Lecture 20 Notes

Lecture 20 Notes - Vandan Desai BIOL 442Developmental...

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Vandan Desai BIOL 442—Developmental Biology 1 Lecture #20—Cell Differentiation and Cancer I. Cell Differentiation :: A. Focus on mechanisms used to replenish differentiated cells in adult organisms— i. Some differentiated cells can divide ; others renew via stem cells But, via both mechanisms, differentiated cells are replenished in finite amounts (i.e., growth is tightly controlled) In contrast, cancer cells divide uncontrollably ii. Specification— loose commitment; i.e., cells can be altered in response to signals from one another (mediated by maternal genes) iii. Determination—unlike specification, this is irreversible (mediated by segmentation genes) B. Background information— i. Each organism is composed of multiple cell types Ex: humans and other large vertebrates have ~200 different mature cell types Cell types can be divided into subtypes: ü Ex: muscle cells = skeletal muscle fibers (red fibers, white fibers, intermediate fibers, muscle spindles, satellite cells), cardiac muscle cells , smooth muscle cells , myoepithelial cells ii. Cell differentiation—process by which a cell achieves its mature state; the way different cell types are derived Ex: neurogenesis (neurons) and myogenesis (muscle cells) iii. Once a cells has differentiated, it does not normally transform into another cell type, as part of normal development Exceptions (examples) = ü Single isolated plant cells can regenerate entire new plants ü The iris of a salamander’s eye can regenerate a new lens iv. Regeneration involves phases of dedifferentiation , during which cells lose their differentiated character and proliferate before they differentiate again in new ways (differentiated cell => dedifferentiation => proliferate => differentiation) C. Cell differentiation occurs throughout life— i. Cell differentiation occurs not only during development , but throughout the lifespan of the organism In adult organism ensures that dying cells are replaced (regeneration) ii. The rate of cell turnover varies from organ to organ Epithelial cells of the small intestine are renewed every day Pancreatic cell renewal takes over a year
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Vandan Desai BIOL 442—Developmental Biology 2 Brain cells are not renewed ü How old are you? You are as old as your brain! => NERD! D. Differentiated cells can be classified based on whether they have the ability to divide; two types of differentiated cells— i. Differentiated cells that no longer divide Renew themselves from stem cells Ex: brain cells, blood cells, epithelial cells, spermatogonia ii. Differentiated cells that have the ability to divide Rare; ex: liver cells E. Differentiated cells that renew themselves from stem cells— i. Tissues in which differentiated cells don’t divide have reserve cells—stem cells, which can be unipotent , pluripotent , or totipotent Unipotent stem cells are committed to give rise to a particular progenitor cell (i.e., they’re limited
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This note was uploaded on 12/09/2010 for the course BIOL 442 taught by Professor Brewster,r during the Fall '08 term at UMBC.

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Lecture 20 Notes - Vandan Desai BIOL 442Developmental...

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