A dystrophin-immunoreactive protein in mammalian brain

Biochemical and histochemical analysis of 71 kDa dystrophin isoform (Dp71f) in rat brain

Dp71 is a member of the dystrophin family and the most abundant dmd gene product in the brain. In the present study, we focused on a short dystrophin transcript named Dp71f, which is alternatively spliced when exon 78 is absent The topographic localization of this protein in the encephalon has not been properly described yet, nor its cellular or subcellular localization, and even less its functions. Dp71f was found to be a cytoplasmic 70 kDa protein and localized in all encephalon regions studied. Double labeling using specific markers for various cell types confirmed Dp71f distribution in the cytoplasm of all cell types studied. Labeling was more conspicuous near the nucleus and diminished towards the periphery of cells. In some cases, we observed cells that were positive for actin and Dp71f in regions corresponding to lamellipodia-like structures. Dp71f and Dp71d isoforms were differently distributed. Our study is the first specific and unambiguous description of the topography and cellular localization patterns of Dp71f in brain, suggesting that Dp71f is a ubiquitous protein.

2.1 kb 5'-flanking region of the brain type dystrophin gene directs the expression of lacZ in the cerebral cortex, but not in the hippocampus

Duchenne muscular dystrophy is a muscle-wasting disease accompanied by a variable, but often significant degree of mental retardation, possibly due to the absence of dystrophin. However, the function of brain type dystrophin remains insufficiently clear. With this background, in order to study the cell-specific regulation of brain type dystrophin expression in mice, we generated transgenic mice carrying the 2.1 kb 5'-fragment of the mouse brain type dystrophin gene, fused to the coding region of the bacterial lacZ gene. Three transgenic mice lines showed lacZ expression in the cerebral cortex. However, lacZ expression was not detected in the CA region of the hippocampus. These results suggest that the 2.1 kb 5'-fragment of the mouse brain type dystrophin gene contains the regulatory element required for its expression in the cerebral cortex, but not in the hippocampus.

Rabbit brain and muscle isoforms containing the carboxy-terminal domain of 427 kDa skeletal muscle dystrophin exhibit similar biochemical properties

The membrane cytoskeletal component dystrophin, which is the protein product of the human Duchenne muscular dystrophy gene, exists in manifold isoforms. Using immunoblot analysis with an antibody to the carboxy-terminal domain of the 427 kDa skeletal muscle dystrophin, we investigated the membrane cytoskeletal properties of dystrophin isoforms from rabbit skeletal muscle, heart and brain. All isoforms identified, including the abundant brain isoforms Dp116 which lacks the amino-terminal actin-binding domain of 427 kDa dystrophin, exhibited similar biochemical properties, i.e. insolubility in non-ionic detergent but extraction from the membrane with alkaline solutions. In muscle, beta-dystroglycan was found to be more tightly associated with dystrophin than alpha-sarcoglycan. These findings agree with the proposed structure of identified muscle and brain dystrophin isoforms and are also consistent with the current model of the dystrophin-glycoprotein complex.

An in vivo and in vitro H-magnetic resonance spectroscopy study of mdx mouse brain: abnormal development or neural necrosis?

Duchenne muscular dystrophy (DMD) is an X-linked genetic disorder primarily affecting young boys, often causing mental retardation in addition to the well-known progressive muscular weakness. Normal dystrophin expression is lacking in skeletal muscle and the central nervous system (CNS) of both DMD children and the mdx mouse model. The underlying biochemical lesion causing mental impairment in DMD is unknown. 1H-magnetic resonance spectroscopy (1H-MRS) detects choline-containing compounds, creatine and N-acetyl aspartate (NAA) in vivo. NAA is commonly used as a chemical marker for neurons, and a decline in NAA is thought to correlate with neuronal loss. Control mice were compared to mdx using a combination of in vivo and in vitro 1H-MRS methods to determine whether neural necrosis or developmental abnormalities occur in dystrophic brain. NAA levels were normal in mdx brain compared to controls suggesting minor, if any, neuronal necrosis in dystrophic brain. In contrast, choline compounds and myo-inositol levels were increased, indicative of gliosis or developmental abnormalities in dystrophic brain.