Human cardiovascular progenitor cells develop from a KDR+ embryonic-stem-cell-derived population

The functional heart is comprised of distinct mesoderm-derived lineages including cardiomyocytes, endothelial cells and vascular smooth muscle cells. Studies in the mouse embryo and the mouse embryonic stem cell differentiation model have provided evidence indicating that these three lineages develop from a common Flk-1(+) (kinase insert domain protein receptor, also known as Kdr) cardiovascular progenitor that represents one of the earliest stages in mesoderm specification to the cardiovascular lineages. To determine whether a comparable progenitor is present during human cardiogenesis, we analysed the development of the cardiovascular lineages in human embryonic stem cell differentiation cultures. Here we show that after induction with combinations of activin A, bone morphogenetic protein 4 (BMP4), basic fibroblast growth factor (bFGF, also known as FGF2), vascular endothelial growth factor (VEGF, also known as VEGFA) and dickkopf homolog 1 (DKK1) in serum-free media, human embryonic-stem-cell-derived embryoid bodies generate a KDR(low)/C-KIT(CD117)(neg) population that displays cardiac, endothelial and vascular smooth muscle potential in vitro and, after transplantation, in vivo. When plated in monolayer cultures, these KDR(low)/C-KIT(neg) cells differentiate to generate populations consisting of greater than 50% contracting cardiomyocytes. Populations derived from the KDR(low)/C-KIT(neg) fraction give rise to colonies that contain all three lineages when plated in methylcellulose cultures. Results from limiting dilution studies and cell-mixing experiments support the interpretation that these colonies are clones, indicating that they develop from a cardiovascular colony-forming cell. Together, these findings identify a human cardiovascular progenitor that defines one of the earliest stages of human cardiac development.     

Generation of chick skeletal muscle cells in groups of 16 from stem cells

The commonly accepted hypothesis explaining the control of skeletal muscle differentiation is that all myogenic precursor cells are equivalent and that they differentiate into post-mitotic muscle cells in response to exogenous signals, specifically low mitogen concentrations. Large clones derived from vertebrate myogenic cells, however, consist both of cycling precursors and of terminally differentiated, post-mitotic muscle cells. Here, we count the total number of cells and the number of terminally differentiated cells (or nuclei, in fused cells) in large myogenic clones. The number of terminally differentiated cells per clone was usually equal to or just below a multiple of 16. This finding is not expected from a model postulating a homogeneous population of muscle precursor cells. Rather, our results suggest that a self-renewing stem cell exists in the skeletal muscle lineage. This cell can generate committed precursors which then give rise to cohorts of 16 terminally differentiated muscle cells. This model of myogenesis provides a simple explanation for the protracted and asynchronous nature of muscle differentiation in vertebrate embryogenesis.     

A lethal mutation in mice eliminates the slow calcium current in skeletal muscle cells

Contraction of a vertebrate skeletal muscle fibre is triggered by electrical depolarization of sarcolemmal infoldings termed transverse-tubules (t-tubules), which in turn causes the release of calcium from an internal store, the sarcoplasmic reticulum (SR). The mechanism that links t-tubular depolarization to SR calcium release remains poorly understood. In principle, this link might be provided by the prominent slow calcium current that has been described in skeletal muscle cells of adult frogs and rats. However, blocking this current does not abolish the depolarization-induced contractile responses of frog muscle, and the function of this slow calcium current is unknown. Here we describe measurements of calcium currents in developing skeletal muscle cells of normal rats and mice, and of mice with muscular dysgenesis, a mutation that causes excitation-contraction (E-C) coupling to fail. We find that a slow calcium current is present in skeletal muscle cells of normal animals but absent from skeletal muscle cells of mutant animals. The effect of the mutation is specific to the slow calcium current of skeletal muscle; a fast calcium current is present in developing skeletal muscle cells of both normal and mutant animals, and slow calcium currents are present in cardiac and sensory neurones of mutant animals. We believe this to be the first report of a mutation affecting calcium currents in a multicellular organism. The effects of the mutation raise important questions about the relationship between the slow calcium current and skeletal muscle E-C coupling.     

