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Cell memory and differentiation

Cell memory and differentiation - December 6 2007 Bio 317...

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December 6, 2007 Bio 317 Cell memory and Tissue Differentiation Part II Myoblast (tiny cell) to a long multinucleated muscle cell, How? At the beginning of the pathway we need an external signal to command the differentiation. The command is in the form of protein secretion, either MyoD, myogenin, Myf 5 or Mrf4. This will turn the myoblast or fibroblast into a muscle cell. Once differentiation is taking place there is no return (once you release the factors they autostimulate production) Initial signal that leads to a defined pathway and there is memory. By memory it just means that initial decisions are being retained through autoregulation. This happens not only in muscle cells but many other types (slide…) Each one goes back to an embryonic stem cell, a cell that is pluripotent (capable of differentiating into a lot of things, aka omnipotent). Same proteins are used in different contexts, which gives each cell a different identity. Cell differentiation is a very modular thing. (check out slide to get a good idea, combinational gene slide in lecture) Nature uses same factors over and over but in different combinations and contexts which is how we get along with only 25,000 genes. Another example that explains differentiation involves a 10 year old experiment that proved pathways exist that are defined. The fly has two spots on the genome, one that gives rise to the eye and one to the leg (demarcated by white and red). If you mess with the spots (the EY gene) you can get a fly with a fly with an eye and leg. Scientists placed an eye gene on the leg position so the fly differential cells saw to make a leg and eye in the same spot and it did. This shows the possibility of adding factors to cells to create a missing organ in a human! An intial signal is sent to the eye spot and two genes are sufficient to differentiate into cells (toy or ey). Once ey is triggered a positive feedback loop is transmitted and the entire area near the eye pathway becomes an eye.
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