Mouse HP1? regulates TRF1 expression and telomere stability

Telomeric Repeat-containing RNA are long non-coding RNAs generated from the telomeres. TERRAs are essential for the establishment of heterochromatin marks at telomeres, which serve for the binding of members of the Heterochromatin Protein 1protein family of epigenetic modifiers involved with chromatin compaction and gene silencing. While HP1? is enriched on gene bodies of actively transcribed mammalian genes, it is unclear if its transcriptional role is important for HP1? function in telomere cohesion and telomere maintenance. We aimed to study the effect of mouse HP1? on the transcription of telomere factors and molecules that can affect telomere maintenance. We investigated the telomere function of HP1? by using HP1? deficient mouse embryonic fibroblastsderiving from 13.5 embryonic day embryos compared to their littermate controls. We used gene expression analysis of HP1? deficient MEFs and validated the molecular and mechanistic consequences of HP1? loss by telomere FISH, immunofluorescence, RT-qPCR and DNA-RNA Immunoprecipitation. Loss of HP1? in primary MEFs led to a downregulation of various telomere and telomere-accessory transcripts, including the shelterin protein TRF1. Its downregulation is associated with increased telomere replication stress and DNA damage (?H2AX), effects more profound in females. We suggest that the source for the impaired telomere maintenance is a consequence of increased telomeric DNARNA hybrids and TERRAs arising at and from mouse chromosomes 18 and X. Our results suggest an important transcriptional control by mouse HP1? of various telomere factors including TRF1 protein and TERRAs that has profound consequences on telomere stability, with a potential sexually dimorphic nature. Overall design: Cleavage Under Targets & Release Using Nuclease (CUT & RUN) for chromatin binding protein HP1?, histone modification H3K27me3 and IgG (negative control) in primary Mouse Embryonic Fibroblast (MEFs) deriving from E13.5 embryos.