Induction embryonic

Baker CV, Bronner-Fraser M (2001) Vertebrate cranial placodes I. Embryonic induction. Dev Biol 232 1-61... 

Baker, C.V., Bronner-Fraser, M. 1997. The origins of the neural crest. Part I embryonic induction. Mech. Dev. 69, 3-11. 

Volume 28. Morphogenesis, differentiation and development I. Fertilization by A. Monroy. II. Behaviour of nucleic acids during early development by J. Brachet. 111. Biochemical pathways in embryos by E. Scarano and G. Augusti-Tocco. IV. Factors of embryonic induction by T. Yamada. V. Biochemistry of amphibian metamorphosis by R. Weber. VI. Biochemical correlations in insect metamorphosis by L. I. Gilbert. Subject index. 

In the following sections, I consider two examples of operations on Hensen s node excision from a donor quail embryo and transplantation to the inner ring of the area opaca of a host chick embryo to demonstrate embryonic induction, as done by Storey et al. (10), and rotation of the node about its rostrocaudal axis in situ, to demonstrate embryonic regulation as done by Abercrombie (14). 

Demonstration of Embryonic Induction by Transplantation of Hensen s Node... 

Fig. 58. Models for control of gene activity during primary embryonic induction. (After Tiedemann, 1967)...

Although realization of inherited information at the tissue level is a principal new qualitative level of the regulatory process, it will be the result of interacting tissue primordia and cellular complexes. At the same time, however, there are periods during which the interacting primordia develop comparatively autonomously. For example, the autonomy of competent tissue maturation was described during primary embryonal induction (Holtfreter, 1948). 

Saxen L, Toivonen S (1963) Primary embryonic induction. IL, Moscow... 

Molecular-Genetic Aspects of the Phenomena of Embryonic Induction... 

Embryonic induction is thus definitely not the result of epigenetic elements of morphogenesis, but the necessary consequence of the existence of a strict genetic program, but a program represented in millions of cells by millions of systems on a local, intracellular scale. 

Uiis general view of the problem of embryonic induction is confirmed by most of the extensive factual material of experimental embryology, particularly if it is examined systematically and not chaotically. First, we know that the possibility of changes taking place in a group of cells in different directions in fact diminishes with each successive phase of development. Induction not only stimulates a group of loci, but as a result of this causes repression of the other systems of specialization. Ihe activated... 

Saxen, L., and Toivonen, S., 1962, Primary Embryonic Induction, Academic Press,... 

Another important matter to be mentioned is the existence of various concentration microgradients of active substances such as inducers, repressors, and so on, with an important role in differentiation. The significance of concentration gradients of inducers in the creation of polarity and symmetry in the case of embryonic induction is well known (Flickinger, 1963). Taylor (1964) has pointed out that concentration gradients may also be important at the chromosomal level, especially in connection with the degree of inhibition of various chromosomal regions by histones. 

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