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E Orozco

Publications and source records attributed to E Orozco.

At least 55 records · Page 3Linked to original sources
PubMed1997

Cytoplasmic DNA in Entamoeba histolytica: its biological significance.

We report a study on the DNA organization in Entamoeba histolytica using a ribosomal DNA probe. The rDNA genes were found forming mers which were separated in a typical ladder pattern by pulse field electrophoresis. DNA rosette structures were visualized through electron microscopy in DNA eluted from bands recognized by the ribosomal probe. The in situ hybridization experiments using a DNA probe suggested that the rDNA genes are portioned between the nucleus and a cytoplasmic structure. These findings provide new data on DNA organization in E. histolytica and open the question concerning the presence of a novel organelle in this eukaryotic parasite.

Animals↗
PubMed1997

Effect of bacterial association on the phenotype and genotype of an Entamoeba histolytica clonal population.

A several-times-cloned population of Entamoeba histolytica trophozoites (clone MAVIII) was cultured under axenic (MAVIIIax), monoxenic (MAVIIImx) and polyxenic (MAVIIIpx) conditions. Clones MAVIIIax and MAVIIImx presented similar virulence in vitro, but differed in their virulence in vivo, whereas MAVIIIpx trophozoites were neither virulent in vitro or in vivo. The MAVIII clones maintained their zymodeme and exhibited three unusual glucose phosphate isomerase bands, absent in other E. histolytica strains studied. Similar patterns were shown by the three MAVIII clones in the signature of a 482-bp DNA fragment from the M17 gene (which encodes for a variable immunodominant antigen), obtained by low stringency single specific primer PCR technique. However, MAVIII clones displayed genotypic variability in the patterns obtained by the random amplified polymorphic DNA technique using total DNA as template. Results suggest that monomorphism is kept in certain regions of the genome, mainly in those carrying protein encoding genes, but a high polymorphism is present in total DNA of cloned trophozoites cultured under different conditions, confirming the plasticity of the E. histolytica genome.

Animals↗
PubMed1996

Entamoeba histolytica: gene linkage groups and relevant features of its karyotype.

We identified some gene linkage groups in Entamoeba histolytica using a 4-M urea improved transversal alternating field electrophoresis (TAFE) method. Complex rosette-structured DNA molecules were found trapped along the gel lanes, explaining the fuzziness of the patterns. Using several episomal probes, including 16 S, 5.8 S, and 25 S ribosomal (r)Dna genes, an autonomous replication sequence (ARS), and EhVR1, we identified a complete ribosomal episome linkage group (CELG) at the 1.2-Mb position. Three other incomplete groups were found: IELG-1, formed by EhVR1, 16 S, 5.8 S, and 25 S genes; IELG-2 formed by EhVR1, 16 S and 25 S; and IELG-3 formed only by 5.8 S. Ehadh3, Ehpfo, and Ehredox genes migrated at the 1.8-Mb position, forming the non-ribosomal linkage group, NRLG-1.8, while the Ehenl-1 gene migrated at 1.6 Mb forming the NRLG-1.6 group. Ehhk was located at 1.2, 0.8, and 0.17 Mb in three different groups: NRLG-1.2, IELG-3-0.8, and NRLG-0.17. Putative lineal chromosomes were also identified using an heterologous telomeric probe. By in situ hybridization experiments, the rDNA and Ehhk genes were located in both nucleus and cytoplasm, while the Ehpfo and Ehredox genes were found mainly in the nucleus. We propose a model hypothezising that the 16 S and 25 S genes are in a linear molecule, duplicated in two inverted repeats, which may be looped out of the linear DNA to form an episome probably lacking or not the 5.8 S sequence, which could be added later by recombination.

Animals↗
PubMed1996

Cloning and expression of an Entamoeba histolytica NAPD+(-)dependent alcohol dehydrogenase gene.

In this paper we cloned, sequenced and expressed a novel Entamoeba histolytica alcohol dehydrogenase gene (Ehadh3). Ehadh3 has a predicted 383 amino acids open reading frame, encoding for a 42.3 kDa protein. The deduced amino acid sequence showed 24 to 26% identity to other type III alcohol dehydrogenases found in prokaryotic and lower eukaryotic organisms, but not in mammalia. There are at least two Ehadh3 gene copies in the genome, but only a 1.2 kb transcript was detected. The EhADH3 fusion protein showed a NADP+(-)dependent ADH activity. Ehadh3 may be a good target for the developing of anti-E. histolytica drugs, without producing damage to the human.

