Regulation of Hematopoietic Stem Cell Function By the Histone H2A Deubiquitinase Usp16

Epigenetic mechanism plays important regulatory roles in hematopoiesis and hematopoietic stem cell (HSC) function. Subunits of Polycomb repressive complex 1 (PRC1), the major histone H2A ubiquitin ligase, are critical for both normal and pathological hematopoiesis; however, it was unclear which H2A deubiquitinase pairs with PRC1 to control H2A ubiquitination (ubH2A) level in vivo and regulates hematopoiesis. Here we investigated the function of Usp16 in mouse hematopoiesis. Deletion of Usp16 in bone marrow resulted in a significant increase of global ubH2A level and mouse lethality. Usp16 deletion was associated with a dramatic reduction of progenitor cell populations and unchanged HSC number, revealing a critical role for Usp16 in HSC differentiation. The HSC differentiation defect was correlated with a great reduction of G1 phase cell population. RNA-seq and RT-qPCR studies revealed that Usp16 regulates the expression of many genes associated with HSC differentiation and self-renewal including cell cycle regulator p21. Significantly, knockdown of p21 largely rescued the undifferentiated phenotype of Usp16 deleted HSCs. Usp16 binds to regions flanking transcription start site and knockdown of PRC1 subunits, which reduced ubH2A levels, largely rescued the altered gene expression pattern associated with Usp16 deletion. Therefore, these studies identified Usp16 as the H2A deubiquitinase that pairs with PRC1 to regulate hematopoiesis in vivo and revealed that Usp16 regulates HSC function by affecting HSC cell cycle progression.