Biomedical subjects

Carlos Ribeiro

Publications and source records attributed to Carlos Ribeiro.

14 recordsLinked to original sources

PubMed2007

The xaxAB genes encoding a new apoptotic toxin from the insect pathogen Xenorhabdus nematophila are present in plant and human pathogens.

Xenorhabdus nematophila, a member of the Enterobacteriaceae, kills many species of insects by strongly depressing the immune system and colonizing the entire body. A peptide cytotoxin has been purified from X. nematophila broth growth, and the cytolytic effect on insect immunocytes and hemolytic effect on mammalian red blood cells of this toxin have been described (Ribeiro, C., Vignes, M., and Brehélin, M. (2003) J. Biol. Chem. 278, 3030-3039). We show here that this toxin, Xenorhabdus alpha-xenorhabdolysin (Xax), triggers apoptosis in both insect and mammalian cells. We also report the cloning and sequencing of two genes, xaxAB, encoding this toxin in X. nematophila. The expression of both genes in recombinant Escherichia coli led to the production of active cytotoxin/hemolysin. However, hemolytic activity was observed only if the two peptides were added in the appropriate order. Furthermore, we report here that inactivation of xaxAB genes in X. nematophila abolished the major cytotoxic activity present in broth growth, called C1. We also show that these genes are present in various entomopathogenic bacteria of the genera Xenorhabdus and Photorhabdus, in Pseudomonas entomophila, in the human pathogens Yersinia enterocolitica and Proteus mirabilis, and in the plant pathogen Pseudomonas syringae. This toxin cannot be classified in any known family of cytotoxins on the basis of amino acid sequences, locus organization, and activity features. It is, therefore, probably the prototype of a new family of binary toxins.

Animals↗

PubMed2006

Polychaetoid/ZO-1 is required for cell specification and rearrangement during Drosophila tracheal morphogenesis.

The development of the complex network of epithelial tubes that ultimately forms the Drosophila tracheal system relies on cell migration, cell shape changes, cell rearrangements, cell differentiation, and branch fusion . Most of these events are controlled by a combination of distinct transcription factors and cell-cell signaling molecules, but few proteins that do not fall within these two functional classes have been associated with tracheal development. We show that the MAGUK protein Polychaetoid (Pyd/ZO-1), the Drosophila homolog of the junctional protein ZO-1 , plays a dual role in the formation of tracheal tubes. pyd/ZO-1 mutant embryos display branch fusion defects due to the lack of reliable determination of the fusion cell fate. In addition, pyd/ZO-1 mutant embryos show impaired cell intercalation in thin tracheal branches. Pyd/ZO-1 localizes to the adherens junctions (AJs) in tracheal cells and might thus play a direct role in the regulation of the dynamic state of the AJ during epithelial remodeling. Our study suggests that MAGUK proteins might play important roles during AJ remodeling in epithelial morphogenesis.

Adherens Junctions↗

PubMed2006

Insect haemocytes: what type of cell is that?

Classification of insect larvae circulating haemocytes is the subject of controversy, and the terminology used to designate each cellular type is often different from one species to another. However, a survey of the literature on insect haemocytes suggests that there are resemblances for most of the cell types and functions, in different insect species. In this review paper, we compare the structure and functions of circulating haemocytes in those insect species that are, by far, the most often used species for insect physiology studies, i.e. lepidopteran species and Drosophila. We show that there is high degree of homology of haemocyte types and suggest possible synonymies in terminology among species from these taxa.

Animals↗

PubMed2005

[Influenza activity 2000/2001].

