转录因子RBP-J通过介导Notch信号调控神经细胞分化
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摘要
中枢神经系统发育是脊椎动物胚胎发育过程中调控最复杂、次序最严谨的事件之一。胚胎神经管中的神经干细胞(neural stem cells,NSCs)是一种维持自我更新的多潜能细胞,可以进一步分化为各种不同类型的神经细胞。在神经发育过程中,NSCs随着发育阶段的不同变换着它们的响应性和发育潜能。在早期扩增阶段,神经干细胞主要进行广泛的增殖来扩大细胞群体。随着发育的进行,一些神经干细胞在区域性神经诱导信号的作用下起始了原神经基因(proneural gene)的表达。Proneural genes是一类碱性-螺旋-环-螺旋(basic helix-loop-helix, bHLH)转录因子,如Mash1、Ngn1/2和Math1等,它们可以诱导神经元特异性基因的表达,从而将多潜能的神经干细胞决定到神经元分化命运上来。随着proneural基因的表达,神经管中原本相对均一的NSCs群体开始形成差异。那些起始表达proneural基因的NSCs分化为神经元前体细胞,而未表达proneural基因的细胞仍然维持干细胞状态。随后,神经元前体细胞开始退出细胞周期,迁移至神经管外侧并分化为神经元。而NSCs仍然维持未分化状态直到神经发生晚期,再在特定神经诱导信号的作用下分化为晚期的神经细胞类型,比如胶质细胞。维持一个适当规模的NSCs群体对于神经发育的正常进行至关重要,如果NSCs提前分化则会导致严重的神经系统发育缺陷。由于NSCs没有得到充分的扩增,会最终导致神经细胞总量的下降。同时,NSCs提前分化只产生早期的神经细胞类型,从而导致晚期神经细胞类型的缺失,因而不能建立正常的中枢神经系统。除此以外,由于NSCs强大的分化潜能和自我更新能力,在医学上还具有治疗神经损伤和神经退行性变等疾病的潜能。
视网膜是研究神经干细胞/神经前体细胞(Neural progenitor cells, NPCs)增殖分化的优异模型。在神经发育早期,视网膜由间脑的神经上皮向两侧形成突起发育而来,是中枢神经系统地一部分。在哺乳类神经发育过程中,视网膜前体细胞(Retinal progenitor cells, RPCs)可以分化形成视网膜中的7种主要神经细胞类型,这些不同的细胞类型在视网膜神经上皮增殖的同时依次分化出现:神经节细胞、视锥细胞及水平细胞最先生成,接着是无长突细胞和视杆细胞,最后才是双极细胞和Müller氏胶质细胞。分化中的神经细胞要迁移到适当的位置,以形成正确的细胞排列,并最终形成视网膜的五个组织层次,包括三个有核层(nuclear layers)及将它们联系在一起的两个突触层(synaptic layers),从而完成光信号的接受、转换和传导。视网膜丰富的细胞类型和规则的层次结构,是视觉功能实现的生物基础。
与视网膜相同,小脑(cerebellem)特别是小脑皮层是中枢神经系统最为高度有序的结构之一。与大脑皮层相比,它的特征性和简单性使其成为研究中枢神经系统发育机制的又一经典模型。发育中过程中,由小脑室区和菱脑唇两个生发中心分化出九型神经细胞:包括浦肯野(氏)细胞、高尔基细胞、颗粒细胞、篮状细胞、星形细胞和Lugaro细胞,单极刷(形)细胞,和烛台(状)细胞,以及小脑特异性的Bergmann (氏)胶质细胞。成熟的小脑皮层由这八型神经元和一型胶质细胞排列成精确的立体结构,并形成复杂的神经环路从而实现运动协调、技能学习等重要的生理功能。
在神经发育过程中,NSC/NPCs的增殖和分化受到多个信号转导途径的精确调控。以细胞膜受体Notch、转录因子RBP-J及其下游效应基因组成的Notch信号途径是调控发育过程的基本信号之一。虽然既往研究揭示出Notch途径在神经细胞分化中发挥重要的调控作用,但操作Notch途径不同分子得到的实验结果具有差别,其发挥作用的下游靶点也存在争议。基于干预单个Notch受体或其下游基因的研究方法,不足以反映Notch信号功能的全貌。由于在哺乳动物中,Rbpj编码的转录因子可以整合并传递来源于四型Notch受体的信号,从而激活下游基因转录。因此在本课题研究中,我们利用Cre-Loxp重组酶系统,在小鼠RPCs和小脑原基的NPCs中特异性剔除Rbpj基因。
Rbpj敲除视网膜与野生型小鼠视网膜相比,出现明显的发育障碍和视网膜层次结构异常。视网膜发育早期,RPCs分化加速,表现为一系列proneural基因表达上调。然而,仅有神经节细胞和感光细胞增多,中间神经元数目减少,提示RBP-J缺失导致神经元提前分化和RPCs的耗竭;发育晚期,通过活体电穿孔在出生后小鼠视网膜中敲除Rbpj主要导致视杆细胞增加和Müller氏胶质细胞减少。提示RBP-J参与调控感光细胞和Müller氏胶质细胞的定向分化。此外,在Rbpj缺失的视网膜中,层状结构的紊乱伴随着视网膜外表面细胞粘附相关分子β-catenin的表达缺失。更为有趣的是,我们通过活体电穿孔在Rbpj缺失的视网膜中过表达β-catenin,观察到视网膜正常层次结构的恢复。
Rbpj敲除小脑与野生型小鼠小脑相比体积显著变小,分叶结构消失。发育早期(E10.5、E12.5)小脑原基脑室区proneural基因Mash1表达上调,神经元提前分化,增殖的NPCs显著减少,表明Notch-RBP-J信号途径维持着小脑原基中NPCs的数量,并控制着小脑神经细胞分化的时程。发育晚期浦肯野细胞和颗粒细胞持续性减少,小脑深部核团几乎消失。此外,Rbpj敲除小鼠中决定菱脑峡组织者(Isthmic Organizer)建立和中后脑分界形成的重要因子在相应区域均有表达,表明Rbpj表达失活对于IO的形成没有显著性影响,同时说明Notch-RBP-J信号途径对于小脑原基发育的调控作用是直接的,而并非间接的通过调节IO建立而发挥影响。
