The redusome hypothesis of aging and the control of biological time during individual development.
The redusome hypothesis of aging and the control of biological time in individual development is proposed. Redusomes are hypothetical perichromosomal particles arising in differentiation events during morphogenesis of an organism. The linear molecule of DNA covered with proteins in the redusome is assumed to be a copy of a segment of chromosomal DNA. Redusomes are located mainly in subtelomeric regions of chromosomes. The redusome does not leave the body of a chromosome even in the course of cellular divisions, being kept in its chromosomal nest. Like telomeric DNA, redusome linear DNA is shortened step by step. Thus, tiny redusomes progressively decrease in size; it is from here their name originates. Together with loss of the length of DNA in a redusome, the number of different genes contained in it also decreases. Shortening of the redusomal DNA molecules (and, coupled to it, changes of the sets of genes in redusomes) is responsible for age-dependent shifts in the level of expression of different chromosomal genes. Owing to this, redusome DNA shortening serves as a key means of measuring biological time in individual development. The main part of DNA of most redusomes is postulated to be occupied by noncoding genes. Low-molecular-weight RNAs (micro RNAs and fountain RNAs, or fRNAs) are assumed to be transcribed from them. These RNAs are involved in regulation of various chromatin repackings that are specific to certain differentiations, while others modulate the levels of expression of chromosomal genes. Hypothetical fountain RNAs can quantitatively regulate the expression levels of chromosomal genes, forming specific complexes with fions. Fions are suggested to be specific sites of a chromosomal DNA which are complementary to different fRNAs. Fions reside in the vicinity of usual chromosomal genes. A complex of the fRNA-fion, specifically interacting with a closed gate of the corresponding ion channel of the internal nuclear membrane, initiates the opening of the gate for a very short time, thus organizing activity of an ion fountain which appears to be automatically aimed at the chromosomal gene nearest to the fion involved. The ion fountain creates, depending on specificity of matching fRNA, fion, and ion channel, a distinctive ionic environment near certain structural genes. Ion fountains exert their action on the configuration of corresponding segments of chromatin and on the transcriptional efficiency of chromosomal genes in a topographically specific manner. Hence, the fountain system of the nucleus is able to regulate the quantitative traits both of cells and organism; it can control dominance of alleles and plays a role in individual development. Significant and escalating truncation of the redusome DNA causes cell aging due to an arising and increasing deficit of fRNAs and, for this reason, the lack of required ions near certain structural genes. Progressive shortening of DNA of redusomes is proposed to result in cellular aging because of a constantly growing shortage of low-molecular-weight RNAs transcribed from redusomal genes. Two types of redusomes are postulated: chronosomes and printosomes. Linear molecules of DNA in these two types of redusomes are called chronomeres and printomeres, respectively. Chronosomes are responsible for measurement of biological time in nondividing cells of the CNS. Printosomes remember positions of cells in the course of interpretation of the positional information in morphogenesis. In accordance with the position of a cell in a morphogenetic field, printomeres do change cellular properties and remember the change made (this is a so-called printomere mechanism of interpretation of positional information). Besides, printomeres participate in maintaining the achieved state of cellular differentiation. Normally, the chronomere is shortened only on the maximum of infradian hormonal rhythm (T-rhythm) which initiates the act of a superhigh velocity of its transcription that is finished with truncation of the end of a chronomere (an effect called scrupting). Theprintomere can be shortened due to the effect of DNA end underreplication and owing to scrupting. The effect of the end underreplication of DNA in doubling cells occurs simultaneously both in printomeres and telomeres. Shortening of telomeres is just a bystander process of aging of cells, whereas the true cause of biological aging is only the shortening of redusome DNA. Processing of certain redusomes in terminally differentiating cells is a cause of a proliferation arrest. Linkage of genes in a eukaryotic chromosome is determined by the distances between genes and redusomes.