Structural diversity despite strong evolutionary conservation in the 5'-untranslated region of the P-type dystrophin transcript

Aberrant location of inhibitory synaptic marker proteins in the hippocampus of dystrophin-deficient mice: implications for cognitive impairment in duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a neuromuscular disease that arises from mutations in the dystrophin-encoding gene. Apart from muscle pathology, cognitive impairment, primarily of developmental origin, is also a significant component of the disorder. Convergent lines of evidence point to an important role for dystrophin in regulating the molecular machinery of central synapses. The clustering of neurotransmitter receptors at inhibitory synapses, thus impacting on synaptic transmission, is of particular significance. However, less is known about the role of dystrophin in influencing the precise expression patterns of proteins located within the pre- and postsynaptic elements of inhibitory synapses. To this end, we exploited molecular markers of inhibitory synapses, interneurons and dystrophin-deficient mouse models to explore the role of dystrophin in determining the stereotypical patterning of inhibitory connectivity within the cellular networks of the hippocampus CA1 region. In tissue from wild-type (WT) mice, immunoreactivity of neuroligin2 (NL2), an adhesion molecule expressed exclusively in postsynaptic elements of inhibitory synapses, and the vesicular GABA transporter (VGAT), a marker of GABAergic presynaptic elements, were predictably enriched in strata pyramidale and lacunosum moleculare. In acute contrast, NL2 and VGAT immunoreactivity was relatively evenly distributed across all CA1 layers in dystrophin-deficient mice. Similar changes were evident with the cannabinoid receptor 1, vesicular glutamate transporter 3, parvalbumin, somatostatin and the GABAA receptor alpha1 subunit. The data show that in the absence of dystrophin, there is a rearrangement of the molecular machinery, which underlies the precise spatio-temporal pattern of GABAergic synaptic transmission within the CA1 sub-field of the hippocampus.

CpG dinucleotide-specific hypermethylation of the TNS3 gene promoter in human renal cell carcinoma

Tensin3 is a cytoskeletal regulatory protein that inhibits cell motility. Downregulation of the gene encoding Tensin3 (TNS3) in human renal cell carcinoma (RCC) may contribute to cancer cell metastatic behavior. We speculated that epigenetic mechanisms, e.g., gene promoter hypermethylation, might account for TNS3 downregulation. In this study, we identified and validated a TNS3 gene promoter containing a CpG island, and quantified the methylation level within this region in RCC. Using a luciferase reporter assay we demonstrated a functional minimal promoter activity for a 500-bp sequence within the TNS3 CpG island. Pyrosequencing enabled quantitative determination of DNA methylation of each CpG dinucleotide (a total of 43) in the TNS3 gene promoter. Across the entire analyzed CpG stretch, RCC DNA showed a higher methylation level than both non-tumor kidney DNA and normal control DNA. Out of all the CpGs analyzed, two CpG dinucleotides, specifically position 2 and 8, showed the most pronounced increases in methylation levels in tumor samples. Furthermore, CpG-specific higher methylation levels were correlated with lower TNS3 gene expression levels in RCC samples. In addition, pharmacological demethylation treatment of cultured kidney cells caused a 3-fold upregulation of Tensin3 expression. In conclusion, these results reveal a differential methylation pattern in the TNS3 promoter occurring in human RCC, suggesting an epigenetic mechanism for aberrant Tensin downregulation in human kidney cancer.

The mouse dystrophin muscle enhancer-1 imparts skeletal muscle, but not cardiac muscle, expression onto the dystrophin Purkinje promoter in transgenic mice

A subset of patients harboring mutations in the dystrophin gene suffer from X-linked dilated cardiomyopathy (XLCM), a familial heart disease that is not accompanied by any clinical signs of skeletal muscle myopathy. As the muscle (M) isoform of dystrophin is not expressed in these patients, the absence of skeletal muscle symptoms has been attributed to expression of the brain (B) and cerebellar Purkinje (CP) isoforms of dystrophin in skeletal, but not cardiac, muscles of XLCM patients. The compensatory mechanism of dystrophin B and CP promoter upregulation is not known but it has been suggested that the dystrophin muscle enhancer from intron 1, DME-1, may be important in this activity. Previous studies have shown that the presence of the DME-1 is essential for a significant increase in dystrophin B and CP promoter activity in skeletal muscle cells in culture. Here, we demonstrate that the mouse dystrophin CP promoter drives expression of a lacZ reporter gene specifically to the cerebellar Purkinje cell layer but not to skeletal or cardiac muscle of transgenic mice. However, if the mouse counterpart of DME-1 is present in the transgene construct, the dystrophin CP promoter is now activated in skeletal muscle, but not in cardiac muscle. Our findings provide in vivo evidence for the importance of the dystrophin muscle enhancer sequences in activating the dystrophin CP promoter in skeletal muscle. Furthermore, they provide support for the model in which muscle enhancers, like DME-1, activate the dystrophin B and CP promoters in skeletal muscle, but not in cardiac muscle, of XLCM patients.

A novel muscle-specific enhancer identified within the deletion overlap region of two XLDC patients lacking muscle exon 1 of the human dystrophin gene

Previous studies point to the involvement of several discrete transcriptional enhancers in the modulation of dystrophin gene expression in skeletal and cardiac muscle. Analysis of deletion breakpoints in two X-linked dilated cardiomyopathy patients with mutations that remove muscle exon 1 identified a 3.2-kb deletion overlap region (XLDC3.2) between -1199 and +2057 bp predicted to contain regulatory elements essential for dystrophin gene expression in cardiac muscle. A novel-sequence-based search strategy was used to identify a 543-bp region downstream of muscle exon 1 rich in cardiac-specific transcriptional elements. Designated dystrophin muscle enhancer 2 (DME2), this candidate enhancer was seen to function in a position- and orientation-independent manner in muscle cell lines but not in fibroblasts. As only modest activity was observed in primary neonatal rat cardiomyocytes, DME2 is thought to play a role in dystrophin gene regulation at later stages of cardiac muscle development.