Visualizing the Dynamics of Inactive X Chromosomes in Living Cells Using Antibody-Based Fluorescent Probes

The inactive X chromosome (Xi) harbors characteristic epigenetic features, including the enrichment of histone H3 lysine 27 trimethylation (H3K27me3) and H4 lysine 20 monomethylation (H4K20me1) as well as a lack of histone acetylation. Recently, these modifications have been visualized not only in fixed specimen, but also in living cells via probes derived from modification-specific antibodies. The probes include fluorescently labeled antigen binding fragments (Fabs), which can be loaded into cells, as well as genetically encoded single-chain variable fragments tagged with the green fluorescent protein. We refer to the latter as modification specific intracellular antibodies, or "mintbodies" for short. By using Fabs or mintbodies to target Xi-specific modifications, the dynamics of Xi in living cells can be visualized.