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Articles by M Ohnishi
Total Records ( 2 ) for M Ohnishi
  M Ohnishi , T Nakatani , B Lanske and M. S. Razzaque

Background— Klotho-knockout mice (klotho–/–) have increased renal expression of sodium/phosphate cotransporters (NaPi2a), associated with severe hyperphosphatemia. Such serum biochemical changes in klotho–/– mice lead to extensive soft-tissue anomalies and vascular calcification. To determine the significance of increased renal expression of the NaPi2a protein and concomitant hyperphosphatemia and vascular calcification in klotho–/– mice, we generated klotho and NaPi2a double-knockout (klotho–/–/NaPi2a–/–) mice.

Methods and Results— Genetic inactivation of NaPi2a activity from klotho–/– mice reversed the severe hyperphosphatemia to mild hypophosphatemia or normophosphatemia. Importantly, despite significantly higher serum calcium and 1,25-dihydroxyvitamin D levels in klotho–/–/NaPi2a–/– mice, the vascular and soft-tissue calcifications were reduced. Extensive soft-tissue anomalies and cardiovascular calcification were consistently noted in klotho–/– mice by 6 weeks of age; however, these vascular and soft-tissue abnormalities were absent even in 12-week-old double-knockout mice. Klotho–/–/NaPi2a–/– mice also regained body weight and did not develop the generalized tissue atrophy often noted in klotho–/– single-knockout mice.

Conclusion— Our in vivo genetic manipulation studies have provided compelling evidence for a pathological role of increased NaPi2a activities in regulating abnormal mineral ion metabolism and soft-tissue anomalies in klotho–/– mice. Notably, our results suggest that serum phosphate levels are the important in vivo determinant of calcification and that lowering serum phosphate levels can reduce or eliminate soft-tissue and vascular calcification, even in presence of extremely high serum calcium and 1,25-dihydroxyvitamin D levels. These in vivo observations have significant clinical importance and therapeutic implications for patients with chronic kidney disease with cardiovascular calcification.

  T Ooka , Y Ogura , M Asadulghani , M Ohnishi , K Nakayama , J Terajima , H Watanabe and T. Hayashi

Mobile genetic elements play important roles in the evolution and diversification of bacterial genomes. In enterohemorrhagic Escherichia coli O157, a major factor that affects genomic diversity is prophages, which generate most of the large-size structural polymorphisms (LSSPs) observed in O157 genomes. Here, we describe the results of a systematic analysis of numerous small-size structural polymorphisms (SSSPs) that were detected by comparing the genomes of eight clinical isolates with a sequenced strain, O157 Sakai. Most of the SSSPs were generated by genetic events associated with only two insertion sequence (IS) elements, IS629 and ISEc8, and a number of genes that were inactivated or deleted by these events were identified. Simple excisions of IS629 and small deletions (footprints) formed by the excision of IS629, both of which are rarely described in bacteria, were also detected. In addition, the distribution of IS elements was highly biased toward prophages, prophage-like integrative elements, and plasmids. Based on these and our previous results, we conclude that, in addition to prophages, these two IS elements are major contributors to the genomic diversification of O157 strains and that LSSPs have been generated mainly by bacteriophages and SSSPs by IS elements. We also suggest that IS elements possibly play a role in the inactivation and immobilization of incoming phages and plasmids. Taken together, our results reveal the true impact of IS elements on the diversification of bacterial genomes and highlight their novel role in genome evolution.

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