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Profile Publications(16)
XB-PERS-1046

Dr.  Richard R. Meehan

Position

Project leader

Research Description

Epigenetics describes the variation of gene expression that is not due to changes in the DNA sequence. There is accumulating evidence that epigenetic mechanisms play crucial roles over the lifetime of an organism (from conception onwards) in setting up and maintaining stable patterns of gene expression in the specialised cells of the body. Our general aim is to describe molecular mechanisms for transcriptional silencing by the DNA methylation machinery that will be applicable in diverse contexts such as developmental gene regulation, imprinting, human disease, assisted reproductive technologies, cloning and cancer.  

We have shown in Xenopus laevis that the maintenance methyltransferase, xDnmt1, is required for the preservation of genome-wide transcriptional silencing that occurs between fertilisation and the mid-blastula transition (MBT)(Stancheva et al. 2000,Genes Dev., 14 313-327). We have also implicated DNA methylation in the precise regulation of developmentally essential genes(Stancheva et al. 2002,Dev.Biol., 243 155-165). The phenotypes of methylation-deficient Xenopus, mouse and zebrafish embryos are broadly similar, implying that the DNA methylation may have functionally similar roles in all three species.

The transcription repression function of DNA methylation is mainly mediated by a family of nuclear factors that preferentially interact with methyl-CpGs(Bird 2002,Genes Dev., 16 6-21). In mammals, MBD1, MBD2, MBD3, and MBD4 all contain a region homologous to the methyl-CpG binding domain (MBD) of MeCP2, which was initially identified biochemically (Lewis et al. 1992,Cell, 69 905-914;Meehan et al. 1992,Nucleic Acids Res., 20 5085-5092). The methyl-CpG-binding protein, MBD2, is a component of the NuRD/MeCP1 histone deacetylase complex that preferentially binds, remodels, and deacetylates methylated nucleosomes in vitro (Feng et al. 2001,Genes Dev., 15 827-832). Another chromatin modifying co-repressor complex contains NCoR and Kaiso, a novel methyl-CpG binding protein that binds methylated DNA with some sequence specificity via zinc-finger motifs(Yoon et al. 2003,Mol.Cell, 12 723-734). Our ongoing analysis suggests that each of these proteins has specific roles during Xenopus development. For example, we have implicated xMeCP2as an important regulator, via the Notch-Delta pathway of primary neurogenesis in Xenopus laevis (Stancheva et al. 2003,Mol.Cell, 12 425-435). We identified the Xenopus homologue of Kaiso, which had the same modular structure with a N-terminal POZ/BTB domain and C-terminal zinc finger (Zf) domains. We could show that xKaiso also regulates zygotic gene activation at MBT. Inhibition of xKaiso function by morpholino (KMO) injection results in embryos that are phenotypically similar to xDnmt1 depleted embryos. In both cases, we observe apotosis and premature gene activation prior to MBT. The mutant phenotypes can be rescued by over-expression of wild type human Kaiso but not by a mutant that cannot bind methylated DNA. In the absence of xKaiso, embryos die at late neurula stage with an exogastrula phenotype. (Ruzov et al. 2004,Development, 131(24):6185-94).

Lab Memberships

British Xenopus Group (Other)
Meehan Lab (Principal Investigator/Director)


Contact

Address:
MRC
Human Genetics Unit
Western General Hospital
Crewe Road
Edinburgh
EH4 2XU, United Kingdom

Email: richard.meehan@hgu.mrc.ac.uk

Web Page: http://wwwlocal.hgu.mrc.ac.uk/

General/Lab Fax:  44 (0) 131 467 8456
Phone:  + 44 (0) 131 332 2471


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