[Show abstract][Hide abstract] ABSTRACT: During early development of the nervous system in vertebrates, expression of the homeobox gene Anf/Hesx1/Rpx is restricted to the anterior neural plate subdomain corresponding to the presumptive forebrain. This expression is essential for normal forebrain development and ectopic expression of Xenopus Anf, Xanf1 (also known as Xanf-1), results in severe forebrain abnormalities. By use of transgenic embryos and a novel bi-colour reporter technique, we have identified a cis-regulatory element responsible for transcriptional repression of Xanf1 that defines its posterior expression limit within the neural plate. Using this element as the target in a yeast one-hybrid system, we identified two transcription factors, FoxA4a/Pintallavis and Xvent2 (also known as Xvent-2), which are normally expressed posterior to Xanf1. Overexpression of normal and dominant-negative versions of these factors, as well as inhibition of their mRNA translation by antisense morpholinos, show that they actually function as transcriptional repressors of Xanf1 just behind its posterior expression limit. The extremely high similarity of the identified Anf cis-regulatory sequences in Xenopus, chick and human, indicates that the mechanism restricting posterior expression of Anf in Xenopus is shared among vertebrates. Our findings support Nieuwkoop's activation-transformation model for neural patterning, according to which the entire neurectoderm is initially specified towards an anterior fate, which is later suppressed posteriorly as part of the trunk formation process.
[Show abstract][Hide abstract] ABSTRACT: A new preparation is described for recording the electroretinogram (ERG) from larval zebrafish (5-8 days postfertilization) which has allowed the investigation of the pharmacology of cone photoreceptor inputs onto bipolar cells. By using a pharmacological cocktail to isolate the photoreceptors and bipolar cells from inhibitory influences, it was found that an excitatory amino acid transporter (EAAT) presumably linked to a Cl() channel mediates most of the synaptic transmission from the cone photoreceptors to the ON bipolar cells, although metabotropic glutamate receptors (presumably mGluR6) also make a small contribution. On the other hand, alpha-amino-3-hydroxy- 5-methyl-4-isoxazolepropionate (AMPA)/kainate receptors mediate synaptic transmission from cone photoreceptors to OFF bipolar cells. The glutamatergic input mechanisms underlying bipolar cell responses in the larval zebrafish are adultlike and similar to those in other teleost species.
[Show abstract][Hide abstract] ABSTRACT: The complete 2,343,479-bp genome sequence of the gram-negative, pathogenic oral bacterium Porphyromonas gingivalis strain W83, a major contributor to periodontal disease, was determined. Whole-genome comparative analysis with other available
complete genome sequences confirms the close relationship between the Cytophaga-Flavobacteria-Bacteroides (CFB) phylum and the green-sulfur bacteria. Within the CFB phyla, the genomes most similar to that of P. gingivalis are those of Bacteroides thetaiotaomicron and B. fragilis. Outside of the CFB phyla the most similar genome to P. gingivalis is that of Chlorobium tepidum, supporting the previous phylogenetic studies that indicated that the Chlorobia and CFB phyla are related, albeit distantly. Genome analysis of strain W83 reveals a range of pathways and virulence determinants
that relate to the novel biology of this oral pathogen. Among these determinants are at least six putative hemagglutinin-like
genes and 36 previously unidentified peptidases. Genome analysis also reveals that P. gingivalis can metabolize a range of amino acids and generate a number of metabolic end products that are toxic to the human host or
human gingival tissue and contribute to the development of periodontal disease.
Full-text · Article · Oct 2003 · Journal of Bacteriology
[Show abstract][Hide abstract] ABSTRACT: For over a century, amphibian embryos have been a source of significant insight into developmental mechanisms, including fundamental discoveries about the process of induction. The recently developed transgenesis for Xenopus offers new approaches to these poorly understood processes, particularly when undertaken in the quickly maturing species Xenopus tropicalis, which greatly facilitates establishment of permanent transgenic lines. Several X. tropicalis transgenic lines have now been generated, and experiments demonstrating the value of these lines to study induction in embryonic tissue recombinants and explants are presented here. A revised protocol for transgenesis in X. tropicalis resulting in a significant increase in the percentage of transgenic animals that reach adulthood is presented, as well as improvements in tadpole and froglet husbandry, which have facilitated the raising of large numbers of adults. Working transgenic populations have been rapidly expanded, and some transgenes have been bred to homozygosity. Established lines include those bearing the promoter regions of Pax-6, Otx-2, Rx, and EF1alpha coupled to fluorescent reporter genes. Multireporter lines combining, in a single animal, up to three gene promoters coupled to different fluorescent reporters have also been established. The value of X. tropicalis transgenic lines for the study of induction is demonstrated by showing activation of Pax-6 by noggin treatment of Pax-6/GFP transgenic animal caps, illustrating how reporter lines allow a rapid, in vivo assay for an inductive response. An experiment showing lens induction in gamma-crystallin/GFP transgenic lens ectoderm when it is recombined with mouse optic vesicle demonstrates conservation of inducing signals from amphibians and mammals. It also shows how the warmer culture temperatures tolerated by X. tropicalis embryos can be used in assays of factors produced by mammalian cells and tissues. The many applications of transgenic reporter lines and other lines designed to target gene expression in particular tissues promise to bring significant new insights to the classic issues first defined in amphibian systems.
Full-text · Article · Dec 2002 · Developmental Dynamics