Numerical data underlying figures.

mDia formin proteins regulate the dynamics and organization of the cytoskeleton through their linear actin nucleation and polymerization activities. We previously showed that mDia1 deficiency leads to aberrant innate immune activation and induces myelodysplasia in a mouse model, and mDia2 regulates enucleation and cytokinesis of erythroblasts and the engraftment of hematopoietic stem and progenitor cells (HSPCs). However, whether and how mDia formins interplay and regulate hematopoiesis under physiological and stress conditions remains unknown. Here, we found that both mDia1 and mDia2 are required for HSPC regeneration under stress, such as serial plating, aging, and reconstitution after myeloid ablation. We showed that mDia1 and mDia2 form hetero-oligomers through the interactions between mDia1 GBD-DID and mDia2 DAD domains. Double knockout of mDia1 and mDia2 in hematopoietic cells synergistically impaired the filamentous actin network and serum response factor-involved transcriptional signaling, which led to declined HSPCs, severe anemia, and significant mortality in neonates and newborn mice. Our data demonstrate the potential roles of mDia hetero-oligomerization and their non-rodent functions in the regulation of HSPCs activity and orchestration of hematopoiesis.mDia Formin蛋白可通过其线状肌动蛋白成核与聚合活性，调控细胞骨架的动态变化与组织架构。我们既往研究显示，在小鼠模型中mDia1缺陷会导致先天免疫异常激活，并诱发骨髓增生异常；而mDia2可调控红细胞成核细胞的去核过程与胞质分裂，以及造血干祖细胞（hematopoietic stem and progenitor cells，HSPCs）的植入定植。然而，mDia Formin家族蛋白是否以及如何在生理与应激条件下相互作用并调控造血过程，目前仍不明晰。本研究发现，在连续传代培养、衰老及髓系细胞清除后的造血重建等应激情境下，mDia1与mDia2均为造血干祖细胞再生所必需。研究证实，mDia1的GBD-DID结构域与mDia2的DAD结构域相互作用，可使二者形成异源寡聚体。在造血细胞中同时敲除mDia1与mDia2，会协同破坏丝状肌动蛋白网络，并损伤血清反应因子（serum response factor）参与的转录信号通路，进而导致造血干祖细胞数量减少、重度贫血，并使新生小鼠出现显著死亡率。本研究数据表明，mDia异源寡聚化过程及其非啮齿类物种相关功能，在调控造血干祖细胞活性与协调造血过程中发挥潜在作用。