Biomedical subjects

S Paul Oh

Publications and source records attributed to S Paul Oh.

11 recordsLinked to original sources

PubMed2006

A murine model for human sepiapterin-reductase deficiency.

Tetrahydrobiopterin (BH(4)) is an essential cofactor for several enzymes, including all three forms of nitric oxide synthases, the three aromatic hydroxylases, and glyceryl-ether mono-oxygenase. A proper level of BH(4) is, therefore, necessary for the metabolism of phenylalanine and the production of nitric oxide, catecholamines, and serotonin. BH(4) deficiency has been shown to be closely associated with diverse neurological psychiatric disorders. Sepiapterin reductase (SPR) is an enzyme that catalyzes the final step of BH(4) biosynthesis. Whereas the number of cases of neuropsychological disorders resulting from deficiencies of other catalytic enzymes involved in BH(4) biosynthesis and metabolism has been increasing, only a handful of cases of SPR deficiency have been reported, and the role of SPR in BH(4) biosynthesis in vivo has been poorly understood. Here, we report that mice deficient in the Spr gene (Spr(-/-)) display disturbed pterin profiles and greatly diminished levels of dopamine, norepinephrine, and serotonin, indicating that SPR is essential for homeostasis of BH(4) and for the normal functions of BH(4)-dependent enzymes. The Spr(-/-) mice exhibit phenylketonuria, dwarfism, and impaired body movement. Oral supplementation of BH(4) and neurotransmitter precursors completely rescued dwarfism and phenylalanine metabolism. The biochemical and behavioral characteristics of Spr(-/-) mice share striking similarities with the symptoms observed in SPR-deficient patients. This Spr mutant strain of mice will be an invaluable resource to elucidate many important issues regarding SPR and BH(4) deficiencies.

Alcohol Oxidoreductases↗

PubMed2006

Generation of activin receptor type IIB isoform-specific hypomorphic alleles.

Activin receptor type IIB (Acvr2b) mediates multiple signals for transforming growth factor-beta (TGF-beta) family members, including Activin, Nodal, Bmp7, Gdf1, Gdf3, Myostatin (Gdf8), and Gdf11. Mouse Acvr2b gene generates four transcriptional isoforms (Acvr2b(1-4)) via alternative splicing of two sequence domains located at the juxtaposition of the transmembrane domain. To investigate whether these splicing domains are essential for signal transduction of the Acvr2b receptor in vivo, we have generated a strain of mutant mice (Acvr2b(4/4)) which produce only the Acvr2b(4) isoform, which lacks both splicing domains. Most homozygous Acvr2b(4(neo)/4(neo)) mice, in which a neomycin-resistant cassette was inserted in Intron 4 displayed a mild form of anterior vertebral transformations. However, the penetrance of the vertebral defect was dramatically decreased when the neomycin-resistant cassette was deleted. These results suggest that the Acvr2b(4) isoform is capable of compensating for the deficiency of the other three isoforms. In the absence of its subfamily receptor Acvr2a, however, the development of Acvr2b(4/4) mice was arrested at the gastrulation stage, recapitulating the Acvr2a(-/-); Acvr2b(+/-) mutant phenotype. In this study, we demonstrate that this phenomenon is most likely due to the reduction in the expressed Acvr2b(4) levels rather than to the functional deficiency of the Acvr2b(4) isoform itself.

Activin Receptors, Type II↗

PubMed2006

Nonoverlapping expression patterns of ALK1 and ALK5 reveal distinct roles of each receptor in vascular development.

