The gene mutated in adult-onset type II citrullinaemia encodes a putative mitochondrial carrier protein

Citrullinaemia (CTLN) is an autosomal recessive disease caused by deficiency of argininosuccinate synthetase (ASS). Adult-onset type II citrullinaemia (CTLN2) is characterized by a liver-specific ASS deficiency with no abnormalities in hepatic ASS mRNA or the gene ASS (refs 1-17). CTLN2 patients (1/100,000 in Japan) suffer from a disturbance of consciousness and coma, and most die with cerebral edema within a few years of onset. CTLN2 differs from classical citrullinaemia (CTLN1, OMIM 215700) in that CTLN1 is neonatal or infantile in onset, with ASS enzyme defects (in all tissues) arising due to mutations in ASS on chromosome 9q34 (refs 18-21). We collected 118 CTLN2 families, and localized the CTLN2 locus to chromosome 7q21.3 by homozygosity mapping analysis of individuals from 18 consanguineous unions. Using positional cloning we identified a novel gene, SLC25A13, and found five different DNA sequence alterations that account for mutations in all consanguineous patients examined. SLC25A13 encodes a 3.4-kb transcript expressed most abundantly in liver. The protein encoded by SLC25A13, named citrin, is bipartite in structure, containing a mitochondrial carrier motif and four EF-hand domains, suggesting it is a calcium-dependent mitochondrial solute transporter with a role in urea cycle function.

Functional studies on the interaction between human replication protein A and Xeroderma pigmentosum group A complementing protein (XPA)

The human replication protein A (RPA; also known as human single-stranded DNA binding protein, HSSB) is a multisubunit complex (70, 34 and 11 kDa subunits) involved in the three processes of DNA metabolism; replication, repair, recombination. We found that both 34 and 70 kDa subunits (p34 and p70, respectively), of RPA interacts with the Xeroderma pigmentosum group A complementing protein (XPA), a protein that specifically recognizes UV-damaged DNA. Our mutational analysis indicated that no particular domains of RPA p70 were essential for its interaction with XPA. We also examined the effect of this XPA-RPA interaction on in vitro simian virus 40 (SV40) DNA replication catalyzed by the crude extract and monopolymerase system. XPA inhibited SV40 DNA replication in vitro through its interaction with RPA. Taken together, these results suggest that there is a role for RPA in the regulation of DNA metabolism through its ability to modulate the interactions of proteins involved in the processes of DNA metabolism.

In vitro antifungal susceptibilities of Candida albicans and other fungal pathogens to polygodial, a sesquiterpene dialdehyde

In vitro antifungal activities of polygodial were investigated against several fungal pathogens. Polygodial showed strong antifungal activity, comparable to amphotericin B, against yeast-like fungi Candida albicans, C. utilis, C. krusei, Cryptococcus neoformans, Saccharomyces cerevisiae and also filamentous fungi including Trichophyton mentagrophytes, T. ruburum, and Penicillium marneffei. Other strains such as Aspergillus fumigatus, A. flavus, P. chrysogenum, C. lipolytica, and C. tropicalis showed moderate to low susceptibility to polygodial. The anti-fungal activity of polygodial was generally not reduced by several susceptibility-testing conditions such as medium, incubation temperature, inoculum size, and medium pH. However, polygodial's antifungal activity was strongly increased at acidic conditions. Unlike amphotericin B, polygodial did not show any hemolytic activity and also its antifungal activity was not diminished in the presence of ergosterol. Based on killing kinetics against growing and nongrowing C. albicans, polygodial showed strong and rapid fungicidal activity.

