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BIOL 442
Lecture 9&amp;10 Notes

Lecture 9&10 Notes - Vandan Desai BIOL... 

Vandan Desai BIOL 442—Developmental Biology 1 Lecture #9—Cell Fate, Potency and Determination, Mosaic vs. Regulative Development, and Genomic Equivalence, & Lecture #10—Cytoplasmic Specification I. Lecture #9 :: A. Fate of a cell —the sum of all structures that the cell or its descendants will form at a later stage of normal development i. People studying them have constructed fate maps of the embryo ii. Use fate mapping techniques to tell us which cells will commit to which fate iii. How do you construct fate maps of an embryo? • W/ tunicate embryo ( styela partita ), there is a portion of cytoplasm of fertilized egg that is yellow (pictured here in red ) ➼ This cytoplasm is readily visible and was easily observed to go to cell that would become muscle • To do fate mapping in other embryos , new methods were developed: ➼ Dye injection into an early blastomere ❧ Need dye which is: (1) bright enough to see after dilution thru many cell division; (2) non-toxic to the cells; (3) cannot diffuse from one cell to another ❧ One commonly used method is to couple a fluorescent dye ( DiI ) to a large metabolically inert carrier molecule which cannot cross cell membranes or go thru cell junctions ❧ When these molecules are microinjected into an early blastomere, one can follow the fates of all descendants of the injected cell B. Potency —ability to trace the fate of descendants of individual blastomeres and cells has made it possible to ask questions about how and when the “ potential ” of a cell gets restricted to a particular fate i. Refer to this wider range of possible fates that a cell could have as its potency ii. If a cell or blastomeres can form all structures or can form a whole embryo , we say that the fertilized egg is totipotent iii. If a cell or blastomeres can form more structures or cell types that it normally would, we say that it is pluripotent • It is potentially restricted ; can form a lot of cell types, but not the entire organism iv. Two types of experiments were used to assess the potency of a cell: (1) isolation experiment , and (2) heterotopic transplantation experiments C. Cell Determination Occurs as a Part of Embryonic Pattern Formation i. The determined state is the result of two major types of processes: • Mosaic Development = cytoplasmic specification • Regulative Development = instructive interactions ii. Mosaic Development – localized cytoplasmic determinants: • In most animals, certain components in the egg cytoplasm are distributed unevenly and partitioned into different blastomeres ➼ These components called localized cytoplasmic determinants • They cause blastomeres to be determined or biased toward forming certain cell lineages/body parts (discussed further in Lecture 10) 

Vandan Desai BIOL 442—Developmental Biology 2 • Cytoplasmic specification tends to occur during earlier stages of embryogenesis and some embryos are more mosaic in their determination process than others iii. Regulative Development – process of stepwise instruction & commitment • 

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