Biomedical subjects

Tomo-o Ishikawa

Publications and source records attributed to Tomo-o Ishikawa.

6 recordsLinked to original sources

PubMed2006

Transgenic mouse for conditional, tissue-specific Cox-2 overexpression.

We constructed a cyclooxygenase-2 (Cox-2) conditional overexpression transgenic mouse (Cox-2 COE). The transgene contains a CAG promoter driving the Cox-2 and humanized Renilla luciferase (hRL) coding regions, linked by an internal ribosomal entry site. The promoter is followed by a loxP-flanked sequence containing enhanced green fluorescent protein (EGFP), a neomycin selection cassette, and a transcriptional/translational STOP sequence. In the presence of Cre recombinase the loxP-flanked sequence is excised. Cox-2/hRL expression can be monitored repeatedly and noninvasively in vivo by imaging hRL activity. To demonstrate conditional Cox-2 and hRL expression, a nonreplicating adenovirus carrying Cre recombinase (Ad.CMV.Cre) was injected intravenously; hepatic Cox-2 expression and hRL signal were elevated. Cox-2 COE embryonic fibroblasts express both Cox-2 and hRL following Ad.CMV.Cre infection. PGE(2) production is also increased following Ad.CMV.Cre infection of Cox-2 COE embryo fibroblasts. Cox-2 COE mice should be valuable for the study of Cox-2 overexpression in cardiovascular disease, acute and chronic inflammatory responses, neurodegenerative diseases, and cancer.

Adenoviridae↗

PubMed2004

Malfunction of respiratory-related neuronal activity in Na+, K+-ATPase alpha2 subunit-deficient mice is attributable to abnormal Cl- homeostasis in brainstem neurons.

Na+, K+-ATPase 2 subunit gene (Atp1a2) knock-out homozygous mice (Atp1a2-/-) died immediately after birth resulting from lack of breathing. The respiratory-related neuron activity in Atp1a2-/- was investigated using a brainstem-spinal cord en bloc preparation. The respiratory motoneuron activity recorded from the fourth cervical ventral root (C4) was defective in Atp1a2-/- fetuses of embryonic day 18.5. The C4 response to electrical stimulation of the ventrolateral medulla (VLM) recovered more slowly in Atp1a2-/- than in wild type during superfusion with Krebs' solution, consistent with the high extracellular GABA in brain of Atp1a2-/-. Lack of inhibitory neural activities in VLM of Atp1a2-/- was observed by optical recordings. High intracellular Cl- concentrations in neurons of the VLM of Atp1a2-/- were detected in gramicidin-perforated patch-clamp recordings. The alpha2 subunit and a neuron-specific K-Cl cotransporter KCC2 were coimmunoprecipitated in a purified synaptic membrane fraction of wild-type fetuses. Based on these results, we propose a model for functional coupling between the Na+, K+-ATPase alpha2 subunit and KCC2, which excludes Cl- from the cytosol in respiratory center neurons.

Amino Acid Sequence↗

PubMed2003

Degeneration of the amygdala/piriform cortex and enhanced fear/anxiety behaviors in sodium pump alpha2 subunit (Atp1a2)-deficient mice.

The sodium pump is the enzyme responsible for the maintenance of Na+ and K+ gradients across the cell membrane. Four isoforms of the catalytic alpha subunit have been identified, but their individual roles remain essentially unknown. To investigate the necessary functions of the alpha2 subunit in vivo, we generated and analyzed mice defective in the alpha2 subunit gene. Mice homozygous for the alpha2 mutation died just after birth and displayed selective neuronal apoptosis in the amygdala and piriform cortex. In these regions, high expression of c-Fos before apoptosis indicated neural hyperactivity, and re-uptake of glutamic acid and GABA into P2 fraction containing crude synaptosome was impaired. These results indicate that the alpha2 subunit plays a critical role regulating neural activity in the developing amygdala and piriform cortex. Further supporting a role of the alpha2 subunit in the function of the amygdala, heterozygous adult mice showed augmented fear/anxiety behaviors and enhanced neuronal activity in the amygdala and piriform cortex after conditioned fear stimuli.

Amygdala↗

PubMed2003

Requirement for tumor suppressor Apc in the morphogenesis of anterior and ventral mouse embryo.

