Biomedical subjects

F Costantini

Publications and source records attributed to F Costantini.

At least 37 records · Page 2Linked to original sources

PubMed1999

A GSK3beta phosphorylation site in axin modulates interaction with beta-catenin and Tcf-mediated gene expression.

Upon binding of a Wnt to its receptor, GSK3beta is inhibited through an unknown mechanism involving Dishevelled (Dsh), resulting in the dephosphorylation and stabilization of beta-catenin, which translocates to the nucleus and interacts with Lef/Tcf transcription factors to activate target gene expression. Axin is a scaffold protein which binds beta-catenin and GSK3beta (as well as several other proteins) and thus promotes the phosphorylation of beta-catenin. Here we report that Axin is phosphorylated on Ser and Thr residues in several regions in vivo, while only one region (amino acids 600-672) is efficiently phosphorylated by GSK3beta in vitro. Site-directed mutagenesis, together with in vitro and in vivo phosphorylation assays, demonstrates that Axin residues T609 and S614 are physiological GSK3beta targets. Substitutions for one or more of these residues, which lie within a beta-catenin binding site, reduce the ability of Axin to modulate Wnt-induced signaling in a Lef/Tcf reporter assay. These amino acid substitutions also reduce the binding between Axin and beta-catenin. We propose a model in which inhibition of GSK3beta activity upon Wnt signaling leads to the dephosphorylation of GSK3beta sites in Axin, resulting in the release of beta-catenin from the phosphorylation complex.

Amino Acid Sequence↗

PubMed1999

Domains of axin involved in protein-protein interactions, Wnt pathway inhibition, and intracellular localization.

Axin was identified as a regulator of embryonic axis induction in vertebrates that inhibits the Wnt signal transduction pathway. Epistasis experiments in frog embryos indicated that Axin functioned downstream of glycogen synthase kinase 3beta (GSK3beta) and upstream of beta-catenin, and subsequent studies showed that Axin is part of a complex including these two proteins and adenomatous polyposis coli (APC). Here, we examine the role of different Axin domains in the effects on axis formation and beta-catenin levels. We find that the regulators of G-protein signaling domain (major APC-binding site) and GSK3beta-binding site are required, whereas the COOH-terminal sequences, including a protein phosphatase 2A binding site and the DIX domain, are not essential. Some forms of Axin lacking the beta-catenin binding site can still interact indirectly with beta-catenin and regulate beta-catenin levels and axis formation. Thus in normal embryonic cells, interaction with APC and GSK3beta is critical for the ability of Axin to regulate signaling via beta-catenin. Myc-tagged Axin is localized in a characteristic pattern of intracellular spots as well as at the plasma membrane. NH2-terminal sequences were required for targeting to either of these sites, whereas COOH-terminal sequences increased localization at the spots. Coexpression of hemagglutinin-tagged Dishevelled (Dsh) revealed strong colocalization with Axin, suggesting that Dsh can interact with the Axin/APC/GSK3/beta-catenin complex, and may thus modulate its activity.

Adaptor Proteins, Signal Transducing↗

PubMed1999

Identification of a domain of Axin that binds to the serine/threonine protein phosphatase 2A and a self-binding domain.

Axin is a negative regulator of embryonic axis formation in vertebrates, which acts through a Wnt signal transduction pathway involving the serine/threonine kinase GSK-3 and beta-catenin. Axin has been shown to have distinct binding sites for GSK-3 and beta-catenin and to promote the phosphorylation of beta-catenin and its consequent degradation. This provides an explanation for the ability of Axin to inhibit signaling through beta-catenin. In addition, a more N-terminal region of Axin binds to adenomatous polyposis coli (APC), a tumor suppressor protein that also regulates levels of beta-catenin. Here, we report the results of a yeast two-hybrid screen for proteins that interact with the C-terminal third of Axin, a region in which no binding sites for other proteins have previously been identified. We found that Axin can bind to the catalytic subunit of the serine/threonine protein phosphatase 2A through a domain between amino acids 632 and 836. This interaction was confirmed by in vitro binding studies as well as by co-immunoprecipitation of epitope-tagged proteins expressed in cultured cells. Our results suggest that protein phosphatase 2A might interact with the Axin.APC.GSK-3.beta-catenin complex, where it could modulate the effect of GSK-3 on beta-catenin or other proteins in the complex. We also identified a region of Axin that may allow it to form dimers or multimers. Through two-hybrid and co-immunoprecipitation studies, we demonstrated that the C-terminal 100 amino acids of Axin could bind to the same region as other Axin molecules.

