GSE210901
Multilevel interrogation of H3.3 dynamics reveals a primordial role in transcription regulation in Tetrahymena [ChIP-seq]
Through epigenetic modifications and selective incorporation of histone variants into chromatin, eukaryotic cells can adjust their transcriptional profile in response to molecular needs. We used the nuclear dimorphic ciliate protozoan, Tetrahymena thermophila, as a model system to investigate the dynamics of H3 variant function. H3.3 is the ancestral H3 variant with key roles in regulating chromatin states and transcription. Functional proteomics and immunofluorescence analyses of H3.1 and H3.3 revealed a conserved role for Nrp1 and Asf1 histone chaperones in nuclear influx of histones. Cac2 and Hir1 have distinct localization patterns during different stages of the Tetrahymena life cycle and suggests that both Cac2 and Hir1 might be dispensable for the replication-dependent and -independent deposition of H3.1 and H3.3, respectively. ChIP-seq experiments in growing Tetrahymena show H3.3 enrichment over promoters, genes bodies, and transcription termination sites of highly transcribed genes. H3.3 knockout followed by RNA-seq reveals large-scale transcriptional alterations in functionally important genes. Our results provide an evolutionary perspective on H3.3's conserved role in maintaining the transcriptional landscape of cells and on the emergence of specialized chromatin assembly pathways. Overall design: Examination of two ChIP-seq biological replicates for H3.3-GFP during Tetrahymena vegetative growth