The notion of primordial building blocks in construction of genes and transcriptional and processing errors due to random occurrence of oligonucleotide signal sequences.
Contrary to the currently popular belief, genes (flanking and internal noncoding sequences included) that specify beta-sheet and alpha-helical proteins are not unique sequences, rather they are degenerate repeats of short primordial building block sequences that are 45 to 48 bases long in the case of genes belonging to the beta-2-microglobulin superfamily. Accordingly, a large number of base decamers, nonomers, octamers, heptamers and hexamers recur within every gene. One consequence of the above is the random and inadvertent occurrence within genes of various oligonucleotide signal sequences for initiation and termination of transcription as well as for processing of transcripts by removal of intervening sequences. Inadvertent transcription of nonsense sequences and missplicing of transcripts may increase with age and contribute to the aging process. There is little doubt that the life span, being one of the species' characteristics, is genetically programmed. The question remains, however, as to whether or not such a program is embodied in each and every somatic cell type. If the cessation of cell proliferation is regarded synonymous with senescence, one is placed in the awkward position of having to state that most neurons of the central nervous system enter the state of senescence at the neonatal stage. An alternative to the above is the assumption of central control; e.g., the programmed secretion of an aging peptide hormone by the pituitary. To be sure somatic cells accumulate randomly sustained mutations as do germ cells and whatever other genetic mishaps (e.g., deletions, duplications) that may affect somatic cells also occur in germ cells. Yet, the monophyletic germ line on this earth has persisted for three billion years and has the potential of being immortal. Furthermore there can be no direct cause-and-effect relationship between the process of differentiation and the loss of immortality, for spermatozoa are one of the most, if not the most, differentiated cell types that can be found in the body. Nevertheless, if one's scope is confined to the types of genetic mishaps that may afflict somatic cells in their given life span, the one particular type that has hitherto escaped notice should be considered.
D000375:Aging; D000818:Animals; D001483:Base Sequence; D006801:Humans; D051379:Mice; D009154:Mutation; D009841:Oligonucleotides / Q000378:metabolism*; D012326:RNA Splicing; D012091:Repetitive Sequences, Nucleic Acid; D014158:Transcription, Genetic
D009841:Oligonucleotides