Axin Protein↗

PubMed1999

In vivo formation of 8-iso-prostaglandin f2alpha and platelet activation in diabetes mellitus: effects of improved metabolic control and vitamin E supplementation.

BACKGROUND: Diabetes mellitus (DM) is associated with enhanced lipid peroxidation and persistent platelet activation. We tested the hypothesis that the in vivo formation of the F2-isoprostane 8-iso-prostaglandin (PG)F2alpha, a bioactive product of arachidonic acid peroxidation, is enhanced in DM and contributes to platelet activation. METHODS AND RESULTS: Urine samples were obtained from 85 diabetic patients and 85 age- and sex-matched healthy subjects for measurement of immunoreactive 8-iso-PGF2alpha and 11-dehydro-thromboxane B2 (TXM), an in vivo index of platelet activation. Sixty-two had non-insulin-dependent (NID)DM, and 23 had insulin-dependent (ID) DM. Vitamin E supplementation, metabolic control, and cyclooxygenase inhibitors were used to investigate the mechanisms of formation of 8-iso-PGF2alpha in this setting. Urinary 8-iso-PGF2alpha excretion was significantly higher (P=0.0001) in NIDDM patients (419+/-208 pg/mg creatinine; range 160 to 1014) than in age-matched control subjects (208+/-92; 41 to 433). Urinary 8-iso-PGF2alpha was linearly correlated with blood glucose and urinary TXM. 8-iso-PGF2alpha excretion was also significantly (P=0. 0001) higher in IDDM patients (400+/-146; 183 to 702) than in control subjects (197+/-69; 95 to 353). Vitamin E supplementation (600 mg/d for 14 days) was associated with a statistically significant reduction in both urinary 8-iso-PGF2alpha (by 37%) and TXM (by 43%) in 10 NIDDM patients. Improved metabolic control was associated with a significant (P=0.0001) reduction in 8-iso-PGF2alpha and TXM excretion by 32% and 41%, respectively, in 21 NIDDM patients. 8-iso-PGF2alpha was unchanged after 2-week dosing with aspirin and indobufen despite profound suppression of TXM excretion. CONCLUSIONS: We conclude that DM is associated with increased formation of F2-isoprostanes, as a correlate of impaired glycemic control and enhanced lipid peroxidation. This may provide an important biochemical link between impaired glycemic control and persistent platelet activation. These results provide a rationale for dose-finding studies of antioxidant treatment in diabetes.

Adult↗

PubMed1999

Expression of green fluorescent protein in the ureteric bud of transgenic mice: a new tool for the analysis of ureteric bud morphogenesis.

The growth and branching of the ureteric bud is a complex process that is ultimately responsible for the organization of the collecting duct system as well as the number of nephrons in the metanephric kidney. While the genes involved in the regulation of this process have begun to be elucidated, our understanding of the cellular and molecular basis of ureteric bud morphogenesis remains rudimentary. Furthermore, the timing and sequence of branching and elongation that gives rise to the collecting system of the kidney can only be inferred from retrospective staining or microdissection of fixed preparations. To aid in the investigation of these issues, we developed strains of transgenic mice in which a green fluorescent protein (GFP) is expressed in the ureteric bud under the control of the Hoxb7 promoter. In these mice, GFP is expressed in every branch of the ureteric bud throughout renal development, and in its derivative epithelia in the adult kidney. As GFP fluorescence can be easily visualized in living tissue, this allows the dynamic pattern of ureteric bud growth and branching to be followed over several days when the kidneys are cultured in vitro. Using confocal microscopy, branching of the ureteric bud in all three dimensions can be analyzed. These mice represent an extremely powerful tool to characterize the normal patterns of ureteric bud morphogenesis and to investigate the response of the bud to growth factors, matrix elements, and other agents that regulate its growth and branching.

