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Syozo OSAWA

About Syozo Osawa's Academic Activities

Born in 1928. Dr. Sci., and an emeritus professor of Nagoya University and Hiroshima University. Recipient of the Promotion Prize from the Japanese Biochemical Society (1966), the Chunichi Culture Award (1985), the Kihara Award of the Genetics Society of Japan (1987), the Promotion Prize from the Japan Genetics Organization (1989), the Japan Academy Prize (1992) and Motoo Kimura Memorial Prize of Science (2001). He is the honorary member of the Genetic Society of Japan and the honorary member of Society of Evolutionary Studies, Japan. He is also an amateur entomologist and belongs to several entomological societies in Japan.
He graduated from Nagoya University, Faculty of Science, Department of Biology in 1951, and then studied biochemistry of the cell nuclei in the laboratory of Dr. Alfred E. Mirsky at the Rockefeller Institute for Medical Research, New York from 1954-1955. See for a review,

Mirsky, A.E., Osawa, S., V.G. Allfrey: The nucleus as a site of biochemical activity,

Cold Spring Harb. Symp. Quant. Biol., 21: 49-58 (1956).

He returned to Nagoya University and worked on molecular biology of translational apparatus at the Department of Biology and the Institute of Molecular Biology (1956-1962) as an instructor and then associate professor. In 1963, he moved to Hiroshima University as professor of the Department of Biochemistry and Biophysics of the Institute of Nuclear Medicine and Biology, where he continued to study on molecular biology of translational apparatus, especially of the biosynthesis, structure and genetics of ribosomes. Several review articles during that time may be enumerated as follows:

*Osawa, S . (1965)

Biosynthesis of ribosomes in bacterial cells. Progr. Nucleic Acid Res. & Mol. Biol., 4: 161-188.

*Osawa, S. (1968)

Ribosome formation and structure. Ann. Rev. Biochem., 37: 109-130.

*Osawa, S. et al. (1972)

Ribosomal protein genes in bacteria. In Cox, R.A., Hasjiolov, A.A. eds., Functional Units in Protein Synthesis. pp. 313-336

He was then appointed as a professor of Molecular Genetics of the Department of Biology, Nagoya University from 1981-1992, where he and his collaborators performed several lines of work, two of which may be considered as representatives during the above period.
1. Pylogenetic trees deduced from 5S ribosomal RNA sequences

The detailed information of this topic may be obtained from HP of Hiroshi Hori(http://www.bio.nagoya-u.ac.jp:8001/~hori/metabacteria.html) ,who was the main worker of this project. In 1979, Hori and Osawa constructed a phylogenetic tree of 5S ribosomal RNAs from 54 eukaryotes and prokaryotes. One of the main conclusions was that Halobacterium (one of the so-called Archaebacterial species) and eukaryotes are the sister group with eubacteria as an outgroup. About ten years after (Hori and Osawa, 1987), a tree of major groups of organisms was constructed from the 352 5S rRNA sequences available at that time when the DNA sequencing technique had not been developed yet. The tree supports the idea that the major groups of eubacteria diverged during the early stages of their evolution, and Metabacteria (named by Hori & Osawa,1982) (=Archaebacteria ) and eukaryotes separated after the emergence of eubacteria. For detail, see the following review articles:

*Hori, H., Itoh, T., Osawa, S. (1982)

The phyologenetic structure of Metabaceria. Zbl. Bakt.Hyg.,I.Abt.Orig. C3, 18-30.

*Hori, H.,Osawa, S. (1987)

Origin and evolution of organisms as deduced from 5S rRNA sequences. Mol. Biol. & Evol., 4: 445-472.

2. Evolution of the genetic code

The genetic code is essential to all forms of life and is of fundamental importance to the whole of biology. Until relatively recently, the code was thought to be invariable, frozen, in all organisms, because of the way in which any change would produce widespread alteration in the amino acid sequences of proteins. The universality of the genetic code was first challenged in 198l, when mammalian mitochondria were found to use a code which deviated somewhat from the universal. It was thought that either the mammalian mitochondrial code represented a remnant of an ancient code, or that the change in the code happened to be tolerable in mitochondria because of their small genome (ten or so genes).

In 1984, we found that a bacterium, Mycoplasma capricolum, used a deviant genetic code, namely that UGA, a universal stop codon, was read as tryptophane. Surprisingly, at about the same time, several workers announced that some ciliated protozoans used UAA and UAG as glutamine codons. These findings, together with the deviant codes in mitochondria, showed that the genetic code, formerly thought to be frozen, is, in fact, in a state of evolution. (There are known at present 11 departures from the universal code; 4 are in the nuclear code and 7 in the mitochondrial code). Obviously, a new theory was needed to account for the changes in codon meanings. Accordingly, Osawa proposed the codon capture theory in 1989 with T.H. Jukes of University of California, Berkeley. The theory was based on experimental and theoretical studies conducted by us, in addition to data available at that time. In short, the variations result from reassignment of codons, which take place by disappearance of codon (unassigned codon) from coding sequences, followed by its reappearance in a new role.
Simultaneously, a changed anticodon of the tRNA must appear. The general model for code changes is that a codon disappeared from coding sequences, typically as a result of directional (GC/AT biased) mutation pressure. The codon reappeared, sometimes as a result of a change of directional mutation pressure, and acquired a new meaning. This can result from a change in an anticodon, or from change in aminoacylation of a tRNA, or from a change in codon-anticodon pairing. All these changes are non-disruptive, i.e., neutral, because there is no change in amino acid sequences of proteins.

