Search PubMed⌕ Search

Biomedical subjects

Margaret J McFall-Ngai

Publications and source records attributed to Margaret J McFall-Ngai.

14 recordsLinked to original sources
PubMed2006

The GacA global regulator of Vibrio fischeri is required for normal host tissue responses that limit subsequent bacterial colonization.

Harmful and beneficial bacterium-host interactions induce similar host-tissue changes that lead to contrasting outcomes of association. A life-long association between Vibrio fischeri and the light organ of its host Euprymna scolopes begins when the squid collects bacteria from the surrounding seawater using mucus secreted from ciliated epithelial appendages. Following colonization, the bacterium causes changes in host tissue including cessation of mucus shedding, and apoptosis and regression of the appendages that may limit additional bacterial interactions. We evaluated whether delivery of morphogenic signals is influenced by GacA, a virulence regulator in pathogens, which also influences squid-colonization by V. fischeri. Low-level colonization by a GacA mutant led to regression of the ciliated appendages. However, the GacA mutant did not induce cessation of mucus shedding, nor did it trigger apoptosis in the appendages, a phenotype that normally correlates with their regression. Because apoptosis is triggered by lipopolysaccharide, we examined the GacA mutant and determined that it had an altered lipopolysaccharide profile as well as an increased sensitivity to detergents. GacA-mutant-colonized animals were highly susceptible to invasion by secondary colonizers, suggesting that the GacA mutant's inability to signal the full programme of light-organ responses permitted the prolonged recruitment of additional symbionts.

Aliivibrio fischeri↗
PubMed2006

Breaching the great wall: peptidoglycan and microbial interactions.

Once thought to be a process that occurred only in a few human pathogens, release of biologically active peptidoglycan fragments during growth by Gram-negative bacteria controls many types of bacterial interaction, including symbioses and interactions between microorganisms. This Perspective explores the role of peptidoglycan fragments in mediating a range of microbial-host interactions, and discusses the many systems in which peptidoglycan fragments released during bacterial growth might be active.

Animals↗
PubMed2006

An annotated cDNA library of juvenile Euprymna scolopes with and without colonization by the symbiont Vibrio fischeri.

BACKGROUND: Biologists are becoming increasingly aware that the interaction of animals, including humans, with their coevolved bacterial partners is essential for health. This growing awareness has been a driving force for the development of models for the study of beneficial animal-bacterial interactions. In the squid-vibrio model, symbiotic Vibrio fischeri induce dramatic developmental changes in the light organ of host Euprymna scolopes over the first hours to days of their partnership. We report here the creation of a juvenile light-organ specific EST database. RESULTS: We generated eleven cDNA libraries from the light organ of E. scolopes at developmentally significant time points with and without colonization by V. fischeri. Single pass 3' sequencing efforts generated 42,564 expressed sequence tags (ESTs) of which 35,421 passed our quality criteria and were then clustered via the UIcluster program into 13,962 nonredundant sequences. The cDNA clones representing these nonredundant sequences were sequenced from the 5' end of the vector and 58% of these resulting sequences overlapped significantly with the associated 3' sequence to generate 8,067 contigs with an average sequence length of 1,065 bp. All sequences were annotated with BLASTX (E-value < -03) and Gene Ontology (GO). CONCLUSION: Both the number of ESTs generated from each library and GO categorizations are reflective of the activity state of the light organ during these early stages of symbiosis. Future analyses of the sequences identified in these libraries promise to provide valuable information not only about pathways involved in colonization and early development of the squid light organ, but also about pathways conserved in response to bacterial colonization across the animal kingdom.

Aliivibrio fischeri↗
PubMed2006

Characterization and role of p53 family members in the symbiont-induced morphogenesis of the Euprymna scolopes light organ.

Within hours of hatching, the squid Euprymna scolopes forms a specific light organ symbiosis with the marine luminous bacterium Vibrio fischeri. Interactions with the symbiont result in the loss of a complex ciliated epithelium dedicated to promoting colonization of host tissue, and some or all of this loss is due to widespread, symbiont-induced apoptosis. Members of the p53 family, including p53, p63, and p73, are conserved across broad phyletic lines and p63 is thought to be the ancestral gene. These proteins have been shown to induce apoptosis and developmental morphogenesis. In this study, we characterized p63-like transcripts from mRNA isolated from the symbiotic tissues of E. scolopes and described their role in symbiont-induced morphogenesis. Using degenerate RT-PCR and RACE PCR, we identified two p63-like transcripts encoding proteins of 431 and 567 amino acids. These transcripts shared identical nucleotides where they overlapped, suggesting that they are splice variants of the same gene. Immunocytochemistry and Western blots using an antibody specific for E. scolopes suggested that the p53 family members are activated in cells of the symbiont-harvesting structures of the symbiotic light organ. We propose that once the symbiosis is initiated, a symbiont-induced signal activates p53 family members, inducing apoptosis and developmental morphogenesis of the light organ.