Transforming growth factor beta (TGF-beta) transmits signals through a heterotetrameric cell-surface complex of type II (TGFBR2) and type I (activin receptor-like kinase 5, ALK5; TGFBR1) serine/threonine kinase receptors, as well as Smad2/3. We have previously shown that another type I receptor, ALK1 (ACVRL1), can also mediate TGF-beta signals via BMP-activated Smads in vascular endothelial cells (ECs). Our group and others have proposed the hypothesis that two TGF-beta signaling pathways via ALK1 and ALK5 in vascular ECs may play a balancing role for controlling the proliferation and migration of ECs during angiogenesis. To address in vivo roles of this balance in vascular development, we have created a knockin mouse line that carries a lacZ reporter in the Alk5 gene locus (Alk5(lacZ)). Throughout development, a well-defined, nonubiquitous expression pattern of Alk5 expression was observed in multiple tissues, and organs. Overall, a high level of Alk5 expression was found in perichondria, periostea, and the mesenchymal layers underlying epithelia in the kidney, lung, and gallbladder. In blood vessels, contrasting to predominant Alk1 expression in arterial endothelium, Alk5 expression was localized in the medial and adventitial layers of blood vessels, but was undetectable in the intimal layer. In addition, although Alk5-null embryos exhibit a defect in the formation of vascular smooth muscle layers, the lumens of blood vessels are generated properly, which stands in contrast to the severe dilation of the vascular lumens in Alk1-null mice. These mutually exclusive expression patterns of Alk1 and Alk5 in blood vessels, as well as the undisturbed formation of the vascular lumens in Alk5-null embryos, suggest that each type I receptor has its own unique functions in vascular development. The Alk5(lacZ) mice will be a valuable resource in identifying the in vivo cellular targets of TGF-beta family signals mediated by Alk5, both during embryonic development as well as in diverse pathological conditions.

Activin Receptors, Type I↗

PubMed2004

Subfertility, uterine hypoplasia, and partial progesterone resistance in mice lacking the Kruppel-like factor 9/basic transcription element-binding protein-1 (Bteb1) gene.

Progesterone receptor (PR), a ligand-activated transcription factor, is a key regulator of cellular proliferation and differentiation in reproductive tissues. The transcriptional activity of PR is influenced by co-regulatory proteins typically expressed in a tissue- and cell-specific fashion. We previously demonstrated that basic transcription element-binding protein-1 (BTEB1), a member of the Sp/Krüppel-like family of transcription factors, functionally interacts with the two PR isoforms, PR-A and PR-B, to mediate progestin sensitivity of target genes in endometrial epithelial cells in vitro. Here we report that ablation of the Bteb1 gene in female mice results in uterine hypoplasia, reduced litter size, and increased incidence of neonatal deaths in offspring. The reduced litter size is solely a maternal genotype effect and results from fewer numbers of implantation sites, rather than defects in ovulation. In the early pregnant uterus, Bteb1 expression in stromal cells temporally coincides with PR-A isoform-dependent decidual formation at the time of implantation. Expression of two implantation-specific genes, Hoxa10 and cyclin D3, was decreased in uteri of early pregnant Bteb1-null mutants, whereas that of Bteb3, a related family member, was increased, the latter possibly compensating for the loss of Bteb1. Progesterone responsiveness of several uterine genes was altered with Bteb1-null mutation. These results identify Bteb1 as a functionally relevant PR-interacting protein and suggest its selective modulation of cellular processes that are regulated by PR-A in the uterine stroma.

Animals↗

PubMed2004

Isolation of a regulatory region of activin receptor-like kinase 1 gene sufficient for arterial endothelium-specific expression.

Activin receptor-like kinase 1 (Acvrl1; Alk1) is a type I receptor for transforming growth factor-beta (TGF-beta). ALK1 plays a pivotal role in vascular development and is involved in the development of hereditary hemorrhagic telangiectasia 2 (HHT2), a dominantly inherited vascular disorder, and pulmonary hypertension. We have previously shown that Alk1 is expressed predominantly in arterial endothelial cells (ECs). Despite recent discoveries of a number of artery-specific genes, the regulatory elements of these genes have not been characterized. To investigate the cis-acting elements essential for the artery-specific Alk1 expression, we have generated a series of transgenic constructs with various lengths and regions of Alk1 genomic fragments connected to a LacZ reporter gene, and analyzed the reporter gene expression in transgenic mice. We found that a 9.2-kb genomic fragment, which includes 2.7-kb promoter region and the entire intron 2, is sufficient to drive arterial endothelium-specific expression. The defined regulatory region, as well as the transgenic mouse lines, would be invaluable resources in studying the mechanisms underlying angiogenesis, arteriogenesis, and vascular disorders, such as HHT and pulmonary hypertension. The full text of this article is available online at http://circres.ahajournals.org.

Activin Receptors, Type I↗

PubMed2004

B-cell translocation gene 2 (Btg2) regulates vertebral patterning by modulating bone morphogenetic protein/smad signaling.