Animals↗

PubMed1999

Blunted nocturnal fall in blood pressure and oxidative stress in men and women with essential hypertension.

Low-density lipoprotein oxidation and antioxidant vitamins E and C were investigated in dipper (nocturnal blood pressure fall > 10%) and nondipper (nocturnal blood pressure fall < 10%) hypertensives. We studied 40 dippers and 28 nondippers balanced for gender, age, and body mass index. Blood samples were drawn for lipid profile determination, assessment of thiobarbituric acid-reactive substances, and fluorescent products of lipid peroxidation in native low-density lipoprotein, evaluation of susceptibility to low-density lipoprotein oxidation in vitro (lag phase and propagation rate), and determination of low-density lipoprotein vitamin E and plasma vitamins E and C contents. Compared with dippers, nondippers had significantly higher thiobarbituric acid-reactive substances and fluorescent products of lipid peroxidation (0.63 +/- 0.1 v 0.77 +/- 0.08 nmol malondialdehyde/mg low-density lipoprotein protein, and 14.5 +/- 6 v 17.9 +/- 4 units of relative fluorescence/mg low-density lipoprotein protein, respectively, both P < .05), shorter lag phase (56 +/- 13 v 49 +/- 9 min, P < .05), and lower plasma vitamin C content (42 +/- 9 v 35 +/- 10 micromol/L, P < .05). When gender was taken into account, differences were not significant between dipper and nondipper men, whereas, compared with dipper women, nondipper women showed significantly higher thiobarbituric acid-reactive substances and fluorescent products of lipid peroxidation (0.56 +/- 0.1 v 0.77 +/- 0.07 nmol malondialdehyde/mg low-density lipoprotein protein, and 12.5 +/- 4 v 17.5 +/- 4.6 units of relative fluorescence/mg low-density lipoprotein protein, respectively, both P < .05), shorter lag phase (62.5 +/- 11 v 49 +/- 9.5 min, P < .05), and lower plasma vitamin C content (44.9 +/- 10 v 34.7 +/- 10.8 micromol/L, P < .05). Given the role of low-density lipoprotein oxidation in the pathogenesis of atherosclerosis and that of vitamin C in protecting against it, our data suggest that nondippers, especially among women, show higher atherogenic risk than dippers.

Adult↗

PubMed1999

Increased systemic oxidative stress after elective endarterectomy: relation to vascular healing and remodeling.

It has been reported that systemic and local redox state may have an important role in the functional and organic changes characterizing the process of vascular response to injury. Carotid endarterectomy to remove atherosclerotic plaque is followed by a long lasting healing and remodeling process that can be carefully followed over time with noninvasive ultrasonography. Plasma vitamin C concentration and native LDL (n-LDL) content in lipid peroxides, vitamin E, beta-carotene, and lycopene as well as LDL susceptibility to peroxidation were assessed in 45 patients undergoing elective endarterectomy for internal carotid stenosis, at baseline, 24 hours, 3 and 15 days, and 1 month after surgery. Serial duplex scans were performed in all patients postoperatively and 3, 6, and 12 months. The changes in far wall thickness (FW) and % renarrowing from postoperatively to 12 months were used as remodeling indices. Plasma antioxidant vitamins and lag-phase showed a sharp and significant decrease during the first 24-hours after surgery remaining unchanged until the third day, whereas, an opposite trend was evidenced for n-LDL content in lipid peroxides and serum ceruloplasmin. After the third day all the parameters returned progressively to baseline within one month from endarterectomy. Interestingly, the n-LDL lipid peroxide content, the serum ceruloplasmin and the plasma vitamin C concentration, measured at 24 and 3 days from surgery, were significantly associated to the change in % renarrowing from postoperatively to 12 months. The higher the LDL content in lipid peroxides, the higher the serum level of ceruloplasmin, the lower the plasma content in vitamin C and the higher the % of vessel renarrowing. In conclusion, carotid endarterectomy with atherosclerotic plaque removal is associated with an acute and prolonged increase in systemic oxidative stress that influences vascular healing and late luminal loss.