Aliivibrio fischeri↗
PubMed2005

Identifying components of the NF-kappaB pathway in the beneficial Euprymna scolopes-Vibrio fischeri light organ symbiosis.

The Toll/NF-kappaB pathway is a common, evolutionarily conserved innate immune pathway that modulates the responses of animal cells to microbe-associated molecular patterns (MAMPs). Because MAMPs have been implicated as critical elements in the signaling of symbiont-induced development, an expressed sequence tag library from the juvenile light organ of Euprymna scolopes was used to identify members of the Toll/NF-kappaB pathway. Full-length transcripts were identified by using 5' and 3' RACE PCR. Seven transcripts critical for MAMP-induced triggering of the Toll/NF-kappaB phosphorylation cascade have been identified, including receptors, signal transducers, and a transcription factor. Further investigations should elucidate the role of the Toll/NF-kappaB pathway in the initiation of the beneficial symbiosis between E. scolopes and Vibrio fischeri.

Aliivibrio fischeri↗
PubMed2004

Microbial factor-mediated development in a host-bacterial mutualism.

Tracheal cytotoxin (TCT), a fragment of the bacterial surface molecule peptidoglycan (PGN), is the factor responsible for the extensive tissue damage characteristic of whooping cough and gonorrhea infections. Here, we report that Vibrio fischeri also releases TCT, which acts in synergy with lipopolysaccharide (LPS) to trigger tissue development in its mutualistic symbiosis with the squid Euprymna scolopes. As components of PGN and LPS have commonly been linked with pathogenesis in animals, these findings demonstrate that host interpretation of these bacterial signal molecules is context dependent. Therefore, such differences in interpretation can lead to either inflammation and disease or to the establishment of a mutually beneficial animal-microbe association.

Aliivibrio fischeri↗
PubMed2004

Reflectins: the unusual proteins of squid reflective tissues.

A family of unusual proteins is deposited in flat, structural platelets in reflective tissues of the squid Euprymna scolopes. These proteins, which we have named reflectins, are encoded by at least six genes in three subfamilies and have no reported homologs outside of squids. Reflectins possess five repeating domains, which are highly conserved among members of the family. The proteins have a very unusual composition, with four relatively rare residues (tyrosine, methionine, arginine, and tryptophan) comprising approximately 57% of a reflectin, and several common residues (alanine, isoleucine, leucine, and lysine) occurring in none of the family members. These protein-based reflectors in squids provide a marked example of nanofabrication in animal systems.

Amino Acid Sequence↗
PubMed2004

NO means 'yes' in the squid-vibrio symbiosis: nitric oxide (NO) during the initial stages of a beneficial association.

During colonization of the Euprymna scolopes light organ, symbiotic Vibrio fischeri cells aggregate in mucus secreted by a superficial ciliated host epithelium near the sites of eventual inoculation. Once aggregated, symbiont cells migrate through ducts into epithelium-lined crypts, where they form a persistent association with the host. In this study, we provide evidence that nitric oxide synthase (NOS) and its product nitric oxide (NO) are active during the colonization of host tissues by V. fischeri. NADPH-diaphorase staining and immunocytochemistry detected NOS, and the fluorochrome diaminofluorescein (DAF) detected its product NO in high concentrations in the epithelia of the superficial ciliated fields, ducts, and crypt antechambers. In addition, both NOS and NO were detected in vesicles within the secreted mucus where the symbionts aggregate. In the presence of NO scavengers, cells of a non-symbiotic Vibrio species formed unusually large aggregates outside of the light organ, but these bacteria did not colonize host tissues. In contrast, V. fischeri effectively colonized the crypts and irreversibly attenuated the NOS and NO signals in the ducts and crypt antechambers. These data provide evidence that NO production, a defense response of animal cells to bacterial pathogens, plays a role in the interactions between a host and its beneficial bacterial partner during the initiation of symbiotic colonization.

Aliivibrio fischeri↗
PubMed2004

Symbiont-induced changes in host actin during the onset of a beneficial animal-bacterial association.

The influence of bacteria on the cytoskeleton of animal cells has been studied extensively only in pathogenic associations. We characterized changes in host cytoskeletal actin induced by the bacterial partner during the onset of a cooperative animal-bacteria association using the squid-vibrio model. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis revealed that Vibrio fischeri induced a dramatic increase in actin protein abundance in the bacteria-associated host tissues during the onset of the symbiosis. Immunocytochemistry revealed that this change in actin abundance correlated with a two- to threefold increase in actin in the apical cell surface of the epithelium-lined ducts, the route of entry of symbionts into host tissues. Real-time reverse transcriptase PCR and in situ hybridization did not detect corresponding changes in actin mRNA. Temporally correlated with the bacteria-induced changes in actin levels was a two- to threefold decrease in duct circumference, a 20% loss in the average number of cells interfacing with the duct lumina, and dramatic changes in duct cell shape. When considered with previous studies of the biomechanical and biochemical characteristics of the duct, these findings suggest that the bacterial symbionts, upon colonizing the host organ, induce modifications that physically and chemically limit the opportunity for subsequent colonizers to pass through the ducts. Continued study of the squid-vibrio system will allow further comparisons of the mechanisms by which pathogenic and cooperative bacteria influence cytoskeleton dynamics in host cells.

