Cl04 - MCDB 4650 DEVELOPMENTAL BIOLOGY CLASS NOTES Class 4...

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MCDB 4650 DEVELOPMENTAL BIOLOGY CLASS NOTES Class 4 4 - 1 Cell fate, determination and commitment (with a little more on signaling) Reading: Chp 1: 10-15, Chp 3:53-62, 66-67 Learning goals: Be able to: 1. Diagram the two major mechanisms of cell determination and explain their general molecular basis. 2. Distinguish (experimentally) between cell fate and cell commitment. 3. Explain what cytoplasmic maternally-contributed determinants are, and justify their importance during development. 4. Describe how the extracellular matrix (ECM) is involved in signaling. Determination and commitment (note: these two terms are interchangeable) Fate vs. commitment: An embryonic fate map describes for each cell in the embryo the structures and tissues it gives rise to in the adult animal. (Or conversely, it identifies the cells in the embryo from which every adult structure or tissue is derived.) The ultimate fate map is the complete cell lineage (ancestry) of all cells in the adult. Fate maps can be constructed from observation only (if the embryo is transparent), or by ablation of cells in the embryo and observation of the results, or by marking early cells and observing where they end up. The normal fate of a cell is not necessarily the only fate that cell can take on. Many experiments in developmental biology are devoted to demonstrating that a cell’s possible range of fates are larger than the fate it normally takes. At some point in embryogenesis, many cells become determined (committed) to a particular cell fate, without changing their morphology or behavior. This point cannot be determined by observation only. Evidence for commitment can be obtained using techniques of experimental embryology; e.g. transplantation of cells or tissues from one location to another, or ablation of neighboring cells and observation of how the remaining cells develop. Lastly, a cell begins to differentiate . This is the actual production and use of function-specific proteins that allow a cell to do its job. Differentiation is not immediate: it can take days if not longer for a muscle cell, for example, to both take on its final shape and to express all the proteins required for its final functions. Mechanisms of determination: Cells become committed by either of two general mechanisms. 1) Signaling: A signal from a neighboring cell triggers synthesis of new determinants : transcription factors, receptors, etc. (“American plan” determination). When a cell’s fate is determined by signaling, it will not take on its normal fate unless in the presence of this other cell type or signal—ie, it cannot make its fate on its own!
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