Tyrosine phosphorylation of SLP-76 is downstream of Syk following stimulation of the collagen receptor in platelets

Collagen-related peptide (CRP), a collagen homologue, induces platelet activation through a tyrosine kinase-dependent pathway, leading to sequential tyrosine phosphorylation of Fc receptor (FcR) gamma-chain, Syk, and phospholipase C-gamma2. Here we report that CRP and the platelet low affinity immune receptor FcgammaRIIA stimulate tyrosine phosphorylation of the T cell adapter SLP-76, whereas the G protein-coupled receptor agonist thrombin induces only minor tyrosine phosphorylation. This suggests that SLP-76 has a specific role downstream of receptors that signal via an immunoreceptor tyrosine-based activation motif. Immunoprecipitation studies demonstrate association of SLP-76 with SLAP-130, Vav, Fyn, Lyn, and the FcR gamma-chain in CRP-stimulated platelets. Several of these proteins, including SLP-76, undergo tyrosine phosphorylation in in vitro kinase assays performed on SLP-76 immunoprecipitates. Tyrosine phosphorylation of all of these proteins in the in vitro kinase assay was abrogated by the Src family kinase inhibitor PP1, suggesting that it is mediated by either Fyn or Lyn. The physiological significance of this is uncertain, however, since tyrosine phosphorylation of SLP-76 in vivo is not altered in either Fyn- or Lyn-deficient platelets. CRP stimulation of Syk-deficient platelets demonstrated that in vivo tyrosine phosphorylation of SLP-76 is downstream of Syk. The absence of Syk in the SLP-76 immunoprecipitates raises the possibility that another protein is responsible for bringing SLP-76 to Syk. Candidates for this include those proteins that co-immunoprecipitate with SLP-76, including the FcR gamma-chain. Tyrosine phosphorylation of PLC-gamma2 and Ca2+ mobilization is markedly attenuated in SLP-76-deficient platelets following CRP stimulation, suggesting that the adapter plays a critical role in the regulation of the phospholipase. The increase in tyrosine phosphorylation of SLAP-130 in response to CRP is also inhibited in SLP-76-deficient platelets, placing it downstream of SLP-76. This work identifies SLP-76 as an important adapter molecule that is regulated by Syk and lies upstream of SLAP-130 and PLC-gamma2 in CRP-stimulated platelets.

Anti-Helicobacter pylori agents from the cashew apple

Anacardic acids and (E)-2-hexenal characterized from the cashew Anacardium occidentale L. (Anacardiaceae) apple have been found to exhibit antibacterial activity against the Gram-negative bacterium Helicobacter pylori, which is now considered to cause acute gastritis. The same antibacterial compounds have also been found to inhibit urease (EC 3.5.1.5).

Fetal hemorrhage and platelet dysfunction in SLP-76-deficient mice

The adapter protein SLP-76 is expressed in T lymphocytes and hematopoietic cells of the myeloid lineage, and is known to be a substrate of the protein tyrosine kinases that are activated after ligation of the T-cell antigen receptor. Transient overexpression of SLP-76 in a T-cell line potentiates transcriptional activation after T-cell receptor ligation, while loss of SLP-76 expression abrogates several T-cell receptor-dependent signaling pathways. Mutant mice that lack SLP-76 manifest a severe block at an early stage of thymocyte development, implicating SLP-76 in signaling events that promote thymocyte maturation. While it is clear that SLP-76 plays a key role in development and activation of T lymphocytes, relatively little is understood regarding its role in transducing signals initiated after receptor ligation in other hematopoietic cell types. In this report, we describe fetal hemorrhage and perinatal mortality in SLP-76-deficient mice. Although megakaryocyte and platelet development proceeds normally in the absence of SLP-76, collagen-induced platelet aggregation and granule release is markedly impaired. Furthermore, treatment of SLP-76-deficient platelets with collagen fails to elicit tyrosine phosphorylation of phospholipase C-gamma2 (PLC-gamma2), suggesting that SLP-76 functions upstream of PLC-gamma2 activation. These data provide one potential mechanism for the fetal hemorrhage observed in SLP-76-deficient mice and reveal that SLP-76 expression is required for optimal receptor-mediated signal transduction in platelets as well as T lymphocytes.