Aged↗

PubMed1999

Dominant effects of RET receptor misexpression and ligand-independent RET signaling on ureteric bud development.

During kidney development, factors from the metanephric mesenchyme induce the growth and repeated branching of the ureteric bud, which gives rise to the collecting duct system and also induces nephrogenesis. One signaling pathway known to be required for this process includes the receptor tyrosine kinase RET and co-receptor GFR(&agr;)-1, which are expressed in the ureteric bud, and the secreted ligand GDNF produced in the mesenchyme. To examine the role of RET signaling in ureteric bud morphogenesis, we produced transgenic mice in which the pattern of RET expression was altered, or in which a ligand-independent form of RET kinase was expressed. The Hoxb7 promoter was used to express RET throughout the ureteric bud branches, in contrast to its normal expression only at the bud tips. This caused a variable inhibition of ureteric bud growth and branching reminiscent of, but less severe than, the RET knockout phenotype. Manipulation of the level of GDNF, in vitro or in vivo, suggested that this defect was due to insufficient rather than excessive RET signaling. We propose that RET receptors expressed ectopically on ureteric bud trunk cells sequester GDNF, reducing its availability to the normal target cells at the bud tips. When crossed to RET knockout mice, the Hoxb7/RET transgene, which encoded the RET9 isoform, supported normal kidney development in some RET-/- animals, indicating that the other major isoform, RET51, is not required in this organ. Expression of a Hoxb7/RET-PTC2 transgene, encoding a ligand-independent form of RET kinase, caused the development of abnormal nodules, outside the kidney or at its periphery, containing branched epithelial tubules apparently formed by deregulated growth of the ureteric bud. This suggests that RET signaling is not only necessary but is sufficient to induce ureteric bud growth, and that the orderly, centripetal growth of the bud tips is controlled by the spatially and temporally regulated expression of GDNF and RET.

Animals↗

PubMed1998

Increased susceptibility in Hp knockout mice during acute hemolysis.

Haptoglobin, a conserved plasma glycoprotein, forms very stable soluble complexes with free plasma hemoglobin. Hemoglobin binding by haptoglobin is thought to be important in the rapid hepatic clearance of hemoglobin from the plasma and in the inhibition of glomerular filtration of hemoglobin. To evaluate these functions, Haptoglobin knockout (-/-) mice were created. These mice were viable but had a small, significant reduction in postnatal viability. Contrary to popular belief, the lack of haptoglobin did not impair clearance of free plasma hemoglobin in -/- mice. Induction of severe hemolysis by phenylhydrazine caused extensive hemoglobin precipitation in the renal tubular cells of both -/- and +/+ mice, with death occurring in 55% of -/- mice and in 18% of +/+ mice. In general, phenylhydrazine-treated -/- mice suffered greater tissue damage, as evidenced by the induction of hepatic acute phase response resulting in increased plasma alpha 1-acid glycoprotein (AGP) levels. Among -/- and +/+ mice that survived, -/- mice tend to suffer greater oxidative damage and failed to repair or regenerate damaged renal tissues, as indicated by their higher plasma malonaldehyde (MDA) and 4-hydroxy-2(E)-nonenal (HNE) levels and lower mitotic indices in their kidneys, respectively. This study suggested that a physiologically important role of hemoglobin-haptoglobin complex formation is the amelioration of tissue damages by hemoglobin-driven lipid peroxidation.

Acute-Phase Reaction↗

PubMed1998

YAC transgenesis: a study of conditions to protect YAC DNA from breakage and a protocol for transfection.

Yeast artificial chromosomes (YACs) are providing a great boon to transgene technology by allowing the easy mutagenesis and study of very large DNAs. The large insert sizes of these vectors permit more accurate analysis of the regulation of transgene expression than smaller, more artificially assembled constructs. Transfection of mammalian cells by YACs can be accomplished by a number of methods; the most prevalent, using gel-purified DNA, is dependent upon compaction by salts to protect the large YAC DNA from breakage. We show that the common reliance on NaCl to compact YAC DNA sufficiently to protect it from breakage is not well-founded. Even the use of mixtures of polyamines and NaCl allows substantial damage to purified YACs. The use of polyamines alone in low salt buffers to compact YAC DNA provides the best protection from breakage and allows very effective transfection of murine embryonic stem (ES) cells. We provide a detailed method for ES cell transfection by YACs utilizing the DOTAP lipofection reagent that optimizes transfection efficiency and recovery of intact YACs.

