Mobilization of retrotransposons as a cause of chromosomal diversification and rapid speciation: the case for the Antarctic teleost genus Trematomus.

BACKGROUND: The importance of transposable elements (TEs) in the genomic remodeling and chromosomal rearrangements that accompany lineage diversification in vertebrates remains the subject of debate. The major impediment to understanding the roles of TEs in genome evolution is the lack of comparative and integrative analyses on complete taxonomic groups. To help overcome this problem, we have focused on the Antarctic teleost genus Trematomus (Notothenioidei: Nototheniidae), as they experienced rapid speciation accompanied by dramatic chromosomal diversity. Here we apply a multi-strategy approach to determine the role of large-scale TE mobilization in chromosomal diversification within Trematomus species. RESULTS: Despite the extensive chromosomal rearrangements observed in Trematomus species, our measurements revealed strong interspecific genome size conservation. After identifying the DIRS1, Gypsy and Copia retrotransposon superfamilies in genomes of 13 nototheniid species, we evaluated their diversity, abundance (copy numbers) and chromosomal distribution. Four families of DIRS1, nine of Gypsy, and two of Copia were highly conserved in these genomes; DIRS1 being the most represented within Trematomus genomes. Fluorescence in situ hybridization mapping showed preferential accumulation of DIRS1 in centromeric and pericentromeric regions, both in Trematomus and other nototheniid species, but not in outgroups: species of the Sub-Antarctic notothenioid families Bovichtidae and Eleginopsidae, and the non-notothenioid family Percidae. CONCLUSIONS: In contrast to the outgroups, High-Antarctic notothenioid species, including the genus Trematomus, were subjected to strong environmental stresses involving repeated bouts of warming above the freezing point of seawater and cooling to sub-zero temperatures on the Antarctic continental shelf during the past 40 millions of years (My). As a consequence of these repetitive environmental changes, including thermal shocks; a breakdown of epigenetic regulation that normally represses TE activity may have led to sequential waves of TE activation within their genomes. The predominance of DIRS1 in Trematomus species, their transposition mechanism, and their strategic location in "hot spots" of insertion on chromosomes are likely to have facilitated nonhomologous recombination, thereby increasing genomic rearrangements. The resulting centric and tandem fusions and fissions would favor the rapid lineage diversification, characteristic of the nototheniid adaptive radiation.

Activation of human neutrophils by electronically transmitted phorbol-myristate acetate.

We report the transfer of the activity of 4-phorbol-12-beta-myristate-13-acetate (PMA) by electronic means. Neutrophils were placed at 37 degrees C on one coil attached to an oscillator, while PMA was placed on another coil at room temperature. The oscillator was then turned on for 15 min, after which cells were usually further incubated for up to 45 min at 37 degrees C before measurement of reactive oxygen metabolites (ROMs) production. In 20 blind experiments, PMA thus 'transmitted' induced ROM production. ROM were not induced when: (1) PMA vehicle or 4-alpha-phorbol 12,13-didecanoate (an inactive PMA analogue) were transmitted; (2) the oscillator was switched off; (3) superoxide dismutase or protein kinase C inhibitors were added to cells before transmission. These results suggest that PMA molecules emit signals that can be transferred to neutrophils by artificial physical means in a manner that seems specific to the source molecules.

New perspectives in multiple sclerosis: retroviral involvement and glial cell death.

Retroviral involvement in the pathogenic cascade in multiple sclerosis (MS) and a cytotoxic activity with narrow specificity towards glial cells have been recently considered as credible working hypotheses to explain some of the complex pathophysiological and neuropathological features of MS. The partial characterization of exogenous retroviral sequences, thought to be associated with MS, has led us to the identification of new human endogenous retroviruses closely related to the extracellular multiple sclerosis associated retrovirus (MSRV). These endogenous retroviruses (HERV-TcR and HERV-7q) have the potential to be transcribed into RNA and proteins. Interestingly, the env domain of HERV-7q could code for a 59.8 kDa secreted glycoprotein (called enverin) with an immunoregulatory region. The presence in various MS biological fluids of a cytotoxic activity able to induce programmed cell death for oligodendrocytes and astrocytes suggests the possibility of a demyelination phenomenon as part of direct glial cell damage. Moreover, both retroviral expression and cytotoxic factor production have been evidenced in MS monocyte/macrophage cultures and MS cerebrospinal fluid. It is now crucial to better characterize the endo/exo retroviruses possibly involved in MS and their pathogenic potential, and to identify the contributing factor(s) to the gliotoxicity found in the MS cerebrospinal fluid or serum, as well as to elucidate the mechanism of induction of the observed programmed glial cell death.

Astrocyte proliferation induced by wobbler astrocyte conditioned medium is blocked by tumor necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) neutralizing antibodies in vitro.

The wobbler mutant mouse (wr/wr) displays motoneuron degeneration and astrocyte reactivity in the spinal cord. We have previously reported that, in vitro, primary wobbler astrocytes display morphological and biochemical changes. In this report, we show that wobbler astrocyte conditioned medium enhances the in vitro proliferation of normal neonatal primary astrocytes. This stimulated proliferation is correlated with high levels of IL1-beta and TNF-alpha cytokines in the conditioned medium of wobbler astrocytes. Neutralizing antibodies directed against both IL1-beta and TNF-alpha block the wobbler astrocyte conditioned medium-enhanced astrocyte proliferation. Moreover, IL1-beta and TNF-alpha mRNAs are elevated in the wobbler spinal cord. All these data suggest that diffusible IL1-beta and TNF-alpha are involved in the processus of astrogliosis observed in the wobbler spinal cord.