Rab11 in dysplasia of Barrett's epithelia

Barrett's esophagus predisposes affected patients to the development of esophageal adenocarcinoma. The development of adenocarcinoma proceeds along a progression through low- and high-grade dysplasia. Surveillance of Barrett's patients requires serial endoscopic investigations and grading mucosal biopsies. Unfortunately, grading of biopsies by conventional hematoxylin and eosin staining is fraught with significant interobserver variations. We have found in both biopsy and resection specimens that immunostaining for the small GTP binding protein Rab11 is increased in low-grade dysplastic cells. This staining is lost in high-grade dysplastic cells. These results suggest that low-grade dysplastic cells undergo an apical trafficking blockade, which is released as cells progress to the less differentiated phenotype of high-grade dysplasia and adenocarcinoma. Examination of the SKGT-4 esophageal adenocarcinoma cell line demonstrated prominent mRNA and protein expression for Rab11. Rab11 immunostaining was present in SKGT-4 cells as a perinuclear nidus of punctate staining along with a more diffuse punctate pattern. Thus, Rab11 expression was present in a esophageal adenocarcinoma cells in culture. Markers of vesicle trafficking may be critical factors for grading of mucosal dysplastic transitions leading to adenocarcinoma.

Production of reactive oxygen intermediates following CD40 ligation correlates with c-Jun N-terminal kinase activation and IL-6 secretion in murine B lymphocytes

Recent studies indicate that reactive oxygen intermediates (ROI) serve as second messengers in cell signaling. ROI have been implicated in the activation of NF-kappaB as well as c-Jun N-terminal kinase (JNK) in response to IL-1 and TNF-alpha stimulation. In this report we examine whether intracellular ROI are involved in CD40 receptor signaling. We show that CD40 engagement on resting splenic B lymphocytes and murine B lymphoma WEHI 231 cells generates ROI. Blocking ROI production by preincubation with the antioxidant N-acetyl-L-cysteine inhibits JNK activation, NF-kappaB-driven luciferase activity, and IL-6 secretion following CD40 ligation, suggesting a role for ROI in CD40-mediated signaling events. Furthermore, transfection of WEHI 231 cells with a plasmid encoding Mn-superoxide dismutase interferes with CD40-induced NF-kappaB activation, providing further support for ROI involvement in this pathway. Collectively, these data demonstrate that ROI may serve as second messengers linking CD40 engagement on B cells to important downstream activation events.

Mutations in a gene encoding a novel protein tyrosine phosphatase cause progressive myoclonus epilepsy

Lafora's disease (LD; OMIM 254780) is an autosomal recessive form of progressive myoclonus epilepsy characterized by seizures and cumulative neurological deterioration. Onset occurs during late childhood and usually results in death within ten years of the first symptoms. With few exceptions, patients follow a homogeneous clinical course despite the existence of genetic heterogeneity. Biopsy of various tissues, including brain, revealed characteristic polyglucosan inclusions called Lafora bodies, which suggested LD might be a generalized storage disease. Using a positional cloning approach, we have identified at chromosome 6q24 a novel gene, EPM2A, that encodes a protein with consensus amino acid sequence indicative of a protein tyrosine phosphatase (PTP). mRNA transcripts representing alternatively spliced forms of EPM2A were found in every tissue examined, including brain. Six distinct DNA sequence variations in EPM2A in nine families, and one homozygous microdeletion in another family, have been found to cosegregate with LD. These mutations are predicted to cause deleterious effects in the putative protein product, named laforin, resulting in LD.

