Effect of cell history on response to helix-loop-helix family of myogenic regulators

Article Abstract:

It is quite clear that muscle cells manufacture specific proteins that make them muscle cells, liver cells make liver cell proteins, and fibroblasts make proteins specific for fibroblasts. But the developmental pathways and events which lead to this differentiated state remain mysterious. Previously, some researchers maintained that muscle cells achieve their differentiated state due to the action of a specific protein, MyoD, or myogenin, which turns on the other genes appropriate for muscle cells. However, new evidence demonstrates that this explanation is inadequate. There are many techniques for introducing active genes into mammalian cells; they may be directly injected or carried in by combination with viruses. These techniques were previously used to show that MyoD induces the expression of muscle proteins in fibroblast cells. However, the same techniques have now been used to show that MyoD cannot induce the expression of these same proteins when introduced into liver cells. That the introduced MyoD remains functional can be shown by fusing the transfected liver cells with fibroblasts; the resulting hybrid cells are quite capable of making the muscle proteins. The results show that MyoD, by itself, is not the determinant of whether a cell is a muscle or not. In order to induce the synthesis of muscle proteins, MyoD must successfully interact with other factors already present in the cell. This is what apparently occurs in fibroblasts, but not in liver cells. The differentiation of cells, at least in this case, appears to be a result of not only specific factors, such as MyoD, but also of the cells' history, which set the stage for the various possibilities of differentiation. (Consumer Summary produced by Reliance Medical Information, Inc.)

Gene expression, Muscle cells, Cell physiology, Antisense DNA

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GPI-anchored proteins are organized in submicron domains at the cell surface

Article Abstract:

Cellular membranes are dynamic structures comprising lipids and much research has focused on the potential presence of membrane micro-domains within them. It is envisaged that such 'rafts' are enriched in sphingolipids, cholesterol, glycosylphosphatidylinositol (GPI)-anchored proteins and specific membrane proteins. Past research has failed to show that such rafts exist in living cells. A new study measure the distance between GPI-anchored proteins and investigates whether their organisation is non-random. The findings support the raft hypothesis.

Observations, Composition, Cell membranes, Plasma membranes, Cell research, Cytological research

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Ecdysone and the onion

Article Abstract:

Regulation of gene networks by the steroid ecdysone in insects became clearer thanks to recent research discussed at the 'Molecular Biology of Ecdysone Response' in Philadelphia, PA, on Mar 11, 1992 and 'Tenth Ecdysone Workshop' in Liverpool, England on Apr 6-9, 1992. The chromosome 'puffing' model led to the molecular analysis of ecdysone response in the fly Drosophila melanogaster and the isolating of genes from defined puffs of the giant polytene chromosomes. Genetic regulation of ecdysone in other insects is similarly complex.

Insects, Ecdysone

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