Influenza viral infections are an important cause of morbidity in all age groups and are associated with a high mortality rate amongst the elderly and in risk groups. The current study analyses data from the epidemiological surveillance of influenza during the 2000/2001-winter season. Clinical, epidemiological and virological data relative to cases of influenza syndrome were collected via the National Influenza Surveillance Scheme, in collaboration with the General Directory of Health and integrates the information obtained by the Network of Sentinel Medical Practitioners and Emergency Units. The data analysis hereby obtained shows a low influenza activity during the 2000/2001-winter season, with an epidemiological period characterized by small duration and intensity. The incidence rate of influenza-like illnesses increased above the base line during three weeks and didn't surpass 74 cases per 1,000,000 inhabitants. Influenza B viruses were predominant with the simultaneous presence of influenza A (H1 and H3). The antigenic and genetic characterisation of the isolates allowed the confirmation of the similarity between these viral strains and the vaccine strains as well as the extent of the antigenic drift. Despite the antigenic similarity between the majority of influenza B isolates and the vaccine strains it's noticeable that the genetic characteristics showed an evolution directed towards the B/Sichuan/379/99 strain, which would later be incorporated in the 2001/2002 influenza vaccine. The co-circulation of two different lineages was consequently observed by the phylogenetic analysis of the B strains isolated in our country.

Adolescent↗

PubMed2005

Comm function in commissural axon guidance: cell-autonomous sorting of Robo in vivo.

Commissureless (Comm) controls axon guidance across the Drosophila melanogaster midline by regulating surface levels of Robo, the receptor for the midline repellent Slit. Two different models have been proposed for how Comm regulates Robo: a 'sorting' model and a 'clearance' model, both based on studies using heterologous cells in vitro. Here, we test these two models in vivo. We establish a genetic rescue assay for Comm, and use this assay to show that midline crossing does not require the presence of Comm in midline cells, as proposed by the clearance model. Moreover, by monitoring the trafficking of a Robo-green fluorescent protein (GFP) fusion in living embryos, we demonstrate that Comm prevents the delivery of Robo-GFP to the growth cone, as predicted by the sorting model. It has also been suggested that Comm must be ubiquitinated by the Nedd4 ubiquitin ligase. We show here, however, that ubiquitination of Comm is not required for its function in vitro or in vivo, and that Nedd4 is unlikely to function in axon guidance at the midline.

Animals↗

PubMed2005

Molecular characterization of the HA gene of influenza type B viruses.

Nucleotide sequences of the HA1 subunit of influenza B viruses isolated in Portugal between 1994 and 2003 influenza winter seasons were analyzed by the Neighbor-Joining algorithm and rates of HA1 evolution estimated by linear regression. From 1994 to 2002, all influenza B viruses studied were of the Yamagata lineage. Strains isolated from 1994 to 1996, 1996 to 1999, and 1999 to 2002 revealed a high similarity with B/Beijing/184/93, B/Yamanashi/166/98, and B/Sichuan/379/99, respectively, and strains isolated during 1994-1995, 1996-1997, and 1998-1999 clustered in more than one branch of the phylogenetic tree. Victoria-related strains reappeared during 2002/2003 and formed only one branch in the phylogenetic tree revealing a closer relationship to B/Shandong/7/97. Evolutionary rates for strains from the Yamagata lineage were estimated as 3.82x10(-3) nucleotides/site/year and 2.62x10(-3) nucleotides/site/year for Victoria-related strains. In order to identify putative influenza B HA1 codons under selective pressure, a codon-substitution model for heterogeneous selective pressure at amino acid sites was used. A percentage of 97.3% of codons under negative selective pressure and 2.7% of codons under positive selective pressure (omega=dN/dS=2.65) were estimated, with posterior probability higher than 0.90. Amino acid sites 75, 197, and 199 were found more likely to be under positive selective pressure.

Antigenic Variation↗

PubMed2005

Modes of phagocytosis of Gram-positive and Gram-negative bacteria by Spodoptera littoralis granular haemocytes.

Haemocytes are the main immunocompetent cells in insect cellular immune reactions. Here, we show that in Spodoptera littoralis, granular haemocytes are the primary phagocyte haemocytes, both in vivo and in vitro. The "trigger" and "zipper" modes of engulfment known in mammal macrophages are active, in vivo, in S. littoralis granular haemocytes, together with macropinocytosis. Lipopolysaccharide as well as lipoteichoic acid inhibit the binding of both Gram-positive (Corynebacterium xerosis) and Gram-negative (Escherichia coli) bacteria on granular haemocytes. In addition, different ligands can inhibit the binding of E. coli. Most of these inhibitors are known as ligands of scavenger receptors in mammal macrophages and we hypothesise that one of the receptors present on S. littoralis granular haemocytes could be a scavenger-like receptor.