上述研究结果共同揭示RBP-J所介导的经典Notch信号途径通过抑制神经细胞分化(differentiation),从而维持足够的NSC/NPCs直至晚期发育;此外,Notch-RBP-J信号也参与神经细胞定向(specification),发挥诸如抑制视网膜感光细胞分化,以及促进Müller氏胶质细胞形成的作用;在形态发生方面,RBP-J还可能通过调控粘附相关分子β-catenin的表达参与视网膜层次结构形成;同时,我们的研究证明RBP-J对于中后脑分界的形成没有显著影响。综上所述,本课题的研究结果发现,转录因子RBP-J通过介导经典Notch信号途径调控神经细胞的定向、分化;并在特定发育环境中调节神经系统形态形成,从而协调神经发生(Neurogenesis)和形态形成(Morphogenesis)两个发育过程,最终确保神经系统正常的结构形成及功能建立。这些研究对于深入理解神经发育过程中的分子机理以及Notch信号全面的调控作用,以及了解相关人类疾病的发病机制,具有较为重要的理论和实际意义。
The development of the Central nervous system (CNS) is one of the most complicatedly-regulated and highly-ordered process in the embryogenesis in vertebrates. The neural stem cells (NSCs) in the neural tube is a type of multipotent stem cell which while keeping self-renewal, can differentiate into different neural cell types. During neural development, NSCs change their intrinsic potency and response ability to extrinsic signals. At early developmental stages, NSCs experience accelerated proliferation to establish an enlarged progenitor pool. At later developmental stages, on the induction of various neurogenic signals, NSCs express proneural genes, such as bHLH family genes Mash1, Ngn1/2 and Math1, which initiate the expression of neuronal specific genes and promote NSCs differentiate into different types of neurons. On the initiation of bHLH genes expression, the homogeneous NSCs in the neural tube become heterogeneous, with proneural genes positive NSCs differentiate into neuronal progenitors, while those proneural genes negative NSCs maintain the stem cell property. The neuronal progenitor cells then exist the cell cycle, migrate into the mantle zone of the neural tube and terminally differentiate into neurons. On the other hand, the NSCs continue to proliferate, and produce late-generated neural cell types, such as glial cells, on responses to inductive neurogenic signals during late developmental stages. The maintainance of the neural progenitor pool is pivotal for the normal development of the CNS. The precocious differentiation and the insufficiency of NSCs proliferation results in the decrease of overall neural cells. Meanwhile, the precocious differentiation of NSCs only produce the early-generated neural cell types, leading to the loss of late-generated neural cell types, therefore completely impeded the normal formation of the CNS.