Actins↗
PubMed2003

Dominance of Vibrio fischeri in secreted mucus outside the light organ of Euprymna scolopes: the first site of symbiont specificity.

Previous studies of the Euprymna scolopes-Vibrio fischeri symbiosis have demonstrated that, during colonization, the hatchling host secretes mucus in which gram-negative environmental bacteria amass in dense aggregations outside the sites of infection. In this study, experiments with green fluorescent protein-labeled symbiotic and nonsymbiotic species of gram-negative bacteria were used to characterize the behavior of cells in the aggregates. When hatchling animals were exposed to 10(3) to 10(6) V. fischeri cells/ml added to natural seawater, which contains a mix of approximately 10(6) nonspecific bacterial cells/ml, V. fischeri cells were the principal bacterial cells present in the aggregations. Furthermore, when animals were exposed to equal cell numbers of V. fischeri (either a motile or a nonmotile strain) and either Vibrio parahaemolyticus or Photobacterium leiognathi, phylogenetically related gram-negative bacteria that also occur in the host's habitat, the symbiont cells were dominant in the aggregations. The presence of V. fischeri did not compromise the viability of these other species in the aggregations, and no significant growth of V. fischeri cells was detected. These findings suggested that dominance results from the ability of V. fischeri either to accumulate or to be retained more effectively within the mucus. Viability of the V. fischeri cells was required for both the formation of tight aggregates and their dominance in the mucus. Neither of the V. fischeri quorum-sensing compounds accumulated in the aggregations, which suggested that the effects of these small signal molecules are not critical to V. fischeri dominance. Taken together, these data provide evidence that the specificity of the squid-vibrio symbiosis begins early in the interaction, in the mucus where the symbionts aggregate outside of the light organ.

Animal Structures↗
PubMed2002

Unseen forces: the influence of bacteria on animal development.

The diversity of developmental programs present in animal phyla first evolved within the world's oceans, an aquatic environment teeming with an abundance of microbial life. All stages in the life histories of these early animals became adapted to microorganisms bathing their tissues, and countless examples of animal-bacterial associations have arisen as a result. Thus far, it has been difficult for biologists to design ways of determining the extent to which these associations have influenced the biology of animals, including their developmental patterns. The following review focuses on an emerging field, the goal of which is to understand the influence of bacteria on animal developmental programs. This integrative area of research is undergoing a revolution that has resulted from advances in technology and the development of suitable animal-bacterial systems for the study of these complex associations. In this contribution, the current status of the field is reviewed and the emerging research horizons are examined.

Animals↗
PubMed2002

Roles of Vibrio fischeri and nonsymbiotic bacteria in the dynamics of mucus secretion during symbiont colonization of the Euprymna scolopes light organ.

During light organ colonization of the squid Euprymna scolopes by Vibrio fischeri, host-derived mucus provides a surface upon which environmental V. fischeri forms a biofilm and aggregates prior to colonization. In this study we defined the temporal and spatial characteristics of this process. Although permanent colonization is specific to certain strains of V. fischeri, confocal microscopy analyses revealed that light organ crypt spaces took up nonspecific bacteria and particles that were less than 2 micro m in diameter during the first hour after hatching. However, within 2 h after inoculation, these cells or particles were not detectable, and further entry by nonspecific bacteria or particles appeared to be blocked. Exposure to environmental gram-negative or -positive bacteria or bacterial peptidoglycan caused the cells of the organ's superficial ciliated epithelium to release dense mucin stores at 1 to 2 h after hatching that were used to form the substrate upon which V. fischeri formed a biofilm and aggregated. Whereas the uncolonized organ surface continued to shed mucus, within 48 h of symbiont colonization mucus shedding ceased and the formation of bacterial aggregations was no longer observed. Eliminating the symbiont from the crypts with antibiotics restored the ability of the ciliated fields to secrete mucus and aggregate bacteria. While colonization by V. fischeri inhibited mucus secretion by the surface epithelium, secretion of host-derived mucus was induced in the crypt spaces. Together, these data indicate that although initiation of mucus secretion from the superficial epithelium is nonspecific, the inhibition of mucus secretion in these cells and the concomitant induction of secretion in the crypt cells are specific to natural colonization by V. fischeri.

Animals↗