Alcohol Oxidoreductases↗
PubMed1996

Physiology and molecular biology of multidrug resistance in Entamoeba histolytica.

In this paper, we present the most relevant facts on multidrug resistance (MDR) in the protozoan parasite Entamoeba histolytica. MDR in E. histolytica presents characteristics similar to transformed mammalian cells. E. histolytica drug resistant mutants show cross-resistance to several drugs, and as in mammalian cells the resistance is reverted by verapamil. Six P-glycoprotein-like genes (EhPgp) have been cloned and characterized. Apparently, four of these genes are transcribed in drug-resistant mutants (EhPgp1, EhPgp2, EhPgp5 and EhPgp6), although only EhPgp1, EhPgp5 and EhPgp6 transcripts were clearly detected. The open reading frame (ORF) of the four completely full length genes is about 1300 amino acids long. EhPgp1, EhPgp2 and EhPgp5 have between 64 and 67% of positional identity among them, while EhPgp6 shows 38 to 46% positional identity to the other ameba genes. Interestingly, the phylogenetic tree suggested that Entamoeba P-glycoproteins are more related to the human and mouse P-glycoproteins than to the Plasmodium and Leishmania P-glycoproteins. Differential gene expression in drug-resistant mutants was detected when specific probes for each Ehpgp gene were used. To understand the differential expression of EhPgp genes we initiated the characterization of the upstream flanking regions of EhPgp1 and EhPgp5 genes. Upstream sequences showed between 53 and 66% of positional identity to Dictyostelium discoideum promoters.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Gene amplification in Entamoeba histolytica.

We show here data suggesting that Entamoeba histolytica, the protozoan responsible for human amebiasis, presents DNA amplification in a fashion similar to that described for transformed mammalian cells. By transmission electron microscopy (TEM), we found linear, circular and concentric circular DNA molecules exhibiting the main events of the unscheduled DNA amplification process. Loops were formed after the recombination of two nonadjacent DNA regions, and bubbles appeared from the recombinant strands without involving the looped-out sequences. Bubbles grew up and underwent further replication rounds to produce a nested set of partially replicated circles. Multicircle complexes were also formed from putative replication origin without recombination of distant DNA regions. Clones derived from the strain HM1:IMSS exhibited different DNA contents, suggesting DNA amplification. The parental clone A and its daughter clone C2 differed in rDNA gene copy numbers, but this was observed only when total DNA was separated by pulse field gel electrophoresis, and no significant differences were detected in nuclear DNA. The dissection of the events observed by TEM led us to propose an onion skin model for gene amplification in E. histolytica.

Animals↗
PubMed1995

Increase in mRNA of multiple Eh pgp genes encoding P-glycoprotein homologues in emetine-resistant Entamoeba histolytica parasites.

With the goal of understanding possible mechanisms of drug resistance by the protozoan parasite Entamoeba histolytica (Eh), two novel Eh P-glycoprotein (Pgp) genes (Eh pgp5 and Eh pgp6) were sequenced, and the expression of four Eh pgp genes determined in wild-type (wt) clone A and emetine-resistant (EmR) clone C2 amebae. The Eh pgp5 gene encodes a 1301-amino acid (aa) protein that is similar to those of Eh pgp1 (64% aa identity), Eh pgp2 (61%), Eh pgp6 (39%) and Homo sapiens MDR (multidrug-resistance-encoding)(Hs MDR1; 38%) genes. The 1282-aa Eh pgp6 open reading frame (ORF), which is 19-28 aa shorter than those encoded by other Eh pgp, is also similar to those of Eh pgp1 (46% aa identity), Eh pgp2 (38%), and Hs MDR1 (39%). Both Eh pgp5 and Eh pgp6 ORF predict two ATP-binding cassettes and twelve hydrophobic alpha-helices, which form the putative transmembrane channel. EmR clone C2 amebae, growing at all concentrations of drug, show increased amounts of Eh pgp1 and Eh pgp6 mRNA when compared to wt clone A amebae. In contrast, only clone C2 amebae selected for growth at the highest concentrations of emetine (100-200 micrograms/ml) show increased Eh pgp5 mRNA, while mRNA of both clone C2 and clone A Eh amebae fail to bind an Eh pgp2-specific probe. It appears then that multiple Pgp may contribute to amebic Em resistance in vitro.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Effect of etofibrate on bile production in the normolipidemic rat.