The retina is an excellent model for research on the proliferation and differentiation of NSC/NPCs. During mammalian development, the retina progenitor cells (RPCs) give rise to seven retinal cell types, which are gradually generated in a conserved chronological sequence: ganglion cells and horizontal cells are born first, followed by cone photoreceptors and amacrine cells during the middle stage of retinogenesis. Rod photoreceptors, bipolar cells and Müller glial cells are the last cell types to be generated, mainly during postnatal stages. In addition to adopting specific cell fates, differentiating retinal cells need to migrate into appropriate laminae during retinogenesis, and thus, are eventually organized into three nuclear layers and two synaptic layers, based on which the light photons can be transduced into neural stimuli, and transmitted into the brain during the process of vision.
Similar to the retina, the cerebellum, especially the cerebellar cortex, is one of the central regions in which ordered organizational patterns are most obvious. Compared with the cerebral cortex, its apparent simplicity and geometrical disposition have made it another ideal model for providing an understanding of the mechanisms involved in the development of the nervous system. During development, eight types of neurons and one type of glial cells are generated from the cerebellar ventricular zone and the rhombic lip, including Purkinje cells, Golgi cells, granule cells, basket cells, stellate cells, Lugaro cells, unipolar brush cells, candelabrum cells and Bergmann glial cells. During development, these cells are arranged into a stereotyped three-dimensional geometry, forming complex and accurate neural circuits responsible for important physiologic functions such as motor-coordinating and skill-learning.
In neural development, the proliferation and differentiation of NSC/NPCs are regulated by many signaling pathways. Among them, the Notch signaling pathway composed of Notch receptors, transcription factor RBP-J and its downstream effectors, is one of the fundamental regulatory pathways during development. Although previous work has revealed that Notch signaling play important roles in neural proliferation and differentiation, various manipulations of different Notch signaling molecules yielded inconsistent results, and also raised different candidates of downstream genes. These might be attributed to that preceded studies have focused on the roles of single Notch receptor or the functions of individual downstream effector genes, which impeded the uncovering of the full scope of Notch functions in retinogenesis. In mammals, Rbpj encodes the transcription factor that integrates signals from all four Notch receptors and mediates the transcriptional activation of Notch target genes. Therefore, in the present study, we used the Cre-LoxP system to conditionally knock out Rbpj in the mouse RPCs and the NPCs in the cerebellar primordium.
Rbpj-deficient retinae exhibited severe developmental disorders accompanied by reduced eye size, compared with that in wild-type animals. In the early retinogenesis, RPCs differentiation was accelerated in the absence of Rbpj expression, as reflected by the enhanced expression of proneural genes for all retinal neurons compared with the controls. However, only photoreceptors and ganglion cells were overrepresented, and other neuronal populations were diminished in the later retinogenesis. These results suggest that RBP-J deficiency led to the precocious differentiation of early born neurons and the depletion of RPCs. In the late retinogenesis, postnatal deletion of Rbpj in retina at P0, P3 and P5 led to increased photoreceptor production and decreased gliogenesis, indicating that RBP-J regulates the cell fate specification of photoreceptors and Müller glial cells. In addition, the retinal laminar structure was distorted accompanied with the gaps in the expression ofβ-catenin, the cell adhension-associate molecule, at the apical surface of the retina. And interestingly, lamination defects in Rbpj-deficient retinae were rescued by the induced-overexpression ofβ-catenin using in vivo electroporation.
Rbpj-deficient cerebellum were severely reduced in size, and lost the folial structure compared with the wild-type cerebellum. At early developmental stages, the expression of proneural gene Mash1 was upregulated in the cerebellar ventricular zone, with neurons prematurely differentiated and NPCs significantly reduced. These results suggests that Notch-RBP-J signaling maintains the NPCs in cerebellar primordium and regulates the timing of cerebellar neurogenesis. At late developmental stages, Purkinje cells and granule cells were greatly reduced and Tbr1 positive deep cerebellar nuclei were almost lost. In addition, the transcription factors and secreted factors of the isthmic organizer (IO) were all expressed in the midbrain hindbrain boundary of the Rbpj-deficient embryos, indicating that the inactivation of Rbpj expression have no obvious effect on the formation of IO. These results also elucidate that Notch-RBP-J signaling directly involved in cerebellar development, instead of regulating cerebellar neurogenesis via affecting IO formation.
