The homeobox gene Pitx2: mediator of asymmetric left-right signaling in vertebrate heart and gut looping.
Left-right asymmetry in vertebrates is controlled by activities emanating from the left lateral plate. How these signals get transmitted to the forming organs is not known. A candidate mediator in mouse, frog and zebrafish embryos is the homeobox gene Pitx2. It is asymmetrically expressed in the left lateral plate mesoderm, tubular heart and early gut tube. Localized Pitx2 expression continues when these organs undergo asymmetric looping morphogenesis. Ectopic expression of Xnr1 in the right lateral plate induces Pitx2 transcription in Xenopus. Misexpression of Pitx2 affects situs and morphology of organs. These experiments suggest a role for Pitx2 in promoting looping of the linear heart and gut. (+info)
Diverse developing mouse lineages exhibit high-level c-Myb expression in immature cells and loss of expression upon differentiation.
The c-myb gene encodes a sequence specific transactivator that is required for fetal hematopoiesis, but its potential role in other tissues is less clear because of the early fetal demise of mice with targeted deletions of the c-myb gene and incomplete of knowledge about c-myb's expression pattern. In the hematopoietic system, c-Myb protein acts on target genes whose expression is restricted to individual lineages, despite Myb's presence and role in multiple immature lineages. This suggests that c-Myb actions within different cell type-specific contexts are strongly affected by combinatorial interactions. To consider the possibility of similar c-Myb actions could extend into non-hematopoietic systems in other cell and tissue compartments, we characterized c-myb expression in developing and adult mice using in situ hybridization and correlated this with stage-specific differentiation and mitotic activity. Diverse tissues exhibited strong c-myb expression during development, notably tooth buds, the thyroid primordium, developing trachea and proximal branching airway epithelium, hair follicles, hematopoietic cells, and gastrointestinal crypt epithelial cells. The latter three of these all maintained high expression into adulthood, but with characteristic restriction to immature cell lineages prior to their terminal differentiation. In all sites, during fetal and adult stages, loss of c-Myb expression correlated strikingly with the initiation of terminal differentiation, but not the loss of mitotic activity. Based on these data, we hypothesize that c-Myb's function during cellular differentiation is both an activator of immature gene expression and a suppressor of terminal differentiation in diverse lineages. (+info)
Dihydropyrimidine dehydrogenase deficiency and fluorouracil-related toxicity.
Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme of 5-fluorouracil (5-FU) catabolism. We report lymphocytic DPD data concerning a group of 53 patients (23 men, 30 women, mean age 58, range 36-73), treated by 5-FU-based chemotherapy in different French institutions and who developed unanticipated 5-FU-related toxicity. Lymphocyte samples (standard collection procedure) were sent to us for DPD determination (biochemical method). Among the whole group of 53 patients, 19 had a significant DPD deficiency (DD; below 150 fmol min(-1) mg(-1) protein, i.e. less than 70% of the mean value observed from previous population study). There was a greater majority of women in the DD group (15 out of 19, 79%) compared with the remaining 34 patients (15 out of 34, 44%, P<0.014). Toxicity was often severe, leading to patient death in two cases (both women). The toxicity score (sum of WHO grading, theoretical range 0-20) was twice as high in patients with marked DD (below 100 pmol min(-1) mg(-1) protein, n = 11, mean score = 13.2) compared with patients with moderate DD (between 150 and 100 pmol min(-1) mg(-1) protein, n = 8, mean score = 6.8), P = 0.008. In the DD group, there was a high frequency of neurotoxic syndromes (7 out of 19, 37%). The two deceased patients both had severe neurotoxicity. The occurrence of cardiac toxicity was relatively rare (1 out of 19, 5%). These data suggest that women are particularly prone to DPD deficiency and allow a more precise definition of the DD toxicity profile. (+info)
The crayfish plasma clotting protein: a vitellogenin-related protein responsible for clot formation in crustacean blood.
Coagulation in crayfish blood is based on the transglutaminase-mediated crosslinking of a specific plasma clotting protein. Here we report the cloning of the subunit of this clotting protein from a crayfish hepatopancreas cDNA library. The ORF encodes a protein of 1,721 amino acids, including a signal peptide of 15 amino acids. Sequence analysis reveals that the clotting protein is homologous to vitellogenins, which are proteins found in vitellogenic females of egg-laying animals. The clotting protein and vitellogenins are all lipoproteins and share a limited sequence similarity to certain other lipoproteins (e.g., mammalian apolipoprotein B and microsomal triglyceride transfer protein) and contain a stretch with similarity to the D domain of mammalian von Willebrand factor. The crayfish clotting protein is present in both sexes, unlike the female-specific vitellogenins. Electron microscopy was used to visualize individual clotting protein molecules and to study the transglutaminase-mediated clotting reaction. In the presence of an endogenous transglutaminase, the purified clotting protein molecules rapidly assemble into long, flexible chains that occasionally branch. (+info)
Efficacy of recombinant human Hb by 31P-NMR during isovolemic total exchange transfusion.
