Silberblick/Wnt11 mediates convergent extension movements during zebrafish gastrulation

Vertebrate gastrulation involves the specification and coordinated movement of large populations of cells that give rise to the ectodermal, mesodermal and endodermal germ layers. Although many of the genes involved in the specification of cell identity during this process have been identified, little is known of the genes that coordinate cell movement. Here we show that the zebrafish silberblick (slb) locus encodes Wnt11 and that Slb/Wnt11 activity is required for cells to undergo correct convergent extension movements during gastrulation. In the absence of Slb/Wnt11 function, abnormal extension of axial tissue results in cyclopia and other midline defects in the head. The requirement for Slb/Wnt11 is cell non-autonomous, and our results indicate that the correct extension of axial tissue is at least partly dependent on medio-lateral cell intercalation in paraxial tissue. We also show that the slb phenotype is rescued by a truncated form of Dishevelled that does not signal through the canonical Wnt pathway, suggesting that, as in flies, Wnt signalling might mediate morphogenetic events through a divergent signal transduction cascade. Our results provide genetic and experimental evidence that Wnt activity in lateral tissues has a crucial role in driving the convergent extension movements underlying vertebrate gastrulation.

Helicobacter pylori infection induces gastric cancer in mongolian gerbils

BACKGROUND & AIMS

Although epidemiological studies have indicated that Helicobacter pylori infection plays a crucial role in gastric carcinogenesis in humans, there is no direct proof that H. pylori is actually associated with gastric carcinogenesis. The purpose of this study was to elucidate the relationship between H. pylori infection and gastric carcinogenesis using an animal model of long-term H. pylori infection.

METHODS

Mongolian gerbils were orally inoculated with H. pylori, and the sequential morphological changes in the stomach were examined for up to 62 weeks.

RESULTS

H. pylori was constantly detected in all infected animals throughout the study. At the 26th week, severe active chronic gastritis, ulcers, and intestinal metaplasia could be observed in infected animals. By the end of the study, adenocarcinoma had developed in the pyloric region of 37% of the infected animals. All tumors consisted of well-differentiated intestinal-type epithelium, and their development seemed to be closely related to intestinal metaplasia.

CONCLUSIONS

We have successfully demonstrated that long-term infection with H. pylori induces adenocarcinoma in Mongolian gerbils. The observations are thus highly suggestive of the involvement of H. pylori infection in gastric carcinogenesis in humans.

Nuclear reprogramming of somatic cells by in vitro hybridization with ES cells

The resetting of a somatic epigenotype to a totipotential state has been demonstrated by successful animal cloning, via transplantation of somatic nuclei into enucleated oocytes. We have established an experimental system, which reproduces the nuclear reprogramming of somatic cells in vitro by fusing adult thymocytes with embryonic stem (ES) cells. Analysis of the lymphoid-cell-specific V-(D)-J DNA rearrangement of the T cell receptor and immunoglobin genes shows that the ES cells have hybridized with differentiated cells. In these ES cell hybrids, the inactivated X chromosome derived from a female thymocyte adopts some characteristics of an active X chromosome, including early replication timing and unstable Xist transcription. We also found that an Oct4-GFP transgene, which is normally repressed in thymocytes, is reactivated 48 hr after cell fusion. The pluripotency of the ES-thymocyte hybrid cells is shown in vivo, since they contribute to all three primary germ layers of chimeric embryos. The somatic DNA methylation pattern of the imprinted H19 and Igf2r genes is maintained in these hybrids, unlike hybrids between ES and EG (embryonic germ) cells in which the differential methylation is erased. Thus, ES cells have the capacity to reset certain aspects of the epigenotype of somatic cells to those of ES cells.

