MYSM1 maintains ribosomal protein gene expression in hematopoietic stem cells to prevent hematopoietic dysfunction I.. MYSM1 maintains ribosomal protein gene expression in hematopoietic stem cells to prevent hematopoietic dysfunction I.

MYSM1 is a transcriptional regulator essential for HSC function and hematopoiesis. We established that HSC dysfunction in Mysm1-deficiency is driven by p53 stress response, however, the molecular function of MYSM1 as a transcriptional activator and its essential role in p53 stress response repression remain difficult to reconcile. Here, we performed genome-wide analyses of MYSM1-regulated genes in hematopoietic stem and progenitor cells (HSPCs). This included RNA-Seq of sorted Mysm1-deficient mouse HSCs and MPPs, and ChIP-Seq mapping of MYSM1 DNA-binding sites in hematopoietic progenitor cell lines. We demonstrate a direct role for MYSM1 in the regulation of genes encoding protein components of the ribosome (RP-genes) and other regulators of translation. Mechanistically, the dysregulation of RP-genes in Mysm1-deficiency was upstream of p53-activation and associated with reduced HSCs protein synthesis rates and p53-dependent anemia. Overall design: To gain insight into the genomic regions directly regulated by MYSM1 in hematopoietic cells, we mapped MYSM1 DNA binding sites by ChIP-Seq. The experiments were carried out in two murine hematopoietic progenitor lines expressing triple-FLAG-tagged MYSM1: a multipotent progenitor line HPC7 widely used as a model to study transcriptional programs of hematopoiesis, and pro-B cell line Ba/F3 that was used in our previous work to model p53-activation and other molecular mechanisms of Mysm1-deficiency (Belle et al., 2016).