BRCA1和BRCA2通过表观调控神经嵴的颅面骨发生

Neural crest (NC) cells are a transient population of stem-cells that arise from neuroepithelial precursors during early embryonic development to generate a wide spectrum of derivatives. Cranial NC cells arise between the posterior fore brain and posterior hindbrain and migrate into the facial primordial to generate the vast majority of the vertebrate head, including the cranial ganglia, connective tissue, tendons, osteoblasts, chondrocytes and melanocytes. Many of the most common human birth defects are related to abnormal neural crest development. Cranial NC malformation can lead to craniofacial defects like cleft lip and palate. Specific cell fates of CNCCs are controlled by positional cues that determine intrinsic gene expression patterns that are partially specified already at emigration from the neural tube. There is growing evidence to support roles for epigenetic regulation as critical for many aspects of neural crest development, including of DNA methylation, histone methylation, histone acetylation and Polycomb repressive complex. Breast cancer susceptibility gene1/2 (BRCA1/2) was identified as a hereditary cancer susceptibility gene which increased risk for the development of breast and ovarian cancer in Brca1/2 mutation carriers. BRCA1/2 also play an important role in embryogenesis, neurogenesis and hair follicle development. To date, a large number of biochemical activities have been linked to BRCA1 function, which include DNA damage response and repair, transcription regulation, chromatin remodeling, heterochromatin maintenance, among others. However, how BRCA1/2 regulates cell differentiation and how BRCA1/2 deregulation contributes to development of neural crest cells remain elusive. In present study, we examined the role of BRCA1/2 in NC development by conditionally ablating BRCA1/2 in premigratory NCCs in vivo. Interestingly, Brca1/2 deficiency derepressed neural crest markers Foxd3 and Sox10, and deregulates the MSCs lineage and osteogenesis markers, such as Dlx5 and Runx2, resulting in defect of craniofacial morphogenesis. Thus, we hypothesis that loss of BRCA1/2 in NCC perturb the NCC specification and terminal differentiation of downstream by epigenetic control. Meanwhile, the difference function of BRCA1 and BRCA2 in NC development will be investigated. Understanding specific role of BRCA1/2 in neural crest development is of great interest and importance to both developmental biology and tumourgenesis.

神经嵴（NC）由干细胞构成，位于神经管的边缘，能够分化成为多种类型细胞。NC发育异常会导致出生缺陷等人类疾病综合症，如颅面发生异常。NC的发育受到多种调控机制，其中表观修饰是研究热点。Brca1/2是抑癌基因，在胚胎发育中具有重要作用。BRCA1/2参与调控细胞周期、转录与DNA损伤修复，维持基因组稳定和表观修饰。目前，关于BRCA1/2在神经嵴发育中的作用未见报道。本研究在小鼠NC细胞中条件性敲除Brca1/2基因，探讨BRCA1/2在NC发育中的作用及机制，并比较BRCA1和BRCA2的功能差异。前期研究表明Brca1/2缺陷小鼠颅面发生异常，引起NC发育不同时期的基因表达失调，包括NC谱系决定，MSC谱系决定及成骨发生等。我们认为BRCA1/2参与基因组水平或表观修饰调控神经嵴的发育。通过本研究可以挖掘抑癌基因在NC发育过程中可能的调控机制，对发育生物学及肿瘤研究尤为重要。

颅面神经嵴（CNC）由中脑和前脑后部的神经嵴细胞发育形成，CNC迁移到预定面部分化形成特定形状的软骨和骨构成颅面，其发育异常会导致出生缺陷等人类疾病综合症。神经嵴（NC）在不同的发育时间节点，细胞谱系对应着不同的表观遗传修饰，因此，表观调控与转录因子协同作用谱系基因从而达到谱系特化的调控。. BRCA1/2是肿瘤抑制基因，在发育中具有重要作用。BRCA1/2参与调控细胞周期、转录与DNA损伤修复，维持基因组稳定和表观修饰。本研究BRCA1和BRCA2在神经嵴发育过程中的作用，用不同模型说明了BRCA1和BRCA2在神经嵴颅面发育中至关重要，确定BRCA1/2通过影响神经嵴谱系的分化调控，表观调控参与其中。对于理解BRCA1/2在发育中的作用提供了确实的证据，同时为临床筛查新生儿颅面缺陷提供参考标记。为进一步揭示表观调控在神经嵴发育中的作用，本研究利用UHRF1和CFP1敲除小鼠模型研究了H3K9me3和H3K4me3修饰作用神经嵴早期谱系决定、迁移和分化，其中UHRF1与BRCA1神经嵴缺失表型特征高度相似，同时确定了H3K9me3和H3K4me3修饰异常影响神经嵴谱系决定、迁移和分化导致严重缺陷。这些成果对于理解颅面神经嵴如何通过时空信息进行谱系决定和分化，如何激活特异性基因程序性表达之后启动不同的命运决定具有重要意义。. 此外，利用神经发育模型，系统阐明了CFP1通过H3K4me3修饰影响皮层发育，其中CFP1通过表观调控神经前体细胞分化和成熟，尤其作用于神经轴突生长，对复杂的神经系统疾病的起因具有重要意义。而DCAF13我们首次发现DCAF13通过泛素化调控ATM，诱导P53通路影响大脑皮层的发育，我们认为DCAF13参与维持前体细胞基因组稳定并对保护神经元损伤，同样在颅面发育中也发现DCAF13缺失引起神经嵴发育严重异常。. 尽管本项目的研究还存在不足，我们可以明确BRCA1和BRCA2在神经嵴颅面发育中是多重作用，维持基因组稳定只是调控的一部分，同时还通过参与表观调控影响神经嵴谱系决定和分化及成骨发生等。而表观调控贯穿整个神经嵴发育的过程，不同时间点组蛋白修饰的作用不同。

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