Neurotrophic effect on isolated chick embryo muscle in culture

Acetylcholinesterase activity in cultures of dissociated skeletal muscle prepared from the thigh muscle of the 10-day-old chick embryo was increased by the presence of innervating spinal cord explants, spinal cord explants in a parabiotic environment, and by media containing brain-spinal cord extract.     

Dystrophic chicken muscle: altered synaptic acetylcholinesterase

Individual motor endplates in the skeletal muscles of chickens genetically homozygous for muscular dystrophy have been compared with those in normal chickens. Measurements were made there, by specific autoradiographic techniques, of the numbers of total cholinesterase-like molecules and of acetylcholinesterase molecules. The acetylcholinesterase is distinctly decreased at the endplates in dystrophic muscles. The various data available on these muscles are compatible with the concept that a neural factor which determines the synaptic acetylcholinesterase, along with a number of other characters in the muscle cell, is defective in this disorder.     

Neurotrophic and neurotoxic effects of amyloid beta protein: reversal by tachykinin neuropeptides

The amyloid beta protein is deposited in the brains of patients with Alzheimer's disease but its pathogenic role is unknown. In culture, the amyloid beta protein was neurotrophic to undifferentiated hippocampal neurons at low concentrations and neurotoxic to mature neurons at higher concentrations. In differentiated neurons, amyloid beta protein caused dendritic and axonal retraction followed by neuronal death. A portion of the amyloid beta protein (amino acids 25 to 35) mediated both the trophic and toxic effects and was homologous to the tachykinin neuropeptide family. The effects of the amyloid beta protein were mimicked by tachykinin antagonists and completely reversed by specific tachykinin agonists. Thus, the amyloid beta protein could function as a neurotrophic factor for differentiating neurons, but at high concentrations in mature neurons, as in Alzheimer's disease, could cause neuronal degeneration.     

Membrane phosphatidylserine regulates surface charge and protein localization

Electrostatic interactions with negatively charged membranes contribute to the subcellular targeting of proteins with polybasic clusters or cationic domains. Although the anionic phospholipid phosphatidylserine is comparatively abundant, its contribution to the surface charge of individual cellular membranes is unknown, partly because of the lack of reagents to analyze its distribution in intact cells. We developed a biosensor to study the subcellular distribution of phosphatidylserine and found that it binds the cytosolic leaflets of the plasma membrane, as well as endosomes and lysosomes. The negative charge associated with the presence of phosphatidylserine directed proteins with moderately positive charge to the endocytic pathway. More strongly cationic proteins, normally associated with the plasma membrane, relocalized to endocytic compartments when the plasma membrane surface charge decreased on calcium influx.     

ATP regulates the phosphorylation and degradation of myofibrillar proteins in ground ovine muscle

Phosphorylation post-translational modification plays an important role in postmortem muscle quality traits. Adenosine triphosphate (ATP) is an energy source and a key substrate of phosphorylation which provides the phosphatase groups to proteins in the presence of protein kinases. However, in postmortem muscle, the effects of ATP content on phosphorylation are poorly studied. The study investigated the effect of ATP on protein phosphorylation and degradation in postmortem ovine muscle. The ground muscle with/without additional ATP were treated/control groups and stored at 25 and 4°C, respectively. The ATP content led to different changes of pH value between the ATP-treated and control groups. The phosphorylation level of myofibrillar proteins was higher (P<0.05) in ATP-treated group compared to the control group at both temperatures, which suggested that ATP played a vital role in postmortem protein phosphorylation. A slower degradation rate of µ-calpain, desmin and troponin T was observed in the ATP-treated group which showed that there was a negative relationship between ATP level and the degradation of proteins. These observations clearly highlighted the role of ATP on the development of meat quality by regulating the phosphorylation and degradation of myofibrillar proteins in postmortem ovine muscle.     

beta-Arrestin: a protein that regulates beta-adrenergic receptor function

Homologous or agonist-specific desensitization of beta-adrenergic receptors is thought to be mediated by a specific kinase, the beta-adrenergic receptor kinase (beta ARK). However, recent data suggest that a cofactor is required for this kinase to inhibit receptor function. The complementary DNA for such a cofactor was cloned and found to encode a 418-amino acid protein homologous to the retinal protein arrestin. The protein, termed beta-arrestin, was expressed and partially purified. It inhibited the signaling function of beta ARK-phosphorylated beta-adrenergic receptors by more than 75 percent, but not that of rhodopsin. It is proposed that beta-arrestin in concert with beta ARK effects homologous desensitization of beta-adrenergic receptors.     

