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Author(s): Björn C. Schroeder [1, 2]; Siegfried Waldegger [1, 2]; Susanne Fehr [1]; Markus Bleich [3]; Richard Warth [3]; Rainer Greger [3]; Thomas J. Jentsch (corresponding author) [1] Mutations in [...]

Abstract Background The kelch repeat protein muskelin mediates cytoskeletal responses to the extracellular matrix protein thrombospondin 1, (TSP1), that is known to promote synaptogenesis in the central nervous system (CNS). Muskelin displays intracellular localization and affects cytoskeletal organization in adherent cells. Muskelin is expressed in adult brain and has been reported to bind the Cdk5 activator p39, which also facilitates the formation of functional synapses. Since little is known about muskelin in neuronal tissues, we here analysed the tissue distribution of muskelin in rodent brain and analysed its subcellular localization using cultured neurons from multiple life stages. Results Our data show that muskelin transcripts and polypeptides are expressed throughout the central nervous system with significantly high levels in hippocampus and cerebellum, a finding that resembles the tissue distribution of p39. At the subcellular level, muskelin is found in the soma, in neurite projections and the nucleus with a punctate distribution in both axons and dendrites. Immunostaining and synaptosome preparations identify partial localization of muskelin at synaptic sites. Differential centrifugation further reveals muskelin in membrane-enriched, rather than cytosolic fractions. Conclusion Our results suggest that muskelin represents a multifunctional protein associated with membranes and/or large protein complexes in most neurons of the central nervous system. These data are in conclusion with distinct roles of muskelin's functional interaction partners.

Ataxia represents a pathological coordination failure that often involves functional disturbances in cerebellar circuits. Purkinje cells (PCs) characterize the only output neurons of the cerebellar cortex and critically participate in regulating motor coordination. Although different genetic mutations are known that cause ataxia, little is known about the underlying cellular mechanisms. Here we show that a mutated axJ gene locus, encoding the ubiquitin-specific protease 14 (Usp14), negatively influences synaptic receptor turnover. AxJ mouse mutants, characterized by cerebellar ataxia, display both increased GABAA receptor (GABAAR) levels at PC surface membranes accompanied by enlarged IPSCs. Accordingly, we identify physical interaction of Usp14 and the GABAAR α1 subunit. Although other currently unknown changes might be involved, our data show that ubiquitin-dependent GABAAR turnover at cerebellar synapses contributes to axJ-mediated behavioural impairment. [ABSTRACT FROM AUTHOR]

The patterns of deposition and immunoreactivity of interstitial amyloid were studied in 11 pituitary glands obtained at autopsy and 9 surgically resected pituitary adenomas using Congo red staining and a panel of antisera directed against 5 major amyloid fibril proteins and all pituitary hormones. The deposition pattern of amyloid in pituitary glands differed from that in adenomas but all amyloid deposits showed an immunostaining with anti-amyloid λ-light chain. The remaining antisera were immunonegative. In situ hybridization using an oligodeoxyribonucleotide-probe complementary to the mRNA coding for the constant region of human λ-light chain yielded no hybridization signals in the pituitaries or pituitary adenomas, excluding local synthesis and secretion of immunoglobulins. Since no case studied suffered from generalized Aλ-amyloidosis and adsorption of immunoglobulins to the unknown amyloid fribril protein of the pituitary seems to be unlikely, crossreaction of the polyclonal antisera with an undefined antigen is probable. The similar immunostaining properties of amyloid deposits in 'normal' pituitaries and pituitary adenomas suggest they both originate from the same precursor protein. [ABSTRACT FROM AUTHOR]

Nitrobacter winogradskyi was grown autotrophically on carbon dioxide and nitrite, mixotrophically on pyruvate and nitrite, and heterotrophically on acetate and pyruvate. N. agilis was grown autotrophically on carbon dioxide and nitrite and heterotrophically on pyruvate, acetate, and yeast extract-peptone. Antisera were then prepared against these cells. Strong cross-reactions occurred between all antisera raised against Nitrobacter agilis cells in the homologous and heterologous reactions with the differently grown Nitrobacter agilis cells. Similar results were obtained with N. winogradskyi; but there were differences between the heterotrophically grown cells and the autotrophically and mixotrophically grown cells. The autotrophically grown cells of N. winogradskyi and N. agilis had nearly no immunological differences, while the cross-reactions of the heterotrophically grown cells differed strongly. So, growth conditions are of considerable influence on the serological behavior of the two bacteria tested. Of twelve lectins tested, five (from Aaptos papillata, Axinella polypoides, Cerianthus sp., Ulex europeus, and Anti-H specific agglutinin of eel serum) agglutinated cells of N. agilis and N. winogradskyi, indicating that N-acetyl-glucosamine, galactose, and fucose may be present in the bacterial cell wall. Immunodiffusion showed that cells of both nitrifying organisms grown under different conditions had at least one antigenic surface structure in common. [ABSTRACT FROM AUTHOR]

Guanidinoacetate methyltransferase (GAMT) deficiency is an autosomal recessively inherited disorder of creatine biosynthesis. The disease occurs in early life with developmental delay or arrest and several neurological symptoms, e.g., seizures and dyskinesia. Both the deficiency of high-energy phosphates in neurons and the neurotoxic action of the accumulated metabolite guanidinoacetate (GAA) are candidate mechanisms for the pathophysiology of this disease. To examine a potential role of GAA accumulation, we analyzed the electrophysiological responses of neurons induced by GAA application in primary culture and acute murine brain slices. GAA evoked picrotoxin- and bicuculline-sensitive GABAA receptor-mediated chloride currents with an EC50 of 167 μM in cortical neurons. Pathophysiologically relevant GAA concentrations hyperpolarized globus pallidus neurons and reduced their spontaneous spike frequency with an EC50 of 15.1 μM. Furthermore, GAA acted as a partial agonist at heterologously expressed GABAA but not GABAB receptors. The interaction of GAA with neuronal GABAA receptors represents a candidate mechanism explaining neurological dysfunction in GAMT deficiency. [Copyright &y& Elsevier]