Extracellular signal-regulated kinase-2, but not c-Jun NH2-terminal kinase, activation correlates with surface IgM-mediated apoptosis in the WEHI 231 B cell line

Both extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase (JNK) have been implicated in mediating the signaling events that precede apoptosis. We studied the activation of these kinases during apoptosis of WEHI 231 B cells. Surface IgM ligation induces apoptosis of WEHI 231 cells. This effect is augmented by simultaneous engagement of CD95 and is inhibited by costimulation with either CD40 or IL-4R. We determined that surface IgM ligation activates ERK2 to a much greater level than JNK, and that IgM-mediated ERK2 activation is enhanced by costimulation with anti-CD95. Costimulation with either IL-4 or anti-CD40 interferes with anti-IgM-stimulated ERK2 activation. Transient expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) inhibits both ERK2 activation and cell death following stimulation with anti-IgM and the combination of anti-IgM plus anti-CD95. CD40 engagement alone activates JNK, but IL-4 stimulation does not. N-acetyl-L-cysteine pretreatment, which blocks CD40-mediated JNK activation, does not affect the ability of CD40 to inhibit anti-IgM-mediated ERK2 activation and apoptosis. Together, these data suggest that JNK activation is not required for CD40 inhibition of surface IgM-induced cell death and that ERK2 plays an active role in mediating anti-IgM-induced apoptosis of WEHI 231 B cells.

Molecular characterization of a common fragile site (FRA7H) on human chromosome 7 by the cloning of a simian virus 40 integration site

Common fragile sites are chromosomal loci prone to breakage and rearrangement, hypothesized to provide targets for foreign DNA integration. We cloned a simian virus 40 integration site and showed by fluorescent in situ hybridization analysis that the integration event had occurred within a common aphidicolin-induced fragile site on human chromosome 7, FRA7H. A region of 161 kb spanning FRA7H was defined and sequenced. Several regions with a potential unusual DNA structure, including high-flexibility, low-stability, and non-B-DNA-forming sequences were identified in this region. We performed a similar analysis on the published FRA3B sequence and the putative partial FRA7G, which also revealed an impressive cluster of regions with high flexibility and low stability. Thus, these unusual DNA characteristics are possibly intrinsic properties of common fragile sites that may affect their replication and condensation as well as organization, and may lead to fragility.

Genomic structure of the human congenital chloride diarrhea (CLD) gene

Congenital chloride diarrhea (CLD) is caused by mutations in a gene which encodes an intestinal anion transporter. We report here the complete genomic organization of the human CLD gene which spans approximately 39kb, and comprises 21 exons. All exon/intron boundaries conform to the GT/AG rule. An analysis of the putative promoter region sequence shows a putative TATA box and predicts multiple transcription factor binding sites. The genomic structure was determined using DNA from several sources including multiple large-insert libaries and genomic DNA from Finnish CLD patients and controls. Exon-specific primers developed in this study will facilitate mutation screening studies of patients with the disease. Genomic sequencing of a BAC clone H_RG364P16 revealed the presence of another, highly homologous gene 3' of the CLD gene, with a similar genomic structure, recently identified as the Pendred syndrome gene (PDS).

Use of leukocyte depletion to decrease injury after lung preservation and rewarming ischemia: an experimental model

BACKGROUND

Hypothermia is critical for proper lung preservation. Ideally, the lungs should be maintained at the optimal preservation temperature during the entire ischemic interval. Lung rewarming during implantation is commonly observed. This study was undertaken to investigate the severity of rewarming ischemia on preservation injury and the possibility of minimizing this by use of leukocyte depletion during initial reperfusion.

METHODS

Four experimental groups were tested as follows: neonatal piglet heart-lung blocks were either (1) placed on an isolated, blood-perfused, working heart-lung circuit without intervening ischemia (control, n = 6), (2) reperfused on the circuit with whole blood (WB, n = 6) after 13 hours of preservation, (3) reperfused with WB after 12 hours of preservation and 1 hour of rewarming (RWB, n = 5), or (4) reperfused with leukocyte-depleted blood for an initial 10 minutes followed by WB, after 12 hours of preservation and 1 hour of rewarming (n = 6). All groups were studied for 4 hours.