Animals↗

PubMed1998

Circadian blood pressure changes and myocardial ischemia in hypertensive patients with coronary artery disease.

OBJECTIVES: We sought to evaluate whether different circadian blood pressure (BP) changes could influence the occurrence of ischemic episodes in untreated and treated hypertensive patients with stable coronary artery disease (CAD). BACKGROUND: In hypertensive patients with CAD the occurrence of myocardial ischemia could be influenced by either high or low BP values. Ambulatory monitoring has shown that circadian BP profile is not uniform in hypertensive patients. METHODS: Twenty-one patients with a nighttime BP fall < 10% ("nondippers"), 35 with a nighttime BP fall between > 10% and < 20% ("dippers") and 14 with a nighttime BP fall > 20% ("overdippers") with CAD underwent simultaneous ambulatory BP and electrocardiographic monitoring before and during drug therapy with nitrates and atenolol or verapamil in a prospective, randomized, open, blinded end point design. RESULTS: Daytime BP was not significantly different among the groups both before and during therapy. Nighttime BP was different by definition. Treatment significantly reduced BP values in each group (p < 0.05). Daytime ischemic episodes did not differ among the groups either before or during therapy. Drug therapy significantly reduced daytime ischemia (p < 0.05). In untreated patients, nighttime ischemia was more frequent in nondippers than in dippers and overdippers (p < 0.05). Drug therapy significantly reduced nocturnal ischemia in nondippers (p < 0.05), had no significant effect in dippers and significantly increased nighttime ischemia in overdippers (p < 0.05). During treatment, nighttime ischemia was more frequent in overdippers than in dippers and nondippers (p < 0.05). The same results were achieved when ischemic episodes were defined with more restrictive criteria (ST segment depression > or = 2 mm). CONCLUSIONS: Circadian BP changes can influence the occurrence of myocardial ischemia in untreated and treated hypertensive patients with CAD. Nocturnal ischemia was found to be more frequent in nondippers among untreated patients and in overdippers among treated patients, potentially suggesting different therapeutic approaches based on circadian BP profile.

Antihypertensive Agents↗

PubMed1998

Copper/zinc ratio and systemic oxidant load: effect of aging and aging-related degenerative diseases.

There is evidence that copper and zinc have pro-oxidant and antioxidant properties, respectively, so that their imbalance may be expected to condition oxidative stress status. Oxidative stress is relevant in aging and in age-related degenerative diseases. In this study, blood content of copper, zinc, and ceruloplasmin as well as of lipid peroxides were investigated in 81 healthy and 62 disabled octo-nonagenarians affected by chronic degenerative diseases, and in 81 healthy adults. Serum copper/zinc ratio and ceruloplasmin were significantly higher in the elderly than in the healthy adults. Moreover, all these parameters were significantly higher in the disabled than in the healthy elderly. Notably, the increased copper/zinc ratio found in healthy elderly was due to high copper values, whereas in the disabled, both high copper and low serum zinc concentrations were present. The copper/zinc ratio was significantly and positively related to systemic oxidative stress status in all groups. The higher the serum copper/zinc ratio the higher the lipid peroxides plasma content. We conclude that there is a strict relationship between copper/zinc ratio and systemic oxidant burden. Moreover, advanced age and, particularly, advanced age-related chronic degenerative diseases are associated with a significant increase in the copper/zinc ratio and systemic oxidative stress.

Aged↗

PubMed1998

Effect of thyroid function on LDL oxidation.

