suppressed by lowering the temperature, the free movement of myosin tail upon heating was suggested to play an important role in the rod aggregate formation in a high salt medium.