The genomics of mycobacteria.

The species Mycobacterium bovis and Mycobacterium avium subspecies paratuberculosis are the causal agents, respectively, of tuberculosis and paratuberculosis in animals. Both mycobacteria, especially M. bovis, are also important to public health because they can infect humans. In recent years, this and the impact of tuberculosis and paratuberculosis on animal production have led to significant advances in knowledge about both pathogens and their host interactions. This article describes the contribution of genomics and functional genomics to studies of the evolution, virulence, epidemiology and diagnosis of both these pathogenic mycobacteria.

Les mycobactéries Mycobacterium bovis et Mycobacterium avium subsp. paratuberculosis sont les agents étiologiques de la tuberculose et de la paratuberculose, respectivement. En outre, les deux mycobactéries (mais plus particulièrement M. bovis) peuvent infecter l'être humain et jouent donc un rôle en santé publique. En raison de cette importance et des effets de la tuberculose et de la paratuberculose sur la production animale, de grands efforts ont été déployés pour faire avancer nos connaissances sur ces deux agents pathogènes et sur leurs interactions avec leurs hôtes. Les auteurs décrivent la contribution de la génomique et de la génomique fonctionnelle dans les études sur l'évolution, la virulence, l'épidémiologie et le diagnostic de ces deux mycobactéries pathogènes.

Las especies Mycobacterium bovis y Mycobacterium avium subsp. paratuberculosis son los agentes causales de la tuberculosis y la paratuberculosis en animales, respectivamente. Además, ambas micobacterias, pero fundamentalmente M. bovis, son importantes para la salud pública, ya que pueden infectar a los humanos. Debido a esto último y al impacto de la tuberculosis y la paratuberculosis en la producción animal, en los últimos años se ha producido un avance significativo en los conocimientos de ambos agentes patógenos y de la interacción con sus hospedadores. En este artículo describiremos la contribución de la genómica y la genómica funcional a los estudios de evolución, virulencia, epidemiología y diagnóstico de ambas micobacterias patógenas.

Co-ordinate control of gene expression. Muscle-specific 7 S RNA contains sequences homologous to 3'-untranslated regions of myosin genes and repetitive DNA.

We have cloned and sequenced a complementary DNA copy (pSS48) of a novel muscle-specific, low molecular weight RNA, 7 S RNA, isolated from embryonic chick cardiac muscle cells. The hybridization pattern of plasmid pSS48 DNA to chick genomic DNA suggests that 7 S RNA is derived from the repetitive chick DNA with a repetition frequency of about 300 copies per haploid genome. Under low stringency, pSS48 DNA also hybridizes with high specificity to the single copy gene for chick myosin light chain (MLC) and to myosin heavy chain (MHC), and possibly to other co-ordinately expressed genes for chick muscle proteins. The sequence analysis of recombinant plasmids pSS48, pML10 and pMHC8, for 7 S RNA, MLC mRNA and MHC RNA, respectively, indicated that short nucleotide stretches homologous to 7 S RNA reside in the 3' untranslated regions of the respective genes. The 7 S RNA sequence appears to be highly specific for the chick muscle tissue, since RNA and DNA from several sources did not hybridize to pSS48 DNA. Furthermore, the 7 S RNA-like sequence(s) appears in chick blastodermal cells preferentially earlier than the onset of transcription of genes for major muscle proteins. These results, taken together, suggest a possible function for 7 S RNA in expression of muscle-specific genes during chick development.

A novel chimeric mitochondrial RNA localized in the nucleus of mouse sperm.

Six identical cDNA clones corresponding to an RNA of 1685 nucleotides that is enriched in mouse sperm compared with testis were isolated from a mouse testis cDNA library. The sequence of these clones corresponds to the 16S mitochondrial RNA plus an inverted repeat of 120 bp covalently joined to the 5' end of the RNA. By RT-PCR, it was demonstrated that this transcript, referred to as chimeric RNA, was present in mouse sperm, testis, liver, kidney, brain, and spleen. The absence of an equivalent sequence in mitochondrial DNA or as a mitochondrial pseudogene in total DNA extracted from sperm, testis, and somatic tissues suggests that the chimeric RNA is a post-transcriptional product, maybe resulting from a trans splicing reaction. The chimeric RNA was found by RT-PCR in total RNA extracted from purified sperm heads. This result was confirmed by in situ hybridization, which showed clear staining of the sperm nucleus with probes corresponding to sequences of the mitochondrial 16S RNA and the inverted repeat.

Understanding the relationship between Mycobacterium bovis spoligotypes from cattle in Latin American countries.

Spoligotyping is the most frequently used method for genotyping isolates of Mycobacterium bovis worldwide. In the current work, we compared spoligotypes from 1684 M. bovis isolates from Argentina (816), Brazil (412), Chile (66), Mexico (274) and Venezuela (116), obtained from cattle, humans, pigs, wild boars, farmed deer, goats, buffaloes, cats, and wild animals. A total of 269 different spoligotypes were found: 142 (8.4%) isolates presented orphan spoligotypes, whereas 1542 (91.6%) formed 113 different clusters. In cattle, SB0140 was the most representative spoligotype with 355 (24.6%) isolates, followed by SB0121 with 149 (10.3%) isolates. Clustering of spoligotypes ranged from 95.2% in Argentina to 85.3% in Mexico. Orphan spoligotypes were also variable, ranging from 23.7% in Mexico to 4.1% in Brazil. A large proportion of spoligotypes were common to the neighboring countries Argentina, Brazil and Chile. In conclusion, despite the diversity of spoligotypes found in the five countries studied, there are major patterns that predominate in these neighboring countries. These clusters may reflect a long-lasting active transmission of bovine tuberculosis or common historical origins of infection.

