Anterior-posterior axis

The anterior-posterior axis in Drosophila is defined at least in part by the products of the bicoid and nanos genes. The bicoid gene product is a major anterior morphogen, and the nanos gene product is a major posterior morphogen. The mRNA from the bicoid gene is synthesized by nurse cells and deposited in the unfertilized egg near its anterior pole. 

FIGURE 28-37 Regulatory circuits of the anterior-posterior axis in a Drosophila egg. The bicoid and nanos mRNAs are localized near the anterior and posterior poles, respectively. The caudal, hunchback, and pumilio mRNAs are distributed throughout the egg cytoplasm. The gradients of Bicoid (Bed) and Nanos proteins lead to accumulation of Hunchback protein in the anterior and Caudal protein in the posterior of the egg. Because Pumilio protein requires Nanos protein for its activity as a translational repressor of hunchback, it functions only at the posterior end. 

Figure 7.5 A phylogenetic tree of animal phyla based on 18S ribosomal DNA from several laboratories (Raff, 1996). The most significant innovations are the appearance of (1) multicellularity, (2) tissues, (3) the anterior-posterior axis and central nervous system, (5) metameric segmentation, (6) pentameral symmetry, (7) neural crest and amplification of Hox clusters.

Rappleye CA, Paredez AR, Smith CW et al. The coronin-like protein POD-1 is required for anterior-posterior axis formation and cellular architecture in the nematode caenorhabditis elegans. Genes Dev 1999 13 2838-51. 

Grandel, H., K. Lun, G.J. Rauch, M. Rhinn, T. Kotrowski, C. Houart, P. Sordino, A. Kuchler, S. Schulte-Merker, R. Geisler, N. Holder, S. Wilson and M. Brand. Retinoic acid signaling in the zebrafish embryo is necessary during presegmentation stages to pattern the anterior-posterior axis of the CNS and to induce a pectoral fin bud. Development 129 2851—2865, 2002. 

Epstein, M., Pillemer, G., Yelin, R., Yisraeli, J.K., Fainsod, A. 1997. Patterning of the embryo along the anterior-posterior axis the role of the caudal genes. Development 124, 3805-3814. 

Huelsken, J., Vogel, R., Brinkmann, V., Erdmann, B., Birchmeier, C., Birchmeier, W. 2000. Requirement for beta-catenin in anterior-posterior axis formation in mice. J. Cell Biol. 148, 567-578. 

Krumlauf, 1992). Genes located at the 3 end of the cluster are expressed earlier and more anteriorly during development than those found at the 5 end. Consequently, Hox genes exhibit nested domains of expression along the anterior-posterior axis and confer positional information to the embryo during development (Fig. 5). 

Frohman, M.A., Boyle, M., Martin, G.R. 1990. Isolation of the mouse Hox-2.9 gene analysis of embryonic expression suggests that positional information along the anterior-posterior axis is specified by mesoderm. Development 110, 589-607. 

Ding, J., Yang, L., Yan, Y.T., Chen, A., Desai, N., Wynshaw-Boris, A., Shen, M.M. 1998. Cripto is required for correct orientation of the anterior-posterior axis in the mouse embryo. Nature 395, 125-133. 

We turn now to determination of the anterior/posterior axis in the early fly embryo while it is still a syncytium. As in determination of the dorsal/ventral axis, specification of anterior/posterior cell fate begins during oogenesis. The initial asymmetry also involves so-called maternal mRNAs, which are produced by nurse cells and transported into the oocyte. In this case they become localized in discrete spatial domains (see Figure 15-14). For example, bicoid mRNA is trapped at the most anterior region, or anterior pole, of the early fly embryo (Figure 15-19). The anterior localization of... 

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