Genomic organization and expression of the ubiquitin-proteasome complex-associated protein Rbx1/ROC1/Hrt1.

Rbx1/ROC1/Hrt1 (Rbx1) has been recently shown to be involved in the regulation of protein turn-over. Here, we report the organization of the human Rbx1 gene, established by both a cloning and a functional genomics approach. The human gene, composed of five exons, encompasses 22.3 kb on chromosome 22q 13. The expression of Rbx1 transcripts (0.5 kb) appears developmentally regulated during mouse embryonic development and is prevalent in the adult mouse genital tract. A Genbank database search for Rbx1 related sequences in various species, from plants to mammals, is indicative of a high degree of evolutionary conservation in mouse rat and zebra fish and also, for the main functional part of the molecule, in other living species, although their gene structures can be significantly altered.

The peripheral nerve and the neuromuscular junction are affected in the tenascin-C-deficient mouse.

A thorough examination of the structure and plasticity of the neuromuscular system was performed in tenascin-C mutant mice deficient in tenascin-C. The study of the peripheral nerve revealed a number of abnormal features. In the motor nerve, numerous unmyelinated and myelinated fibers with degraded myelin were present. Schwann cell processes often enclosed degenerative terminals. Transgene (beta-galactosidase) expression analyzed at the ultrastructural level was found to be unequally distributed in the mutant's neuromuscular tissues. At the NMJ, preterminal disorganization was prevalent. Some axon terminals exhibited abnormal overgrowth. A surprising lack of beta-galactosidase expression at some cellular sites known to possess tenascin-C in wild type mice correlated best with marked changes in the cytoarchitecture of the peripheral nerve and NMJ. In some other -but not all- cellular sites which normally express the molecule, immunofluorescence analysis suggested the presence of significant but low levels of tenascin-C-like immunoreactivity together with beta-galactosidase expression. Messenger RNA detection by RT-PCR confirmed the presence of low amounts of tenascin-C mRNA in skeletal muscle suggesting that the mice deficient in tenascin-C are not complete knock-outs of this gene, but low-expression mutants. Following in vivo injections of botulinum type-A toxin, we observed a greatly reduced sprouting response of the motor nerves in tenascin-C mutant mice. We also observed that N-CAM and beta-catenin were overexpressed in the mutant. Our results suggest that tenascin-C is involved both in stabilization and in plasticity of the NMJ.

The activity of the highly inducible mouse phenylalanine hydroxylase gene promoter is dependent upon a tissue-specific, hormone-inducible enhancer.

Expression of the phenylalanine hydroxylase gene in livers and kidneys of rodents is activated at birth and is induced by glucocorticoids and cyclic AMP in the liver. Regulatory elements in a 10-kb fragment upstream of the mouse gene have been characterized. The promoter lacks TAATA and CCAAT consensus sequences and shows only extremely weak activity in transitory expression assays with phenylalanine hydroxylase-producing hepatoma cells. No key elements for regulation of promoter activity are localized within 2 kb of upstream sequences. However, a liver-specific DNase I-hypersensitive site at kb -3.5 comprises a tissue-specific and hormone-inducible enhancer. This enhancer contains multiple protein binding sites, including sites for ubiquitous factors (NF1 and AP1), the glucocorticoid receptor, and the hepatocyte-enriched transcription factors hepatocyte nuclear factor 1 (HNF1) and C/EBP. Mutation revealed that the last two sites are critical not only for basal activity but also for obtaining a maximal hormone response. Efficient transcription from the highly inducible promoter shows absolute dependence upon the enhancer at kb - 3.5, which in turn requires HNF1 and C/EBP as well as hormones. The regulatory region of the mouse phenylalanine hydroxylase gene differs totally from that of humans, even though the genes of both species are expressed essentially in the liver. Furthermore, the phenylalanine hydroxylase gene of mice shows an expression pattern very similar to those of the rodent tyrosine aminotransferase and phosphoenolpyruvate carboxykinase genes, yet each shows a different organization of its regulatory region.

[Development of molecular biomarkers for the detection of nonbiocompatible substances in the environment]. / Développement de biomarqueurs moléculaires pour la détection de substances nonbiocompatibles dans l'environnement.

Many difficult issues confront toxicologists. For instance, animal studies have proved to be difficult for the assessment of human toxicity especially to measure directly the impact of low doses of toxic compounds. Recently, novel molecular approaches to cellular mechanisms involved in the response of "toxic stress" has broaden the field of toxicology. Indeed, the development of biological markers capable of detecting exposure to toxicants before a full-blown toxic response is an important current focus of environmental research. Cells from various organisms respond rapidly to toxic stress by altering their metabolic rates, cell growth or gene transcription controlling basic functions. Examples included are oxidative stress conveyed by peroxisomes, stress proteins implicated in protein folding and in detoxification and/or resistance. A number of potential practical applications of the stress response and stress proteins can be envisioned. Stress gene expression may be considered as a potential "biomonitor" to assess whether cells or organisms are experiencing metabolic stress within their environment. Such biological indicators should provide an early, sensitive, readily and measurable response for monitoring the actions of pollutants. In addition, the development of molecular and cellular probes may lead to new classification schemes for toxic compounds based upon various cellular and molecular responses rather than on toxicant structure.