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The human polycomb group complex associates with pericentromeric heterochromatin to form a novel nuclear domain.

Saurin AJ, Shiels C, Williamson J, Satijn DP, Otte AP, Sheer D, Freemont PS - J. Cell Biol. (1998)

Bottom Line: The Polycomb group (PcG) complex is a chromatin-associated multiprotein complex, involved in the stable repression of homeotic gene activity in Drosophila.Furthermore, these heterochromatin-bound PcG complexes remain stably associated throughout mitosis, thereby allowing the potential inheritance of the PcG complex through successive cell divisions.We discuss these results in terms of the known function of the PcG complex as a transcriptional repression complex.

View Article: PubMed Central - PubMed

Affiliation: Molecular Structure and Function Laboratory, Imperial Cancer Research Fund, London WC2A 3PX, United Kingdom.

ABSTRACT
The Polycomb group (PcG) complex is a chromatin-associated multiprotein complex, involved in the stable repression of homeotic gene activity in Drosophila. Recently, a mammalian PcG complex has been identified with several PcG proteins implicated in the regulation of Hox gene expression. Although the mammalian PcG complex appears analogous to the complex in Drosophila, the molecular mechanisms and functions for the mammalian PcG complex remain unknown. Here we describe a detailed characterization of the human PcG complex in terms of cellular localization and chromosomal association. By using antibodies that specifically recognize three human PcG proteins- RING1, BMI1, and hPc2-we demonstrate in a number of human cell lines that the PcG complex forms a unique discrete nuclear structure that we term PcG bodies. PcG bodies are prominent novel nuclear structures with the larger PcG foci generally localized near the centromeres, as visualized with a kinetochore antibody marker. In both normal fetal and adult fibroblasts, PcG bodies are not randomly dispersed, but appear clustered into defined areas within the nucleus. We show in three different human cell lines that the PcG complex can tightly associate with large pericentromeric heterochromatin regions (1q12) on chromosome 1, and with related pericentromeric sequences on different chromosomes, providing evidence for a mammalian PcG-heterochromatin association. Furthermore, these heterochromatin-bound PcG complexes remain stably associated throughout mitosis, thereby allowing the potential inheritance of the PcG complex through successive cell divisions. We discuss these results in terms of the known function of the PcG complex as a transcriptional repression complex.

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PcG bodies preferentially associate to chromosome 1 territories in 2C4 cells. Digitally merged images of numerous interphase 2C4 cells localizing the chromosome 1 in situ–hybridized  probe by immunofluorescence showing the entire chromosome 1  territories (red) and immunofluorescent localization of PcG bodies using the anti-RING1 antibody (green) are shown. The green  channel–labeled PcG bodies can always be seen associated with  the red channel–labeled chromosome 1 territories in nuclei of  2C4 cells (yellow).
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Figure 4: PcG bodies preferentially associate to chromosome 1 territories in 2C4 cells. Digitally merged images of numerous interphase 2C4 cells localizing the chromosome 1 in situ–hybridized probe by immunofluorescence showing the entire chromosome 1 territories (red) and immunofluorescent localization of PcG bodies using the anti-RING1 antibody (green) are shown. The green channel–labeled PcG bodies can always be seen associated with the red channel–labeled chromosome 1 territories in nuclei of 2C4 cells (yellow).

Mentions: The PcG complex in Drosophila is known to associate directly with specific chromosomal sites along polytene chromosomes (Zink and Paro, 1989). To study possible chromosomal associations of the human PcG complex, we used a protocol whereby the procedures for immunofluorescent localization of protein complexes and FISH of specific genetic loci were combined to produce a method that allows the identification of any PcG body–chromatin association in interphase cells. By labeling PcG bodies with the anti-RING1 antibody and sequentially hybridizing chromosome-specific paints to interphase 2C4 nuclei, we find that PcG bodies present in these cells consistently localize to regions of the nucleus occupied by chromosome 1 (Fig. 4). We do not see any instance where PcG bodies are not localized with chromosome 1, nor do we see any colocalization or association with any of the other chromosome territories (data not shown). This approach provides us with evidence that PcG bodies in 2C4 cells may be chromosomally associated, as is the case for the PcG complex in Drosophila. We therefore used this technique to map the association of PcG bodies finely with chromosome 1 and related sequences in a variety of cell lines.