Xwnt11 is a target of Xenopus Brachyury: regulation of gastrulation movements via Dishevelled, but not through the canonical Wnt pathway

Gastrulation in the amphibian embryo is driven by cells of the mesoderm. One of the genes that confers mesodermal identity in Xenopus is Brachyury (Xbra), which is required for normal gastrulation movements and ultimately for posterior mesoderm and notochord differentiation in the development of all vertebrates. Xbra is a transcription activator, and interference with transcription activation leads to an inhibition of morphogenetic movements during gastrulation. To understand this process, we have screened for downstream target genes of Brachyury (Tada, M., Casey, E., Fairclough, L. and Smith, J. C. (1998) Development 125, 3997–4006). This approach has now allowed us to isolate Xwnt11, whose expression pattern is almost identical to that of Xbra at gastrula and early neurula stages. Activation of Xwnt11 is induced in an immediate-early fashion by Xbra and its expression in vivo is abolished by a dominant-interfering form of Xbra, Xbra-En(R). Overexpression of a dominant-negative form of Xwnt11, like overexpression of Xbra-En(R), inhibits convergent extension movements. This inhibition can be rescued by Dsh, a component of the Wnt signalling pathway and also by a truncated form of Dsh which cannot signal through the canonical Wnt pathway involving GSK-3 and (beta)-catenin. Together, our results suggest that the regulation of morphogenetic movements by Xwnt11 occurs through a pathway similar to that involved in planar polarity signalling in Drosophila.

A prospective randomised study of "covered" versus "uncovered" diamond stents for the management of distal malignant biliary obstruction

BACKGROUND AND AIM

Covered self-expandable metal stents (EMS) were recently developed to overcome tumour ingrowth in conventional EMS. However, supporting evidence for the efficacy of covered EMS is lacking.

PATIENTS AND METHODS

We enrolled 112 patients with unresectable distal biliary malignancies. They were randomly assigned to polyurethane covered (n = 57) or original diamond stent (n = 55).

RESULTS

Stent occlusion occurred in eight patients (14%) after a mean of 304 days in the covered group, and in 21 patients (38%) after a mean of 166 days in the uncovered group. The incidence of covered EMS occlusion was significantly lower than that of uncovered EMS (p = 0.0032). The cumulative stent patency of covered stents was significantly higher than that of uncovered stents (p = 0.0066). No tumour ingrowth occurred in the covered group while it was observed in 15 patients in the uncovered group. In subgroup analysis, the cumulative patency of the covered EMS was significantly higher in pancreatic cancer (p = 0.0363) and metastatic lymph nodes (p = 0.0354). There was no significant difference in survival between the two groups. Acute cholecystitis was observed in two of the covered group and in none of the uncovered group. Mild pancreatitis occurred in five of the covered group and in one of the uncovered group.

CONCLUSIONS

Covered diamond stents successfully prevented tumour ingrowth and were significantly superior to uncovered stents for the treatment of patients with distal malignant biliary obstruction. However, careful attention must be paid to complications specific to covered self-expandable metal stents, such as acute cholecystitis and pancreatitis.

Delayed effects of sublethal ischemia on the acquisition of tolerance to ischemia

The infarct-limiting effect of ischemic preconditioning is believed to be a transient phenomenon. We examined the delayed effects of repetitive brief ischemia on limiting infarct size in an open-chest dog model by an occlusion (90 minutes) of the left anterior descending coronary artery (LAD) followed by reperfusion (5 hours). The dogs were preconditioned with four brief repeated ischemic episodes induced by 5-minute LAD occlusions with subsequent reperfusion. The size of infarcts initiated by a sustained occlusion immediately or 24 hours after preconditioning was significantly smaller when compared with infarcts in sham-operated dogs (for the immediate occlusion, 14.4 +/- 2.0% versus 39.0 +/- 3.7%, respectively [p < 0.01]; and for the delayed occlusion, 18.8 +/- 3.4% versus 35.1 +/- 4.6%, respectively [p < 0.05]); however, when the infarction was induced 3 hours (31.2 +/- 3.7% versus 37.5 +/- 4.2%, respectively) or 12 hours (25.4 +/- 4.8% versus 35.0 +/- 5.3%, respectively) after repetitive ischemia, the infarct size did not differ. No differences were seen in regional myocardial blood flow or rate-pressure products between the two groups. These results indicate that an infarct-limiting effect of brief repeated ischemia can be observed 24 hours after sublethal preconditioning.