Btg2 is a primary p53 transcriptional target gene which may function as a coactivator-corepressor and/or an adaptor molecule that modulates the activities of its interacting proteins. We have generated Btg2-null mice to elucidate the in vivo function of Btg2. Btg2-null mice are viable and fertile but exhibit posterior homeotic transformations of the axial vertebrae in a dose-dependent manner. Consistent with its role in vertebral patterning, Btg2 is expressed in the presomitic mesoderm, tail bud, and somites during somitogenesis. We further provide biochemical evidence that Btg2 interacts with bone morphogenetic protein (BMP)-activated Smads and enhances the transcriptional activity of BMP signaling. In view of the genetic evidence that reduced BMP signaling causes posteriorization of the vertebral pattern, we propose that the observed vertebral phenotype in Btg2-null mice is due to attenuated BMP signaling.

Alleles↗

PubMed2003

Arterial endothelium-specific activin receptor-like kinase 1 expression suggests its role in arterialization and vascular remodeling.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant vascular disorder characterized by epistaxis, mucocutaneous telangiectases, and arteriovenous malformations (AVM). Two genes are linked to HHT: endoglin (ENG) in HHT1 and activin receptor-like kinase 1 (ACVRL1; ALK1) in HHT2. Although both genes are involved in the transforming growth factor beta signaling pathways, the pathogenetic mechanisms for HHT remain elusive. It was shown that mutations in the Alk1 gene in mice and zebrafish resulted in an embryonic lethal phenotype due to severe dilation of blood vessels. We created a novel null mutant mouse line for Alk1 (Alk1lacZ) by replacing its exons, including the one that encodes the transmembrane domain, with the beta-galactosidase gene. Using Alk1lacZ mice, we show that Alk1 is predominantly expressed in developing arterial endothelium. Alk1 expression is greatly diminished in adult arteries, but is induced in preexisting feeding arteries and newly forming arterial vessels during wound healing and tumor angiogenesis. We also show that hemodynamic changes, which require vascular remodeling, may regulate Alk1 expression. Our studies suggest the role of Alk1 signaling in arterialization and remodeling of arteries. Contrary to the current view of HHT as venous disease, our findings suggest that the arterioles rather than the venules are the primary vessels affected by the loss of an Alk1 allele, and that blood vessels with reduction in Alk1 expression may harbor defects in responding to demands for vascular remodeling.

Activin Receptors, Type I↗

PubMed2003

A mouse model for hereditary hemorrhagic telangiectasia (HHT) type 2.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal-dominant disorder characterized by the age-dependent development of focal arteriovenous malformations and telangiectases. HHT type 2 is caused by loss of function mutations in activin receptor-like kinase 1 (ACVRL1 or ALK1). However, the factors that initiate lesion formation and those that influence disease progression remain unknown. Because heterozygous mice contain the appropriate genotype for an animal model of this disorder, mice heterozygous for a loss-of-function mutation in Acvrl1 were carefully examined for an HHT-like phenotype. These mice developed age-dependent vascular lesions in the skin, extremities, oral cavity and in the internal organs (lung, liver, intestine, spleen and brain), similar to those seen in HHT patients. Major histopathological features of the lesions included thin-walled dilated vessels in close proximity to each other, hemorrhage and fibrosis. Similar to HHT patients, the mice also exhibited gastrointestinal bleeding, as evidenced by positive fecal occult blood tests. An Acvrl1(+/-) mouse with profound liver involvement also displayed a secondary cardiac phenotype, similar to that observed in human patients. The similarity of affected organs, age-dependent penetrance, histological similarity of the lesions and recapitulation of a secondary phenotype suggest that the Acvrl1(+/-) mice are an appropriate animal model for the identification of additional genetic and environmental factors that cause pathology in HHT type 2 patients. In addition, studies utilizing this animal model can yield valuable information on the role of ALK1 in maintenance of adult vascular architecture including arteriovenous identity.

Animals↗

PubMed2003

Developmental expression of mouse muscleblind genes Mbnl1, Mbnl2 and Mbnl3.

