Abstract
The HP1 family proteins are involved in several aspects of chromatin function and regulation in Drosophila, mammals and the fission yeast. Here we investigate the localization of LHP1, the unique Arabidopsis thaliana HP1 homolog known at present time, to approach its function. A functional LHP1–GFP fusion protein, able to restore the wild-type phenotype in the lhp1 mutant, was used to analyze the subnuclear distribution of LHP1 in both A. thaliana and Nicotiana tabacum. In A. thaliana interphase nuclei, LHP1 was predominantly located outside the heterochromatic chromocenters. No major aberrations were observed in heterochromatin content or chromocenter organization in lhp1 plants. These data indicate that LHP1 is mainly involved in euchromatin organization in A. thaliana. In tobacco BY-2 cells, the LHP1 distribution, although in foci, slightly differed suggesting that LHP1 localization is determined by the underlying genome organization of plant species. Truncated LHP1 proteins expressed in vivo allowed us to determine the function of the different segments in the localization. The in foci distribution is dependent on the presence of the two chromo domains, whereas the hinge region has some nucleolus-targeting properties. Furthermore, like the animal HP1β and HP1γ subtypes, LHP1 dissociates from chromosomes during mitosis. In transgenic plants expressing the LHP1–GFP fusion protein, two major localization patterns were observed according to cell types suggesting that localization evolves with age or differentiation states. Our results show conversed characteristics of the A. thaliana HP1 homolog with the mammal HP1γ isoform, besides specific plant properties.
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Abbreviations
- PI:
-
Propidium iodide
- DAPI:
-
4′,6-diamidino-2-phenylindole
- HP1:
-
Heterochromatin protein 1
- CD:
-
Chromo domain
- CSD:
-
Chromo shadow domain
- HR:
-
Hinge region
- RHF:
-
Relative heterochromatin fraction
- FISH:
-
Fluorescent in-situ hybridization
- NLS:
-
Nuclear localization signal
- NoLS:
-
Nucleolar localization signal
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Acknowledgments
ML was supported by a graduate studentship from the French ministry of Research. We thank our colleagues Y. Chupeau and H. Höfte. We are grateful to N. Houba-Herin, J. Davison and V. Colot (URGV, Evry, France) for critical reading of the manuscript, to O. Grandjean and S. Brown (ISV, Gif/Yvette, France) for confocal analysis support, to C. Bergounioux and C. Perennes (IBP, Orsay, France) for tobacco BY-2 cell lines transformations and W. Bickmore and N. Gilbert (MRC, Edinburgh, U.K.) for advices on MNase protocols.
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Libault, M., Tessadori, F., Germann, S. et al. The Arabidopsis LHP1 protein is a component of euchromatin. Planta 222, 910–925 (2005). https://doi.org/10.1007/s00425-005-0129-4
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DOI: https://doi.org/10.1007/s00425-005-0129-4