Molecular analysis of protein assembly in muscle development

The challenge presented by myofibril assembly in striated muscle is to understand the molecular mechanisms by which its protein components are arranged at each level of organization. Recent advances in the genetics and cell biology of muscle development have shown that in vivo assembly of the myofilaments requires a complex array of structural and associated proteins and that organization of whole sarcomeres occurs initially at the cell membrane. These studies have been complemented by in vitro analyses of the renaturation, polymerization, and three-dimensional structure of the purified proteins.     

A G protein directly regulates mammalian cardiac calcium channels

A possible direct effect of guanine nucleotide binding (G) proteins on calcium channels was examined in membrane patches excised from guinea pig cardiac myocytes and bovine cardiac sarcolemmal vesicles incorporated into planar lipid bilayers. The guanosine triphosphate analog, GTP gamma S, prolonged the survival of excised calcium channels independently of the presence of adenosine 3',5'-monophosphate (cAMP), adenosine triphosphate, cAMP-activated protein kinase, and the protein kinase C activator tetradecanoyl phorbol acetate. A specific G protein, activated Gs, or its alpha subunit, purified from the plasma membranes of human erythrocytes, prolonged the survival of excised channels and stimulated the activity of incorporated channels. Thus, in addition to regulating calcium channels indirectly through activation of cytoplasmic kinases, G proteins can regulate calcium channels directly. Since they also directly regulate a subset of potassium channels, G proteins are now known to directly gate two classes of membrane ion channels.     

犬旋毛虫肌幼虫的体外培养

系统地探讨了不同培养条件对犬旋毛虫肌幼虫体外培养的影响．结果表明，犬旋毛虫肌幼虫包囊最佳消化时间为38℃下消化14h；最佳培养温度为37℃，气体条件为8％CO2，培养液为pH=7．0的RPMI-1640．按所选择的最佳条件进行培养，明显延长了犬旋毛虫肌幼虫的体外培养时间，体外培养持续时间达24d。     

Differential development of two classes of acetylcholine receptors in Xenopus muscle in culture

Physiological properties of acetylcholine receptors on muscle cells at very early stages of ontogeny were compared with those of cells at later stages. Two changes were observed that contributed to an overall shortening of the mean open time of single-channels. First, there was a shift in the relative proportions of two receptor types with different conductances and mean open times, such that the contribution of receptors with large conductance and short open time increased as development proceeded. Second, there was a sharp reduction in the mean open time of channels having small conductance, with no similar change in channels having large conductance.     

Brain cells in culture: morphological transformation by a protein

One type of elmbryonic rat brain cell having an epithelioid morphology in the monolayer culture can be transformed by brain extract into cells having extensive processes resembling mature astrocytes. The transforming factor is a protein with a molecular weight of 350,000. A partially purified sample showed that it is active at a concentration as low as 1 x 10(-8)M. The transforming actvity is high in adult brains but low in embryonic brains and tumors of the nervous systems.     

SMEDWI-2 is a PIWI-like protein that regulates planarian stem cells

We have identified two genes, smedwi-1 and smedwi-2, expressed in the dividing adult stem cells (neoblasts) of the planarian Schmidtea mediterranea. Both genes encode proteins that belong to the Argonaute/PIWI protein family and that share highest homology with those proteins defined by Drosophila PIWI. RNA interference (RNAi) of smedwi-2 blocks regeneration, even though neoblasts are present, irradiation-sensitive, and capable of proliferating in response to wounding; smedwi-2(RNAi) neoblast progeny migrate to sites of cell turnover but, unlike normal cells, fail at replacing aged tissue. We suggest that SMEDWI-2 functions within dividing neoblasts to support the generation of cells that promote regeneration and homeostasis.     

