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First published online 12 September 2007
doi: 10.1242/jcs.012955

Journal of Cell Science 120, 3425-3435 (2007)
Published by The Company of Biologists 2007
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Research Article

Variant-specific patterns and humoral regulation of HP1 proteins in human cells and tissues

Eleni Ritou1,3, Maria Bai2 and Spyros D. Georgatos1,3,*

1 Stem Cell and Chromatin Group, Laboratory of Biology, The University of Ioannina School of Medicine
2 Laboratory of Pathology, The University of Ioannina School of Medicine, Dourouti, 45 110 Ioannina, Greece
3 Biomedical Institute of Ioannina (FORTH/BRI), Dourouti, 45 110 Ioannina, Greece

* Author for correspondence (e-mail: sgeorgat{at}cc.uoi.gr)

Accepted 19 July 2007

We have examined the occurrence and distribution of HP1{alpha} and HP1beta under in vivo, ex vivo and in vitro conditions. Consistent with a non-essential role in heterochromatin maintenance, both proteins are diminished or undetectable in several types of differentiated cells and are universally downregulated during erythropoiesis. Variant-specific patterns are observed in almost all human and mouse tissues examined. Yet, the most instructive example of HP1 plasticity is observed in the lymph nodes, where HP1{alpha} and HP1beta exhibit regional patterns that are exactly complementary to one another. Furthermore, whereas HP1{alpha} shows a dispersed sub-nuclear distribution in the majority of peripheral lymphocytes, it coalesces into large heterochromatic foci upon stimulation with various mitogens and IL-2. The effect of inductive signals on HP1{alpha} distribution is reproduced by coculture of immortalized T- and B-cells and can be confirmed using specific markers. These complex patterns reveal an unexpected plasticity in HP1 variant expression and strongly suggest that the sub-nuclear distribution of HP1 proteins is regulated by humoral signals and microenvironmental cues.

Key words: HP1, Chromatin, Lymphocytes, Immunocytochemistry


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G. K. Dialynas, S. Terjung, J. P. Brown, R. L. Aucott, B. Baron-Luhr, P. B. Singh, and S. D. Georgatos
Plasticity of HP1 proteins in mammalian cells
J. Cell Sci., October 1, 2007; 120(19): 3415 - 3424.
[Abstract] [Full Text] [PDF]


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