Direct association of the gap junction protein connexin-43 with ZO-1 in cardiac myocytes

The gap junction protein connexin-43 is normally located at the intercalated discs of cardiac myocytes, and it plays a critical role in the synchronization of their contraction. The mechanism by which connexin-43 is localized within cardiac myocytes is unknown. However, localization of connexin-43 likely involves an interaction with the cytoskeleton; immunofluorescence microscopy showed that in cardiac myocytes, connexin-43 specifically colocalizes with the cytoskeletal proteins ZO-1 and alpha-spectrin. In transfected HEK293 cells, immunoprecipitation experiments using coexpressed epitope-tagged connexin-43 and ZO-1 indicated that ZO-1 links connexin-43 with alpha-spectrin. The domains responsible for the protein-protein interaction between connexin-43 and ZO-1 were identified using affinity binding assays with deleted ZO-1 and connexin-43 fusion proteins. Immunoblot analysis of associated proteins showed that the C-terminal domain of connexin-43 binds to the N-terminal domain of ZO-1. The role of this linkage in gap junction formation was examined by a dominant-negative assay using the N-terminal domain of ZO-1. Overexpression of the N-terminal domain of ZO-1 in connexin-43-expressing cells resulted in redistribution of connexin-43 from cell-cell interfaces to cytoplasmic structures; this intracellular redistribution of connexin-43 coincided with a loss of electrical coupling. We therefore conclude that the linkage between connexin-43 and alpha-spectrin, via ZO-1, may serve to localize connexin-43 at the intercalated discs, thereby generating functional gap junctions in cardiac myocytes.

Pretreatment of plastic Petri dishes with fetal calf serum. A simple method for macrophage isolation

We have developed a simple method which can recover the highly purified macrophages or monocytes in suspension from mouse peritoneal exudate cells and human perpheral blood mononuclear cells. Plastic Petri dishes coated overnight with heat-inactivated fetal calf serum (FCS) selectively bind macrophages and monocytes. The adherent macrophages and monocytes are easily removed by incubation in phosphate-buffered saline containing 0.2% ethylenediamine tetraacetate (EDTA) and 5% FCS, and recovered as a cell suspension with greater than 95% purity. A small number of isolated cells can restore the mitogenic response to phytohemagglutinin (PHA-P) of macrophages-depleted lymphocytes and can lyse 51Cr-labeled target cells in an antibody-dependent cell-mediated cytotoxicity system. Thus, the method should be valuable for studies of various functions of macrophages and monocytes from different immune tissues of man and animals.

Embryonic germ cells induce epigenetic reprogramming of somatic nucleus in hybrid cells

Genomic reprogramming of primordial germ cells (PGCs), which includes genome-wide demethylation, prevents aberrant epigenetic modifications from being transmitted to subsequent generations. This process also ensures that homologous chromosomes first acquire an identical epigenetic status before an appropriate switch in the imprintable loci in the female and male germ lines. Embryonic germ (EG) cells have a similar epigenotype to PGCs from which they are derived. We used EG cells to investigate the mechanism of epigenetic modifications in the germ line by analysing the effects on a somatic nucleus in the EG-thymic lymphocyte hybrid cells. There were striking changes in methylation of the somatic nucleus, resulting in demethylation of several imprinted and non-imprinted genes. These epigenetic modifications were heritable and affected gene expression as judged by re-activation of the silent maternal allele of Peg1/Mest imprinted gene in the somatic nucleus. This remarkable change in the epigenotype of the somatic nucleus is consistent with the observed pluripotency of the EG-somatic hybrid cells as they differentiated into a variety of tissues in chimeric embryos. The epigenetic modifications observed in EG-somatic cell hybrids in vitro are comparable to the reprogramming events that occur during germ cell development.

Nature and site of phospholamban regulation of the Ca2+ pump of sarcoplasmic reticulum

The rapid removal of Ca2+ ions from the cytosol, necessary for the efficient relaxation of cardiac muscle cells, is performed by the Ca2+-pumping ATPase of the sarcoplasmic reticulum. The calcium pump is activated by cyclic AMP- and calmodulin-dependent phosphorylation of phospholamban, an integral membrane protein of the sarcoplasmic reticulum. Using a heterobifunctional crosslinking agent which can be cleaved and photoactivated, we provide evidence for a direct interaction between the two proteins. Only the non-phosphorylated form of phospholamban interacts with the ATPase, demonstrating that phospholamban is an endogenous inhibitor that is removed from the ATPase by phosphorylation. Non-phosphorylated phospholamban interacts only with the calcium-free conformation of the ATPase and is released when it is converted to the calcium-bound state. We localized the site of interaction to a single peptide isolated after cyanogen bromide cleavage of the ATPase. The peptide derives from a domain just C-terminal to the aspartyl phosphate of the active site. This domain is unique to ATPases of the sarcoplasmic reticulum in that it has no homology with any other phosphorylation-type ion pump. The domain occurs in both slow- and fast-twitch isoforms of the ATPase, even though phospholamban is not expressed in fast-twitch muscles.

