Comptes rendus des seances de la Societe de biologie et de ses filiales最新文献

Tetanus (TeNT) neurotoxin and botulinum (BoNT, serotypes A-G) neurotoxins are di-chain bacterial proteins of MW-150 kDa which are also termed as clostridial neurotoxins. They are the only causative agents of two severe neuroparalytic diseases, namely tetanus and botulism. The peripheral muscle spasms which characterise tetanus are due to a blockade of inhibitory (GABAergic and glycinergic) synapses in the central nervous system leading to a motor neurones desinhibition. In contrast, botulism symptoms are only peripheral. They are consequent to a near irreversible and highly selective inhibition of acetyl-choline release at the motor nerve endings innervating skeletal muscles. During the past decade, the cellular and molecular modes of action of clostridial neurotoxins has been near completely elucidated. After a binding step of the neurotoxins to specific membrane acceptors located only on nerve terminals, BoNTs and TeNT are internalized into neurons. Inside their target neurones, the intracellularly active moiety (their light chain) is translocated from the endosomal compartment to the cytosol. The neurotoxins' light chains are zinc-dependent (endopeptidases which are specific for one among three synaptic proteins (VAMP/synaptobrevin, syntaxin or SNAP-25) implicated in neurotransmitter exocytosis. The presence of distinct targets for BoNTs and TeNT correlates well with the observed quantal alterations of neurotransmitter release which characterize certain toxin serotypes. In addition, evidence for a second, non-proteolytic, inhibitory mechanism of action has been provided recently. Most likely, this additional blocking action involves the activation of neurone transglutaminases. Due to their specific action on key proteins of the exocytosis apparatus, clostridial neurotoxins are now widely used as molecular tools to study exocytosis.

Melanin-concentrating hormone (MCH) and dynorphin genes are expressed in two discrete neuron populations of the rat lateral hypothalamus. Their roles remain hypothetical in mammals. In order to analyze changes in MCH and dynorphin gene expression, we developed a multiplex competitive semi-quantitative RT-PCR allowing to study simultaneously the variations of their mRNAs. This technique was used to examine MCH and dynorphin mRNAs contents in rats food-deprived for 24 or 48 hours as compared to controls. A 2-fold induction of dynorphin mRNA by 24 hours, followed by a sharp decrease at 48 hours and return to control level were observed. A moderate increase in MCH mRNA content was noticed by 24 hours. A 48 hours fasting restored the control levels.

The filamentous fungus Podopsora anserina presents an unavoidable arrest of vegetative growth (Senescence) determined by a cytoplasmic and infectious factor. Senescence is correlated with a disorganization of the mitochondrial DNA. This disorganization is caused by an event which is not the appearance of the first defective DNA molecules. These ones are generated constitutively and their accumulation during Senescence requires the presence of an additional factor. Life span of the strains is under nuclear and cytoplasmic genetic control. At least 600 nuclear genes influence longevity. Our analysis focuses on the role of the genes involved in cytosolic translation, since mutations in these genes seem to display the most drastic effects on longevity but also on the structure of the defective mitochondrial DNA molecules that accumulate during Senescence. We have detected in some Podospora anserina mutant strains (permissive strains) the presence of a novel cytoplasmic and infectious determinant that entails an easily discernible phenotype associated with a severe growth alteration (Crippled Growth). This growth alteration is not associated with mitochondrial DNA modifications. Only the strains that have an increased translational accuracy present Crippled Growth. However, the Crippled Growth Determinant is found in all the strains during the stationary phase; it is eliminated from the non permissive strains during the exit of the stationary phase. The mutants, that have an increased translational accuracy, probably lack a factor which is needed to eliminate the determinant when cells enter the growth phase.