Animals↗

PubMed2004

Genetic control of cell intercalation during tracheal morphogenesis in Drosophila.

BACKGROUND: Branching morphogenesis transforms an epithelial sheet into a tubular network with distinct features regarding the length and diameter of individual tubes. Branching is controlled by several signaling pathways, but the molecular consequences of these pathways in the responding cells are poorly understood. RESULTS: We have undertaken a detailed characterization of cell rearrangements during tracheal branching morphogenesis in Drosophila embryos with a GFP fusion protein labeling the adherens junctions (AJs) and high-resolution live imaging. To analyze the branching process at the cellular level, we further developed an imaging approach that allows us to follow single cells during the branching process. We find that controlled cell intercalation, which requires extensive AJ remodeling, is key to the formation of tracheal branches of different cellular complexities. In particular, most branches consist of tubes with individual cells wrapped around the lumen. These branches form through cell intercalation, which requires the transformation of most of the initial intercellular AJs into autocellular AJs. We propose a step-wise model explaining how this AJ remodeling occurs and use this model to better understand defects in various mutants. We find that Dpp and Wnt signaling control cell intercalation by regulating the expression of Spalt, a zinc finger transcription factor; Spalt inhibits intercalation, leading to the formation of large, multicellular tubes. CONCLUSION: Tracheal morphogenesis is regulated by an interplay of different signaling systems that control cell migration and cell intercalation, respectively. Only the combined action of these signaling systems allows efficient branch elongation and the formation of morphologically distinct branches.

Adherens Junctions↗

PubMed2003

Epithelial tube morphogenesis during Drosophila tracheal development requires Piopio, a luminal ZP protein.

The formation of branched epithelial networks is fundamental to the development of many organs, such as the lung, the kidney or the vasculature. Little is known about the mechanisms that control cell rearrangements during tubulogenesis and regulate the size of individual tubes. Recent studies indicate that whereas the basal surface of tube cells interacts with the surrounding tissues and helps to shape the ramification pattern of tubular organs, the apical surface has an important role in the regulation of tube diameter and tube growth. Here we report that two proteins, Piopio (Pio) and Dumpy (Dp), containing a zona pellucida (ZP) domain are essential for the generation of the interconnected tracheal network in Drosophila melanogaster. Pio is secreted apically, accumulates in the tracheal lumen and possibly interacts with Dp through the ZP domains. In the absence of Pio and Dp, multicellular tubes do not rearrange through cell elongation and cell intercalation to form narrow tubes with autocellular junctions; instead they are transformed into multicellular cysts, which leads to a severe disruption of the branched pattern. We propose that an extracellular matrix containing Pio and Dp provides a structural network in the luminal space, around which cell rearrangements can take place in an ordered fashion without losing interconnections. Our results suggest that a similar structural role might be attributed to other ZP-domain proteins in the formation of different branched organs.

Adherens Junctions↗

PubMed2003

Signaling systems, guided cell migration, and organogenesis: insights from genetic studies in Drosophila.

During development, cells change their position extensively. Although the basic cellular mechanisms involved in cell locomotion have been studied mostly in cultured cells, genetic and molecular approaches using model organisms are starting to shed light on the complex events influencing cell migration during development. Recent technical advances in following and analyzing migrating cells inside the living embryo offer the possibility of understanding how different signaling systems regulate the fundamental cellular processes underlying guided cell migration in vivo. In Drosophila melanogaster, studies of migrating cells have concentrated mainly on hemocytes, germ cells, border cells, and tracheal cells. Interestingly, most of these cells were recently shown to make different cellular extensions and to use receptor tyrosine kinases to sense the chemoattractive signal. This review describes our current understanding of how different signaling networks control guided migration in these four systems and discusses the impact of novel imaging techniques on the study of guided cell migration during development.

