Analysis of the transcriptomic changes of myoblasts lacking Daxx or both Daxx and Hira histone chaperones

DAXX, a H3.3 histone chaperone known for its role in heterochromatin maintenance, has been understudied in the context of gene expression regulation. In this study, we generated Daxx knockout myogenic cells and observed a significant loss of myogenic markers expression and impaired differentiation. Transcriptome analysis revealed broad dysregulations in Daxx KO cells, including loss of myogenic identity and a concurrent upregulation of genes involved in DNA replication and telomere maintenance. Chromatin immunoprecipitation followed by sequencing demonstrated a marked reduction in H3.3 deposition, particularly in intronic and intergenic regions. Further analysis indicated that loss of DAXX leads to decreased H3K27ac at myogenic loci and a shift in repressive histone marks, which led to impaired gene expression. Intriguingly, double knockout of Daxx and Hira resulted in distinct transcriptomic alterations, demonstrating that DAXX and HIRA have both overlapping and unique roles in H3.3 incorporation. Our work also suggests the presence of additional histone chaperone complexes in maintaining chromatin integrity in myoblasts. Our findings establish DAXX as a critical regulator of myogenic gene expression and muscle cell identity through a distinct mechanism from that of HIRA and highlighted an unanticipated plasticity in the deposition loci for DAXX and HIRA in myoblasts.