RESULTS

The partial pressure of arterial oxygen and lung compliance were significantly lower in the RWB group than in controls (113.8+/-33.1 vs 417.3+/-6.2 mm Hg, p < 0.01; and 0.8+/-0.2 vs 2.9+/-0.4 ml/cm H2O, p < 0.05, respectively). Pulmonary vascular resistance and lung wet/dry weight ratios were significantly higher in the RWB group than in controls (15884.1+/-11354.8 vs 6108.3+/-1309.9 dyne x sec x cm[-5], p < 0.05; and 7.13+/-0.24 vs 5.82+/-0.35, p < 0.05, respectively). The WB and leukocyte-depleted groups did not differ significantly from controls for any measured parameter.

CONCLUSIONS

This model confirms that rewarming ischemia during lung implantation exacerbates reperfusion injury. Leukocyte-depleted reperfusion as tested for a short period of time (10 minutes) ameliorates this injury and therefore should be considered for clinical lung transplantation.

Risk of recurrent seizures after two unprovoked seizures

BACKGROUND

Patients with a single unprovoked seizure have about a 35 percent risk of recurrence in the subsequent five years. We studied the risk of recurrence after two unprovoked seizures.

METHODS

We prospectively followed 204 patients with a first unprovoked seizure from the day of the initial seizure. Information was obtained from patients (and verified by a review of their medical records) about the dates and circumstances of any subsequent seizures. The risk of a second, third, and fourth seizure was estimated by the Kaplan-Meier method.

RESULTS

Of the 204 patients, 63 had a second seizure, 41 a third seizure, and 26 a fourth seizure. The mean age of the patients was 36 years, 10 percent were less than 16 years of age, 70 percent were male, 71 percent had epilepsy of unknown cause, and 66 percent had generalized seizures. The risk of a second unprovoked seizure was 33 percent. Among those with a second seizure, the risk of a third unprovoked seizure was 73 percent; among those with a third unprovoked seizure, the risk of a fourth was 76 percent. Most recurrences occurred within one year of the second or third seizure. The risk of a third seizure was higher in those with a presumed cause of epilepsy (relative risk, 1.9; 95 percent confidence interval, 1.0 to 3.4).

CONCLUSIONS

Although only about one third of patients with a first unprovoked seizure will have further seizures within five years, about three quarters of those with two or three unprovoked seizures have further seizures within four years.

Malignant rhabdoid tumor of the duodenum

A polypoid malignant rhabdoid tumor of the duodenum is presented. The pattern of metastatic spread in this 58-year-old man included multiple duodenal and small intestinal transmural tumor implants and a large peribronchial lymph node causing superior vena cava syndrome. Microscopically, the tumor was composed of a diffuse population of rhabdoid cells characterized by homogeneous globular cytoplasmic inclusions that tended to indent or displace eccentric, vesicular nuclei with nucleoli. No glandular features were noted. Immunohistochemical and ultrastructural evaluation revealed that these inclusions contained vimentin, an intermediate filament of the mesenchymal cytoskeleton. Phenotypic features of a rhabdoid tumor have been reported in 10 poorly differentiated malignancies of the gastrointestinal tract. This is the first case report of a malignant rhabdoid tumor of the small intestine. Regardless of the site of the lesion, tumors showing these features are generally associated with a poor prognosis.

Gastrointestinal pathology in sickle cell disease

The literature was reviewed to investigate the existence of unique gastrointestinal (GI) pathological lesions in sickle-cell disease (SCD). Chole- and choledocholithiasis have long been recognized, but bilirubin gallstones can occur in any chronic hemolytic anemia. Acute pancreatitis has been reported as a possible ischemic consequence of sickling. It is unclear if the hepatic lesions of SCD differ from those of any chronically transfused population. Hepatic failure has been associated with massive sickling and hyperviscous bile ("sludge") has been linked to SCD. Elevated 5'-nucleotidase in the presence of elevated aminotransferase may suggest both hepatic and biliary tree involvement in a subgroup of patients with SCD. Low levels of the hepatically produced coagulation inhibitors, Protein S and Protein C, have been identified in SCD, but their precise relation to thrombosis in this instance remains unclear. Finally, a syndrome of intracanalicular cholestasis, sinusoidal dilation. Kupffer cell hyperplasia, and erythrophagocytosis has been linked to SCD. It has been suggested that the use of exchange transfusion prior to liver biopsy in this group of pediatric SCD patients may mask the pathophysiological role of sickled red blood cells in hepatic dysfunction. With the exception of some of the situations cited, it is concluded that most GI lesions in SCD are common to a heavily transfused population with chronic hemolytic anemia.

