Krox20 inactivation in the PNS leads to CNS/PNS boundary transgression by central glia

CNS/PNS interfaces constitute cell boundaries, since they delimit territories with different neuronal and glial contents. Despite their potential interest in regenerative medicine, the mechanisms restricting oligodendrocytes and astrocytes to the CNS, and Schwann cells to the PNS in mammals are not known. To investigate the involvement of peripheral glia and myelin in the maintenance of the CNS/PNS boundary, we have first made use of different mouse mutants. We show that inactivation of Krox20/Egr2, a master regulatory gene for myelination in Schwann cells, results in transgression of the CNS/PNS boundary by astrocytes and oligodendrocytes and in myelination of nerve root axons by oligodendrocytes. In contrast, such migration does not occur with the Trembler(J) mutation, which prevents PNS myelination without affecting Krox20 expression. Altogether these data suggest that maintenance of the CNS/PNS boundary requires a new Krox20 function separable from myelination control. Finally, we have analyzed a human patient affected by a congenital amyelinating neuropathy, associated with the absence of the KROX20 protein in Schwann cells. In this case, the nerve roots were also invaded by oligodendrocytes and astrocytes. This indicates that transgression of the CNS/PNS boundary by central glia can occur in pathological situations in humans and suggests that the underlying mechanisms are common with the mouse.

Validation of an integrated experimental set-up for kinetic and kinematic three-dimensional analyses in a training environment

Biomechanical analyses using synchronized tools [electromyography (EMG), motion capture, force sensors, force platform, and digital camera] are classically performed in a laboratory environment that could influence the performance. We present a system for studying the running sprint start that synchronizes motion capture, EMG, and ground reaction force data. To maximize motion capture (Vicon 612 with six cameras), a special dim environment was created in the stadium. "Classical" tools were combined with "purpose-built" tools intended to analyse the different aspects of movement. For example, a synchronization system was built to create a common time-base for all data recordings and a portable EMG system was synchronized by a cable that was "disconnected" by the athlete's movement out of the blocks. This disconnection represented an independent event recorded by different tools. A "gap" was measured for some sprint start events between kinetic and kinematic (motion capture) data. Calibration results, measurements of time "gap", and duration of the independent event were used to validate the accuracy of motion capture and the synchronization system. The results validate the entire experimental set-up and suggest adjustment values for motion capture data. This environment can be used to study other movements and can easily be applied to several sports.

Lipid rafts: microenvironments for integrin-growth factor interactions in neural development

The development of a complex multicellular organ such as the nervous system requires precise regulation of cell migration, proliferation and survival. This regulation in turn requires the integration of long-range signals, such as growth factors, with short-range cues that define the precise location and cellular neighbours for any given cell. This short review examines one integrative mechanism, integrin-growth factor receptor interactions, and explores the role of lipid rafts in the molecular mechanisms that underlie the receptor interactions.

A genotypically unique Babesia gibsoni-like parasite recovered from a dog in Oklahoma

A small Babesia gibsoni-like parasite was identified and isolated as the cause of clinical babesiosis in a dog from Oklahoma. Because this was potentially the first documented case of B. gibsoni infection in Oklahoma, further characterization was warranted, and the 18S nuclear small subunit ribosomal RNA gene was sequenced. Sequence comparison with other piroplasms from dogs showed significant nucleotide sequence differences between this isolate and both B. canis and B. gibsoni. These findings demonstrate that in domestic dogs in North America there are at least 2 "small" B. gibsoni-like organisms with distinct nucleotide sequences and that the geographic distribution of the "small" canine Babesia species may be wider than previously recognized.

Oligodendrocyte precursor migration and differentiation: combined effects of PSA residues, growth factors, and substrates

Using the oligosphere strategy (V. Avellana-Adalid et al., 1996, J. Neurosci. Res. 45, 558-570), we compared the migratory behavior of oligodendrocyte preprogenitors (OPP) that expressed the polysialylated form of the neural cell adhesion molecule (PSA-NCAM) and of GD3-positive oligodendrocyte progenitors (OP). To study the role of PSA in OPP migration, we used endoneuraminidase-N, which specifically cleaves PSA from NCAM. Kinetic data showed that (i) migration velocity decreased with time and was favored on polyornithine compared to Matrigel; (ii) cells emerging from spheres enriched in PSA-NCAM+ OPP migrated farther than those from spheres enriched in GD3+ OP, their migration being enhanced by the addition of growth factors; (iii) removal of PSA from NCAM moderately reduced OPP migration and induced their differentiation in GD3+ OP and GFAP+ astrocytes; (iv) blocking integrins reduced their migration, suggesting an alternative mechanism of migration. Altogether these data illustrate that motility and differentiation of OPP involve the combinatorial action of PSA-NCAM, molecules of the ECM and their receptors, and growth factors.

