HP1γ associates with euchromatin and heterochromatin in mammalian nuclei and chromosomesMinc E. · Courvalin J.-C. · Buendia B.
Département de Biologie Cellulaire, Institut Jacques Monod, CNRS, Universités Paris 6 and 7, Paris (France)
Heterochromatin protein 1 (HP1) is a nonhistone chromosomal protein, first identified in Drosophila, that plays a dose-dependent role in gene silencing. Three orthologs, HP1α, HP1β, and HP1γ, have been characterized in mammals. While HP1α and HP1β have been unambiguously localized in heterochromatin by immunocytochemical methods, HP1γ has been found either exclusively associated with euchromatin or present in both euchromatin and heterochromatin. Here, using an antibody directed against a peptide epitope at the carboxyl-terminal end of the molecule, we localize HP1γ in both euchromatin and heterochromatin compartments of interphase nuclei, as well as in the pericentromeric chromatin and arms of mitotic chromosomes of 3T3 cells. This dual location was also observed in nuclei expressing HP1γ as a fusion protein with green fluorescent protein. In contrast, when the distribution of HP1γ was analyzed with antibodies directed against an amino-terminal epitope, the protein was detectable in euchromatin and not in heterochromatin, except for transient heterochromatin staining during the late S phase, when the heterochromatin undergoes replication. These data suggest that the controversial immunolocalization of HP1γ in chromatin is due to the use of antibodies directed against topologically distinct epitopes, those present at the amino-terminal end of the molecule being selectively masked in nonreplicative heterochromatin.
Request reprints from Dr. Brigitte Buendia, Département de Biologie Cellulaire,Institut Jacques Monod, CNRS, Université Paris 7, Tour 43, 2 Place JussieuF–75251 Paris cedex 05 (France); telephone: 33-1-44-27-76-21;fax: 33-1-44-27-59-94; e-mail: email@example.com.
Supported by a grant from the Association pour la Recherche sur le Cancer (ARC 9227) to J.-C.C. E.M. was supported by a grant from the Ministère de la Recherche et de la Technologie (MRT), and J.-C.C. by the Institut National de la Santé et de la Recherche Médicale (INSERM).
Received: Received 23 June 2000;
revision accepted 9 August 2000.
Number of Print Pages : 6
Number of Figures : 5, Number of Tables : 0, Number of References : 45
Cytogenetics and Cell Genetics
Founded 1962 as Cytogenetics by H.P. Klinger
Vol. 90, No. 3-4, Year 2000 (Cover Date: 2000)
Journal Editor: H.P. Klinger, Bronx, N.Y.; M. Schmid, Würzburg
ISSN: 0301–0171 (print), 1422–9816 (Online)
For additional information: http://www.karger.com/journals/ccg