BRCA1 and BRCA2 tumor suppressors in neural crest cells are essential for craniofacial bone development

Craniofacial abnormalities, including facial skeletal defects, comprise approximately one-third of all birth defects in humans. Since most bones in the face derive from cranial neural crest cells (CNCCs), which are multipotent stem cells, craniofacial bone disorders are largely attributed to defects in CNCCs. However, it remains unclear how the niche of CNCCs is coordinated by multiple gene regulatory networks essential for craniofacial bone development. Here we report that tumor suppressors breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) are required for craniofacial bone development in mice. Disruption of Brca1 in CNCC-derived mesenchymal cells, but not in epithelial-derived cells, resulted in craniofacial skeletal defects. Whereas osteogenic differentiation was normal, both osteogenic proliferation and survival were severely attenuated in Brca1 mutants. Brca1-deficient craniofacial skeletogenic precursors displayed increased DNA damage and enhanced cell apoptosis. Importantly, the craniofacial skeletal defects were sufficiently rescued by superimposing p53 null alleles in a neural crest-specific manner in vivo, indicating that BRCA1 deficiency induced DNA damage, cell apoptosis, and that the pathogenesis of craniofacial bone defects can be compensated by inactivation of p53. Mice lacking Brca2 in CNCCs, but not in epithelial-derived cells, also displayed abnormalities resembling the craniofacial skeletal malformations observed in Brca1 mutants. Our data shed light on the importance of BRCA1/BRCA2 function in CNCCs during craniofacial skeletal formation.颅面部畸形（含面部骨骼缺陷）约占人类所有出生缺陷的三分之一。由于面部多数骨骼起源于颅神经嵴细胞（cranial neural crest cells, CNCCs）——一类多能干细胞——因此颅面部骨骼疾病大多归因于CNCC功能异常。然而，目前尚不清楚在颅面部骨骼发育过程中，CNCC的微环境是如何由多种关键基因调控网络协同调控的。本研究发现，肿瘤抑制因子乳腺癌1型（breast cancer 1, BRCA1）与乳腺癌2型（breast cancer 2, BRCA2）对小鼠颅面部骨骼发育不可或缺。在CNCC来源的间充质细胞中敲除Brca1（而非上皮来源细胞），会导致小鼠出现颅面部骨骼缺陷。尽管Brca1突变体的成骨分化过程未受影响，但其成骨增殖与细胞存活均受到严重抑制。Brca1缺陷的颅面部骨骼发生前体细胞表现出DNA损伤加剧与细胞凋亡增强的表型。值得注意的是，在体内以神经嵴特异性方式引入p53纯合缺失等位基因，可充分挽救Brca1缺陷引发的颅面部骨骼畸形。上述结果提示，BRCA1缺失所诱导的DNA损伤与细胞凋亡，可通过p53失活缓解颅面部骨骼缺陷的病理进程。在CNCC中敲除Brca2（而非上皮来源细胞）的小鼠，同样表现出与Brca1突变体相似的颅面部骨骼畸形表型。本研究数据揭示了BRCA1/BRCA2在CNCC中参与颅面部骨骼形成的重要作用。