In this study, the effect of different levels of thyroid hormone and metabolic activity on low density lipoprotein (LDL) oxidation was investigated. Thus, in 16 patients with hyperthyroidism, 16 with hypothyroidism, and 16 age- and sex-matched healthy normolipidemic control subjects, the native LDL content in lipid peroxides, vitamin E, beta-carotene, and lycopene, as well as the susceptibility of these particles to undergo lipid peroxidation, was assessed. Hyperthyroidism was associated with significantly higher lipid peroxidation, as characterized by a higher native LDL content in lipid peroxides, a lower lag phase, and a higher oxidation rate than in the other two groups. This elevated lipid peroxidation was associated with a lower LDL antioxidant concentration. Interestingly, hypothyroid patients showed an intermediate behavior. In fact, in hypothyroidism, LDL oxidation was significantly lower than in hyperthyroidism but higher than in the control group. Hypothyroidism was also characterized by the highest beta-carotene LDL content, whereas vitamin E was significantly lower than in control subjects. In hyperthyroidism but not in the other two groups, LDL oxidation was strongly influenced by free thyroxine blood content. In fact in this group, the native LDL lipid peroxide content and the lag phase were directly and indirectly, respectively, related to free thyroxine blood levels. On the contrary, in hypothyroidism LDL oxidation was strongly and significantly related to serum lipids. In conclusion, both hypothyroidism and hyperthyroidism are characterized by higher levels of LDL oxidation when compared with normolipidemic control subjects. In hyperthyroid patients, the increased lipid peroxidation was strictly related to free thyroxine levels, whereas in hypothyroidism it was strongly influenced by serum lipids.

Antioxidants↗

PubMed1998

Low-density lipoprotein oxidation and vitamins E and C in sustained and white-coat hypertension.

Low-density lipoprotein oxidation and antioxidant vitamins E and C were investigated in white-coat hypertension in comparison with sustained hypertension and normotension. We selected 21 sustained hypertensive subjects, 21 white-coat hypertensive subjects, and 21 normotensive subjects matched for gender, age, and body mass index. White-coat hypertension was defined as clinical hypertension and daytime ambulatory blood pressure <139/90 (subjects were also reclassified using 134/90 and 135/85 mm Hg as cutoff points for daytime blood pressure). Blood samples were drawn for lipid profile determination, assessment of fluorescent products of lipid peroxidation in native LDL, evaluation of susceptibility to LDL oxidation in vitro (lag phase and propagation rate), and determination of LDL vitamin E and plasma vitamins E and C contents. Compared with sustained hypertensive subjects, white-coat hypertensives had significantly lower fluorescent products of lipid peroxidation (15.4+/-3.4 versus 10.2+/-3 units of relative fluorescence/mg LDL protein, P<.05), longer lag phase (54+/-10 versus 88+/-10 minutes, P<.05), lower propagation rate (8.2+/-2.5 versus 5.95+/-2.1 nmol diene/min per mg LDL cholesterol, P<.05), higher LDL vitamin E content (8.3+/-1.1 versus 10.1+/-1.8 nmol/mg LDL cholesterol, P<.05), and plasma vitamin C content (40+/-13 versus 57+9 micromol/L, P<. 05). No significant difference was observed between white-coat hypertensive and normotensive subjects. The results did not change after reclassification of subjects. Our data show that white-coat hypertensive subjects do not show an enhanced propensity to LDL oxidation or reduction in antioxidant vitamins. Given the role of LDL oxidation in the development of atherosclerosis and that of vitamin E and C in protecting against it, these findings suggest that white-coat hypertension per se carries a low atherogenic risk.

Adult↗

PubMed1997

A shortened life span of EKLF-/- adult erythrocytes, due to a deficiency of beta-globin chains, is ameliorated by human gamma-globin chains.

