Abstract
In vertebrate definitive hematopoiesis, nascent hematopoietic stem/progenitor cells (HSPCs) migrate to and reside in proliferative hematopoietic microenvironment for transitory expansion. In this process, well-established DNA damage response pathways are vital to resolve the replication stress, which is deleterious for genome stability and cell survival. However, the detailed mechanism on the response and repair of the replication stress-induced DNA damage during hematopoietic progenitor expansion remains elusive. Here we report that a novel zebrafish mutantcas003 with nonsense mutation in topbp1 gene encoding topoisomerase II β binding protein 1 (TopBP1) exhibits severe definitive hematopoiesis failure. Homozygous topbp1cas003 mutants manifest reduced number of HSPCs during definitive hematopoietic cell expansion, without affecting the formation and migration of HSPCs. Moreover, HSPCs in the caudal hematopoietic tissue (an equivalent of the fetal liver in mammals) in topbp1cas003 mutant embryos are more sensitive to hydroxyurea (HU) treatment. Mechanistically, subcellular mislocalization of TopBP1cas003 protein results in ATR/Chk1 activation failure and DNA damage accumulation in HSPCs, and eventually induces the p53-dependent apoptosis of HSPCs. Collectively, this study demonstrates a novel and vital role of TopBP1 in the maintenance of HSPCs genome integrity and survival during hematopoietic progenitor expansion.
Highlights
Hematopoietic stem/progenitor cells (HSPCs) possess the capabilities of self-renewal and differentiation into all lineages of mature blood cells [1]
The rapidly proliferating hematopoietic stem/progenitor cells (HSPCs) require well-established DNA damage response/repair pathways to resolve the DNA replication stressinduced DNA damage, which is deleterious for the genome stability and cell survival
We reported a novel function of topoisomerase II β binding protein 1 (TopBP1) in definitive hematopoiesis through characterizing zebrafish mutantcas003 with a nonsense mutation in topbp1 gene encoding TopBP1
Summary
Hematopoietic stem/progenitor cells (HSPCs) possess the capabilities of self-renewal and differentiation into all lineages of mature blood cells [1]. With multiple unique advantages including external fertilization and development, optically transparent embryos, small size and high fecundity, zebrafish is extraordinarily suitable for the unbiased large scale forward genetics screening to identify novel genes regulating HSPCs self-renewal in the embryonic development [10]. HSPCs originate in the ventral wall of dorsal aorta (an equivalent of the aortagonad-mesonephros [AGM] in mammals) through endothelium to hematopoietic transition (EHT) from 26 hours post fertilization (hpf) [13,14], and colonize in caudal hematopoietic tissue (CHT, an equivalent to the fetal liver [FL] in mammal) (at 2 days post fertilization [dpf]), thymus (at 3dpf) and kidney marrow to support adult hematopoiesis (equivalent to bone marrow (BM) in mammal) (after 5dpf) [15,16]. It has been reported that 95–100% of HSPCs are actively cycling in the mouse fetal liver, whereas most of adult HSPCs are in a quiescent state [17]
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