RNA helicase DDX21 sustains hematopoietic stem cell homeostasis by preventing nucleolar stress

Hematopoietic stem cell (HSC) homeostasis is critically dependent on precisely regulated protein synthesis, with the nucleolus serving as the principal orchestrator of ribosome biogenesis and cellular stress sensing. DDX21, a nucleolus-localized DEAD-box RNA helicase, serves as a master regulator in ribosomal DNA (rDNA) transcription and ribosome assembly. Nevertheless, its precise function in adult hematopoiesis remains incompletely understood. Here, we reveal that conditional knockout of Ddx21 in the murine hematopoietic system triggers collapse of HSC homeostasis, characterized by loss of quiescence, impaired self-renewal capacity, and raised apoptosis. Mechanistically, we demonstrate that DDX21 physically associates with both rDNA loci and promoters of ribosomal protein genes. Its loss disrupts ribosome production, causes nucleolar stress, culminates in p53-mediated cell cycle arrest and apoptosis in HSPCs. Taken together, our study establishes DDX21 as a master regulator in HSCs, integrating ribosome biogenesis with nucleolar stress induction and hematopoietic homeostasis. • DDX21 is essential for hematopoietic stem cell maintenance in adult hematopoiesis. • DDX21 regulates rDNA transcription and ribosome biogenesis • Ddx21 deficiency leads to nucleolar stress in HSCs.