The CHARGE syndrome ortholog CHD-7 regulates TGF-b pathways in C. elegans

CHARGE syndrome is a complex developmental disorder caused by mutations in the chromodomain helicase DNA-binding protein7 (CHD7) and characterized by retarded growth and malformations in the heart and nervous system. Despite the public health relevance of this disorder, relevant cellular pathways, and targets of CHD7 that relate to disease pathology are still poorly understood. Here we report that chd-7, the nematode ortholog of Chd7, is required for dauer morphogenesis, lifespan determination, stress response and body size determination. Consistent with our discoveries, we found chd-7 to be allelic to scd-3, a previously identified dauer suppressor from the DAF-7/TGF-E pathway. Epistatic analysis places CHD-7 at the level of the DAF-3/DAF-5 complex, but we found that CHD-7 also directly impacts the expression of multiple components of this pathway. Transcriptomic analysis revealed that chd-7 mutants fail to repress daf 9 for execution of the dauer program. In addition, CHD-7 regulates the DBL-1/BMP pathway components and shares roles in male tail development and cuticle synthesis. To explore a potential conserved function for chd-7 in vertebrates, we used Xenopus laevis embryos, an established model to study craniofacial development. Morpholino mediated knockdown of Chd7 led to a reduction in col2a1 mRNA levels, a collagen whose expression depends on TGF-E signaling. Both embryonic lethality and craniofacial defects in Chd7- depleted tadpoles were partially rescued by over-expression of col2a1 mRNA. We suggest that Chd7 has conserved roles in regulation of the TGF-E signaling pathway and pathogenic Chd7 could lead to a defective extracellular matrix deposition. RNA-seq on chd-7;daf-2 vs. daf-2

CHARGE综合征（CHARGE syndrome）是一种由染色质域解旋酶DNA结合蛋白7（chromodomain helicase DNA-binding protein 7, CHD7）突变引发的复杂发育障碍，以生长迟缓、心脏与神经系统畸形为典型特征。尽管该疾病具有重要的公共卫生价值，但目前学界对其相关细胞通路及CHD7介导疾病病理的分子靶点仍知之甚少。本研究证实，chd-7——CHD7的线虫同源基因——对于秀丽隐杆线虫的dauer（滞育幼虫）形态发生、寿命调控、应激响应及体型决定均不可或缺。与本研究发现一致的是，我们证实chd-7与scd-3互为等位基因，而scd-3是此前从DAF-7/TGF-E通路中鉴定得到的dauer抑制因子。上位性分析显示，CHD-7作用于DAF-3/DAF-5复合物的调控层级，但我们同时发现，CHD-7可直接调控该通路多个组分的表达水平。转录组分析显示，chd-7突变体无法抑制daf-9基因以启动dauer发育程序。此外，CHD-7还可调控DBL-1/BMP通路的相关组分，并在雄性尾部发育与表皮合成中发挥作用。为探究chd-7在脊椎动物中的保守功能，我们选用非洲爪蟾（Xenopus laevis）胚胎——这是研究颅面发育的经典实验模型。通过吗啉代寡核苷酸（Morpholino）介导的Chd7基因敲低，可使col2a1的mRNA水平显著下调；col2a1编码一种依赖TGF-E信号通路表达的胶原蛋白。Chd7敲低的蝌蚪所出现的胚胎致死与颅面畸形，均可通过过表达col2a1 mRNA得到部分挽救。我们提出，Chd7在TGF-E信号通路的调控中具有保守功能，而致病性CHD7突变可引发细胞外基质沉积异常。针对chd-7;daf-2与daf-2两组样本的RNA测序（RNA-seq）