Temporal identity in axonal target layer recognition
Temporal identity in axonal target layer recognition
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DOI：
10.1038/nature07407
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发表时间：
2008-12-11
期刊：
影响因子：
64.8
通讯作者：
Hummel, Thomas
中科院分区：
文献类型：
--
作者：
Petrovic, Milan;Hummel, Thomas
轴突和树突投射分离成不同的突触层是神经系统组织的基本原理，也是大脑信息处理的结构基础（1）。层特异性识别分子，使突出的神经元，以稳定短暂的接触，并启动突触发生（2，3）已被确定.然而，大多数对层组织至关重要的神经元细胞表面分子在发育中的神经系统中广泛表达（4，5），这就提出了这些所谓的容许粘附分子如何支持突触特异性的问题.在这里，我们表明，锌指蛋白红杉的时间表达动态是果蝇感光细胞连接到不同的突触层的主要决定因素。相邻的R8和R7光感受器显示出升高的红杉表达的连续峰，这对应于它们的顺序靶层神经支配。红杉在R7中的损失导致投射切换到R8受体层，而在R8中的延长表达诱导它们的轴突重定向到R7层。红杉诱导的轴突靶向是通过广泛表达的钙粘蛋白- N细胞粘附分子介导的。我们的数据支持一个模型，其中识别特异性突触层形成过程中产生的时间限制轴突的能力，以响应广泛表达的粘附分子。由于支配同一目标区域的发育中的神经元通常以不同的出生顺序依赖性序列投射，因此时间身份似乎包含不仅在神经元分裂期间产生细胞类型多样性的关键信息（6），而且还包含投射神经元的连接多样性。
The segregation of axon and dendrite projections into distinct synaptic layers is a fundamental principle of nervous system organization and the structural basis for information processing in the brain(1). Layer- specific recognition molecules that allow projecting neurons to stabilize transient contacts and initiate synaptogenesis(2,3) have been identified. However, most of the neuronal cell- surface molecules critical for layer organization are expressed broadly in the developing nervous system(4,5), raising the question of how these so- called permissive adhesion molecules support synaptic specificity. Here we show that the temporal expression dynamics of the zinc- finger protein sequoia is the major determinant of Drosophila photoreceptor connectivity into distinct synaptic layers. Neighbouring R8 and R7 photoreceptors show consecutive peaks of elevated sequoia expression, which correspond to their sequential target- layer innervation. Loss of sequoia in R7 leads to a projection switch into the R8 recipient layer, whereas a prolonged expression in R8 induces a redirection of their axons into the R7 layer. The sequoia- induced axon targeting is mediated through the ubiquitously expressed Cadherin- N cell adhesion molecule. Our data support a model in which recognition specificity during synaptic layer formation is generated through a temporally restricted axonal competence to respond to broadly expressed adhesion molecules. Because developing neurons innervating the same target area often project in a distinct, birth- order- dependent sequence, temporal identity seems to contain crucial information in generating not only cell type diversity during neuronal division(6) but also connection diversity of projecting neurons.