The human polycomb group complex associates with pericentromeric heterochromatin to form a novel nuclear domain.

Saurin AJ, Shiels C, Williamson J, Satijn DP, Otte AP, Sheer D, Freemont PS - J. Cell Biol. (1998)

PcG bodies preferentially associate to chromosome 1 territories in 2C4 cells. Digitally merged images of numerous interphase 2C4 cells localizing the chromosome 1 in situ–hybridized  probe by immunofluorescence showing the entire chromosome 1  territories (red) and immunofluorescent localization of PcG bodies using the anti-RING1 antibody (green) are shown. The green  channel–labeled PcG bodies can always be seen associated with  the red channel–labeled chromosome 1 territories in nuclei of  2C4 cells (yellow).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2132874&req=5

Figure 4: PcG bodies preferentially associate to chromosome 1 territories in 2C4 cells. Digitally merged images of numerous interphase 2C4 cells localizing the chromosome 1 in situ–hybridized probe by immunofluorescence showing the entire chromosome 1 territories (red) and immunofluorescent localization of PcG bodies using the anti-RING1 antibody (green) are shown. The green channel–labeled PcG bodies can always be seen associated with the red channel–labeled chromosome 1 territories in nuclei of 2C4 cells (yellow).
Mentions: The PcG complex in Drosophila is known to associate directly with specific chromosomal sites along polytene chromosomes (Zink and Paro, 1989). To study possible chromosomal associations of the human PcG complex, we used a protocol whereby the procedures for immunofluorescent localization of protein complexes and FISH of specific genetic loci were combined to produce a method that allows the identification of any PcG body–chromatin association in interphase cells. By labeling PcG bodies with the anti-RING1 antibody and sequentially hybridizing chromosome-specific paints to interphase 2C4 nuclei, we find that PcG bodies present in these cells consistently localize to regions of the nucleus occupied by chromosome 1 (Fig. 4). We do not see any instance where PcG bodies are not localized with chromosome 1, nor do we see any colocalization or association with any of the other chromosome territories (data not shown). This approach provides us with evidence that PcG bodies in 2C4 cells may be chromosomally associated, as is the case for the PcG complex in Drosophila. We therefore used this technique to map the association of PcG bodies finely with chromosome 1 and related sequences in a variety of cell lines.

Bottom Line: The Polycomb group (PcG) complex is a chromatin-associated multiprotein complex, involved in the stable repression of homeotic gene activity in Drosophila.Furthermore, these heterochromatin-bound PcG complexes remain stably associated throughout mitosis, thereby allowing the potential inheritance of the PcG complex through successive cell divisions.We discuss these results in terms of the known function of the PcG complex as a transcriptional repression complex.

View Article: PubMed Central - PubMed

Affiliation: Molecular Structure and Function Laboratory, Imperial Cancer Research Fund, London WC2A 3PX, United Kingdom.

ABSTRACT
The Polycomb group (PcG) complex is a chromatin-associated multiprotein complex, involved in the stable repression of homeotic gene activity in Drosophila. Recently, a mammalian PcG complex has been identified with several PcG proteins implicated in the regulation of Hox gene expression. Although the mammalian PcG complex appears analogous to the complex in Drosophila, the molecular mechanisms and functions for the mammalian PcG complex remain unknown. Here we describe a detailed characterization of the human PcG complex in terms of cellular localization and chromosomal association. By using antibodies that specifically recognize three human PcG proteins- RING1, BMI1, and hPc2-we demonstrate in a number of human cell lines that the PcG complex forms a unique discrete nuclear structure that we term PcG bodies. PcG bodies are prominent novel nuclear structures with the larger PcG foci generally localized near the centromeres, as visualized with a kinetochore antibody marker. In both normal fetal and adult fibroblasts, PcG bodies are not randomly dispersed, but appear clustered into defined areas within the nucleus. We show in three different human cell lines that the PcG complex can tightly associate with large pericentromeric heterochromatin regions (1q12) on chromosome 1, and with related pericentromeric sequences on different chromosomes, providing evidence for a mammalian PcG-heterochromatin association. Furthermore, these heterochromatin-bound PcG complexes remain stably associated throughout mitosis, thereby allowing the potential inheritance of the PcG complex through successive cell divisions. We discuss these results in terms of the known function of the PcG complex as a transcriptional repression complex.

Show MeSH