Characterization of 5'-flanking region of heart myosin light chain 2A gene. Structural and functional evidence for promoter activity.

Two recombinant clones, lambda LC5 and lambda LC13, encompassing the entire regulatory myosin light chain 2 (MLC2A) gene of chicken heart muscle were isolated. Of these, lambda LC5 which contains a large 5'-flanking sequence of about 7.0 kb, was characterized by a partial nucleotide sequence analysis. A TATA-like sequence (TATTTTTA) and a CAAT-box (CAAAAGT) are located at positions -32 and -59, respectively, which most likely constitute the functional promoter region in the gene. Based on primer extension reaction with a synthetic 20-mer corresponding to the 5'-leader sequence and total poly(A+) RNA, the probable transcription initiation site in the gene was located. The gene promoter activity was demonstrated following transient expression of recombinant genomes containing the chicken upstream sequence fused to the bacterial chloramphenicol acetyltransferase (CAT) or to the rat preproinsulin II genes. The extracts from a Quail fibroblast cell line (QT35) transfected with the construct (pLCo5.2iCat) containing the putative chicken promoter, and the CAT gene promoted the formation of 3'-acetate chloramphenicol. Another construct (pBC12LC5.2f) contains the rat preproinsulin II gene placed under the control of chicken promoter and a simian virus 40 origin of replication. Transfection of COS cell line with pBC12LC5.2f DNA resulted in an efficient expression of rat preproinsulin mRNA initiating from the chicken promoter. The transfection assay also allowed detection of chicken MLC2A gene transcripts by S1-nuclease protection of end-labeled DNA probes. A comparison of the MLC2A upstream gene sequence with those available for skeletal myosin light chains revealed no common sequence elements, suggesting that cardiac MLC2A gene promoter region has diverged considerably from its counterparts in skeletal muscle.

Assay of chloramphenicol acetyl transferase by high-performance liquid chromatography.

A procedure to measure chloramphenicol acetyl transferase (CAT) activity by reverse-phase high-performance liquid chromatography is described. The antibiotic as well as the acetylated derivatives are well resolved on a Superspher RP-18 column using equal parts of acetonitrile and 10 mM sodium acetate (ph 5.0) as a solvent. Under these conditions, less than 100 pmol of each derivative can be easily detected within 10 minutes, and no radioactive chloramphenicol is needed. The present procedure has been used to measure the activity of the enzyme in extracts of chicken fibroblast transfected with the recombinant plasmid pSV2-cat containing the CAT gene.

fos-mediated repression of cardiac myosin light chain-2 gene transcription.

The transcription of the chicken cardiac myosin light chain-2 (MLC-2) promoter containing a 1.3 Kb 5'-flanking DNA segment is repressed upon co-transfection with an expression vector (pMMV) containing the proto-oncogene fos in embryonic chicken cardiac muscle cells in culture. Similar concentrations of co-transfectants containing other genes e.g. luciferase were ineffective. To identify the DNA element(s) in MLC-2 gene that responds to fos-mediated inhibition, 5'-sequential deletion mutants of MLC-2 promoter were tested in a transient transfection assay. A mutant, in which the 5' distal sequence was deleted upto -1200 bp upstream of the mRNA start site was sensitive to fos inhibition, but the mutant containing -1130 bp was not, suggesting that a fos responsive element (FRE) is located between -1130 to -1200 bp upstream of the transcription initiation site. The same FRE sequence was also responsive to fos-inhibition in chicken skeletal muscle cells as well. Since over-expression of fos is implicated in repression of myogenic process, the selective inhibition of MLC-2 promoter activity by fos and identification of FRE sequence potentially important in understanding the relationship between myogenesis and the oncoprotein-mediated signal pathway(s).

Partial sequencing of Reissner's fiber glycoprotein I (RF-Gly I).

The bulk of the secretion of the subcommissural organ is formed by glycoproteins that appear to be derived from two precursor forms of 540 and 320 kDa. Upon release into the ventricle, these glycoproteins aggregate to form Reissner's fiber. We report the isolation of three cDNA clones from a cDNA library prepared from bovine subcommissural organ RNA, by using an anti-Reissner's fiber serum for immunoscreening. Inserts of 0.7, 1.2, and 2.5 kb were amplified by the polymerase chain reaction, subcloned into pUC18 vector, and sequenced. Although restriction mapping of the three inserts initially suggested that all of them were derived from the same mRNA, sequence analysis showed that a short non-homologous region was present in the 0.7-kb insert when compared with the 1. 2-kb and 2.5-kb inserts, suggesting that they corresponded to two different, although highly homologous, mRNAs. Northern analyses showed a single mRNA species of approximately 9.5 kb present in the subcommissural organ and missing in the choroid plexus, brain cortex, and liver. In situ hybridization confirmed that the expression of the RNA was restricted to cells of the bovine subcommissural organ. Polyclonal antibodies raised against a synthetic peptide, whose amino-acid sequence was deduced from the 2.5-kb cDNA, reacted specifically with the bovine and rat subcommissural organ-Reissner's fiber complex. In immunoblots of bovine subcommissural organ, this antibody revealed the precursor 540-kDa form and its putative processed form of 450 kDa. It is concluded that the cloned cDNA encodes for the major constitutive glycoprotein of Reissner's fiber, here designated as RF-Gly I. The sequenced region of RF-Gly I displays a high degree of homology with some regions of the von Willebrand factor and certain mucins; it also displays two motifs homologous with repeats present in proteins of the spondin family and other proteins. A core sequence of the RF-Gly I repeats suggests that this molecule displays protein-binding properties.