GABAC receptors are localized with microtubule-associated protein 1B in mammalian cone photoreceptors.

Protein MAP1B was recently reported to link GABA(C) receptors to the cytoskeleton at neuronal synapses. This interaction was demonstrated in the mammalian retina, where GABA(C) receptors were thought to be exclusively expressed in bipolar cells. Our previous studies on cultured photoreceptors suggested however the presence of GABA(C) receptors in cones. To further investigate GABA(C) receptor expression in cones, we measured GABA responses in mammalian photoreceptors in situ, and we examined the distribution of the receptor and that of protein MAP1B in the mammalian outer retina. Photoreceptors were recorded from flat-mounted retinas of retinal degeneration mice at an age when the retina becomes cone-dominated after rod cell death. GABA(A) and GABA(C)-gated currents were produced only in cones but not rods. Recording freshly dissociated retinal cells from wild-type C57 mice confirmed the presence of GABA(A) and GABA(C) receptors in cones. Immunohistochemical labeling of mouse and rat retinal sections localized GABA(C) receptors to cone terminals that were identified by peanut agglutinin lectin staining. As expected from previous studies on bipolar cells, the punctate immunostaining was not restricted to cone terminals in the outer plexiform layer. MAP1B immunolabeling was obtained in rat and pig retinas and was similarly found in cone terminals identified by the peanut agglutinin lectin staining. These results provide physiological and histological evidence that cones receive a GABA feedback in the mammalian retina and are consistent with the notion that protein MAP1B links GABA(C) receptors to the cytoskeleton at postsynaptic sites.

Mosaic expression of two dystrophins in a boy with progressive muscular dystrophy.

A boy with a Becker muscular dystrophy (BMD) phenotype presented unique muscular dystrophin expression. Western blot analysis showed the presence of two dystrophins of different sizes, i.e., a 400-kDa dystrophin and a 500-kDa form. An immunofluorescent study revealed mosaic expression of these dystrophins in the sarcolemma, with matching alpha-sarcoglycan and beta-dystroglycan staining patterns. DNA and RNA analysis did not reveal any mutation in the dystrophin gene, and the karyotype was normal.

Merosin positive congenital muscular dystrophy with mental deficiency, epilepsy and MRI changes in the cerebral white matter.

A girl born from consanguineous Turkish parents had marked hypotonia from birth and delayed milestones. She was able to stand unaided by 3 years of age with then progressive worsening of motor abilities. She had a severe non-progressive mental deficiency. Epilepsy occurred by 6 years of age. Ophthalmological investigation was normal. A marked white matter high signal was seen on magnetic resonance imaging without cortical dysplasia. Dystrophic changes were seen on muscle biopsy. Two brothers had had a similar history with early death. Muscular immunocytochemical studies showed a normal staining for dystrophin and all dystrophin related glycoproteins (including 43 and 50 DAG). Merosin staining was normal. This case differs from Fukuyama's congenital dystrophy, from merosin negative congenital muscular dystrophy, or from other congenital muscular dystrophy with CNS dysfunction. It underlines the heterogeneity of congenital muscular dystrophy and the non-specific aspect of white matter changes on neuro-imaging.

Structural and biochemical properties of kinesin heavy chain associated with rat brain mitochondria.

Kinesin, a mechanochemical enzyme that translocates membranous organelles, was initially identified and purified from soluble extracts from vertebrate brains. However, immunocytochemical and morphological approaches have demonstrated that kinesin could be associated to intracellular membranous organelles. We used an antibody raised against the head portion of the Drosophila kinesin heavy chain to reveal the presence of this protein in membranous organelles from rat brain. By using differential centrifugation and immunoblotting we observed a 116 kDa protein that crossreacts with this antibody in microsomes, synaptic vesicles, and mitochondria. This protein could be extracted from mitochondria with low salt concentrations or ATP. The 116 kDa solubilized protein has been identified as conventional kinesin based on limited sequence analysis. We also show that a polyclonal antibody raised against mitochondria-associated kinesin recognizes soluble bovine brain kinesin. The soluble and mitochondrial membrane-associated kinesins show a different isoform pattern. These results are consistent with the idea that kinesin exists as multiple isoforms that might be differentially distributed within the cell. In addition digitonin fractionation of mitochondria combined with KI extraction revealed that kinesin is a peripheral protein, preferentially located in a cholesterol-free outer membrane domain; this domain has the features of contact points between the mitochondrial outer and inner membranes. The significance of these observations on the functional regulation of the mitochondria-associated kinesin is discussed.

Glyceraldehyde-3-phosphate dehydrogenase is a microtubule binding protein in a human colon tumor cell line.

A protein which binds to tubulin polymer was isolated from a human colonic tumor cell line. This protein has a molecular mass of 35 kDa, as determined by polyacrylamide slab gel electrophoresis. The protein was purified by affinity chromatography on taxol-stabilized microtubules, and it did not cross-react with anti-MAP2 or anti-tau antibodies. This protein was identified as glyceraldehyde-3-phosphate dehydrogenase by its enzyme activity and immunoblotting experiments. The purified protein caused a pronounced enhancement in the turbidity increase produced by in vitro tubulin polymerization, and electron microscopic observations revealed the presence of bundles of microtubules.