DNA methyltransferases

In this study, we used high-speed video microscopy with motion vector analysis to investigate the contractile characteristics of hiPS-CM monolayer, in addition to further characterizing the motion with extracellular field potential (FP), traction force and the Ca(2+) transient. Results of our traction force microscopy demonstrated that the force development of hiPS-CMs correlated well with the cellular deformation detected by the video microscopy with motion vector analysis. In the presence of verapamil and isoproterenol, contractile motion of hiPS-CMs showed alteration in accordance with the changes in fluorescence peak of the Ca(2+) transient, i.e., upstroke, decay, amplitude and full-width at half-maximum. Simultaneously recorded hiPS-CM motion and FP showed that there was a linear correlation between changes in the motion and field potential duration in response to verapamil (30-150nM), isoproterenol (0.1-10μM) and E-4031 (10-50nM). In addition, tetrodotoxin (3-30μM)-induced delay of sodium current was corresponded with the delay of the contraction onset of hiPS-CMs. These results indicate that the electrophysiological and functional behaviors of hiPS-CMs are quantitatively reflected in the contractile motion detected by this image-based technique. In the presence of 100nM E-4031, the occurrence of early after-depolarization-like negative deflection in FP was also detected in the hiPS-CM motion as a characteristic two-step relaxation pattern. These findings offer insights into the interpretation of the motion kinetics of the hiPS-CMs, and are relevant for understanding electrical and mechanical relationship in hiPS-CMs.

Heterochromatin protein 1 (HP1) plays an important role in heterochromatin formation. Three subtypes of HP1, namely HP1α, β, and γ, have been identified in humans. In this study, using yellow fluorescent protein(YFP) fusion constructs, we examined the intracellular localization of human HP1 subtypes during the cell cycle. During interphase, all three HP1 subtypes were localized to centromeric heterochromatin and to promyelocytic leukemia(PML) nuclear bodies. Different preferences, however, were observed among the subtypes: during interphase HP1β localized most preferentially to centromeric heterochromatin, whereas HP1α and γ were more preferentially localized to PML nuclear bodies. During metaphase, only HP1α, was localized to the centromere. We thus determined which molecular domains of HP1 were necessary for their intracellular localization. Our results showed that the C-terminal fragment (amino acid residues 101-180)of HP1α was necessary for localization to the metaphase centromere and the N-terminal fragment (amino acid residues 1-76) of HP1β was necessary for localization to the interphase centromere. Interestingly, simultaneous observations of residues 101-180 of HP1α and residues 1-76 of HP1βin living HeLa cells revealed that during late prophase, the HP1βfragment dissociated from centromeric regions and the HP1α fragment accumulated in centromeric regions. These results indicate that different specific regions of human HP1α and HP1β mediate localization to metaphase and interphase centromeric regions resulting in association of different subtypes of HP1 with the centromere at different times during the cell cycle.

Epigenetic gene silencing is one of the fundamental mechanisms for ensuring proper gene expression patterns during cellular differentiation and development. Histone deacetylases (HDACs) are evolutionally conserved enzymes that remove acetyl modifications from histones and play a central role in epigenetic gene silencing. In cells, HDAC forms a multiprotein complex (HDAC complex) in which the associated proteins are believed to help HDAC carry out its cellular functions. Though each HDAC complex contains distinct components, the presence of isoforms for some of the components expands the variety of complexes and the diversity of their cellular roles. Recent studies have also revealed a functional link between HDAC complexes and specific histone demethylases. In this paper, we summarize the distinct and cooperative roles of four class I HDAC complexes, Sin3, NuRD, CoREST, and NCoR/SMRT, with respect to their component diversity and their relationship with specific histone demethylases.