Dynamic Changes in the Localization of Five Members of the Methyl Binding Domain (MBD) Gene Family During Murine and Bovine Preimplantation Embryo Development

There are five methyl binding domain (MBD) proteins characterized by a methyl CpG- binding domain. Four MBD proteins (MeCP2 and MBDs 1-3) are linked to transcriptional repression and one (MBD4), to DNA repair. During preimplantation devel- opment, the embryo undergoes global demethylation following fertilization and selectiveremethylation follow- ing the maternal to zygotic transition (MZT). This study characterized changes in MBD mRNA expression and protein localization during both murine and bovine preimplantation development. These species were se- lected because they undergo MZT at different devel- opmental stages. Gene expression profiling during preimplantation development detected the presence of allMBDsexamined,althoughstage andspecies-specific differences were observed. MBD2 was not expressed in murineorbovineoocytesandMeCP2wasnotdetectedin murine blastocysts, subcellular protein localization was foundtovaryattimepointscriticalindevelopment.Most MBDsshowedspecies-specificityinlocalizationpatterns and differences were found between individual MBDs. MBD1 localization is consistent with a novel role during MZTforbothspecies.MBD3,knowntoplayacrucialrole in murine embryogenesis, was highly localized to the nucleus before and after, but not during the MZT in the bovine. MBD2, MBD4, and MeCP2 show varying patterns of localization which indicate possible roles in the early cleavage stages and in inner cell mass differ- entiation. Further experimentsare currently underwayto define discreet functional roles for specific MBDs during bovine preimplantation embryogenesis. Mol. Reprod. Dev.75:48-59, 2008. 2007Wiley-Liss,Inc.