We are also working on regulation of transcription associated with specialized chromatin structures at methylated regions of the genome. Cytosine methylation in vertebrate genomes occurs almost exclusively at CpG dinucleotides and results in marked transcriptional repression in vivo. DNA methylation is classically associated with imprinted genes, retrotransposons and their relics, and the inactive X chromosome in female mammals.  A family of DNA binding proteins that selectively binds methylated DNA shares a common DNA interaction domain termed the methyl CpG binding domain, or MBD (Wade, 2001).  MeCP2, the prototype MBD protein, participates in repression of transcription in vivo. Mutations of specific residues have been linked to the Rett syndrome. To better understand the molecular basis of MeCP2 function, we characterized the nucleoprotein assemblages formed upon interaction of MeCP2 with defined nucleosomal arrays in vitro.  Electrophoresis, analytical ultracentrifugation and electron microscopy experiments indicated that stoichiometric amounts of MeCP2 caused the nucleosomal arrays to condense into novel secondary chromatin structures (see Fig. 1-2), which subsequently oligomerized into filamentous supramolecular assemblies.  These results suggest that MeCP2 is an architectural chromatin binding protein capable of both local and large-scale reorganization of the genome (Georgel et al., 2003).

We are currently investigating the effects of histone N-termini (deletion and post-translational modifications) on MeCP2 binding and chromatin condensation. The techniques used for that purpose are: standard electrophoretic mobility shift assays (EMSA) and QAGE. Our results suggest that chromatin condensation occurs through DNA of neighboring nucleosome (see Fig. 3).

Below references you will find images of this subject matter.  

- Wade, P. A. Oncogene 2001, 20, 3166-3173.
- Georgel, P. T.; Horowitz, R. A,; Woodcock, C. L.; Adkins, N. A.; Wade, P. A.; Hansen, J. C. J. Biol. Chem, 2003, 278, 32181-32188.