Primary embryonic induction

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... 

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

Immortalized hepatocytes A major drawback of the use of primary hepatocytes is that hepatocytes can not be expanded in culture. To overcome this problem, researchers have embarked on the immortalization of primary hepatocyte cultures (e.g. Bayad et al. 1991 Li et al. 2005). Currently, immortalized human hepatocyte cell lines are available commercially and may represent convenient screening experimental systems for enzyme induction studies. Unfortunately, at the time of this writing, there are no peer-reviewed publications on the application of human immortalized hepatocytes in induction studies. It is important to ensure that the induced isoforms in the cell lines are the mature P450 isoforms rather than the embryonic forms. For instance, the use of HepG2 cells may not be appropriate as the embryonic P450 isoforms CYP1A1... 

Lopashov attached great importance to the interaction of embryonic cells with intercellular medium. According to his view, these interactions could have an important effect on primary cell differentiation. Specifically, the internal medium of the blastocele and gastrocele - into which a surface layer of compact cells turns -could contain certain proteinaceous compounds. In the presence of these compounds the cell surfaces do not compact. Therefore, these cells retain their ability for inductional interactions (Lopashov, 1965, 1977). 

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