Why is only the packaging of genetic material and the regulation of gene expression considered the most important role of chromatin?
Keywords:chromatin, condensed chromatin, heterochromatin, thermoregulation, cell thermoregulation, temperature homeostasis.
Chromatin is a complex of DNA and histone proteins. There are two types of chromatin: euchromatin and heterochromatin. It is now generally accepted that the packaging of genetic material and regulating gene expression are the most important role of chromatin. However, we believe that some fundamental features and properties of heterochromatin do not support this point of view. Namely, heterochromatin: a) is the densest domains in a interphase cell; b) spatially segregates from euchromatin in the nucleus and is localized preferentially toward the nuclear periphery; c) is closely associated with the lamina and the inner nuclear membrane; d) surrounds the nucleolus; e) forms the chromocenters; f) heterochromatic regions of autosomes 1, 9 and 19 and Y of the human chromosome, which do not contain ribosomal cystrones, are in close connection (in the body) of the nucleolus; h) differs in wide variability in the quantitative contents both within and between species; g) chromosomal heterochromatin regions of plants, poikilothermic and homoeothermic animals, as well as humans have significant differences. Investigations of chromosomal heterochromatin regions variability in human populations living permanently in different climatic and geographical conditions of Eurasia and Africa, in norm and pathology as well as analysis of existing literary data on the condensed chromatin (CC) speak in favor of the point of view that it is possible, the most important role of heterochromatin, the main component of CC, is its participation in the maintenance of intracellular temperature homeostasis. CC, being the densest domains in a cell, and being located between the nucleus and the cytoplasm apparently conducts heat when there is a difference in temperature between them. The assumed heat conductivity effect of CC is stipulated by its principal features: a condensed state during the interphase, association with the lamina and the inner nuclear membrane, replication at the end of the S period of a cell cycle, formation of the chromocenter, close connection with the nucleolus, genetic inertness, and wide variability in the quantitative contents both within and between species.
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