Develop.10.OAK - NOTE!! These files are provided for the...

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Unformatted text preview: NOTE!! These files are provided for the sole purpose of assisting BSci 110 students to study for exams in the class. Some of the material in these files may be copyrighted, and it is not OK for you to share these files with anyone who is not a student in this class or to use them for any purpose other than to study for the exams of our class. Thanks, Carl Johnson Stages of Development (echinoderm example) 1 Purves 19.1 Maternal inheritance: Nearly all the cytoplasm of the zygote is from the egg, and it is rich in nutrients (e.g., yolk), ribosomes, mitochondria, and mRNAs. The sperms mitochondria degenerate, so all mitochondria in the zygote come from the egg (therefore, mtDNA is maternally inherited). 3 Development Purves 20.2 Fertilization : in many species, the point of entry of the sperm creates an asymmetry in the radially symmetrical egg that enables a bilateral body plan to emerge. In frogs, pigments in the egg cytoplasm allow easy study of development. Specific sperm- binding sites ensure that the sperm always enters the egg at the "animal hemisphere." After fertilization, the cortical cytoplasm rotates toward the site of sperm entry and exposes a less pigmented band opposite the point of sperm entry, called the gray crescent . C&R 47.7 Development 4 Purves 20.3 Frogs: localization of factors within the egg set up gradients within the developing embryo. !-catenin , a transcriptional factor, and GSK-3, a protein kinase are found throughout the cytoplasm, but an inhibitor of GSK-3 is segregated in the vegetal pole. !-catenin can be phosphorylated by GSK-3 and when it is phosphorylated, it is targeted for degradation. After sperm entry, the inhibitor is in the cortex that moves to the gray crescent and it there prevents degradation of !-catenin. Therefore, the concentration of !-catenin becomes higher on the dorsal side than on the ventral side of the embryo. gray crescent !-catenin GSK-3 GSK Inhibitor Purves 19.8 Development 5 Purves 20.3 cleavage Cleavage: These changes in !- catenin localization are distributed and perpetuated among the cells in the embryo as a consequence of mitotic cleavage. Later, !-catenin turns on genes in the dorsal part of the embryo that result in differentiation. Cleavage: C&R 47.8 Purves 20.12 Experimental Manipulations: If !-catenin is depleted: no gastrulation. If !-catenin is overexpressed in another region of the embryo: a second axis of embryo formation is induced. Therefore, !-catenin appears to act like the "primary embryonic organizer" described by Spemann (see later). !-catenin is a transcriptional factor that interacts with other factors to turn on gene expression, such as the cascade that leads to Goosecoid and Siamois expression (these are other transcriptional factors)....
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This note was uploaded on 11/12/2010 for the course BSCI BSCI 110B taught by Professor Johnson during the Spring '09 term at Vanderbilt.

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Develop.10.OAK - NOTE!! These files are provided for the...

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