The RNA-mediated pathogenesis model for the myotonic dystrophies DM1 and DM2 proposes that mutant transcripts from the affected genes sequester a family of double-stranded RNA-binding factors, the muscleblind proteins MBNL1, MBNL2 and MBNL3, in the nucleus. These proteins are homologues of the Drosophila muscleblind proteins that are required for the terminal differentiation of muscle and photoreceptor tissues, and thus nuclear sequestration of the human proteins might impair their normal function in muscle and eye development and maintenance. To examine this model further, we analyzed the expression pattern of the mouse Mbnl1, Mbnl2, and Mbnl3 genes during embryonic development and compared muscleblind gene expression to Dmpk since the RNA pathogenesis model for DM1 requires the coordinate synthesis of mutant Dmpk transcripts and muscleblind proteins. Our studies reveal a striking overlap between the expression of Dmpk and the muscleblind genes during development of the limbs, nervous system and various muscles, including the diaphragm and tongue.

Animals↗

PubMed2002

Activin type IIA and IIB receptors mediate Gdf11 signaling in axial vertebral patterning.

Vertebral bodies are segmented along the anteroposterior (AP) body axis, and the segmental identity of the vertebrae is determined by the unique expression pattern of multiple Hox genes. Recent studies have demonstrated that a transforming growth factor beta (TGF-beta) family protein, Gdf11 (growth and differentiation factor 11), and the activin type II receptor, ActRIIB, are involved in controlling the spatiotemporal expression of multiple Hox genes along the AP axis, and that the disruption of each of these genes causes anterior transformation of the vertebrae. Skeletal defects are more severe in Gdf11-null mice than in ActRIIB-null mice, however, leaving it uncertain whether Gdf11 signals via ActRIIB. Here we demonstrate using genetic and biochemical studies that ActRIIB and its subfamily receptor, ActRIIA, cooperatively mediate the Gdf11 signal in patterning the axial vertebrae, and that Gdf11 binds to both ActRIIA and ActRIIB, and induces phosphorylation of Smad2. In addition, we also show that these two receptors can functionally compensate for one another to mediate signaling of another TGF-beta ligand, nodal, during left-right patterning and the development of anterior head structure.

Activin Receptors, Type II↗

PubMed2002

Gene-dosage-sensitive genetic interactions between inversus viscerum (iv), nodal, and activin type IIB receptor (ActRIIB) genes in asymmetrical patterning of the visceral organs along the left-right axis.

We have shown previously that mice deficient in the activin type IIB receptor (ActRIIB) exhibit right isomerism, which is characterized by mirror-image symmetrical right lungs, complex cardiac malformations, and hypoplasia of the spleen. These observations led us to hypothesize that the signaling of a TGF-beta family member by means of ActRIIB is necessary for the determination of the left-sidedness of the visceral organs. To test this hypothesis, we examined laterality defects in mice carrying mutations in both ActRIIB and inversus viscerum (iv) genes, because iv(-/-) mice display a spectrum of laterality defects, including situs inversus, right isomerism, and left isomerism. We found that all mice homozygous for both iv and ActRIIB mutations displayed the right isomerism. The phenotype of right isomerism in the double mutants was also more severe than that in ActRIIB(-/-) mice as shown by persistent left inferior vena cava, right atrial isomerism, and hypoplasia of spleen. Interestingly, the incidence of right isomerism also increased significantly in iv(-/-);ActRIIB(+/-) and iv(+/-);ActRIIB(-/-) mice compared with homozygous mice carrying either of single gene mutations. A mechanism of the genetic modulation between ActRIIB and iv genes may be that iv modulates the asymmetric expression of a TGF-beta family member that signals through activin type II receptors, ActRIIA and ActRIIB, to specify the "left-sidedness." Nodal is the most likely candidate. We show here that the penetrance and severity of the right isomerism is significantly elevated in nodal(+/-); ActRIIB(-/-) mice, compared with ActRIIB(-/-) mice. Furthermore, the chimeric mice derived from nodal(-/-) ES cells displayed right isomerism, indistinguishable from that in (iv(-/-);ActRIIB(-/-)) mice. We propose that iv functions to establish asymmetric expression of nodal in a gene-dosage-sensitive manner and that nodal signals through the activin type II receptors to specify the left-sidedness by means of a threshold mechanism.

Activin Receptors, Type II↗