微囊化基质细胞对脐带血造血干/祖细胞扩增支持

将脐带血单个核细胞与包埋有兔骨髓间充质干细胞的海藻酸钙微胶珠在3种不同的培养液中进行了7d的体外静态共培养.每24h进行总有核细胞计数,在0、72和168h进行流式CD34+细胞分析以及甲基纤维素集落检验.实验结果表明:经过7d的静态共培养,在添加常规剂量造血生长因子的培养液中,总有核细胞扩增了(15±2.85)倍,CD34+细胞扩增了(5.33±0.32)倍,CFU-Cs扩增了(5.6±1.21)倍.微胶囊可以作为一种新的共培养隔离手段,微囊化兔骨髓间充质干细胞在添加适量血清或者造血生长因子组合的条件下对于脐带血造血干/祖细胞在静态下的扩增有明显的促进作用.     

Mice overexpressing human uncoupling protein-3 in skeletal muscle are hyperphagic and lean

Uncoupling protein-3 (UCP-3) is a recently identified member of the mitochondrial transporter superfamily that is expressed predominantly in skeletal muscle. However, its close relative UCP-1 is expressed exclusively in brown adipose tissue, a tissue whose main function is fat combustion and thermogenesis. Studies on the expression of UCP-3 in animals and humans in different physiological situations support a role for UCP-3 in energy balance and lipid metabolism. However, direct evidence for these roles is lacking. Here we describe the creation of transgenic mice that overexpress human UCP-3 in skeletal muscle. These mice are hyperphagic but weigh less than their wild-type littermates. Magnetic resonance imaging shows a striking reduction in adipose tissue mass. The mice also exhibit lower fasting plasma glucose and insulin levels and an increased glucose clearance rate. This provides evidence that skeletal muscle UCP-3 has the potential to influence metabolic rate and glucose homeostasis in the whole animal.     

Fbxw7/Cdc4 is a p53-dependent, haploinsufficient tumour suppressor gene

The FBXW7/hCDC4 gene encodes a ubiquitin ligase implicated in the control of chromosome stability. Here we identify the mouse Fbxw7 gene as a p53-dependent tumour suppressor gene by using a mammalian genetic screen for p53-dependent genes involved in tumorigenesis. Radiation-induced lymphomas from p53+/- mice, but not those from p53-/- mice, show frequent loss of heterozygosity and a 10% mutation rate of the Fbxw7 gene. Fbxw7+/- mice have greater susceptibility to radiation-induced tumorigenesis, but most tumours retain and express the wild-type allele, indicating that Fbxw7 is a haploinsufficient tumour suppressor gene. Loss of Fbxw7 alters the spectrum of tumours that develop in p53 deficient mice to include a range of tumours in epithelial tissues such as the lung, liver and ovary. Mouse embryo fibroblasts from Fbxw7-deficient mice, or wild-type mouse cells expressing Fbxw7 small interfering RNA, have higher levels of Aurora-A kinase, c-Jun and Notch4, but not of cyclin E. We propose that p53-dependent loss of Fbxw7 leads to genetic instability by mechanisms that might involve the activation of Aurora-A, providing a rationale for the early occurrence of these mutations in human cancers.     

3-甲基组氨酸三室模型在研究猪骨骼肌蛋白质降解中的应用

3-甲基组氨酸(3MH)主要是动物骨胳肌蛋白分解代谢产物，它不能再用于合成蛋白，因而3MH是研究动物骨胳肌蛋白降解率的一个可行示踪物．将标记的3MH经颈静脉注射，对血液中的同位素丰度进行观测，再根据猪体内3MH代谢特点，构建出猪骨胳肌蛋白降解的三分域模型．本文着重对该模型的的理论基础进行了讨论。     

运动与骨骼肌中的基因表达

通过献资料法阐述了运动对骨骼肌基因表达的影响,以便深入理解骨骼肌的工作原理,为客观指导运动训练提供依据．