Biomedical subjects

S Shigenobu

Publications and source records attributed to S Shigenobu.

3 recordsLinked to original sources

PubMed2000

Genome sequence of the endocellular bacterial symbiont of aphids Buchnera sp. APS.

Almost all aphid species (Homoptera, Insecta) have 60-80 huge cells called bacteriocytes, within which are round-shaped bacteria that are designated Buchnera. These bacteria are maternally transmitted to eggs and embryos through host generations, and the mutualism between the host and the bacteria is so obligate that neither can reproduce independently. Buchnera is a close relative of Escherichia coli, but it contains more than 100 genomic copies per cell, and its genome size is only a seventh of that of E. coli. Here we report the complete genome sequence of Buchnera sp. strain APS, which is composed of one 640,681-base-pair chromosome and two small plasmids. There are genes for the biosyntheses of amino acids essential for the hosts in the genome, but those for non-essential amino acids are missing, indicating complementarity and syntrophy between the host and the symbiont. In addition, Buchnera lacks genes for the biosynthesis of cell-surface components, including lipopolysaccharides and phospholipids, regulator genes and genes involved in defence of the cell. These results indicate that Buchnera is completely symbiotic and viable only in its limited niche, the bacteriocyte.

Aerobiosis↗

PubMed1992

Neuroprotective effect of 5-HT3 receptor antagonist on ischemia-induced decrease in CA1 field potential in rat hippocampal slices.

The effect of 5-HT3 receptor agonists and antagonists on the hypoxia/hypoglycemia (ischemia)-induced decrease in CA1 field potential elicited by stimulation of Schaffer collaterals was investigated using rat hippocampal slices. Treatment with the 5-HT3 receptor agonist, 2-methyl-5-HT (1-10 microM), exacerbated the ischemia-induced decreased in CA1 field potential, whereas treatment with the 5-HT3 receptor antagonist, Y-25130 (0.1-100 microM), or the 5-HT2 receptor antagonist, ketanserin (10, 100 microM), produced dose-dependent neuroprotection against the ischemia-induced decrease. However, in normal non-ischemic solution these treatments did not significantly change the CA1 field potential. The protective action of Y-25130 was blocked by co-treatment with 2-methyl-5-HT. The magnitude of protection in the Y-25130-treated group (EC50, 1.8 microM) was about 20 times greater than that in the ketanserin-treated group (EC50, 33 microM). The present study demonstrated that stimulation of 5-HT3 receptors plays a detrimental role in the development of ischemic damage, whereas blockade of the 5-HT3 receptor plays a neuroprotective role in ischemic damage, suggesting a facilitatory role of 5-HT neurons in ischemia-induced neuronal deficits.

5,7-Dihydroxytryptamine↗

PubMedDate not supplied

Accumulation of species-specific amino acid replacements that cause loss of particular protein functions in Buchnera, an endocellular bacterial symbiont.

Endosymbiotic bacteria live in animal cells and are transmitted vertically at the time of the host's reproduction. In view of their small and asexual populations with infrequent chances of recombination, these endocellular bacteria are expected to accumulate mildly deleterious mutations. Previous studies showed that the DNA sequences of these bacteria evolved faster than those of free-living bacteria. In this study, we compared all the ORFs of Buchnera, an endocellular bacterial symbiont of aphids, with those of 34 other prokaryotic organisms and estimated the effect of the accelerated evolution of Buchnera on the functions of its proteins. It was revealed that Buchnera proteins contain many mutations at the sites where sequences are conserved in their orthologues in many other organisms. In addition, amino acid replacements at the conserved sites are mostly changes to physicochemically different amino acids. These results suggest that functions and conformations of Buchnera proteins have been seriously impaired or strongly modified. Indeed, extensive loss of functional motifs was observed in some Buchnera proteins. In many Buchnera proteins mutations were not detected evenly throughout each molecule but tended to accumulate in some functional units, possibly leading to loss of specific functions. As Buchnera has an unusual and limited gene repertory, it is conceivable that the manner of interactions among its proteins has been changed, and thus, functional constraints over their amino acid residues have also been changed during evolution. This may account for the loss of some functional units only in the Buchnera proteins. We obtained evidence that amino acid replacements in Buchnera were not always deleterious, but neutral or, in some cases, even positively selected.

Amino Acid Motifs↗