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Biomedical subjects

A Sibatani

Publications and source records attributed to A Sibatani.

At least 19 recordsLinked to original sources
PubMed1993

Stability of arbitrary structures. Its implications for heredity and evolution. Part I.

I designate the stance of seeking, in biological processes, essential isomorphism with the phenomena encountered in the human mind, reverse-reductionism, from which I expect to find an alternative way of reconstructing biology. From the axiom that structure (relationship among components) is arbitrary as is known from the Saussurean linguistic theory, it follows that relevant structures in various living processes are potentially multiple rather than unique. Moreover, a structure may take more than one configuration, whose transition should be conceived as transformation. However, structure itself is stable, or invariant by definition, and not subject to transformation. Both structure and its configurations are hereditary in the sense that they bind, with necessity, biological processes including genetic constitution. Such an invisible structure can be maintained dynamically over generations through the constraints imposed on the survival of organisms. Many characters, including genes, in an organism are only cryptically held, and may come to be manifested under certain unusual environmental conditions. Evolution is viewed as configurational transformations and emergence of new structures: once a structure emerges, all of its possible configurations are logically laid down, at the very outset, to channel the future course of its evolution, whose materialization, however, is a matter of contingency.

Adaptation, Physiological↗
PubMed1987

In vitro senescence of human keratinocyte cultures.

Human keratinocytes have been serially cultivated in low (0.015 mM) and high (1.8 mM) calcium containing medium. The calcium concentration of the growth medium significantly influenced the cell growth period in vitro. Cells grown in low calcium medium underwent 35-40 population doublings over 16-17 passages, while cells grown in high calcium medium ceased to proliferate after 20 population doublings over 7 passages. Changing the keratinocytes from one in vitro environment to the other drastically altered the lifespan in culture of populations derived from the same primary tissue. The degree of DNA methylation of human keratinocytes was shown to decrease with age in both high and low calcium culture conditions but does not appear to be associated with differentiation.

Calcium↗
PubMed1983

A plausible molecular interpretation of the polar coordinate model with a centripetal degeneracy of distinctive field values.

I have attempted to interpret, in molecular terms, the polar coordinate model for epimorphic regulation, revised to accommodate the rigorously-held constraints of the polar coordinate system (Sibatani, 1981). If the angular coordinate of the field value is represented by a physical variable in the form of a proportion function, R, to be defined as the intensity ratio of two morphogen curves then R can stay unchanged along any radius mapped on the actual space, while the intensity of the two morphogens together approaches zero towards the field centre, satisfying the requirement of the centripetal degeneracy of the distinctive angular field values. Implications of this idea are discussed in theoretical and molecular terms as well as in respect of interpretations of some experimental data.

Animals↗
PubMed1975

Differential variations in the DNA of Drosophila melanogaster during development.

Evidence is presented that during development there is active regulation of the information content of the genome of Drosophila melanogaster. This regulation involves a large fraction of the DNA sequences active in transcription. RNA/DNA hybrids formed under the conditions described were primarily with middle repetitive DNA sequences. RNA molecules transcribed from the highly repetitive centromeric DNA sequences or from the attached less repetitive "spacer' DNA (Kram et al., 1972) are not present in larval RNA. The hybrids formed were divided into (a) rRNA hybrids (formed by the two major rRNA species), and (b) non-ribosomal hybrids (formed by hnRNA and mRNA). There was a six-fold reduction in the production of non-ribosomal RNA/DNA hybrid formed with DNA of larvae collected 40 hours after hatching compared with that formed with DNA of eggs and adults. 90 hour larval DNA contained twice the proportion of these sequences present in 40 hour larval DNA. This was not due to the under-representation of the Y-chromosome in polytene tissues, nor could artifacts of extraction account for the differences. These findings are discussed in relation to the "one gene, one chromosome' concept, various anomolies in the behaviour of polytene chromosomes, intercalary heterochromatin and regulation of the content of the genome during development.

Animals↗