Inactivation of glutathione peroxidase by nitric oxide. Implication for cytotoxicity

S-nitro-N-acetyl-DL-penicillamine (SNAP), a nitric oxide (NO) donor, inactivated bovine glutathione peroxidase (GPx) in a dose- and time-dependent manner. The IC50 of SNAP for GPx was 2 microM at 1 h of incubation and was 20% of the IC50 for another thiol enzyme, glyceraldehyde-3-phosphate dehydrogenase, in which a specific cysteine residue is known to be nitrosylated. Incubation of the inactivated GPx with 5 mM dithiothreitol within 1 h restored about 50% of activity of the start of the SNAP incubation. A longer exposure to NO donors, however, irreversibly inactivated the enzyme. The similarity of the inactivation with SNAP and reactivation with dithiothreitol of GPx to that of glyceraldehyde-3-phosphate dehydrogenase, suggested that NO released from SNAP modified a cysteine-like essential residue on GPx. When U937 cells were incubated with 100 microM SNAP for 1 h, a significant decrease in GPx activity was observed although the change was less dramatic than that with the purified enzyme, and intracellular peroxide levels increased as judged by flow cytometric analysis using a peroxide-sensitive dye. Other major antioxidative enzymes, copper/zinc superoxide dismutase, manganese superoxide dismutase, and catalase, were not affected by SNAP, which suggested that the increased accumulation of peroxides in SNAP-treated cells was due to inhibition of GPx activity by NO. Moreover, stimulation with lipopolysaccharide significantly decreased intracellular GPx activity in RAW 264.7 cells, and this effect was blocked by NO synthase inhibitor N omega-methyl-L-arginine. This indicated that GPx was also inactivated by endogenous NO. This mechanism may at least in part explain the cytotoxic effects of NO on cells and NO-induced apoptotic cell death.

Virulence factors of Helicobacter pylori responsible for gastric diseases in Mongolian gerbil

Helicobacter pylori infection induces various gastroduodenal diseases. We examined the role of two genes, vacA and cagE, in the gastric pathogenesis induced by H. pylori using a long-term (62 wk) animal model. Reportedly, both genes are associated with the virulence of H. pylori: vacA encodes vacuolating cytotoxin, and cagE, with other genes in the cag pathogenicity islands, encodes a type IV secretion system. Mongolian gerbils were challenged in this study by a wild-type TN2 strain and its isogenic mutants of cagE or vacA. The wild-type and vacA mutants induced severe gastritis, whereas cagE mutants induced far milder changes. Gastric ulcer was induced at the highest rate (22/23) by the wild-type TN2, followed by the vacA mutant (19/28). No ulcer was found in the gerbils infected with the cagE mutant (0/27) or in controls (0/27). Intestinal metaplasia was also found in the gerbils infected with the wild-type (14/23) or vacA mutant (15/28). Gastric cancer developed in one gerbil with wild-type infection and in one with vacA mutant infection. In conclusion, the knocking out of the cagE gene deprived wild-type H. pylori of the pathogenicity for gastritis and gastric ulcer, suggesting that the secretion system encoded by cag pathogenicity island genes plays an essential role.

