Intact satellite cells lead to remarkable protection against Smn gene defect in differentiated skeletal muscle

Deletion of murine Smn exon 7, the most frequent mutation found in spinal muscular atrophy, has been directed to either both satellite cells, the muscle progenitor cells and fused myotubes, or fused myotubes only. When satellite cells were mutated, mutant mice develop severe myopathic process, progressive motor paralysis, and early death at 1 mo of age (severe mutant). Impaired muscle regeneration of severe mutants correlated with defect of myogenic precursor cells both in vitro and in vivo. In contrast, when satellite cells remained intact, mutant mice develop similar myopathic process but exhibit mild phenotype with median survival of 8 mo and motor performance similar to that of controls (mild mutant). High proportion of regenerating myofibers expressing SMN was observed in mild mutants compensating for progressive loss of mature myofibers within the first 6 mo of age. Then, in spite of normal contractile properties of myofibers, mild mutants develop reduction of muscle force and mass. Progressive decline of muscle regeneration process was no more able to counterbalance muscle degeneration leading to dramatic loss of myofibers. These data indicate that intact satellite cells remarkably improve the survival and motor performance of mutant mice suffering from chronic myopathy, and suggest a limited potential of satellite cells to regenerate skeletal muscle.     

Effects of acute reduction of temperature on ventricular fibrillation activation patterns

Because of its electrophysiological effects, hypothermia can influence the mechanisms that intervene in the sustaining of ventricular fibrillation. We hypothesized that a rapid and profound reduction of myocardial temperature impedes the maintenance of ventricular fibrillation, leading to termination of the arrhythmia. High-resolution epicardial mapping (series 1; n = 11) and transmural recordings of ventricular activation (series 2; n = 10) were used to analyze ventricular fibrillation modification during rapid myocardial cooling in Langendorff-perfused rabbit hearts. Myocardial cooling was produced by the injection of cold Tyrode into the left ventricle after induction of ventricular fibrillation. Temperature and ventricular fibrillation dominant frequency decay fit an exponential model to arrhythmia termination in all experiments, and both parameters were significantly correlated (r = 0.70, P < 0.0001). Termination of the arrhythmia occurred preferentially in the left ventricle and was associated with a reduction in conduction velocity (-60% in left ventricle and -54% in right ventricle; P < 0.0001) and with activation maps predominantly exhibiting a single wave front, with evidence of wave front extinction. We conclude that a rapid reduction of temperature to <20 degrees C terminates ventricular fibrillation after producing an important depression in myocardial conduction.     

The C. elegans ric-3 gene is required for maturation of nicotinic acetylcholine receptors

Mutations in ric-3 (resistant to inhibitors of cholinesterase) suppress the neuronal degenerations caused by a gain of function mutation in the Caenorhabditis elegans DEG-3 acetylcholine receptor. RIC-3 is a novel protein with two transmembrane domains and extensive coiled-coil domains. It is expressed in both muscles and neurons, and the protein is concentrated within the cell bodies. We demonstrate that RIC-3 is required for the function of at least four nicotinic acetylcholine receptors. However, GABA and glutamate receptors expressed in the same cells are unaffected. In ric-3 mutants, the DEG-3 receptor accumulates in the cell body instead of in the cell processes. Moreover, co-expression of ric-3 in Xenopus laevis oocytes enhances the activity of the C.elegans DEG-3/DES-2 and of the rat alpha-7 acetylcholine receptors. Together, these data suggest that RIC-3 is specifically required for the maturation of acetylcholine receptors.     

Mutations in the extracellular domain and in the membrane-spanning domains interfere with nicotinic acetylcholine receptor maturation

The deg-3(u662) mutation is a degeneration-causing mutation in a Caenorhabditis elegans nicotinic acetylcholine receptor. In a large screen for mutations that suppress the deleterious effects of this mutation we identified 32 mutations in the deg-3 gene. Among these, 11 are missense mutations, affecting seven residues within the extracellular domain or the membrane-spanning domains. All of these mutations greatly reduce the degeneration-causing activity of deg-3(u662). All but one of these mutations cause defective localization of the DEG-3 protein, as seen in immunohistochemical analysis. Thus our screen identifies multiple residues within the nicotinic acetylcholine receptor needed for normal folding, assembly, or trafficking of this receptor. Interestingly, these mutations lead to distinct localization defects suggesting differences in their effect on DEG-3's maturation process. Specifically, mutations in the extracellular domain lead to a phenotype more severe than mutations in the membrane-spanning domains. Differences in the effects of the mutations are also predicted by homology-based modeling, showing that some mutations in the extracellular domain are likely to disrupt the native fold of the protein, while others are likely to disrupt trafficking.     

Short Time Scale Changes in Underwater Irradiance in a Wind-exposed Lagoon (Vaccarès Lagoon,France): Efficiency of Infrequent Field Measurements of Water Turbidity or Weather Data to Predict Irradiance in the Water Column

High frequency water sampling in the wind-exposed Vaccarès lagoon revealed frequent and rapid changes in suspended solid (SS) concentrations in the water column. SS concentrations, sometimes higher than 800 mg l⁻¹, were significantly correlated with antecedent wind conditions. Mean wind velocity during the 5–33 h before water sampling or maximal wind velocity during the previous 8.5–22 h were good predictors of SS concentrations in the water column. Underwater irradiance at canopy level was modeled (r² = 0.66, n = 7584) using the SS calculated from the relationship between SS and antecedent mean wind velocity and the surface irradiance data measured at the weather station close to the study site. On the other hand, we have shown that in this wind-exposed lagoon, mean underwater irradiance can not be effectively estimated using infrequent measurements of the optical properties of water.     