Do central nervous system axons remyelinate?

In multiple sclerosis (MS), one of the most frequent demyelinating diseases in man, remyelination of demyelinating lesions exists but is often incomplete. Also reported in experimental models of demyelination, this phenomenom confirms the regenerating potential of the demyelinated central nervous system (CNS) and, in particular, the existence of an endogenous mechanism of oligodendrocyte renewal. Failure in efficient remyelination could result from exhaustion of the pool of remyelinating cells, loss of axons and absence of a permissive environment for remyelination. Identifying the nature and the origin of the cells capable of generating new oligodendrocytes for remyelination could contribute to strategies to activate these cells, and thereby enhance their potential for myelin repair. Within the adult CNS, several cell types are capable of generating new oligodendrocytes following myelin damage: post-mitotic oligodendrocytes frequently found at the lesion site, oligodendrocyte progenitors whose existence has been confirmed both in vitro and in vivo, and multipotent cells localized in the germinative areas of the brain and the spinal cord. Although restricted to particular sites of the CNS, these multipotent cells, which maintain the capacity to self-renew and to migrate throughout adulthood, could constitute a powerful source of remyelinating cells. The study of the mechanisms of proliferation, migration and differentiation of these cells in response to demyelination should allow the definition of new strategies to promote endogenous remyelination and develop therapeutic approaches for demyelinating diseases such as MS. This goal is an appealing alternative to the transplantation of myelin-forming cells and should efficiently complement strategies aimed at reducing neuronal loss and inflammation.

Progenitor cells of the adult mouse subventricular zone proliferate, migrate and differentiate into oligodendrocytes after demyelination

Identifying a source of cells with the capacity to generate oligodendrocytes in the adult CNS would help in the development of strategies to promote remyelination. In the present study, we examined the ability of the precursor cells of the adult mouse subventricular zone (SVZ) to differentiate into remyelinating oligodendrocytes. After lysolecithin-induced demyelination of the corpus callosum, progenitors of the rostral SVZ (SVZa) and the rostral migratory pathway (RMS), expressing the embryonic polysialylated form of the neural cell adhesion molecule (PSA-NCAM), increased progressively with a maximal expansion occurring after 2 weeks. This observation correlated with an increase in the proliferation activity of the neural progenitors located in the SVZa and RMS. Moreover, polysialic acid (PSA)-NCAM-immunoreactive cells arizing from the SVZa were detected in the lesioned corpus callosum and within the lesion. Tracing of the constitutively cycling cells of the adult SVZ and RMS with 3H-thymidine labelling showed their migration toward the lesion and their differentiation into oligodendrocytes and astrocytes but not neurons. These data indicate that, in addition to the resident population of quiescent oligodendrocyte progenitors of the adult CNS, neural precursors from the adult SVZ constitute a source of oligodendrocytes for myelin repair.

Prolonged exercise alters beta-adrenergic responsiveness in healthy sedentary humans

To examine whether beta-adrenergic desensitization occurs after prolonged exercise, echocardiograms, heart rate responses to isoproterenol, plasma catecholamines, and circulating lymphocyte beta-adrenergic receptors were examined in 10 sedentary normal subjects at rest and after brief (10 min) and exhaustive (mean duration 95 min) cycle exercise. Resting end-diastolic volume and ejection fraction were significantly reduced after exercise (from 120 +/- 34 to 100 +/- 26 ml and from 60 +/- 0.4 to 54 +/- 0.6%, respectively; both P < 0.05). The amount of isoproterenol needed to increase heart rate 15 and 25 beats/min increased in a dose- (exercise duration) related fashion, and the increase in amount of isoproterenol needed after prolonged exercise was closely related to the decrease in ejection fraction (r2 = 0.67, P = 0.004). Circulating lymphocyte beta-receptor density and affinity, agonist binding, and adenylylcyclase levels were unchanged with prolonged exercise. In conclusion, prolonged exercise in sedentary normal subjects resulted in reduced cardiac chronotropic responsiveness to isoproterenol that was not reflected in peripheral lymphocyte beta-adrenergic-receptor downregulation.