In summary, our data indicate that RBP-J and, by extension, canonical Notch signaling inhibit neuronal cell type differentiation in neurogenesis, and therefore maintain the amount of NSC/NPCs till late developmental stages. In addition, Notch-RBP-J signaling participates in retinal cell specification, such as inhibiting photoreceptor production and promoting Müller glial cell differentiation in the retina developmental context. On the other hand, Notch-RBP-J signaling is likely to be involved in morphogenesis as well during neural development. RBP-J participates in retinal lamination through regulating the expression of cell adhesion molecules, such asβ-catenin. Meanwhile, our results also indicate that RBP-J dose not affect the pattern formation of midbrain hindbrain boundary. Taken together, our research demonstrate that transcription factor RBP-J is essential as a multifunctional regulator in NSC/NPCs specification and differentiation; In addition, RBP-J is also involved in morphogenesis in specific developmental context, therefore coordinates neurogenesis and morphogenesis, and ensures the normal establishment of the structure and function of the CNS. In that way, our research work has offered theoretical and practical significances in the understanding of the mechanisms of neural development, the uncovering of the full-scale Notch function, and the elucidating of the pathological mechanisms underlying related diseases of the CNS.
视网膜是研究神经干细胞/神经前体细胞(Neural progenitor cells, NPCs)增殖分化的优异模型。在神经发育早期,视网膜由间脑的神经上皮向两侧形成突起发育而来,是中枢神经系统地一部分。在哺乳类神经发育过程中,视网膜前体细胞(Retinal progenitor cells, RPCs)可以分化形成视网膜中的7种主要神经细胞类型,这些不同的细胞类型在视网膜神经上皮增殖的同时依次分化出现:神经节细胞、视锥细胞及水平细胞最先生成,接着是无长突细胞和视杆细胞,最后才是双极细胞和Müller氏胶质细胞。分化中的神经细胞要迁移到适当的位置,以形成正确的细胞排列,并最终形成视网膜的五个组织层次,包括三个有核层(nuclear layers)及将它们联系在一起的两个突触层(synaptic layers),从而完成光信号的接受、转换和传导。视网膜丰富的细胞类型和规则的层次结构,是视觉功能实现的生物基础。
与视网膜相同,小脑(cerebellem)特别是小脑皮层是中枢神经系统最为高度有序的结构之一。与大脑皮层相比,它的特征性和简单性使其成为研究中枢神经系统发育机制的又一经典模型。发育中过程中,由小脑室区和菱脑唇两个生发中心分化出九型神经细胞:包括浦肯野(氏)细胞、高尔基细胞、颗粒细胞、篮状细胞、星形细胞和Lugaro细胞,单极刷(形)细胞,和烛台(状)细胞,以及小脑特异性的Bergmann (氏)胶质细胞。成熟的小脑皮层由这八型神经元和一型胶质细胞排列成精确的立体结构,并形成复杂的神经环路从而实现运动协调、技能学习等重要的生理功能。
在神经发育过程中,NSC/NPCs的增殖和分化受到多个信号转导途径的精确调控。以细胞膜受体Notch、转录因子RBP-J及其下游效应基因组成的Notch信号途径是调控发育过程的基本信号之一。虽然既往研究揭示出Notch途径在神经细胞分化中发挥重要的调控作用,但操作Notch途径不同分子得到的实验结果具有差别,其发挥作用的下游靶点也存在争议。基于干预单个Notch受体或其下游基因的研究方法,不足以反映Notch信号功能的全貌。由于在哺乳动物中,Rbpj编码的转录因子可以整合并传递来源于四型Notch受体的信号,从而激活下游基因转录。因此在本课题研究中,我们利用Cre-Loxp重组酶系统,在小鼠RPCs和小脑原基的NPCs中特异性剔除Rbpj基因。
Rbpj敲除视网膜与野生型小鼠视网膜相比,出现明显的发育障碍和视网膜层次结构异常。视网膜发育早期,RPCs分化加速,表现为一系列proneural基因表达上调。然而,仅有神经节细胞和感光细胞增多,中间神经元数目减少,提示RBP-J缺失导致神经元提前分化和RPCs的耗竭;发育晚期,通过活体电穿孔在出生后小鼠视网膜中敲除Rbpj主要导致视杆细胞增加和Müller氏胶质细胞减少。提示RBP-J参与调控感光细胞和Müller氏胶质细胞的定向分化。此外,在Rbpj缺失的视网膜中,层状结构的紊乱伴随着视网膜外表面细胞粘附相关分子β-catenin的表达缺失。更为有趣的是,我们通过活体电穿孔在Rbpj缺失的视网膜中过表达β-catenin,观察到视网膜正常层次结构的恢复。
Rbpj敲除小脑与野生型小鼠小脑相比体积显著变小,分叶结构消失。发育早期(E10.5、E12.5)小脑原基脑室区proneural基因Mash1表达上调,神经元提前分化,增殖的NPCs显著减少,表明Notch-RBP-J信号途径维持着小脑原基中NPCs的数量,并控制着小脑神经细胞分化的时程。发育晚期浦肯野细胞和颗粒细胞持续性减少,小脑深部核团几乎消失。此外,Rbpj敲除小鼠中决定菱脑峡组织者(Isthmic Organizer)建立和中后脑分界形成的重要因子在相应区域均有表达,表明Rbpj表达失活对于IO的形成没有显著性影响,同时说明Notch-RBP-J信号途径对于小脑原基发育的调控作用是直接的,而并非间接的通过调节IO建立而发挥影响。