Phospholamban inhibitory function is activated by depolymerization

Phospholamban (PLN), a homopentameric, integral membrane protein, reversibly inhibits cardiac sarcoplasmic reticulum Ca2+-ATPase (SERCA2a) activity through intramembrane interactions. Here, alanine-scanning mutagenesis of the PLN transmembrane sequence was used to identify two functional domains on opposite faces of the transmembrane helix. Mutations in one face diminish inhibitory interactions with transmembrane sequences of SERCA2a, but have relatively little effect on the pentameric state, while mutations in the other face activate inhibitory interactions and enhance monomer formation. Double mutants are monomeric, but loss of inhibitory function is dominant over activation of inhibitory function. These observations support the proposal that the SERCA2a interaction site lies on the helical face which is not involved in pentamer formation. Four highly inhibitory mutants are effectively devoid of pentamer, suggesting that pentameric PLN represents a less active or inactive reservoir that dissociates to provide inhibitory monomeric PLN subunits. A model is presented in which the degree of PLN inhibition of SERCA2a activity is ultimately determined by the concentration of the inhibited PLN monomer.SERCA2a heterodimeric complex. The concentration of this inhibited complex is determined by the dissociation constant for the PLN pentamer (which is mutation-sensitive) and by the dissociation constant for the PLN/SERCA2a heterodimer (which is likely to be mutation-sensitive).

Regulation of myocardial Ca2+-ATPase and phospholamban mRNA expression in response to pressure overload and thyroid hormone

The sarcoplasmic reticulum (SR) and the contractile protein myosin play an important role in myocardial performance. Both of these systems exhibit plasticity--i.e., quantitative and/or qualitative reorganization during development and in response to stress. Recent studies indicate that SR Ca2+ uptake function is altered in adaptive cardiac hypertrophy and failure. The molecular basis (genetic and phenotypic) for these changes is not understood. In an effort to determine the underlying causes of these changes, we characterized the rabbit cardiac Ca2+-ATPase phenotype by molecular cloning and ribonuclease A mapping analysis. Our results show that the heart muscle expresses only the slow-twitch SR Ca2+-ATPase isoform. Second, we quantitated the steady-state mRNA levels of two major SR Ca2+ regulatory proteins, the Ca2+-ATPase and phospholamban, to see whether changes in mRNA content might provide insight into the basis for functional modification in the SR of hypertrophied hearts. In response to pressure overload hypertrophy, the relative level of the slow-twitch/cardiac SR Ca2+-ATPase mRNA was decreased to 34% of control at 1 week. The relative Ca2+-ATPase mRNA level increased to 167% of control after 3 days of treatment with thyroid hormone. In contrast, in hypothyroid animals, the relative Ca2+-ATPase mRNA level decreased to 51% of control at 2 weeks. The relative level of phospholamban mRNA was decreased to 36% in 1-week pressure overload. Hyperthyroidism induced a decrease to 61% in the phospholamban mRNA level after 3 days of treatment, while hypothyroidism had virtually no effect on phospholamban mRNA levels. These data indicate that the expression of SR Ca2+-ATPase and phospholamban mRNA may not be coordinately regulated during myocardial adaptation to different physiological conditions.

Analysis of K-ras gene mutation in hyperplastic duct cells of the pancreas without pancreatic disease

BACKGROUND & AIMS

We and others have previously shown that the mutation of K-ras codon 12 was found in the majority of pancreatic adenocarcinomas. The mutation has also been identified in the pancreatic duct with mucous cell hyperplasia in association with chronic pancreatitis. Ductal hyperplasia is also frequently found in the pancreas free from pancreatic carcinoma or chronic pancreatitis. The aim of this study was to assess the incidence and types of mutations in hyperplastic foci in these cases.

METHODS

The nucleotide sequence of the K-ras gene at codon 12 of the DNA extracted from microdissected hyperplastic epithelium of the pancreatic duct obtained at autopsy in patients without pancreatic adenocarcinoma or chronic pancreatitis was analyzed.

RESULTS

Of 38 patients with 79 hyperplastic foci, 12 patients (with 19 hyperplastic foci) had mutations. None of the 16 normal ducts in 12 specimens had this mutation. The nucleotide sequence of the codon in 53% of ductal hyperplastic foci was TGT or AGT, both of which were not found in 30 cases of adenocarcinoma.

CONCLUSIONS

These results suggest that the ras gene mutation occurs frequently in multifocal hyperplastic foci of pancreatic duct and that the mutations may not have direct relevance to the carcinogenesis of pancreatic cancer.

