The Molecular Biology of Drosophilo fcmbryogenesis (p. 590)

FIGURE 18-1 Microarray grids comparing expression patterns in two tissues (muscles and neurons) in C. elegans. Each circle in the grid contains a short DNA segment from the coding region of a angle gene in the C elegans genome. RNA was extracted from musdes and neurons, and labeled with fluorescent dyes (red end green, respectively). Thus, the red circles indicate genes expressed in tnusde, whereas the green reflect genes expressed in neurons. The yellow circles indicate genes expressed in both ceil types. It is clear that the two samples express distinct sets of genes. (Source: Courtesy of Stuart Kim.)

fertilization fertilized egg with localized RNA

signal signal

FIGURE 18-2 The three strategies for initiating differential gene activity during development, (a) tn some animals, certain "maternal" RNAs present in the egg become localized either before or after fertilization In this example, a specific mRNA (green squiggles) becomes localized to vegetal (bottom) regions after fertilization (fa) Cell A must physically interact wilh tell B to it/nutate the rett^tor present on the surface of cell B This is because the "ligand" produced by cell A is tethered to the plasma membrane, (c) In this example of long-range cell signaling, cell 0 secretes a signaling molecule that diffuses through the extaceilular matrix Different celts (1 r 2, 3) receive the signal and ultimately undergo changes in gene activity.

unfertilized egg with uniform distribution of RNA

unfertilized egg with uniform distribution of RNA

first half of this chapter, we describe bow cells communicate with each other during development to ensure that each expresses the particular set of genes required for their proper development. Simple examples of each of these strategies are then described. In the second half of the chapter, we describe how these strategies are used in combination with the transcriptional regulatory mechanisms described in Chapter 17 to control the development of an entire organism—-in this case, the fruit fly.

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