DNA methylation had been implicated in the assembly of multiprotein repressory complexes that affect chromatin architecture thereby rendering genes inactive. Proteins containing methyl binding domains (MBDs) are major components of these complexes. MBD3 is a component of the HDAC associated chromatin remodeling complex Mi2/NuRD. The addition of MBD2 to the Mi2/NuRD complex creates MeCP1, a complex that is known to inactivate methylated promoters. The undermethylated state of the mouse preimplantation embryo prompted us to investigate the known repressory complexes at this developmental stage. We found individual components of Mi2/NuRD: MBD3, Mi2, HDAC1 and HDAC2 to be expressed from a very early stage of embryo development and to localize in close proximity with each other and with constitutive heterochromatin by the blastula stage. Expression of MBD2, a component of MeCP1, starts in the blastula stage. Then it is also found to be in proximity with heterochromatin (based on DAPI staining) and with MBD3, Mi2 and HDAC1. In contrast, expression of MeCP2, an MBD containing component of a third repressory complex (MeCP2/Sin3A), is not seen in the preimplantation embryo. Our results suggest that both Mi2/NuRD and MeCP1 complexes are already present at the very early stages of embryo development, while a MeCP2 complex is added to the arsenal of repressory complexes post-implantation at a stage when DNA methylation takes place.
Bibliographical noteFunding Information:
This work was supported by grants from the NIH, Israel Science Foundation Center of Excellence (A.R.) and Rett Syndrome Research Foundation (RSRF). We are grateful to Dr Ben-Zion Tsuberi for providing fertilized mouse oocytes. We are grateful to our colleagues who provided us with high quality antibodies. Rabbit anti-human Mi2 was a gift from Dr Paul Wade, rat anti-mouse HP1 (M31) from Dr Prim Singh and sheep anti-mouse MBD2 was kindly provided by Dr Adrian Bird.
- Chromatin structure
- DNA methylation
- Embryo development
- Gene repressory complexes
- Histone deacetylase
- Mouse embryo