Targeted inactivation of the Septin2 and Septin9 genes in myelinating Schwann cells of mice

The formation of axon-enwrapping myelin sheaths by oligodendrocytes in the central nervous system (CNS) involves the assembly of a scaffolding septin filament comprised of the subunits SEPTIN2, SEPTIN4, SEPTIN7 and SEPTIN8. Conversely, in the peripheral nervous system (PNS) myelin is synthesized by a different cell type termed Schwann cells, and it remained unknown if septins also assemble as a multimer in PNS myelin. According to prior proteome analysis, PNS myelin comprises the subunits SEPTIN2, SEPTIN7, SEPTIN8, SEPTIN9 and SEPTIN11, which localize to the paranodal and abaxonal myelin sub-compartments. Here we use the Cre/loxP-system to delete the Septin9-gene specifically in Schwann cells, causing a markedly reduced abundance of SEPTIN9 in sciatic nerves, implying that Schwann cells are the main cell type expressing SEPTIN9 in the nerve. However, Septin9-deficiency in Schwann cells did not affect the abundance or localization of other septin subunits. In contrast, when deleting the Septin2-gene in Schwann cells the abundance of all relevant septin subunits was markedly reduced, including SEPTIN9. Notably, we did not find evidence that deleting Septin2 or Septin9 in Schwann cells impairs myelin biogenesis, nerve conduction velocity or motor/sensory capabilities, at least at the assessed timepoints. Our data thus show that SEPTIN2 but not SEPTIN9 is required for the formation or stabilization of a septin multimer in PNS myelin in vivo; however, its functional relevance remains to be established

Allelic mutations of the sodium channel SCN8A reveal multiple cellular and physiological functions

Allelic mutations of Scn8a in the mouse have revealed the range of neurological disorders that can result from alternations of one neuronal sodium channel. Null mutations produce the most severe phenotype, with motor neuron failure leading to paralysis and juvenile lethality. Two less severe mutations cause ataxia, tremor, muscle weakness, and dystonia. The electrophysiological effects have been studied at the cellular level by recording from neurons from the mutant mice. The data demonstrate that Scn8a is required for the complex spiking of cerebellar Purkinje cells and for persistent sodium current in several classes of neurons, including some with pacemaker roles. The mouse mutations of Scn8a have also provided insight into the mode of inheritance of channelopathies, and led to the identification of a modifier gene that affects transcript splicing. These mutations demonstrate the value of mouse models to elucidate the pathophysiology of human disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42795/1/10709_2004_Article_5381441.pd

Abstracts from the 8th International Conference on cGMP Generators, Effectors and Therapeutic Implications

This work was supported by a restricted research grant of Bayer AG

Developmental control of the excitability of muscle: transplantation experiments on a myotonic mouse mutant.

Developmental aspects of an animal model of myotonia, the mouse mutant called "arrested development of righting response" (ADR phenotype), were studied. Adult ADR muscle is characterized by a low chloride conductance of the membrane, leading to hyperexcitability, and by a low parvalbumin content. The myotonic hyperexcitability (as measured by the extent of "aftercontractions") of ADR muscle increased steeply between postnatal days 9 and 18, by which time it had approached the adult level. To study the tissue autonomy of the myotonic phenotype, muscle grafts were performed in all four combinations between ADR and wildtype (WT phenotype) donors and hosts. In most experiments, the relative contributions of donor and host to the regenerated muscles were determined by an allelic marker (glucose phosphate isomerase). In WT and ADR hosts, ADR grafts showed myotonic responses that in WT nude mouse hosts were incomplete and similar to those of juvenile ADR muscle. In no case did grafts from WT donors show any myotonia. This shows that the myotonic ADR phenotype is based on an intrinsic muscle property most likely related to the plasma membrane. The parvalbumin contents of grafted muscles, when compared with those of untransplanted muscles, indicated graft-host interaction in the expression of this secondary phenotypic property

Long-term expression of isomyosins and myoendocrine functions in ectopic grafts of atrial tissue.

Tissue fragments of newborn rat atria were transplanted under the dorsal skin or into the bed of the anterior tibial muscle of nude mice. After 5-11 weeks, the grafts, which had reorganized into beating atrium-like structures, were analyzed and compared to ventricular tissue transplanted the same way. As revealed by monoclonal antibodies against alpha- and beta-type myosin heavy chains, atrial grafts retained a typical pattern of myosin expression distinct from that of ventricular grafts. The majority of ectopic atrial myocytes contained specific atrial granules in which cardiodilatin-immunoreactive material has been localized. Specific granules and cardiodilatin immunoreactivity were not found in myocytes of ventricular grafts. We conclude that the long-term maintenance of isomyosin expression and of the myoendocrine function of atrial tissue is largely independent of the anatomical environment