Stabilization of Liquid Crystal-in-Water Dispersion with Polymer/Surfactant Mixture: Nematic Curvilinear Aligned Phase Composite Film

The effect of nonionic surfactant (H(OCH2-CH2)8-OC6H4-C9H19) on the stability of liquid crystal-in-water dispersions stabilized by copolymers of acrylamide with hydrophobic monomers have been studied. It was observed that the addition of surfactant increases the stability of liquid crystal (LC) dispersion and improves the electrooptical properties of the nematic curvilinear aligned phase (NCAP) system. According to the interfacial tension measurements, it was proposed that the presence of surfactant allows to form the nonpolar microenvironment in the round of LC droplet and finally reduces the anchoring effect between LC and the polymeric wall. Copyright 1998 Academic Press. Copyright 1998Academic Press

Increased immunoreactivity for Rab11, a small GTP-binding protein, in low-grade dysplastic Barrett's epithelia

Adenocarcinoma of the esophagus develops from metaplastic Barrett's columnar epithelia through the evolution of dysplastic epithelial intermediates. Although the role of dysplasia leading to adenocarcinoma is well established, far less is known regarding the cellular changes involved in this process. Because the development of dysplasia is characterized by the loss of apical secretory specializations, we hypothesized that changes in apical trafficking might be involved in the dysplastic process. We have sought to evaluate the expression of an important candidate regulator of apical trafficking, the small GTP-binding protein, Rab11, in resection and biopsy tissue from patients with Barrett's esophagus. Sections from esophageal resection specimens from 4 patients and endoscopic biopsies from 60 patients were stained with antibodies against Rab11 and Rab25 as well as protein markers of the Golgi apparatus and p53 protein. Rab11 staining in low-grade dysplastic regions was similar to that observed with monoclonal antibodies against Rab25 and gamma-adaptin and colocalized with staining for the Golgi marker, the mannose-6-phosphate receptor. In the esophageal adenocarcinoma resections, prominent Rab11 immunostaining was observed in the supranuclear region of low-grade dysplastic cells. In contrast, regions of high-grade dysplasia demonstrating strong nuclear p53 staining showed only diffuse or absent Rab11 staining. In endoscopic biopsies, 91% of biopsies that were read unanimously as low-grade dysplasia demonstrated supranuclear Rab11 staining. Fourteen percent of biopsies unanimously graded as being without dysplasia demonstrated perinuclear Rab11 staining. No p53 immunostaining was observed in any of the low-grade dysplasia biopsy specimens. An increase in Rab11 immunoreactivity seems to correlate with low-grade dysplasia, whereas p53 immunostaining correlates with high-grade dysplasia. The colocalization of Rab11 staining with increased immunoreactivity for markers of the trans-Golgi system is consistent with a defect in apical trafficking due to an expansion of either the trans-Golgi compartment or the apical recycling vesicle system.

Resources for human genetics on the World Wide Web

A little over a century ago, the HMS Beagle sailed the Pacific Ocean bringing Charles Darwin to the perfect environment in which to piece together his observations forming the theory of evolution. Now, geneticists and laypeople alike surf the equally formidable waters of the internet in search of enlightenment. Here, we attempt to help you navigate towards resources for human genetics by providing maps to three destinations: The Human Genome Project (Box 1), education (Box 2), and human genetic diseases (Box 3). For each, we highlight a few sites that we consider are the most informative and original. A more extensive list containing other useful sites has been compiled and posted on a 'jump site' at: http:/(/)www.cgdn.generes.ca/.