The viable but non-culturable state of wine micro-organisms during storage

Colony counting and DEFT did not give the same results when wine micro-organisms were enumerated. Both methods were used to monitor the population of acetic acid bacteria (AAB) and lactic acid bacteria (LAB) during wine storage. Results suggest that part of the populations had reached a viable but non-culturable (VBNC) state. These cells were unable to produce colonies but could hydrolyse fluorescent esters and could be counted by DEFT. For AAB, O2 deprivation quickly induced this state. Recovery from this state was very rapid as soon as O2 was available. The response was not so clear for LAB during wine storage. However, a similar state was induced by sulfiting. Moreover, filtration of wine stored in barrels and contaminated by Brettanomyces, AAB and LAB demonstrated that cell size was not homogeneous. Cells which remained in wine after several weeks could pass through a 0.45-microm membrane. However, when they re-entered a growing phase, they were again retained by membrane filtration. During and after the decline phase, wine micro-organisms might survive as smaller cells in a VBNC state.     

Formation of the boundary between the midbrain and the hindbrain: involvement of Otx2 and Gbx2 genes

We have studied the neuromeric organisation of the mesencephalic-metencephalic (mes-met) territory of the avian neural tube using chick/quail transplantation experiments and analysing the expression of various regulatory genes in chimeric and normal embryos. Homotopic grafts demonstrate the presence of an interneuromeric boundary separating the mesencephalic and cerebellar territories (the mes-met or midbrain/hindbrain boundary). This boundary is characterised from HH10 onwards by the confrontation of the Otx2-Wnt1 and Gbx2-Fgf8 expressing domains, while En2 and Pax2 genes are expressed at both sides of the mes-met boundary. The evolution of the position of the Otx2/Gbx2 boundary with respect to the vesicles and constriction observed within the mes-met domain between stages HH10 and HH20, allows us to redefine the fate map of this region and to propose a new nomenclature for HH10. Transplantation between the prosencephalic neuroepithelium and the mes-met domain shows the possibility of inducing a mes-met phenotype within the two caudal-most prosomeres, preceded by its characteristic genetic cascade. The induction selectively takes place along the boundary between the graft (Otx2 positive) and the host cerebellar territory (expressing high levels of Gbx2); this includes the induction inside the graft of a new Otx2/Gbx2 boundary. Conversely, no induction is ever observed when the graft is confronted to the host Otx2 expressing domain. Although Fgf8 may be involved in the inductive events, our data strongly suggest that confrontation between Otx2 and Gbx2 is essential as an organiser of the mes-met domain.     

Morphogenetic and cellular movements that shape the mouse cerebellum; insights from genetic fate mapping

We used the cerebellum as a model to study the morphogenetic and cellular processes underlying the formation of elaborate brain structures from a simple neural tube, using an inducible genetic fate mapping approach in mouse. We demonstrate how a 90 degrees rotation between embryonic days 9 and 12 converts the rostral-caudal axis of dorsal rhombomere 1 into the medial-lateral axis of the wing-like bilateral cerebellar primordium. With the appropriate use of promoters, we marked specific medial-lateral domains of the cerebellar primordium and derived a positional fate map of the murine cerebellum. We show that the adult medial cerebellum is produced by expansion, rather than fusion, of the thin medial primordium. Furthermore, ventricular-derived cells maintain their original medial-lateral coordinates into the adult, whereas rhombic lip-derived granule cells undergo lateral to medial posterior transverse migrations during foliation. Thus, we show that progressive changes in the axes of the cerebellum underlie its genesis.     

Establishment and characterization of continuous hematopoietic progenitors-derived pig normal mast cell lines

Mast cells (MCs) are tissue resident, hematopoietic stem cells-derived elements, distributed throughout the body. They are the pivotal mediating cells of allergic reactions. In addition, in mice, MCs play a critical role in the defense against several pathogens, such as bacteria, parasites and viruses. Whereas the biology of rodent and human MCs has been extensively studied using in vitro derived populations, the role of MCs in pigs has not yet been evaluated, given the very low availability of pure porcine MCs populations. In the present report, we describe an original method to obtain continuous factor-dependent normal pig MCs (PMC) lines from fetal hematopoietic progenitors. These Stem Cell Factor (SCF) and Interleukin-3- (IL-3)-dependent PMC lines retain their capacity to growth after conventional freezing methods and exhibit most of the morphological and biochemical properties of normal, although immature, MCs, including metachromatic granules containing sulfated polysaccharides, the expression of c-kit and high-affinity IgE receptors (FcepsilonRI), and the ability to store histamine that is released upon cross-linking of FcepsilonRI. In vitro derived PMC lines might thus be valuable tools to further investigate the reactivity of these elements towards several parasites frequently encountered in pig, such as, but not limited to, Ascaris suum, Trichinella spiralis or Trichuris suis, or towards antigens derived from these pathogens.