Conformation of hyaluronate in neutral and alkaline solutions

Increasing the pH of a neutral salt solution of sodium hyaluronate to 12.5 produces a rapid drop in viscosity which is reversible upon restoring the pH to neutrality. Light scattering data showing a decrease in radius of gyration with no change in molecular weight and negative results with chondroitin and other acidic glycosaminoglycans suggest that the conformational change is specific for hyaluronate molecules.

Comparative studies of water sorption of hyaline cartilage

Vapor phase, water sorption isotherms were obtained for specimens of bovine, sturgeon and shark cartilage and for membranes composed of collagen and various proportions of cartilage proteoglycan. The data were interpreted in the light of an elementary model for swelling of gels which regards equilibrium swelling a resultant of a balance between contractile forces of an elastic matrix and expansive forces, principally osmotic in nature. Swelling ratios for bovine and sturgeon cartilage compared at the same water vapor pressure are nearly identical, whereas the swelling ratios for shark cartilage are elevated. These high values are due principally to a higher ratio of glycosaminoglycan to collagen but also reflect a higher salt and urea content and possibly also a different type of collagen fibril network.

Attentional processes in overtraining

The effects of overtraining were examined using two dependent variables, choice response and eye fixations. Although an overtraining reversal effect was nor found using choice-response, examinations of a number of eye fixations both before and after reversal suggest that the introduction of reversal training produces greater shifts in attention in the overtrained ( n = 6) as opposed to the criterion trained group ( n = 6). Results are interpreted as supporting a theory of discrimination learning which proposes that S is developing a plan in which inputs are tested or compared against some centrally organized process.

The effect of acid mucopolysaccharides and acid mucopolysaccharide-proteins on fibril formation from collagen solutions

1. The effects of acid mucopolysaccharides and acid mucopolysaccharide-proteins on the size and rate of formation of fibril aggregates from collagen solutions in pH7.6 buffers were studied by turbidimetric and light-scattering methods. 2. Serum albumin, orosomucoid, methylated cellulose, chondroitin sulphate A and chondroitin sulphate C of molecular weight less than 20000, and hyaluronate of molecular weight less than 40000 did not influence rates of fibril formation. Chondroitin sulphate A, chondroitin sulphate C and hyaluronate of high molecular weight retarded the rate of fibril formation. This effect of high-molecular-weight chondroitin sulphate C decreased with increasing ionic strength. Heparin, though of low molecular weight (13000), was highly effective, as was also heparitin sulphate. The chondroitin sulphate-proteins of very high molecular weight were highly effective, despite the fact that for some preparations the component chondroitin sulphate chains had molecular weights much less than 20000. 3. Agents that had delayed fibril formation were also effective in producing an increase in degree of aggregation of fibrillar collagen, as indicated by dissymmetry changes observed in light-scattering experiments at low collagen concentrations. Methylated cellulose and heparin at 2.5mug./ml. were unusual in decreasing aggregation, but heparin at 0.25mug./ml. increased aggregation. Electron microscopy of gels showed fibrils and fibril aggregates with ;normal' collagen spacing and dimensions consistent with the light-scattering results. 4. The rates of electrical transport of agents and of solvent (electro-osmosis) through collagen gels indicated a contribution of molecular entanglement that increased with increase in molecular size of the agents. Electrostatic binding of heparin to collagen was noted. Binding to collagen during fibril formation was also found for heparitin sulphate and a chondroitin sulphate with extra sulphate groups. 5. Electrostatic binding of acid mucopolysaccharide-proteins to collagen may be an important factor in the organization and functioning of connective tissues at all stages of growth and development. Excluded-volume (molecular-entanglement) effects may also be important. These factors operate simultaneously and interact mutually so that precise assessment of their relative importance is difficult.