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Unformatted text preview: 584 Chapter 18 The Genetic Basis of Development have their high points at the anterior pole. In somewhat different ways, the gradients of both these proteins de- pend on the diffusion of protein from a localized origin: each protein is produced through localized translation of an mRNA species, one tethered to microtubules at the anterior pole of the syncitial embryo, and the other teth- ered at the posterior pole. The origin of the BCD gradient is quite straightfor- ward. The maternal bcd mRNA, packaged during oogen- esis into the developing oocyte, is tethered to the 2 (mi- nus) ends of microtubules, which are located at the anterior pole (Figure 18-10a). Translation of BCD pro- tein begins midway through the early nuclear divisions of the embryo. The protein diffuses in the common cytoplasm of the syncitium. Because the protein is a transcription factor, it contains signals that direct it to the nuclei. Those nuclei nearer to the anterior pole incorporate a higher concentration of the diffusing BCD protein than do those farther away; this difference re- sults in the steep BCD protein gradient (Figure 18-10b)....
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This note was uploaded on 01/10/2011 for the course BIOL BIOL taught by Professor Johnson during the Spring '08 term at Aberystwyth University.
- Spring '08