Linker histone H1 regulates homeostasis of heterochromatin-associated cRNAs
Paula Bujosa,
Oscar Reina,
Adrià Caballé,
Anna Casas-Lamesa,
Mònica Torras-Llort,
Juan Pérez-Roldán,
Ana Silvina Nacht,
Guillermo P. Vicent,
Jordi Bernués,
Fernando Azorín
Affiliations
Paula Bujosa
Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
Oscar Reina
Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
Adrià Caballé
Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
Anna Casas-Lamesa
Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
Mònica Torras-Llort
Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
Juan Pérez-Roldán
Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain
Ana Silvina Nacht
Centre de Regulació Genòmica (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain
Guillermo P. Vicent
Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Centre de Regulació Genòmica (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain
Jordi Bernués
Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain; Corresponding author
Fernando Azorín
Institute of Molecular Biology of Barcelona, CSIC, Baldiri Reixac, 4, 08028 Barcelona, Spain; Institute for Research in Biomedicine, IRB Barcelona. The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028 Barcelona, Spain; Corresponding author
Summary: Chromatin-associated RNAs (cRNAs) are a poorly characterized fraction of cellular RNAs that co-purify with chromatin. Their full complexity and the mechanisms regulating their packaging and chromatin association remain poorly understood. Here, we address these questions in Drosophila. We find that cRNAs constitute a heterogeneous group of RNA species that is abundant in heterochromatic transcripts. We show that heterochromatic cRNAs interact with the heterogeneous nuclear ribonucleoproteins (hnRNP) hrp36/hrp48 and that depletion of linker histone dH1 impairs this interaction. dH1 depletion induces the accumulation of RNA::DNA hybrids (R-loops) in heterochromatin and, as a consequence, increases retention of heterochromatic cRNAs. These effects correlate with increased RNA polymerase II (RNAPII) occupancy at heterochromatin. Notably, impairing cRNA assembly by depletion of hrp36/hrp48 mimics heterochromatic R-loop accumulation induced by dH1 depletion. We also show that dH1 depletion alters nucleosome organization, increasing accessibility of heterochromatin. Altogether, these perturbations facilitate annealing of cRNAs to the DNA template, enhancing R-loop formation and cRNA retention at heterochromatin.