1. The effect of etofibrate, the ethandiol-1,2 diester of nicotinic and clofibric acids on bile production was studied in male rats that received a daily dose of 300 mg of etofibrate/kg body weight by stomach tube for 10 days and were compared with control rats receiving the medium. 2. The bile duct was cannulated, animals were intravenously given 1 microCi (4-14C)-cholesterol/100 b.w. and bile was collected at different intervals for a total of 4 hr. 3. Etofibrate treatment decreased plasma cholesterol and triglyceride concentrations and increased the bile flow. The cummulative amount of both bile volume and total bile radioactivity secreted increased linearly in all the animals; the respective slopes being higher in etofibrate treated rats than in controls. 4. The main labelled component found in the bile was always bile acids rather than cholesterol and the proportion of each of these compounds was similar in both groups. Neither was any difference between the groups found in the concentration of bile acids, cholesterol and phospholipids nor in the cholesterol/(bile+phospholipid) ratio. 5. Besides other factors, the present results indicate that an increase in bile flow and biliary cholesterol excretion in its free form and after its conversion into bile acids should contribute to the hypocholesterolemic effect of etofibrate.

Animals↗
PubMed1994

Cloning, genomic organization and transcription of the Entamoeba histolytica alpha-tubulin-encoding gene.

We have isolated and characterized an Entamoeba histolytica alpha-tubulin (alpha Tub)-encoding gene (Eh alpha tub). A 700-bp DNA fragment was amplified by PCR using primers derived from consensus alpha- and beta-Tub amino acid (aa) sequences from different organisms and E. histolytica DNA as the template. These PCR fragments were used to screen both genomic DNA and cDNA libraries in order to isolate an Eh alpha tub structural gene. Two overlapping clones containing the complete alpha tub ORF (1392 bp) were isolated from the genome and cDNA libraries. The deduced aa sequence of Eh alpha Tub has 55.5, 50 and 52% identity to Plasmodium falciparum alpha Tub 2, Saccharomyces cerevisiae alpha Tub 2 and human alpha Tub, respectively. Interestingly, the predicted Eh alpha Tub protein lacks a poly-acidic motif at its C terminus which is involved in Tub polymerization and microtubule-associated protein binding in other organisms. This fact may indicate a difference in tubule assembly in this organism and could provide a potential key for the development of therapeutic agents. According to Southern blot experiments and the sequences of several clones, at least two non-adjacent copies of alpha tub are present in the E. histolytica genome. A 1.5-kb transcript corresponding to the alpha tub mRNA was detected in mRNA from asynchronous E. histolytica trophozoites.

Amino Acid Sequence↗
PubMed1994

Proteins of Entamoeba histolytica trophozoites involved in the adhesion to target cells.

To identify the molecules involved in the adhesion of Entamoeba histolytica trophozoites to target cells we used monoclonal antibodies (MAbs) and adhesion-deficient mutants. Human red blood cells (RBCs) were also used as specific carriers to identify the ameba molecules with affinity to the target cell receptors. MAbs Adh-1 and Adh-2 inhibited adhesion of RBCs to the trophozoites and recognized a 112-kDa surface protein that was present in the wild type strain, but was absent or modified in adhesion-deficient mutants. In other experiments, live trophozoites were incubated with fixed-RBCs and after lysis of the trophozoites, proteins attached to the RBCs surface were separated by PAGE, electrotransferred to nitrocellulose membranes and detected by polyclonal antibodies. The 112 kDa protein was found attached to the RBCs. Other molecules identified as proteins involved in the target cell-parasite contact were the 210, 160, 90, 70, 50 and 24 kDa proteins. The 112, 90 and 24 kDa polypeptides were functionally altered in adhesion-deficient mutants.

Animals↗