RNA polymerase III component Rpc9 regulates hematopoietic stem and progenitor cell maintenance in zebrafish

Hematopoietic stem and progenitor cells (HSPCs) are capable of self-renewal and replenishing all lineages of blood cells throughout life and are thus crucial for tissue homeostasis. However, the mechanism regulating HSPC development is still incompletely understood. Here, we isolate a zebrafish mutant with defective T lymphopoiesis and positional cloning identifies that Rpc9, a component of DNA-directed RNA polymerase III (Pol III) complex, is responsible for the mutant phenotype. Further analysis shows that rpc9 deficiency leads to the impairment of HSPCs and their derivatives in zebrafish embryos. Excessive apoptosis is observed in the caudal hematopoietic tissue (CHT; the equivalent of fetal liver in mammals) of rpc9(-/-) embryos and the hematopoietic defects in these embryos can be fully rescued by suppression of p53. Thus, our work illustrates that Rpc9, a component of Pol III, plays an important tissue-specific role in HSPC maintenance during zebrafish embryogenesis and might be conserved across vertebrates, including mammals.