Figure 1

Subcellular localisation of Dnmt1 isoforms in mouse somatic cells and preimplantation embryos. A) Schematic representation of GFP-Dnmt1 fusion proteins. The start codons of the long (ATG_L) and the short (ATG_S) isoforms are indicated. The catalytic domain of Dnmt1 is in black. Subcellular localisation of GFP-Dnmt1 fusions in somatic cells (B) and 2-cell embryos (C). In B mouse C2C12 myoblasts were transfected with either the GFP-Dnmt1S (left pair of panels) or the GFP-Dnmt1L expression constructs (right pair of panels) and imaged by confocal microscopy. The left panel in each pair shows the phase contrast image, while the right panel shows GFP fluorescence (scale bars = 5 μm). In C the same expression constructs were microinjected in pronuclei at the 1-cell stage and embryos were further cultured until the 2-cell stage (scale bars = 20 μm). Both the short and the long isoforms of Dnmt1 are localised in the nucleus of myoblasts and in the cytoplasm of 2-cell embryos. Small amounts of fusion proteins in embryonic nuclei (arrowheads) are due to overexpression of Dnmt1 and consequent saturation of the cytoplasmic retention mechanism.