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A role for methyl-CpG binding domain protein 2 in olfactory neuronal development Cheng, Jenny S.

Abstract

Methylation of DNA is a common modification of CpG di-nucleotides and is associated with transcriptional repression. This mechanism of gene silencing can be mediated by methyl-CpG binding domain (MBD) proteins, which form repressor complexes that are important in linking DNA methylation and transcriptional repression by altering chromatin structure. We have identified MBD2 as a gene that is highly upregulated following bulbectomy in mouse. MBD2 has been shown to bind methylated DNA and belongs to the MeCPl repressor complex, which includes the histone deacetylases HDAC1 and HDAC2 and the histone binding proteins RbAp46 and RbAp48 (Hendrich and Bird, 1998; Bird and Wolffe, 1999). The bulbectomy paradigm recapitulates ORN developmental events and suggests that MBD2 is important in regulating gene expression during ORN development. This study sought to determine if MBD2 is involved in ORN development by silencing genes that are no longer needed for ORNs to achieve a mature phenotype. MBD2 was found to be dynamically expressed by ORNs at different stages of maturation during development. In the absence of MBD2 there are abnormalities in the primary neuraxis. MBD2-/- neonates have more ORNs, more axon bundles and significantly larger axon bundles and glomeruli, when compared to MBD2+/+ controls for OMP and NCAM staining. We have also generated an in vitro model of ORN development to help us understand ORN developmental events and in particular, MBD2 function. Conditionally immortalized temperature sensitive cell lines were generated from the embryonic mouse olfactory placode. Two of these, OP6 and OP27 were chosen for further characterization and confirmed to be olfactory neuron-like in nature. Both OP6 and OP27 express general neuronal and ORN markers, neurotrophin receptors and after differentiation, express OMP. Both express endogenous ORs and respond to odorant stimulation. OP6 and OP27 also express MBD2 and MBD3 in a differentiation dependent manner consistent with observations in vivo. Both OP6 and OP27 also express MeCP2, mSin3A, HDAC1 and HDAC2, all potential protein interactors of MBD2. The in vivo and in vitro data demonstrate that MBD2 is important in regulating gene expression during olfactory neuronal development.

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