Peg3 imprinted gene on proximal chromosome 7 encodes for a zinc finger protein

Genetic and embryological studies in the mouse demonstrated functional differences between parental chromosomes during development. This is due to imprinted genes whose expression is dependent on their parental origin. In a recent systematic screen for imprinted genes, we detected Peg3 (paternally expressed gene 3). Peg3 is not expressed in parthenogenones. In interspecific hybrids, only the paternal copy of the gene is expressed in the embryos, individual tissues examined in d9.5-13.5 embryos, neonates and adults. Peg3 mRNA is a 9 kb transcript encoding an unusual zinc finger protein with eleven widely spaced C2H2 type motifs and two groups of amino acid repeats. Peg3 is expressed in early somites, branchial arches and other mesodermal tissues, as well as in the hypothalamus. Peg3 maps to the proximal region of chromosome 7. Consistent with our findings, maternal duplication of the proximal chromosome 7 causes neonatal lethality. This region is syntenic with human chromosome 19q13.1-13.3 (refs 10,11), where the genes for myotonic dystrophy and a putative tumour suppressor gene are located.

Conservation of BMP signaling in zebrafish mesoderm patterning

To investigate the conservation of mechanisms for mesodermal patterning between zebrafish and Xenopus, we isolated two cDNA clones encoding bone morphogenetic protein (BMP)-related proteins from a zebrafish cDNA library. Based on their predicted amino acid sequences, these two clones were designated as zbmp-2 and zbmp-4. Whole-mount in situ hybridization analysis revealed that in gastrula embryo, both genes were localized in the ventral part of the embryo, consistent with the proposed function of Xenopus BMP-4 in ventral mesoderm specification. zbmp-4 expression, however, was also seen in the embryonic shield, the most dorsal mesodermal structure. To examine the ability of zbmp-2 to ventralize mesoderm, we injected synthetic mRNA into zebrafish embryos and found that overexpression of this gene eliminated dorsal structures including notochord at both morphological and molecular level. In contrast, expression of ventral marker gene eve1 was expanded to the dorsal side. These effects are analogous to the ventralization of embryos caused by ectopic xBMP-4 expression. Taken together, one may conclude that the developmental mechanisms for mesodermal patterning regulated by BMPs are evolutionarily conserved between amphibians and teleosts.

Complete complementary DNA-derived amino acid sequence of canine cardiac phospholamban

Complementary DNA (cDNA) clones specific for phospholamban of sarcoplasmic reticulum membranes have been isolated from a canine cardiac cDNA library. The amino acid sequence deduced from the cDNA sequence indicates that phospholamban consists of 52 amino acid residues and lacks an amino-terminal signal sequence. The protein has an inferred mol wt 6,080 that is in agreement with its apparent monomeric mol wt 6,000, estimated previously by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Phospholamban contains two distinct domains, a hydrophilic region at the amino terminus (domain I) and a hydrophobic region at the carboxy terminus (domain II). We propose that domain I is localized at the cytoplasmic surface and offers phosphorylatable sites whereas domain II is anchored into the sarcoplasmic reticulum membrane.

Linkage of familial moyamoya disease (spontaneous occlusion of the circle of Willis) to chromosome 17q25

BACKGROUND AND PURPOSE

Moyamoya disease is a cerebrovascular disease of unknown cause that mainly affects Japanese children. The incidence of familial occurrence accounts for 9% of cases. The characteristic lesions of moyamoya disease are occasionally seen in neurofibromatosis type 1, of which the causative gene (NF1) has been assigned to chromosome 17q11.2.

METHODS

To determine whether a gene related to moyamoya disease is located on chromosome 17, we conducted microsatellite linkage analyses on 24 families containing 56 patients with moyamoya disease. Leukocyte DNA extracted from the family members was subjected to polymerase chain reaction for a total of 22 microsatellite markers on chromosome 17. The amplified polymerase chain reaction fragments were analyzed with GeneScan on an automated sequencer.

RESULTS

Two-point linkage analysis gave a maximum log(10) odds (LOD) score of 3.11 at the recombination fraction of 0.00 for the marker at locus D17S939. The affected pedigree member method also showed a significantly low P value (<1. 0x10(-5)) for the 5 adjacent markers at 17q25. Multipoint linkage analysis also indicated that the disease gene is contained within the 9-cM region of D17S785 to D17S836, with a maximum LOD score of 4. 58.

CONCLUSIONS

A gene for familial moyamoya disease is located on chromosome 17q25.