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PRC1 Components Exhibit Different Binding Kinetics in Polycomb Bodies

B. Vandenbunder, N. Fourré, A. Leray, F. Mueller, P. Völkel, P.O. Angrand and L. Héliot

Biology of the Cell 106, 111-125 (2014) [Accès à la revue]


Les protéines CBX du groupe Polycomb et leurs partenaires BMI1 et RING1 forment des foyers de différentes tailles et intensités dans le noyau de cellules de mammifères. L’analyse des courbes de retour de fluorescence après photoblanchiment (FRAP) à l’extérieur de ces foyers suggère que la dynamique de ces protéines est gouvernée par la diffusion sous forme de complexes et la fixation sur leurs gènes cibles. Les courbes de retour de fluorescence dans les foyers sont beaucoup plus lentes et très variables. L’analyse des paramètres cinétiques des fractions lentes et immobiles fournit des informations sur la nucléation et l’organisation dynamique de ces foyers Polycomb.


Abstract: Background information. Polycomb group (PcG) proteins keep the memory of cell identity by maintaining the repression of numerous target genes. They accumulate into nuclear foci called Polycomb bodies, which function in Drosophila cells as silencing compartments where PcG target genes convene. PcG proteins also exert their activities elsewhere in the nucleoplasm. In mammalian cells the dynamic organization and function of Polycomb bodies remain to be determined. Results. Fluorescently tagged PcG proteins CBXs and their partners BMI1 and RING1 form foci of different sizes and intensities in human U2OS cells. FRAP (Fluorescence Recovery After Photobleaching) analysis reveals that PcG dynamics outside foci is governed by diffusion as complexes and transient binding. In sharp contrast, recovery curves inside foci are substantially slower and exhibit large variability. The slow binding component amplitudes correlate with the intensities and sizes of these foci, suggesting that foci contained varying numbers of binding sites. CBX4-GFP foci were more stable than CBX8-GFP foci; yet the presence of CBX4 or CBX8-GFP in the same focus had a minor impact on BMI1 and RING1 recovery kinetics. Conclusion. We propose that FRAP recovery curves provide information about PcG binding to their target genes outside foci and about PcG spreading onto chromatin inside foci.


Thème : Thème 2011-2014 : Signalisation et régulation

Equipe : Dynamique spatiotemporelle de cellules vivantes (PhLAM)