Hematopoietic stem cells (HSCs) and skeletal stem cells (SSCs) cohabit in the bone marrow. KITL (C-KIT ligand) from LEPR⁺ adult bone marrow stromal cells is pivotal for HSC maintenance. In contrast, it remains unclear whether KITL/C-KIT signaling also regulates SSCs. Here, we lineage traced C-KIT⁺ cells and found that C-KIT was expressed by fetal, but not postnatal skeletal progenitors. Fetal C-KIT⁺ cells gave rise to 20% of LEPR⁺ stromal cells in adult bone marrow, forming nearly half of all osteoblasts. Disruption of mTOR signaling in fetal C-KIT⁺ cells impaired bone formation. Notably, conditional deletion of Kitl from PRX1⁺ fetal bone marrow stromal cells, but not LEPR⁺ adult bone marrow stromal cells, significantly increased bone formation. Thus, our work identified C-KIT⁺ skeletal progenitors as an important source of bones formed during development.

造血干细胞（HSC）和骨骼干细胞（SSC）在骨髓中共存。LEPR ⁺成年骨髓基质细胞的KITL（C-KIT配体）对于维持HSC至关重要。相比之下，仍不清楚KITL / C-KIT信令是否也调节SSC。在这里，我们沿袭追踪C-KIT ⁺细胞，发现C-KIT是由胎儿表达的，而不是由胎儿骨骼祖细胞表达的。胎儿的C-KIT ⁺细胞在成年骨髓中产生了20％的LEPR ⁺基质细胞，几乎占所有成骨细胞的一半。胎儿C-KIT ⁺细胞中mTOR信号的破坏破坏了骨形成。值得注意的是，有条件的删除了kitl从PRX1 ⁺胎儿的骨髓基质细胞，而不是LEPR ⁺成年的骨髓基质细胞，可显着增加骨形成。因此，我们的工作将C-KIT ⁺骨骼祖细胞确定为发育过程中形成的重要骨骼来源。