Using homologous recombination, both EKLF alleles in murine embryonic stem (ES) cells were inactivated. These EKLF-/- ES cells were capable of undergoing in vitro differentiation to form definitive erythroid colonies that were similar in size and number to those formed by wild-type ES cells. However, the EKLF-/- colonies were poorly hemoglobinized and enucleated erythrocytes in these colonies contained numerous Heinz bodies. Reverse transcriptase-polymerase chain reaction (RT-PCR) analyses revealed that adult and embryonic globin genes were appropriately regulated, with the exception of beta h1-globin, which continued to be expressed at a very low level. The ratio of adult beta-globin/alpha-globin mRNA in the mutant ES cells was 1/15 of that in wild-type ES cells. When the EKLF-/- cells were injected into blastocysts, they did not contribute at a detectable level to the mature erythrocyte compartment of the chimeric animals, based on analysis of glucose phosphate isomerase-1 (GPI-1) isozymes and hemoglobins that distinguish ES cell-derived erythrocytes from host blastocyst-derived erythrocytes. In contrast, semiquantitative RT-PCR analysis of RNA from reticulocytes of the same chimeric animals suggested that the ES cell-derived reticulocytes were present at a level of 6% to 8%. This indicated that the EKLF-/- erythrocytes in adult animals must be short-lived, apparently due to the imbalance of beta-versus alpha-globin chains, leading to the precipitation of excess alpha-globin chains to form Heinz bodies. Consistent with this hypothesis, the short life span was ameliorated by introduction into the EKLF-/- ES cells of a human LCR/gamma-globin gene, as evidenced by the presence of ES cell-derived reticulocytes as well as mature erythrocytes in the blood of the chimeric animals.

Animals↗

PubMed1997

The mouse Fused locus encodes Axin, an inhibitor of the Wnt signaling pathway that regulates embryonic axis formation.

Mutations at the mouse Fused locus have pleiotropic developmental effects, including the formation of axial duplications in homozygous embryos. The product of the Fused locus, Axin, displays similarities to RGS (Regulators of G-Protein Signaling) and Dishevelled proteins. Mutant Fused alleles that cause axial duplications disrupt the major mRNA, suggesting that Axin negatively regulates the response to an axis-inducing signal. Injection of Axin mRNA into Xenopus embryos inhibits dorsal axis formation by interfering with signaling through the Wnt pathway. Furthermore, ventral injection of an Axin mRNA lacking the RGS domain induces an ectopic axis, apparently through a dominant-negative mechanism. Thus, Axin is a novel inhibitor of Wnt signaling and regulates an early step in embryonic axis formation in mammals and amphibians.

Amino Acid Sequence↗

PubMed1997

RET proto-oncogene is important for the development of respiratory CO2 sensitivity.

Brain stem muscarinic cholinergic pathways are important in respiratory carbon dioxide (CO2) chemosensitivity. Defects in the muscarinic system have been reported in children with congenital/developmental disorders of respiratory control such as sudden infant death syndrome (SIDS) and congenital central hypoventilation syndrome (CCHS). This early onset of disease suggests a possible genetic basis. The muscarinic system is part of the autonomic nervous system which develops from the neural crest. Ret proto-oncogene is important for this development. Thus, a potential role for ret in the development of respiratory CO2 chemosensitivity was considered. Using plethysmography, we assessed the ventilatory response to inhaled CO2 in the unanesthetized offsprings of ret +/- mice. Fractional increases in minute ventilation during hypercapnia relative to isocapnia were 5.1 +/- 3.2, 3.0 +/- 1.6 and 1.4 +/- 0.8 for the ret +/+, ret +/- and ret +/- mice, respectively. The ret knockout mice have a depressed ventilatory response to inhaled CO2. Therefore, the ret gene is an important factor in the pathway of neuronal development which allow respiratory CO2 chemosensitivity.

Animals↗

PubMed1997

K:Cl cotransport in red cells of transgenic mice expressing high levels of human hemoglobin S.

K:Cl cotransport is involved in generating dense red blood cells (RBCs) in homozygotes for HbS (SS). We report on the properties of this transport system in RBCs from control and transgenic mice expressing high levels of human alpha(H) and beta(S) chains. Unlike human SS RBCs, mouse RBCs incubated in isotonic media exhibited a Cl(-)-dependent K+ efflux and therefore have a different set-point for activation. This basal efflux was slightly stimulated by cell swelling to values five times smaller than that in human SS cells; in addition, the delay time for activation was shorter in transgenic than in control mice, but fourfold longer than that of human SS cells. These properties cast doubt on the physiological impact of the mouse K:Cl cotransporter on RBC volume regulation in the mouse and suggest that there are intrinsic differences between the human K:Cl cotransporter and the putative transporter in mice.

Animals↗