Histone Variant H1.0 Regulates Terminal Erythroid Differentiation via Phase Separation-Mediated Chromatin Organization

Mammalian erythroblasts require enucleation to form mature red blood cells during terminal stage of erythroid differentiation, in which chromatin and nuclear condensation are considered prerequisites for enucleation. Linker histone H1 is a key player in heterochromatin condensation and silencing, but it is unclear how H1 compresses chromatin and regulates erythroid differentiation. Here, we demonstrated that H1.0 was significantly overexpressed in terminal erythropoiesis among all histone H1 variants, whose deletion resulted in abnormal chromatin and nuclear condensation, impaired enucleation and increased apoptosis in terminal erythropoiesis. In addition, we established that H1.0 deficiency decompressed chromatin by increasing chromatin long-range and proximal interactions and remodeling topologically associating domain (TAD) boundaries of the genome. We demonstrated that H1.0 compressed chromatin via binding to nucleosomal DNA to form a phase separation, which required the C/N-terminal intrinsically disordered region (C-IDR) and G domain (GD). A truncated H1.0 lacking the C-IDR failed to compress chromatin in H1.0-deleted erythroid cells, whereas a truncated H1.0 lacking the N-IDR partially rescues this defect. In conclusion, our findings suggest that H1.0 remodels chromatin high-order structure and regulates erythropoiesis through a phase separation mechanism, providing novel insights into the regulation of chromatin condensation and enucleation in terminal erythropoiesis.