Universal Blood Stem Cell (p. 512/513)
Role of Myogenin in Myogenesis (p. 521/522)
Blau H.M., Brazelton T.R. and Weimann J.M. (2001) The evolving concept of a stem cell: Entity or function? Cell 105: 829-841
Clarke D. and Frisen J. (2001) Differentiation potential of adult stem cells. Curr. Opin. Genet. Dev. 5: 575-580
Roman B.L. and Weinstein B.M. (2000) Building the vertebrate vasculature: research is going swimmingly. BioEssays 22: 882-893
Clarke D.L., Johansson C.B., Wilbertz J., Veress B., Nilsson E., Karlstrom H., Lendahl U. and Frisen J. (2000) Generalized potential of adult neural stem cells. Science 288: 1660-1663
This study was designed to analyze the potency of adult neural stem cells. The investigators injected stem cells from brains of mice labeled with a lacZ transgen into the amniotic cavity of gastrulating chicken embryos. Of 109 surviving embryos, 24 contained descendants of the transplanted mouse cells, which were found in derivatives of all three germ layers. The same results were obtained when clones grown from single mouse neural stem cells were transplanted. When injected into mouse blastocysts as hosts, the labeled neural stem cells also contributed to a variety of cell lineages. The results of these and other experiments suggest that stem cells from adult tissues have greater potencies than previously thought.
Summerbell D., Ashby P.R., Coutelle O., Cox D., Yee S.-P. and Rigby P.W.J. (2000) The expression of Myf5 in the developing mouse embryo is controlled by discrete and dispersed enhancers specific for particular populations of skeletal muscle precursors. Development 127: 3745-3757
In the mouse embryo, Myf5 is the first of the four myogenic bHLH proteins to be synthesized. Mutational studies also indicate that this protein acts early in the process of muscle cell determination. The investigators have therefore analyzed the regulation of the Myf5+ gene using transgenic expression of a lacZ reporter gene under the control of myf5 enhancers. They found discrete and dispersed enhancer elements that drive reporter gene expression particular subsets of skeletal muscle precursors. For instance, there are separate enhancers of Myf5+ for the precursors of epaxial muscles, hypaxial muscles, and facial muscles. The authors suggest that this complex mechanism of control has evolved because different inductive signals operate in each subset of muscle precursors, so that distinct enhancers and cognate transcription factors are required to interpret them.
Yamashita Y., Itoh H., Harashima M., Ogawa M., Nishikawa S., Yurugi T., Naito M., Nakao K. and Nishikawa S.-I. (2000) Flk1-positive cells derived from embryonic stem cells serve as vascular progenitors. Nature 408: 92-96
The traditional view about the histogenesis of blood vessels has been that endothelial cells and mural cells (pericytes and vascular smooth muscle) arise from separate lineages. This study shows that mouse embryonic stem cells expressing Flk1+, depending on the growth factor to which they are exposed, can give rise to either endothelial cells or mural cells. Flk1-positive cells cultured in the presence of platelet-derived growth factor BB express the molecular markers that characterize mural cell development. In contrast, exposure of the same cells to vascular endothelial growth factor elicits the markers of endothelial cell formation. When cultured in collagen gels, the Flk1-positive cells can form organized, blood vessel-like structures as well as blood cells. When injected into chicken embryos, the Flk1-positive mouse stem cells form both endothelium and mural cells and contribute to the developing blood vessels in vivo.
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