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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 are associated with kinetochores in  three different cell lines. Human centromeres were localized using an autoimmune  sera against kinetochores,  and are shown in red. Their  spatial relationship with PcG  bodies, labeled with the anti-RING1 antibody (green),  are shown in (a) 2C4 cells,  (b) U-2 OS cells, and (c)  CS22F cells. All images are a  digital overlay of the two optical channels obtained from  a single 1-μm optical confocal section. Any colocalization observed is shown by a  yellow signal.
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Figure 3: PcG bodies are associated with kinetochores in three different cell lines. Human centromeres were localized using an autoimmune sera against kinetochores, and are shown in red. Their spatial relationship with PcG bodies, labeled with the anti-RING1 antibody (green), are shown in (a) 2C4 cells, (b) U-2 OS cells, and (c) CS22F cells. All images are a digital overlay of the two optical channels obtained from a single 1-μm optical confocal section. Any colocalization observed is shown by a yellow signal.

Mentions: We previously reported that PcG bodies do not colocalize with kinetochore complexes, present at centromeres on all human chromosomes, in human SW480 cells (Satijn et al., 1997b). However, upon closer reexamination of numerous labeled cells from different cell lines, we noticed that there was a distinct relationship between the PcG structures and kinetochores revealed by a partial overlap of the two fluorescent signals (see Fig. 3 and Satijn et al., 1997b). By analyzing fluorescently labeled PcG bodies and kinetochores on single 1-μm confocal sections, we observe that a significant proportion of both PcG bodies in 2C4 cells always colocalizes with two kinetochore-labeled centromeres (Fig. 3 a and inset).


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 are associated with kinetochores in  three different cell lines. Human centromeres were localized using an autoimmune  sera against kinetochores,  and are shown in red. Their  spatial relationship with PcG  bodies, labeled with the anti-RING1 antibody (green),  are shown in (a) 2C4 cells,  (b) U-2 OS cells, and (c)  CS22F cells. All images are a  digital overlay of the two optical channels obtained from  a single 1-μm optical confocal section. Any colocalization observed is shown by a  yellow signal.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132874&req=5

Figure 3: PcG bodies are associated with kinetochores in three different cell lines. Human centromeres were localized using an autoimmune sera against kinetochores, and are shown in red. Their spatial relationship with PcG bodies, labeled with the anti-RING1 antibody (green), are shown in (a) 2C4 cells, (b) U-2 OS cells, and (c) CS22F cells. All images are a digital overlay of the two optical channels obtained from a single 1-μm optical confocal section. Any colocalization observed is shown by a yellow signal.
Mentions: We previously reported that PcG bodies do not colocalize with kinetochore complexes, present at centromeres on all human chromosomes, in human SW480 cells (Satijn et al., 1997b). However, upon closer reexamination of numerous labeled cells from different cell lines, we noticed that there was a distinct relationship between the PcG structures and kinetochores revealed by a partial overlap of the two fluorescent signals (see Fig. 3 and Satijn et al., 1997b). By analyzing fluorescently labeled PcG bodies and kinetochores on single 1-μm confocal sections, we observe that a significant proportion of both PcG bodies in 2C4 cells always colocalizes with two kinetochore-labeled centromeres (Fig. 3 a and inset).

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
Related in: MedlinePlus