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BIOLOGY 205/SECTION 7 DEVELOPMENT- LILJEGREN Lecture 7 Determination and Differentiation 1. DETERMINATION vs. DIFFERENTIATION vs. FATE vs. SPECIFICATION a. We’ve already talked about cells having a certain FATE, that is often specified or modulated by induction events. A level of commitment beyond cell fate is specification . A specified cell has been told what it should be. If it is experimentally isolated, it will follow those instructions; however, its fate can still be influenced by different environments. Beyond cell specification is determination. At this level of commitment, the cell cannot be made to change fates by a different environment, that cell is said to be DETERMINED. A cell is said to be determined if it has made an irreversible (usually) developmental choice among options. A more rigorous definition is that a cell is determined when it has undergone an internal and self-perpetuating change distinguishing itself & its descendents from other cells and committing to a specialized course. This concept differs from DIFFERENTIATION because that refers to the elaboration of the fate of a cell. Differentiation is overt cell specialization: a cell gaining new detectable differences. In other words, a cells knows what it will become (it is determined) before it actually becomes that type of cell (it differentiates). b. Another aspect of determination is that the fate decision becomes self- perpetuating , so that the subsequent progeny of the determined cell usually have the fate (sometimes in modified form) of that cell. 2. Evidence for determination during development. a. Transplant experiments (Spemann 1918): showed changes in cell determination 1. Experiment #1: If take an amphibian embryo at early gastrulation and transplant prospective epidermis (skin) where neural tube would normally form, the transplant tissue forms neural tube and brain. If you reverse the experiment, and put prospective neural plate where skin usually forms, it will form skin. THEREFORE AT THIS STAGE OF DEVELOPMENT BOTH FATES CAN BE SWITCHED BY CHANGING THE ENVIRONMENT. THE CELLS ARE NOT YET DETERMINED . 2. Experiment #2: The same experiment done during a later stage of gastrulation, gives a very different result. At this point prospective epidermis will make epidermis even if it is put where neural plate normally develops. Likewise the prospective neural plate will form neural plate at a epidermal location. THEREFORE AT THIS STAGE BOTH FATES CANNOT BE SWITCHED BY CHANGING ENVIRONMENT, AND THE CELLS ARE DETERMINED . However, when the experiment was done, the cells had not yet differentiated into epidermis or neural plate.
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This note was uploaded on 05/26/2011 for the course BIO 205 taught by Professor Reed during the Spring '11 term at UNC.

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