Animals↗

PubMed2002

Xenorhabdus nematophila (enterobacteriacea) secretes a cation-selective calcium-independent porin which causes vacuolation of the rough endoplasmic reticulum and cell lysis.

Xenorhabdus nematophila and Photorhabdus luminescens are two related enterobacteriaceae studied for their use in biological control and for synthesis of original virulence factors and new kinds of antibiotics. X. nematophila broth growth exhibits different cytotoxic activities on insect (Spodoptera littoralis, lepidoptera) immunocytes (hemocytes). Here we report the purification of the flhDC-dependent cytotoxin, a 10,790-Da peptide we have called alpha-Xenorhabdolysin (alpha X). We show that plasma membrane of insect hemocytes and of mammal red blood cells is the first target of this toxin. Electrophysiological and pharmacological approaches indicate that the initial effect of alpha X on macrophage plasma membrane is an increase of monovalent cation permeability, sensitive to potassium channel blockers. As a consequence, several events can occur intracellularly, such as selective vacuolation of the endoplasmic reticulum, cell swelling, and cell death by colloid-osmotic lysis. These effects, inhibited by potassium channel blockers, are totally independent of Ca(2+). However, the size of the pores created by alpha X on macrophage or red blood cell plasma membrane increases with toxin concentration, which leads to a rapid cell lysis.

Animals↗

PubMed2002

Tracheal development in Drosophila melanogaster as a model system for studying the development of a branched organ.

The development of the tracheal system of Drosophila melanogaster represents a paradigm for studying the molecular mechanisms involved in the formation of a branched tubular network. Tracheogenesis has been characterized at the morphological, cellular and genetic level and a series of successive, but linked events have been described as the basis for the formation of the complex network of tubules which extend over the entire organism. Tracheal cells stop to divide early in the process of tracheogenesis and the formation of the interconnected network requires highly controlled cell migration events and cell shape changes. A number of genes involved in these two processes have been identified but in order to obtain a more complete view of branching morphogenesis, many more genes carrying essential functions have to be isolated and characterized. Here, we provide a progress report on our attempts to identify further genes expressed in the tracheal system. We show that empty spiracles (ems), a head gap gene, is required for the formation of a specific tracheal branch, the visceral branch. We also identified a Sulfotransferase and a Multiple Inositol Polyphosphate phosphatase that are strongly upregulated in tracheal cells and discuss their possible involvement in tracheal development.

Animals↗

PubMed2002

In vivo imaging reveals different cellular functions for FGF and Dpp signaling in tracheal branching morphogenesis.

In the developing tracheal system of Drosophila melanogaster, six major branches arise by guided cell migration from a sac-like structure. The chemoattractant Branchless/FGF (Bnl) appears to guide cell migration and is essential for the formation of all tracheal branches, while Decapentaplegic (Dpp) signaling is strictly required for the formation of a subset of branches, the dorsal and ventral branches. Using in vivo confocal video microscopy, we find that the two signaling systems affect different cellular functions required for branching morphogenesis. Bnl/FGF signaling affects the formation of dynamic filopodia, possibly controlling cytoskeletal activity and motility as such, and Dpp controls cellular functions allowing branch morphogenesis and outgrowth.

Animals↗

PubMed2002

Regulation of cell migration during tracheal development in Drosophila melanogaster.

Most of the knowledge concerning the intracellular mechanisms involved in cell locomotion have been obtained from in vitro studies of cells in culture. Many of the concepts derived from these studies have been partially confirmed in in vivo systems but numerous questions regarding the developmental control of cell migration remain to be addressed. Tracheal morphogenesis in Drosophila melanogaster embryos represents an in vivo model system to study the genetic control of cell migration. We review what is known about tracheal development and regulation of tracheal cell migration. We try to link these in vivo studies and the movement of cells over two dimensional substrates and elaborate on important questions which remain to be addressed in the future.

Animals↗