上述研究结果共同揭示RBP-J所介导的经典Notch信号途径通过抑制神经细胞分化(differentiation),从而维持足够的NSC/NPCs直至晚期发育;此外,Notch-RBP-J信号也参与神经细胞定向(specification),发挥诸如抑制视网膜感光细胞分化,以及促进Müller氏胶质细胞形成的作用;在形态发生方面,RBP-J还可能通过调控粘附相关分子β-catenin的表达参与视网膜层次结构形成;同时,我们的研究证明RBP-J对于中后脑分界的形成没有显著影响。综上所述,本课题的研究结果发现,转录因子RBP-J通过介导经典Notch信号途径调控神经细胞的定向、分化;并在特定发育环境中调节神经系统形态形成,从而协调神经发生(Neurogenesis)和形态形成(Morphogenesis)两个发育过程,最终确保神经系统正常的结构形成及功能建立。这些研究对于深入理解神经发育过程中的分子机理以及Notch信号全面的调控作用,以及了解相关人类疾病的发病机制,具有较为重要的理论和实际意义。
The development of the Central nervous system (CNS) is one of the most complicatedly-regulated and highly-ordered process in the embryogenesis in vertebrates. The neural stem cells (NSCs) in the neural tube is a type of multipotent stem cell which while keeping self-renewal, can differentiate into different neural cell types. During neural development, NSCs change their intrinsic potency and response ability to extrinsic signals. At early developmental stages, NSCs experience accelerated proliferation to establish an enlarged progenitor pool. At later developmental stages, on the induction of various neurogenic signals, NSCs express proneural genes, such as bHLH family genes Mash1, Ngn1/2 and Math1, which initiate the expression of neuronal specific genes and promote NSCs differentiate into different types of neurons. On the initiation of bHLH genes expression, the homogeneous NSCs in the neural tube become heterogeneous, with proneural genes positive NSCs differentiate into neuronal progenitors, while those proneural genes negative NSCs maintain the stem cell property. The neuronal progenitor cells then exist the cell cycle, migrate into the mantle zone of the neural tube and terminally differentiate into neurons. On the other hand, the NSCs continue to proliferate, and produce late-generated neural cell types, such as glial cells, on responses to inductive neurogenic signals during late developmental stages. The maintainance of the neural progenitor pool is pivotal for the normal development of the CNS. The precocious differentiation and the insufficiency of NSCs proliferation results in the decrease of overall neural cells. Meanwhile, the precocious differentiation of NSCs only produce the early-generated neural cell types, leading to the loss of late-generated neural cell types, therefore completely impeded the normal formation of the CNS.
The retina is an excellent model for research on the proliferation and differentiation of NSC/NPCs. During mammalian development, the retina progenitor cells (RPCs) give rise to seven retinal cell types, which are gradually generated in a conserved chronological sequence: ganglion cells and horizontal cells are born first, followed by cone photoreceptors and amacrine cells during the middle stage of retinogenesis. Rod photoreceptors, bipolar cells and Müller glial cells are the last cell types to be generated, mainly during postnatal stages. In addition to adopting specific cell fates, differentiating retinal cells need to migrate into appropriate laminae during retinogenesis, and thus, are eventually organized into three nuclear layers and two synaptic layers, based on which the light photons can be transduced into neural stimuli, and transmitted into the brain during the process of vision.