Tumor suppressor Apc (adenomatous polyposis coli) is implicated in the Wnt signaling pathway that is involved in the early embryonic development and tumorigenesis in vertebrates. While the heterozygous null mutant mice develop intestinal polyps, the homozygous embryos die before gastrulation. To investigate the role of Apc in later embryonic development, we constructed a novel hypomorphic Apc allele whose expression was attenuated by approximately 80%. In the hypomorphic Apc homozygous ES cells, reduction in Apc expression caused beta-catenin accumulation and Wnt signaling activation. The homozygous mutant mouse embryos survived 3 days longer than the null mutant embryos. Interestingly, they showed anterior truncation, partial axis duplication, and defective ventral morphogenesis. To determine the tissues where Apc functions for anterior and ventral morphogenesis, we constructed chimeric embryos whose epiblast was derived predominantly from the Apc hypomorphic homozygous cells but the visceral endoderm was from the wild type. Although these chimeric embryos still showed some anterior defects, their ventral morphogenesis was rescued. In addition, marker studies indicated that the axial mesendoderm was also defective in the homozygous embryos. Our results provide genetic evidence that expression of Apc at the normal level is essential for both anterior and ventral development, in the epiblast derivatives and visceral endoderm.

Alleles↗

PubMed2002

Gastrointestinal hamartomatous polyposis in Lkb1 heterozygous knockout mice.

Peutz-Jeghers syndrome (PJS) is a hereditary disorder characterized by gastrointestinal hamartomatous polyposis associated with mucocutaneous pigmentation. Germ-line mutations of the gene encoding LKB1 (STK11), a serine/threonine kinase, are identified in most PJS patients. To investigate the role of LKB1 in the PJS phenotypes, we introduced a germ-line mutation in the mouse Lkb1 gene by homologous recombination in mouse embryonic stem cells. In most Lkb1 (+/-) mice >20 weeks of age, hamartomatous polyps developed in the glandular stomach, often in the pyloric region. Small intestinal hamartomas also developed in approximately one-third of the Lkb1 (+/-) mice >50 weeks of age. A genomic PCR and sequence analysis showed that all hamartomas retained both the wild-type and targeted Lkb1 alleles, indicating that allelic loss of the wild-type Lkb1 was not the cause of polyp formation. Moreover, the LKB1 protein level was not reduced in hamartomatous polyps compared with that in the Lkb1 (+/-) normal gastric mucosa. In addition, the remaining allele showed neither missense mutations in the coding sequence nor produced truncated LKB1 in the hamartoma. Taken together, these data suggest that the wild-type Lkb1 is expressed in the hamartoma at the haploid amount. Accordingly, the gastrointestinal hamartomas appear to develop because of the Lkb1 haploinsufficiency. Although additional genetic events may be critical in hamartoma and adenocarcinoma development, these data strongly suggest that the initiation of polyposis is not the result of loss of heterozygosity in Lkb1.

AMP-Activated Protein Kinases↗

PubMed2002

Cyclooxygenase 2- and prostaglandin E(2) receptor EP(2)-dependent angiogenesis in Apc(Delta716) mouse intestinal polyps.

To investigate angiogenesis during intestinal polyp development, we determined the microvessel density (MVD) in polyps of Apc knockout (Apc(Delta716)) mice, a model for human familial adenomatous polyposis. We scored MVD also in several compound mutants carrying Apc(Delta716), namely, mice with an additional mutation in Smad4, in which the polyps progress into invasive adenocarcinomas; mice with a cyclooxygenase (COX)-2 gene (Ptgs2) mutation, in which adenoma growth is suppressed; and mice with prostaglandin E(2) EP receptor gene mutations. In both simple Apc(Delta716) and compound Apc(Delta716) Smad4 mutants, MVD increased in a polyp size-dependent manner only in the polyps expanded beyond a threshold of about 1 mm in diameter. These results indicate that tumor angiogenesis is stimulated only after tumors grow to a certain size, and this angiogenic switch is common to both benign adenomas and malignant adenocarcinomas. In Apc(Delta716) polyposis attenuated by the COX-2 gene mutation, in contrast, MVD did not increase even in polyps larger than 1 mm. The same phenomenon was observed in the compound mutant mice with Apc(Delta716) and the EP(2) receptor gene mutations, but not in other EP compound mutants. We also immunohistochemically studied COX-2 and angiogenic factors, vascular endothelial growth factor and basic fibroblast growth factor. Interestingly, expression of these proteins was also increased in polyps larger than 1 mm. These results suggest that, in both benign and malignant mouse intestinal tumors, stromal expression of COX-2 results in elevated prostaglandin E(2) levels that stimulate cell surface receptor EP(2), followed by induction of vascular endothelial growth factor that causes tumor angiogenesis.

Adenocarcinoma↗