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DevelopmentW2010.Lecture13notes - Development BIO 120...

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Development BIO 120 Winter 2010 Jeremy Lee Patrick Yuh Eva Murdock Lecture 13 A: Drosophila Axis Specification; Homeotic Selector Genes in Drosophila and Mammals B: Dosage Compensation, Sex Determination and Reproductive Development A: Dosage Compensation, Sex Determination and Reproductive Development I. Life History of Drosophila , a holometabolous insect (Figs. #1, #2, #3) II. Sequential gene expression : Expression of five sets of genes, in developmental sequence, determines body axes, segment boundaries, differentiation of cells within a segment, identity of each segment (Figs #4, #5) a. Maternal effect genes (aka cytoplasmic polarity genes): 1. Depending on the specific gene, either mRNAs or proteins produced from these genes are deposited into the egg by the mother. 2. In the case of mRNAs deposited by the mother, they are translated inside the egg, frequently as a result of egg activation, to produce the corresponding proteins. 3. Following fertilization, the proteins derived from maternal effect genes (those from mRNAs deposited in the egg by mom then translated and those proteins directly deposited by mom) are utilized to set up the main body axes of the embryo. b. Gap genes: Expression determined by proteins encoded by the maternal effect genes and other gap genes. The gap genes show broad bands of expression. c. Pair-rule genes : expressed in stripes delimiting parasegments. Expression is regulated primarily by gap gene proteins but also to an extent by maternal effect genes. d. Segment polarity genes: determine segment boundaries and cell identities within a segment. Expression is regulated by proteins encoded by pair-rule gene and other segment polarity genes. e. Homeotic selector genes: determine segment identity. Expression is regulated by a combination of proteins encoded by pair-rule genes and segment-polarity genes. III. Cytoplasmic polarity (aka maternal effect) genes : 2 genes are particularly important a. bicoid : mRNA deposited in egg by mother’s nurse cells; required for development of anterior structures (Figure #6, #7) b. nanos: mRNA deposited in egg by mother’s nurse cells; required for development of posterior structures (Figure #8.1) c. Localization of bicoid and nanos mRNAs (Fig. #8.2) 1. Nucleus of oocyte moves toward posterior end of egg chamber, expresses Gurken protein. 2. Gurken protein binds Torpedo, a receptor protein expressed on posterior follicle cells. 3. Posterior follicle cells respond to Torpedo activation by signaling back to egg, activating protein kinase A. 4. Protein kinase A orients microtubules with growing end (+) toward posterior.
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5. bicoid mRNA associates with Dynein, a protein that carries bicoid mRNA along microtubules toward anterior end of egg. 6. oskar mRNA associates with kinesin I, which carries oskar mRNA along microtubules toward posterior end of egg.
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