*See Osawa, S. (1995): Evolution of the Genetic Code. 205 pp. Oxford University Press.

*See also Pdf file1

After retirement from Nagoya University in 1992, he became to be the advisor of JT Biohistory Research Hall, Takatsuki, Osaka, where he and his associates studied the molecular phylogeny of the carabid ground beetles from 1992 to 2000. The outline of this study is as follows.

3．Molecular Phylogeny and Evolution of Carabid Ground Beetles

Carabid ground beetles, sometimes called "walking jewels," are among the most thoroughly investigated insects in the world. The specimens used in this study consist of more than 2000 individuals including 350 species and covering more than 90% of the known genera from 500 localities in 35 countries. These comprehensive analyses using mitochondrial DNA-based dating suggest led to surprising conclusions, in that carabid diversification took place about 40 to 50 million years ago as an explosive radiation of the major genera, coinciding with the collision of the Indian subcontinent and Eurasian land mass. This was followed by occasional radiations with various scales including a singular morphological transformation. Sometimes parallel morphological evolution took place among phylogenetically distinct lineages either allopatrically or sympatrically.
There are also a good number of examples showing that fundamental morphology has remained unchanged for a long time among geographically isolated populations even within the same species, where only the DNA-clock has been ticking (silent evolution). Thus, the carabid evolution would have proceeded discontinuously with alternatively having a phase of rapid morphological change with various scales and a silent phase of various lengths. Whatever the underlying mechanisms, the major process of morphological differentiation does not seem to have proceeded by a gradual accumulation of small changes and thus does not run in parallel with the time elapsed after emergence of the respective species.

The discontinuous evolution has been proposed based on paleontological evidence ("punctuated equilibrium theory" by Gould and Eldredge,1977, etc). Here we propose "the discontinuous and parallel evolution theory" to explain all the evolutionary events discussed above, which, at preset, can be deduced only by molecular phylogenetic study in conjunction with morphology. Morphology alone cannot give substantial evidence for these evolutionary phenomena.

Also, a scenario for origin and establishment of the Japanese carabid fauna has been deduced. There are roughly two types of the Japanese Carabina species with respect to their origin. A good number of species can be considered to be the autochthons, the ancestors of most of which inhabited the ancient Japan area (eastern periphery of the Eurasian Continent) before its split from the continent (>1,500 million years ago), and the others are the recent invaders from the continent through Sakhalin and/or the Kuriles, or the Korean Peninsula via land bridges during the glacial era (<20 million years ago).
The number of known Japanese species is about 40, which may be classified into two categories from the viewpoint of their origin. The first category includes species that were directly derived from ancestors that inhabited the ancient Japan area when it was attached to the eastern periphery of the Eurasian Continent ca. 15 million years ago (the autochthons). The second category contains species that invaded from the Eurasian Continent through Sakhalin and/or the Kurile Islands or from the Korean Peninsula during the glacial era (after 2 million years ago; the invaders).

Among these Japanese carabid beetles, the mode of diversification within the Ohomopterus species is of special interest. A phylogenetic tree of the nuclear ITS I roughly reflects the relations of morphological species group, while mitochondrial ND5 gene shows a considerable different topology on the tree; there exist several geographically-linked lineages, most of which consist of more than one species. These results suggest that the replacement of mitochondria has occurred widely in the Ohomopterus species. In most cases hybridization is unidirectional, i.e., the species A (male) hybridized with another species (female) and not vice versa, with accompanied replacement of mitochondria of A by those of B. The results also suggest that partial or complete occupation of the distribution territory by a hybrid-derived morphological species without hybrid-breakdown. The morphological appearance of the resultant hybrid-derivatives are recognized as that of the original species A. Emergence of a morphological new species from a hybrid-derived population has taken place (Ohomopterus uenoi; a derivative of O. arrowianus (female) x O. kiiensis (male)).

The studies discussed above present us with the dynamic principles of evolution and the magnificent geographic history of the earth as revealed by the study of the ground beetles.

* See Osawa, S., Su, Z..-H., Imura, Y. : Phylogeny and Evolution of the Carabid Ground Beetles,

　　Springer Verlag Tokyo, January 2004.

* See also Pdf file2

For all publications by Osawa, except those written in Japanese, see "List of Publications" in this HP.

Representative Books: 　; Evolution of the Genetic Code; Syozo OSAWA; Oxford University Press (1995)

Molecular Phylogeny and Evolution of Carabid Ground Beetles

Osawa, S., Su, Z.-H., Imura, Y.

Springer Verlag Tokyo, January 2004.

List of Publications（chronological order）

Osawa Insect Museum: 　; The beetles described by, or dedicated to, Osawa are illustrated with explanations written in Japanese. Please just enjoy morphological diversity of beetles !