Cardiovascular diseases represent the first cause of mortality in chronic renal failure patients treated by hemodialysis. Alterations in lipid metabolism and oxidative stress are recognized as vascular risk factors. Their corrections could be of interest for atherosclerosis prevention. In order to evaluate interest of an therapeutic intervention, we have analyzed oxidative metabolism in hemodialysis patients by determining the production of oxygen reactive species (ROS), the level of defense mechanisms, and the balance between nitric oxide (NO) and ROS, responsible for anti- or proxidant effects of NO. During dialysis sessions performed with cellulosic membrane (Cuprophan) an increase in hydroperoxide production by platelets was noted (12 HETE) (5.62 +/- 0.94 pg); similarly, superoxide anion (O2(0)-) production by monocytes (fluorescence index: 115 +/- 24) and by polynuclear cells (fluorescence index: 115 +/- 24) was enhanced. On the other hand, anti-oxidant defenses were significantly reduced with a decrease in RBC SOC activity (0.92 +/- 0.06 U/mg Hg) and in RBC vitamin E (0.7 +/- 0.07 mg/l) concentration. We have demonstrated a profound alteration in the L-arginine/NO pathway consequently to an accumulation of NO synthases inhibitors or activators. The necessity to reduce the production of ROS during dialysis sessions justifies the use of more biocompatible membranes, such as modified cellulosic or synthetic membranes, decreasing leucocyte activation. In addition, NO synthetase inhibitors can be preferentially eliminated by convection. Finally, a supplementation with an exogenous anti-oxidant, such as oral vitamin E (500 mg/day for 6 months) normalizes RBC vitamin E levels and concomitantly allows a decrease in MDA concentrations In conclusion, oxidative metabolism alterations observed in hemodialysis are multifactorial: preventive measures include the use of a more biocompatible material, the reequilibrium of the NO/ROS balance, and supplementation with exogenous anti-oxidants.

This review focuses on the regrowth of respiratory pathways after nerve grafting within the central nervous system of the adult rat. After a general presentation of the background and of the grafting procedure, we summarize our nerve grafting results of while it is now well established that severed axons of adult central neurons can regenerate within segments of peripheral nerve partially implanted within the brain or spinal cord, the functional properties of the regenerating neurons remain generally unknown. With a view to assessing the extent to which the functional capacities of central neurons can be maintained after axonal regeneration, we have carried out experiments on central respiratory neurons which are a good example of a highly organized neuronal network with characteristic patterns of spontaneous discharge. We have shown that axonal regrowth of central respiratory neurons was successfully induced in blind-ended medullary and spinal autografts implanted respectively within the respiratory centers of the medulla oblongata and within the cervical spinal cord at the level of descending respiratory pathways. The grafts consisted of true "supplementary nerve" in which normal afferent and efferent respiratory pathways were confirmed by recording respiratory unitary discharges from teased fibers within the grafts. The efferent discharges reflected the activity of central respiratory neurons that had regenerated axons within the grafts: these neurons manifested spontaneous activity and normal responsiveness to respiratory stimuli that resemble those of normal respiratory cells. In order to evaluate the possibility of experimental nerve banking, the feasibility of using short-term and long-term stored nerves as potential spinal nerve grafts was established using in vitro pre-degenerated nerve and cryopreserved nerve grafts after assessment of Schwann cell viability. The extent of respiratory reinnervation of the different grafts (medullary, spinal and stored nerve grafts) was compared. The discussion focuses on the main data and the strategy for future nerve grafting is evoked: functional characteristics of regenerating respiratory axons, extent of graft reinnervation, functional schwann cell survey within stored/grafted nerve and post-traumatic grafting.

Radiotoxicology is a science aiming firstly to estimate the biological effects induced by radiation in workers and general population after internal contamination of radionuclides, secondly evaluate the risk on health. After internal contamination, the analysis of biokinetics of radioactive compounds allow to understand their behaviour in the body. Those complex processes describe routes of radionuclide intake, direct blood uptake or transfer of soluble form to blood from deposit area, urine and fecal excretions, distribution and retention of radionuclides in different target organs. These processes are modelled to establish mathematical calculations. Data obtained are important to the interpretation of bioassay measurement for initial activity deposit expressed in becquerel (Bq: transformation.s-1) and committed effective dose calculation, expressed in sievert (Sv). This committed effective dose corresponds to the absorbed dose expressed in gray (Gy), weighted by a radiation weighting factor related to the quality of radiation and a tissue weighting factor which represents the contribution of the target organ to the total detriment due to effects induced by uniform irradiation of the whole body. This committed effective dose is a specific parameter for risk assessment which characterizes the radiotoxicology as a special part of toxicology.

