The Phenomenon of Transdetermination in Cell Populations

The activation period - when intercellular interactions occur. These interactions are accompanied by the interchanging of biologically active macromolecules that penetrate into the cells of the reacting system and interact with cytoplasmic elements. Transcription, apparently, does not change during this period. 

The period of stabilization of determination at the tissue level (sometimes called maturation). This stabilization occurs with the interaction of the protein regulators with chromosomal DNA (see Part 1) and with the intensification of transcription. 

The period of stabilization and determination at the cell level, called programing by Elsdale and Jones (1963). In this period, the functional condition of the chromosomes is stabilized on the molecular level. This stabilization sets the development of the cell in a certain direction. The ability of cells to maintain this determination after several cell generations has been termed epigenomic heredity by Olenov (1967) and Vachtin (1974). 

Transdetermination often leads to the appearance of a phenocopy of a known mutation. Moreover, there are many so-called homeotic mutations in Drosophila (first described by Astaurov in 1927), which cause allotypic organ formation. Ari-stopedia is one example of such a mutation (leg instead of antennal structures are formed). 

The mechanism of transdetermination is not clear. It is, however, known that only cultures with a high rate of proliferation will undergo transdetermination. There is, in fact, a positive correlation between the rate of proliferation and the frequency of transdetermination. Some hypotheses for this were experimentally examined (Hadarn, 1967 Gehring and Nothiger, 1973)  

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