Another feature of induction is the reciprocal nature of many inductive interactions. To continue the preceding example, once the lens has formed, it induces other tissues. One of these responding tissues is the optic vesicle itself; thus, the inducer becomes the induced. Under the influence of factors secreted by the lens, the optic vesicle becomes the optic cup, and the wall of the optic cup differentiates into two layers: the pigmented retina and the neural retina (see Figure 16.7; Cvekl and Piatigorsky 1996; Stricker et al. 2007). Such interactions are called reciprocal inductions.
Another principle can be seen in such reciprocal inductions: a structure does not need to be fully differentiated to have a function. As we will detail in Chapter 16, the optic vesicle induces the surface ectoderm to become a lens before the optic vesicle has become the retina. Similarly, the developing lens reciprocates by inducing the optic vesicle before the lens forms its characteristic fibers. Thus, before a tissue has its “adult” functions, it has critically important transient functions in building the organs of the embryo.
Cvekl, A. and J. Piatigorsky. 1996. Lens development and crystallin gene expression: Many roles for Pax-6. BioEssays 18: 621–630.
Raible, F. and M. Brand. 2001. Tight transcriptional control of the ETS domain factors Erm and Pea3 by Fgf signaling during early zebrafish development. Mech. Dev. 107: 105–117.
Stokoe, D., S. G. Macdonald, K. Cadwallader, M. Symons and J. F. Hancock. 1994. Activation of raf as a result of recruitment to the plasma membrane. Science 264: 1463–1467.
Stricker, A. G., Y. Yamamoto and W. R. Jeffery. 2007. The lens controls cell survival in the retina: Evidence from the blind cavefish, Astyanax. Dev. Biol.311: 512–523.
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