The role of RNA in the maintenance of chromatin domains as revealed by antibody mediated proximity labelling coupled to mass spectrometry

Eukaryotic chromatin is organised in individual domains, which are defined by their location within the nuclear space, the molecular interactions within each other and their distinct proteomic compositions. In contrast to cellular organelles surrounded by lipid membranes, the composition of distinct chromatin domains is rather ill described and highly dynamic. To identify proteins associated with a specific chromatin domain and to better understand how those domains are established and maintained, we used a new method, which we termed AMPL-MS (Antibody mediated proximity labelling mass spectrometry). This method is based on antibodies and does not require the expression of fusion proteins and therefore constitutes a versatile and very sensitive method to characterize chromatin domains containing specific signature proteins or histone modifications. We used AMPL-MS to characterize the composition of chromocenter as well as the chromosome territory containing the hyperactive X-chromosome in Drosophila. As an outcome of this method, we show the importance of RNA in maintaining the integrity of these domains as treatment with RNAse alters their proteomic composition. Our data demonstrate the power of AMPL-MS to characterize the composition of non-membranous nuclear domains.