转录因子Zeb2在视网膜细胞分化和维持中的调控功能研究

Mowat-Wilson syndrome is a developmental genetic disorder associated with multiple and variable anomalies including structural eye phenotypes such as microphthalmia and retinal coloboma. Mutations in the ZEB2 gene are found to cause Mowat-Wilson syndrome. However, at present, it is unclear how ZEB2 mutations cause retinal atrophy associated with this syndrome. Our preliminary studies showed that Zeb2 is not expressed in the mouse retina until late embryonic stages and that its expression is maintained in numerous cells within the inner nuclear layer and ganglion cell layer of the mature retina. Moreover, retina-specific ablation of Zeb2 in mice caused gradual thinning of the retina and loss of retinal cells，but did not result in any defect during initial stages of retinal development. These results have prompted us to propose that Zeb2 may play an essential role in controlling terminal differentiation and long-term survival of inner retinal cells, but may not be involved in the determination of progenitor cell fates. In this project, we plan to utilize a variety of experimental approaches including conditional knockout, overexpression and bioinformatic analysis to determine the role of Zeb2 in retinal generation, degeneration and visual processing; as well as to further identify Zeb2 downstream target genes and characterize the gene regulatory network in which Zeb2 participates. Our proposed studies are expected to not only unravel a novel mechanism underlying retinal development and maintenance but also provide a useful framework for clinical diagnosis and therapy of Mowat-Wilson syndrome.

Mowat-Wilson综合症是一种与发育相关的遗传病，伴随多种身体异常，包括小眼和视网膜缺损等眼部异常。研究表明转录因子ZEB2的突变是导致该综合症的原因，但其突变如何引起Mowat-Wilson综合症相关视网膜病变尚不清楚。我们预实验结果显示Zeb2在小鼠胚胎后期才开始表达于视网膜内并长期保持在成熟视网膜的内核层和神经节细胞层。Zeb2条件性敲除会引起小鼠视网膜逐渐变薄和细胞缺失，但并不导致视网膜初期发育异常。我们由此提出Zeb2可能具有调控视网膜内层细胞末端分化并维持这些细胞长期存活的关键功能，但不参与前体细胞命运的决定。本项目拟采用条件性敲除、过表达以及生物信息学等手段，明确Zeb2对视网膜发生、病变和视觉功能的作用，并进一步鉴定Zeb2的下游靶基因，构建其基因调控网络。本项目有望揭示视网膜发育和存活的新机制，并为Mowat-Wilson综合症的诊断和治疗提供有力参考依据。

人先天性疾病Mowat-Wilson综合征是由转录因子Zeb2突变引起的，其疾病特征包括小头畸形、Hirschsprung疾病、智障、癫痫、小眼、视网膜缺损、视神经萎缩等。小鼠Zeb2参与神经和晶体形成、神经管闭合、以及神经脊细胞和脑皮层神经的特化、分化和迁移。迄今为止，仍不清楚Zeb2突变如何导致视网膜缺损，失活Zeb2是否引起视网膜变性、Zeb2是否充分促进视网膜细胞类型的分化？我们发现，在小鼠视网膜发育过程中，Zeb2在视网膜前体细胞、非感光细胞（双极、水平、无长突、穆勒和神经节细胞）中表达。视网膜特异性敲除Zeb2导致上述非感光细胞类型严重丢失、前体细胞命运向感光细胞方向分化、凋亡细胞增加，引起年龄渐进性视网膜变性、视神经萎缩、视盘水肿、视网膜电图（ERG）反应减退。而且，过表达Zeb2能充分促进非感光细胞的命运，同时抑制感光细胞命运。总体而言，我们的数据不但显示Zeb2对于非感光细胞的发育既充分且必要，同时通过降低感光细胞特化和分化的转录因子抑制感光细胞命运，而且揭示了Zeb2对于长期维护视网膜各类细胞的必要性。本工作发现了Mowat-Wilson综合征视网膜萎缩的病因，对于临床疾病的诊断和治疗具有重要意义。