Affiliation évolutionnaire de la cyanobactérie marine fixatrice d'azote Trichodesmium sp. souche NIBB 1067

The 165 rRNA sequence of Trichodesmium sp. strain NlBB 1067 was determined and used for the construction of a distance tree and bootstrap analysis. The tree shows that, among the available cyanobacterial 165 rRNA sequences, Trichodesmium NlBB 1067 has Oscillatoria PCC 7515 as its closest relative, presenting 94.9% of sequence similarity with the latter strain. This is in contrast to a difference of 9 mol O/O G + C in mean genomic DNA base composition between the two organisms. Nevertheless, the genotypic heterogeneity presented by a number of strains assigned to the genus Oscillatoria hinders a taxonomic decision on the separate existence of the genera Trichodesmium and Oscillatoria. The sequence of the internal transcribed spacer (ITS) between the 165 and 23s rRNA genes was also determined, as a possible marker to study inter- and intraspecif ic variability. The ITS contains the genes coding for tRNA1Ie and tRNAAia and its total length is 547 nucleotides. In six out of eight sequenced clones, there is a duplication of 29 nucleotides, surrounding the 5' end of the tRNA1Ie

Small ribosomal subunit RNA sequences, evolutionary relationships among different life forms, and mitochondrial origins

A tree was constructed from a structurally conserved area in an alignment of 83 small ribosomal subunit sequences of eukaryotic, archaebacterial, eubacterial, plastidial, and mitochondrial origin. The algorithm involved computation and optimization of a dissimilarity matrix. According to the tree, only plant mitochondria belong to the eubacterial primary kingdom, whereas animal, fungal, algal, and ciliate mitochondria branch off from an internal node situated between the three primary kingdoms. This result is at variance with a parsimony tree of similar size published by Cedergren et al. (J Mol Evol 28∶98–112, 1988), which postulates the mitochondria to be monophyletic and to belong to the eubacterial primary kingdom. The discrepancy does not follow from the use of conflicting sequence alignments, hence it must be due to the use of different treeing algorithms. We tested our algorithm on a set of sequences resulting from a simulated evolution and found it capable of faith-fully reconstructing a branching topology that involved very unequal evolutionary rates. The use of more limited or more extended areas of the complete sequence alignment, comprising only very conserved or also more variable portions of the small ribosomal subunit structure, does have some influence on the tree topology. In all cases, however, the nonplant mitochondria seem to branch off before the emergence of eubacteria, and the differences are limited to the branching pattern among different types of mitochondria

Phylogenetic study of cyanobacteria on the basis of 1S ribosomal RNA sequences

In this study, the 16S rRNA sequences of five filamentous cyanobacteria (Cyanophyceae) have been determined. These sequences were used to construct, by a distance matrix method, a tree topology to depict the phylogenetic relationships among cyanobacteria

Downregulation of two novel genes in Sl/Sld and W(LacZ)/Wv mouse jejunum.

Interstitial cells of Cajal (ICC) are the so-called pacemaker cells of the gut. W(LacZ)/Wv and Sl/Sld mice lack ICC surrounding the myenteric plexus (MP) in the jejunum. We compared the gene expression profile of wild type (WT) and W(LacZ)/Wv and Sl/Sld mice using suppression subtractive hybridization (SSH), generating a cDNA library of 1303 clones from which 48 unique sequences were differentially expressed with Southern blot. Among them, we identified heme oxygenase2, TROY, and phospholamban in ICC using immunohistochemistry. Using RT-qPCR, c-Kit and two new transcripts Dithp and prenylcysteine oxidase1 were significantly lower expressed in Sl/Sld and W(LacZ)/Wv versus WT. Prenylcysteine oxidase1 appeared cytotoxic for COS-7 cells and was highly expressed in liver while Dithp was mainly expressed in small intestine. The combination of SSH, Southern blot, RT-qPCR, and immunohistochemistry turned out to be a useful approach to identify rarely expressed genes and genes with small differences in expression.Journal ArticleSCOPUS: ar.jinfo:eu-repo/semantics/publishe

Discriminations systémiques : Justice

Complete small ribosomal subunit RNA sequences were used to infer the relationship between several basidiomycetous yeasts, and to resolve the evolutionary position of the basidiomycetes among the fungi. The sequences were determined for Rhodosporidium toruloides (anamorph Rhodotorula glutinis), Filobasidiella neoformans (anamorph Cryptococcus neoformans), Trichosporon cutaneum, Bullera alba and Sporobolomyces roseus. The sequence of Leucosporidium scottii (anamorph formerly named Candida scottii) srRNA has already been published previously (Hendriks et al., J. Mol. Evol. 32, 167-177 (1991)). Using a tree construction program based on a distance matrix, a phylogenetic tree was constructed for all hitherto known fungal srRNA sequences, oomycetes and slime moulds not included. It showed the ascomycetes and the basidiomycetes to be sister groups, probably evolved from a zygomycete-like ancestor and diverged from each other about 840 Myr ago. Among the basidiomycetes, two clearly distinct groups can be recognized, one formed by the teliospore forming species (Rhodosporidium toruloides and Leucosporidium scottii), and the asexual yeast Sporobolomyces roseus, and the other formed by the non-teliospore forming species Filobasidiella neoformans and the asexual yeasts Bullera alba and Trichosporon cutaneum