The xipotl mutant of Arabidopsis reveals a critical role for phospholipid metabolism in root system development and epidermal cell integrity

Phosphocholine (PCho) is an essential metabolite for plant development because it is the precursor for the biosynthesis of phosphatidylcholine, which is the major lipid component in plant cell membranes. The main step in PCho biosynthesis in Arabidopsis thaliana is the triple, sequential N-methylation of phosphoethanolamine, catalyzed by S-adenosyl-l-methionine:phosphoethanolamine N-methyltransferase (PEAMT). In screenings performed to isolate Arabidopsis mutants with altered root system architecture, a T-DNA mutagenized line showing remarkable alterations in root development was isolated. At the seedling stage, the mutant phenotype is characterized by a short primary root, a high number of lateral roots, and short epidermal cells with aberrant morphology. Genetic and biochemical characterization of this mutant showed that the T-DNA was inserted at the At3g18000 locus (XIPOTL1), which encodes PEAMT (XIPOTL1). Further analyses revealed that inhibition of PCho biosynthesis in xpl1 mutants not only alters several root developmental traits but also induces cell death in root epidermal cells. Epidermal cell death could be reversed by phosphatidic acid treatment. Taken together, our results suggest that molecules produced downstream of the PCho biosynthesis pathway play key roles in root development and act as signals for cell integrity.     

Endoplasmic reticulum export sites and Golgi bodies behave as single mobile secretory units in plant cells

In contrast with animals, plant cells contain multiple mobile Golgi stacks distributed over the entire cytoplasm. However, the distribution and dynamics of protein export sites on the plant endoplasmic reticulum (ER) surface have yet to be characterized. A widely accepted model for ER-to-Golgi transport is based on the sequential action of COPII and COPI coat complexes. The COPII complex assembles by the ordered recruitment of cytosolic components on the ER membrane. Here, we have visualized two early components of the COPII machinery, the small GTPase Sar1p and its GTP exchanging factor Sec12p in live tobacco (Nicotiana tabacum) leaf epidermal cells. By in vivo confocal laser scanning microscopy and fluorescence recovery after photobleaching experiments, we show that Sar1p cycles on mobile punctate structures that track with the Golgi bodies in close proximity but contain regions that are physically separated from the Golgi bodies. By contrast, Sec12p is uniformly distributed along the ER network and does not accumulate in these structures, consistent with the fact that Sec12p does not become part of a COPII vesicle. We propose that punctate accumulation of Sar1p represents ER export sites (ERES). The sites may represent a combination of Sar1p-coated ER membranes, nascent COPII membranes, and COPII vectors in transit, which have yet to lose their coats. ERES can be induced by overproducing Golgi membrane proteins but not soluble bulk-flow cargos. Few punctate Sar1p loci were observed that are independent of Golgi bodies, and these may be nascent ERES. The vast majority of ERES form secretory units that move along the surface of the ER together with the Golgi bodies, but movement does not influence the rate of cargo transport between these two organelles. Moreover, we could demonstrate using the drug brefeldin A that formation of ERES is strictly dependent on a functional retrograde transport route from the Golgi apparatus.     

Interleukin-1 beta (IL-1beta) induces tumor necrosis factor alpha (TNF-alpha) expression on mouse myeloid multipotent cell line 32D cl3 and inhibits their proliferation

Interleukin-1 alpha (IL-1alpha) and beta (IL-1beta) are well known factors that stimulate hematopoiesis, nevertheless there are reports that show that they can also inhibit this activity. While both IL-1alpha and IL-1beta induce the expression of hematopoietic cytokines, such as growth factors and their receptors on myeloid cells, helping thus to regulate hematopoiesis, it is not known if their inhibitory activity is also mediated through the induction of other specific cytokines. In this work we show that recombinant human IL-1beta (rhIL-1beta) inhibits the proliferation of a mouse IL-3-dependent myeloid multipotent cell line (32D cl3), without inducing its differentiation. We show that rhIL-1beta induces in 32D cl3 cells the expression of the tumor necrosis factor alpha (TNF-alpha) gene, a well known growth inhibitor, and that the rhIL-1beta growth inhibition property on 32D cl3 cells is partially due to this secreted TNF-alpha, hinting thus that the inhibition of hematopoiesis by IL-1 is mediated through other induced cytokines.     

Circulating TNF-alpha and its soluble receptors during experimental acute pancreatitis

Clinical and experimental studies have shown increased concentrations of TNF-alpha and its soluble receptors in serum of patients with acute pancreatitis. In this work, we have investigated the time-course of TNF-alpha and its soluble receptors during taurocholate-induced acute pancreatitis. In addition, since TNF-alpha itself could mediate the shedding of its receptors, we have assessed the effect of inhibiting TNF-alpha production on the release of soluble TNF-alpha receptors in experimental acute pancreatitis. Our results indicate that soluble receptors are released in the early stages of the disease and this increase is concomitant with the release of TNF-alpha, which is mainly bound to specific proteins. The increased concentrations of its receptors strongly suggest that they could be these binding proteins. Inhibition of TNF-alpha generation with pentoxifylline abrogated the shedding of sTNF-alphaR1, but had no effect on sTNF-alphaR2. This finding suggests that the shedding of sTNF-alphaR1 is induced by TNF-alpha itself, but in the case of sTNF-alphaR2, the shedding appears to be induced by another mechanism.     

Age at acquisition of Helicobacter pylori infection: comparison of two areas with contrasting risk of gastric cancer

Background. Helicobacter pylori infection is usually acquired during childhood and is a known risk factor for the development of gastric malignancies in adulthood. It has been reported that early age at first infection may determine a neoplastic outcome in adults. The purpose of this study was to determine the prevalence of Helicobacter pylori infection in children residing in areas with high (Pasto) and low risk (Tumaco) of gastric cancer in Colombia to evaluate whether differences in the age of acquisition of H. pylori infection were present in the two populations. Materials and Methods. The study sample was based on a census taken in 1999. Using the ¹³C‐urea breath test, we compared the prevalence of H. pylori infection among children aged 1–6 years. Results. Among 345 children in Pasto, 206 (59.7%) were H. pylori‐positive, compared with 188 (58.6%) among 321 children in Tumaco. The two populations share a common pattern of very early age at infection and marked increase in prevalence during the first 4 years of life. No differences in any one year were observed when comparing the two groups. Conclusions. The prevalence of infection was similarly high and increased with age in both populations. In these populations the age of acquisition of H. pylori after 1 year of age does not appear to be a primary factor responsible for the differences in the rates of gastric cancer incidence in adults. Previous findings in adults showed lower prevalence of the most virulent genotypes in Tumaco compared to Pasto, and bacterial virulence may play a key role in determining cancer outcome.     

Genetic demography of Antioquia (Colombia) and the Central Valley of Costa Rica

We report a comparative genetic characterization of two population isolates with parallel demographic histories: the Central Valley of Costa Rica (CVCR) and Antioquia (in northwest Colombia). The analysis of mtDNA, Y-chromosome and autosomal polymorphisms shows that Antioquia and the CVCR are genetically very similar, indicating that closely related parental populations founded these two isolates. In both populations, the male ancestry is predominantly European, whereas the female ancestry is mostly Amerind. In agreement with their isolation, the Amerindian mtDNA diversity of Antioquia and the CVCR is typical of ethnically-defined native populations and is markedly lower than in other Latin American populations. A comparison of linkage disequilibrium (LD) at 18 marker pairs in Antioquia and the CVCR shows that markers in LD in both populations are located at short genetic distances (相似文献