Skeletal muscles in the vertebrate body are derived from the somites, epithelial spheres of cells which segment from the paraxial mesoderm in a rostral-caudal developmental gradient on either side of the neural tube. Initially, cells in the somite are multipotent and their fate depends on the environmental influences exerted by neighbouring tissues, notably the axial structures (neural tube and notochord), and the dorsal ectoderm. The ventralizing influence exerted by the notochord and floor plate of the neural tube through the action of sonic hedgehog, results in the differentiation of sclerotome which will give rise to cartilage and bone of the vertebral column and ribs. The dorsal derivatives of the somite, formed from cells in the dermomyotome, are derm and skeletal muscle. The onset of skeletal myogenesis is characterized by expression of myogenic factors, notably myf-5 and MyoD, members of the superfamily of helix-loop-helix transcription factors. Another member of the myogenic factor family, myogenin, is subsequently expressed and leads to muscle cell differentiation with activation of the downstream muscle-specific genes. Dorsalization of the somite and subsequent myogenesis depends on the presence of axial structures and dorsal ectoderm. The Wnt family of signalling molecules are potentially implicated in this process. Muscle progenitor cells present in the medial part of the dermomyotome activate myf-5 first and explant experiments have shown that the axial structures lead to the activation of this myogenic factor and subsequent myogenesis which results in the formation of the dorsal myotome in the central region of the somite. This contributes to the formation of axial muscles. Muscle progenitor cells in the lateral part of the dermomyotome preferentially activate MyoD and this depends on the presence of dorsal ectoderm. These cells will form the ventral aspect of the myotome, and later contribute to body wall muscles, for example. Part of the lateral progenitor population migrates away from the somite to form peripheral body muscles and the muscles of the limb. In this case myogenic factors are not initially expressed and these migratory cells are characterized by the expression of the paired-box gene Pax3. In explant experiments lateral mesoderm retards the induction of MyoD expression by dorsal ectoderm; in vivo this may be important to permit cell migration prior to differentiation. In mice carrying mutations in both MyoD and myf-5 no skeletal muscle forms, whereas myogenesis can take place in the absence of either MyoD or myf-5. Normally, cells in which one gene is activated first, subsequently co-express the other, so that there rapidly cease to be distinct MyoD+ or myf-5+ populations in the embryo. In myf-5-/- mice no myotome forms initially, but MyoD is subsequently activated. This takes place medially, as well as laterally, under the influence of the more mature neural tube and notochord. By targetting the myf-5 gene wit

From nematode to man, the transmembrane receptors of the Notch family act throughout embryonic and post-embryonic development to regulate the acquisition and/or maintenance of specific differentiative states. We will review here our current state of knowledge on Notch receptors structure and signalling activity.

Most of the genes involved in the regulation of proliferation and differentiation of neural cells remain to be identified. With the aim of identifying such genes, the strategy we used was to search for cDNAs which both hybridized with helix-loop-helix degenerated probes and corresponded to RNAs expressed preferentially when neural precursor cells become growth-arrested and began to differentiate. This led to the isolation of NPDC-1 cDNA and then of the genomic sequence. We observed that NPDC-1 is specially expressed in the nervous system and that the transfection of neural precursors with NPDC-1 cDNA results in the inhibition of cell proliferation. Moreover, the stable introduction of NPDC-1 into transformed cells downregulates cell proliferation both by increasing the generation time and by suppressing transformed and tumorigenic properties. We verified that these biological effects were reversed by NPDC-1 anti-sense oligonucleotides. Then we have examined the expression of NPDC-1 mRNA along mouse development and the interactions of the NPDC-1 protein with cell cycle regulatory proteins. The results showed that NPDC-1 mRNA begins to be expressed in a variety of neural structures, when the precursors enter their terminal differentiation. In addition, we have observed that NPDC-1 protein interacts with the transcription factor E2F-1. As a whole, the present results show that NPDC-1 down-regulates the proliferation of neural precursors, is able to suppress oncogenic transformation, is involved in the terminal differentiation of neural cells and acts probably through interactions with E2F-1.

Commitment and differentiation of hematopoietic stem cells are associated with the progressive restriction of cellular proliferation and the progressive expression of a subset of genes encoding the markers of mature cells. These two processes are genetically regulated and, in this paper, I review the expression and function of the GATA family of transcription factors as an example of this genetic regulation. GATA cis-acting elements are found in most of the regulatory regions of T-lymphoid, erythrocytic and megakaryocytic restricted genes. These GATA motifs are recognized by the members of a family of transcriptional regulators: the GATA family. Three members of this family, GATA-1, 2 and 3 are expressed in hematopoietic cells. They are necessary for the erythrocytic and megakaryocytic lineages (GATA-1), for the T-lymphoid lineage (GATA-3), and for the proliferation of uncommitted hematopoietic precursors (GATA-2). GATA-1 displays at least four functions: activation of the erythrocytic and megakaryocytic specific genes, regulation of the epsilon-->gamma globin switch and control of the cell cycle. These two last functions will be discussed to show the multiple facets of GATA-1 in the genetic regulation of hematopoiesis.