造血干细胞发育过程中，其产生于主动脉-性腺-中肾区并在胎肝扩增，最后移居骨髓以维持造血系统平衡。虽然骨髓内微环境如骨形成等外在因素影响造血干细胞从胎肝移位骨髓，但内在因素对其移位影响鲜有报道。本项目借助敲除Hem1基因降低骨髓内造血干细胞数量和功能但不影响胎肝造血干细胞的优势，探索WAVE复合体成员Hem1在造血干细胞由胎肝向骨髓移居过程中的作用及机制。利用非竞争性、竞争性和逆向骨髓移植确认Hem1缺失对造血干细胞的影响是由内在因素还是外在微环境所致。进一步检测Hem1基因敲除造血干细胞的凋亡、增殖、移位、黏附和极性等特点探究其机制。结合分子生物学、细胞培养和流式细胞术等，考察细胞内信号通路尤其c-Abl通路在敲除Hem1影响造血干细胞由胎肝向骨髓移居中的重要作用。本项目将揭示由Hem1组成的WAVE复合体等内在因素对造血干细胞移位定居骨髓的重要性，且为分析出生后造血系统发育异常拓宽思路。

During the development of hematopoietic stem cells (HSCs), definitive HSCs with long-term repopulation activity have been found in the aorta-gonad-mesonephros (AGM) region and subsequently shift to fetal livers where HSCs are extremely amplified. Finally, HSCs in fetal livers migrate and reside in bone marrow (BM) to maintain life-long hematopoietic hemostasis. Despite abnormal microenviroment in bone marrow, such as the deformation of bones and vessels, negatively affects HSC residence, the effects of intrinsic factors on fetal liver HSC translocation remain unknown. In the present proposal, we will take advantage of Hem1 knockout mice along with damaging BM HSCs but not fetal liver HSCs. To investigate whether the intrinsic or extrinsic factors injure BM HSC in Hem-/- mice, non-competitive transplantation, competitive transplantation and reverse transplantation will be utilized. The capacities of proliferation, apoptosis, migration, adhesion and polarization in Hem1-/- HSCs from fetal liver and bone marrow will be examined in vivo and in vitro. Furthermore, molecular cloning, cell culture and flow cytometry will be applied to explore the changes of multiple intracellular signaling in Hem1-/- HSCs. Particularly, c-Abl signaling pathway will be extensively investigated by upregulation and downregulation of c-Abl in fetal liver and bone marrow HSCs. Through performing the project, we will not only reveal the importance of HSC intrinsic factors, such as WAVE complex component Hem1, on hematopoietic stem cell translocation from fetal liver to bone marrow, but also open a new avenue to analyze the abnormal development of hematopoietic system after birth.