鹌鹑脏器、肌肉蛋白质多型座位电泳技术

将应用于家畜血液蛋白质多型座位的电泳技术加以改进，成功地应用于鹌鹑脏器、肌肉蛋白质多型座位的检测，使可检测的鹌鹑蛋白质多型座位数从国内报道的３个增至３２个。详细介绍了检测３２个鹌鹑脏器、肌肉蛋白质多型座位的淀粉凝胶电泳技术，为客观评价鹌鹑遗传资源提供了科学的研究方法。     

Genetic variation in human erythrocyte acetylcholinesterase

A method for solubilization of human erythrocyte membranes was developed and used to survey 70 unselected human blood samples for isozymic variation of stromal acetylcholinesterase. Three variants were observed. Pedigrees of families studied by this method indicated that this variation represented the phenotypic expression of two codominant alleles at a single locus.     

Nucleoprotein constituents stimulating growth in tissue culture: active protein fraction

A new method has been developed for removing the nucleic acid portion of the nucleoprotein fraction which stimulates growth in tissue culture. Biological activity resides in the purified protein fraction, while the high-polymer nucleic acid fraction is inert. The active protein fraction contains extractable lipids which have no effect on the biological activity.     

Effects of rumen-degradable protein balance on rumen fermentation in continuous culture fermenters

Twelve dual-flow continuous culture fermenters (culture 8 d with 5 d for adjustment and 3 d for sample collection) were used to evaluate the effects of rumen-degradable protein balance (RDPB) on rumen fermentation. The different RDPB levels in six diets were as follows: − 16.84, − 8.87, − 0.87, + 7.13, + 15.13, and + 23.12 g RDPB /kg DM. Results indicated that RDPB had a significant effect on fermenter NH3-N (P < 0.0001), but had less effect on the fermenter pH (P = 0.058), total VFA concentration (P = 0.57), or acetate molar proportion (P = 0.70). The decrease in rumen-available N in the diets with the RDPB levels at + 15.13, + 7.13, − 0.87, − 8.87, − 16.84 g RDPB/kg DM resulted in NH₃-N concentration decreasing at 9%, 52%, 104% and 118% in rumen compared with the diet of + 23.12 g RDPB/kg DM. Total VFA concentration, acetic acid and valeric acid at different time points was altered (P < 0.05) by the treatment. With the increase of dietary RDPB, the total NH₃-N flowing out of fermenters linearly increased, and the N losses also increased.     

广东池养梭鱼肌肉营养成分的分析及评价

对广东池养梭鱼肌肉中一般成分(水分、粗蛋白、粗脂肪、灰分)、氨基酸、脂肪酸、营养元素进行测定,并进行了较为全面的分析和比较。结果表明,其肌肉鲜样中水分含量为76.9%,粗蛋白含量为20.2%,粗脂肪含量为1.2%,灰分含量为1.13%。肌肉中18种氨基酸的总量为湿重的19.43%。其中,8种必需氨基酸的总量占湿重的8.77%,占氨基酸总量的45.14%,必需氨基酸与非必需氨基酸的比例为97.23%,符合FAO/WHO的标准。梭鱼的第一、二限制性氨基酸分别为缬氨酸和蛋氨酸+胱氨酸,必需氨基酸指数(EAAI)为61.56。梭鱼肌肉中含有22种脂肪酸,不饱和脂肪酸含量丰富,与饱和脂肪酸的比例约为3∶1;EPA+DHA的含量占干重的5.92%,高于其他一些经济鱼类;梭鱼微量元素的比例合理。     

AMP-activated protein kinase regulates neuronal polarization by interfering with PI 3-kinase localization

Axon-dendrite polarization is crucial for neural network wiring and information processing in the brain. Polarization begins with the transformation of a single neurite into an axon and its subsequent rapid extension, which requires coordination of cellular energy status to allow for transport of building materials to support axon growth. We found that activation of the energy-sensing adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway suppressed axon initiation and neuronal polarization. Phosphorylation of the kinesin light chain of the Kif5 motor protein by AMPK disrupted the association of the motor with phosphatidylinositol 3-kinase (PI3K), preventing PI3K targeting to the axonal tip and inhibiting polarization and axon growth.