The ability of recombinant human Hb (rHb1.1), which is being developed as an oxygen therapeutic, to support metabolism was measured by in vivo 31P-NMR surface coil spectroscopy of the rat abdomen in control animals and in animals subjected to isovolemic exchange transfusion to hematocrit of <3% with human serum albumin or 5 g/dl rHb1.1. No significant changes in metabolite levels were observed in control animals for up to 6 h. The albumin-exchange experiments, however, resulted in a more than eightfold increase in Pi and a 50% drop in phosphocreatine and ATP within 40 min. The tissue pH dropped from 7.4 to 6.8. The decrease in high-energy phosphates obeyed Michaelis-Menten kinetics, with a Michaelis-Menten constant of 3% as the hematocrit at which a 50% drop in high-energy phosphates was observed. Exchange transfusion with rHb1.1 resulted in no significant drop in high-energy phosphates, no rise in Pi, and no change in tissue pH from 7.35 +/- 0.15 for up to 5 h after exchange. By these criteria, rHb1.1 at a plasma Hb concentration of approximately 5 g/dl after total exchange transfusion was able to sustain energy metabolism of gut tissue at levels indistinguishable from control rats with a threefold higher total Hb level in erythrocytes. (+info)
Expression and localization of aquaporins in rat gastrointestinal tract.
A family of water-selective channels, aquaporins (AQP), has been demonstrated in various organs and tissues. However, the localization and expression of the AQP family members in the gastrointestinal tract have not been entirely elucidated. This study aimed to demonstrate the expression and distribution of several types of the AQP family and to speculate on their role in water transport in the rat gastrointestinal tract. By RNase protection assay, expression of AQP1-5 and AQP8 was examined in various portions through the gastrointestinal tract. AQP1 and AQP3 mRNAs were diffusely expressed from esophagus to colon, and their expression was relatively intense in the small intestine and colon. In contrast, AQP4 mRNA was selectively expressed in the stomach and small intestine and AQP8 mRNA in the jejunum and colon. Immunohistochemistry and in situ hybridization demonstrated cellular localization of these AQP in these portions. AQP1 was localized on endothelial cells of lymphatic vessels in the submucosa and lamina propria throughout the gastrointestinal tract. AQP3 was detected on the circumferential plasma membranes of stratified squamous epithelial cells in the esophagus and basolateral membranes of cardiac gland epithelia in the lower stomach and of surface columnar epithelia in the colon. However, AQP3 was not apparently detected in the small intestine. AQP4 was present on the basolateral membrane of the parietal cells in the lower stomach and selectively in the basolateral membranes of deep intestinal gland cells in the small intestine. AQP8 mRNA expression was demonstrated in the absorptive columnar epithelial cells of the jejunum and colon by in situ hybridization. These findings may indicate that water crosses the epithelial layer through these water channels, suggesting a possible role of the transcellular route for water intake or outlet in the gastrointestinal tract. (+info)
Tissue tropism related to vector competence of Frankliniella occidentalis for tomato spotted wilt tospovirus.
The development of tomato spotted wilt tospovirus (TSWV) infection in the midgut and salivary glands of transmitting and non-transmitting thrips, Frankliniella occidentalis, was studied to elucidate tissue tropism and the virus pathway within the body of this vector. Immunohistological techniques used in this study showed that the midgut, foregut and salivary glands were the only organs in which virus accumulated. The first signals of infection, observed as randomly distributed fluorescent granular spots, were found in the epithelial cells of the midgut, mainly restricted to the anterior region. The virus subsequently spread to the circular and longitudinal midgut muscle tissues, a process which occurred late in the larval stage. In the adult stage, the infection occurred in the visceral muscle tissues, covering the whole midgut and foregut, and was abolished in the midgut epithelium. The infection of the salivary glands was first observed 72 h post-acquisition, and simultaneously in the ligaments connecting the midgut with these glands. The salivary glands of transmitting individuals appeared heavily or completely infected, while no or only a low level of infection was found in the glands of non-transmitting individuals. Moreover, the development of an age-dependent midgut barrier against virus infection was observed in second instar larvae and adults. The results show that the establishment of TSWV infection in the various tissues and the potential of transmission seems to be regulated by different barriers and processes related to the metamorphosis of thrips. (+info)
Endogenous nitric oxide in the maintenance of rat microvascular integrity against widespread plasma leakage following abdominal laparotomy.
1. The role of nitric oxide (NO) in the maintenance of microvascular integrity during minor surgical manipulation has been evaluated in the rat. 2. The NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME, 5 mg kg(-1), s.c.) and N(G)-monomethyl-L-arginine (L-NMMA, 50 mg kg(-1), s.c.) had no effect on microvascular leakage of radiolabelled albumin over 1 h in the stomach, duodenum, jejunum, colon, lung and kidney in the un-operated conscious or pentobarbitone-anaesthetized rat. 3. In contrast, in anaesthetized rats with a midline abdominal laparotomy (5 cm), L-NAME (1-5 mg kg(-1), s.c.) or L-NMMA (12.5-50 mg kg(-1), s.c.) dose-dependently increased gastrointestinal, renal and pulmonary vascular leakage, effects reversed by L-arginine pretreatment (300 mg kg(-1), s.c., 15 min). These actions were not observed in anaesthetized rats that had only received a midline abdominal skin incision (5 cm). 4. Pretreatment with a rabbit anti-rat neutrophil serum (0.4 ml kg(-1), i.p.), 4 h before laparotomy, abolished the plasma leakage induced by L-NAME in all the organs investigated. 5. These results indicate that the following abdominal laparotomy, inhibition of constitutive NO synthase provokes vascular leakage in the general microcirculation, by a process that may involve neutrophils. Such effects could thus confound studies on the microvascular actions of NO synthase inhibitors using acute surgically prepared in vivo models. The findings thus suggest that constitutively-formed NO has a crucial role in the maintenance of acute microvascular integrity following abdominal surgical intervention. (+info)