Similar to the retina, the cerebellum, especially the cerebellar cortex, is one of the central regions in which ordered organizational patterns are most obvious. Compared with the cerebral cortex, its apparent simplicity and geometrical disposition have made it another ideal model for providing an understanding of the mechanisms involved in the development of the nervous system. During development, eight types of neurons and one type of glial cells are generated from the cerebellar ventricular zone and the rhombic lip, including Purkinje cells, Golgi cells, granule cells, basket cells, stellate cells, Lugaro cells, unipolar brush cells, candelabrum cells and Bergmann glial cells. During development, these cells are arranged into a stereotyped three-dimensional geometry, forming complex and accurate neural circuits responsible for important physiologic functions such as motor-coordinating and skill-learning.
In neural development, the proliferation and differentiation of NSC/NPCs are regulated by many signaling pathways. Among them, the Notch signaling pathway composed of Notch receptors, transcription factor RBP-J and its downstream effectors, is one of the fundamental regulatory pathways during development. Although previous work has revealed that Notch signaling play important roles in neural proliferation and differentiation, various manipulations of different Notch signaling molecules yielded inconsistent results, and also raised different candidates of downstream genes. These might be attributed to that preceded studies have focused on the roles of single Notch receptor or the functions of individual downstream effector genes, which impeded the uncovering of the full scope of Notch functions in retinogenesis. In mammals, Rbpj encodes the transcription factor that integrates signals from all four Notch receptors and mediates the transcriptional activation of Notch target genes. Therefore, in the present study, we used the Cre-LoxP system to conditionally knock out Rbpj in the mouse RPCs and the NPCs in the cerebellar primordium.
Rbpj-deficient retinae exhibited severe developmental disorders accompanied by reduced eye size, compared with that in wild-type animals. In the early retinogenesis, RPCs differentiation was accelerated in the absence of Rbpj expression, as reflected by the enhanced expression of proneural genes for all retinal neurons compared with the controls. However, only photoreceptors and ganglion cells were overrepresented, and other neuronal populations were diminished in the later retinogenesis. These results suggest that RBP-J deficiency led to the precocious differentiation of early born neurons and the depletion of RPCs. In the late retinogenesis, postnatal deletion of Rbpj in retina at P0, P3 and P5 led to increased photoreceptor production and decreased gliogenesis, indicating that RBP-J regulates the cell fate specification of photoreceptors and Müller glial cells. In addition, the retinal laminar structure was distorted accompanied with the gaps in the expression ofβ-catenin, the cell adhension-associate molecule, at the apical surface of the retina. And interestingly, lamination defects in Rbpj-deficient retinae were rescued by the induced-overexpression ofβ-catenin using in vivo electroporation.
Rbpj-deficient cerebellum were severely reduced in size, and lost the folial structure compared with the wild-type cerebellum. At early developmental stages, the expression of proneural gene Mash1 was upregulated in the cerebellar ventricular zone, with neurons prematurely differentiated and NPCs significantly reduced. These results suggests that Notch-RBP-J signaling maintains the NPCs in cerebellar primordium and regulates the timing of cerebellar neurogenesis. At late developmental stages, Purkinje cells and granule cells were greatly reduced and Tbr1 positive deep cerebellar nuclei were almost lost. In addition, the transcription factors and secreted factors of the isthmic organizer (IO) were all expressed in the midbrain hindbrain boundary of the Rbpj-deficient embryos, indicating that the inactivation of Rbpj expression have no obvious effect on the formation of IO. These results also elucidate that Notch-RBP-J signaling directly involved in cerebellar development, instead of regulating cerebellar neurogenesis via affecting IO formation.
In summary, our data indicate that RBP-J and, by extension, canonical Notch signaling inhibit neuronal cell type differentiation in neurogenesis, and therefore maintain the amount of NSC/NPCs till late developmental stages. In addition, Notch-RBP-J signaling participates in retinal cell specification, such as inhibiting photoreceptor production and promoting Müller glial cell differentiation in the retina developmental context. On the other hand, Notch-RBP-J signaling is likely to be involved in morphogenesis as well during neural development. RBP-J participates in retinal lamination through regulating the expression of cell adhesion molecules, such asβ-catenin. Meanwhile, our results also indicate that RBP-J dose not affect the pattern formation of midbrain hindbrain boundary. Taken together, our research demonstrate that transcription factor RBP-J is essential as a multifunctional regulator in NSC/NPCs specification and differentiation; In addition, RBP-J is also involved in morphogenesis in specific developmental context, therefore coordinates neurogenesis and morphogenesis, and ensures the normal establishment of the structure and function of the CNS. In that way, our research work has offered theoretical and practical significances in the understanding of the mechanisms of neural development, the uncovering of the full-scale Notch function, and the elucidating of the pathological mechanisms underlying related diseases of the CNS.
引文
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