CNP-induced cGMP signalling in neural differentiation and functional integration

由分泌的因子C型利钠肽（CNP）与其受体鸟苷酸环化酶B（GC-B）结合触发的cGMP信号传导途径已与多种显著的生理功能相关联。我们自己的研究表明，从胚胎背根神经节神经元的轴突在脊髓背根进入区的分叉关键取决于cGMP信号通路，包括CNP，GC-B和cGMP依赖性蛋白激酶I α（cGKI α）。在第一个资助期，我们建立了一个GC-B-LacZ-报告基因小鼠系用于表达作图，并建立了一个GC-B-CreERT 2小鼠系，该小鼠系与适当的条件性报告基因相结合，能够可视化单个GC-B表达神经元。我们可以证明，与DRG神经元类似，CNP/GC-B/cGKI α信号通路也调节胚胎后脑颅感觉神经节神经元的轴突分叉。利用各自的LacZ-报告小鼠系对CNP和GC-B在中枢神经系统中的表达模式进行的分析揭示了配体及其受体在海马中的有趣分布，海马是一种参与记忆形成并对成年神经发生突出的脑结构。我们确定了海马中表达CNP和GC-B的神经元亚群以及这些表达模式的发育时间过程。因此，我们观察到海马结构中表达GC-B的齿状颗粒细胞（DGCs）数量的年龄相关性减少。免疫细胞化学研究的应用程序的BrdU GC-B-LacZ-报告小鼠证明了GC-B阳性DGCs在成年大脑的补充。此外，我们已经建立了一个遗传的方法，荧光标记的GC-B阳性DGC的目的是表征其电生理特性和连接。初步结果表明GC-B在控制DGC兴奋性中的作用。这些研究将继续进行，并辅以行为测试。为此，我们已经产生了一个条件GC-B小鼠模型，允许GC-B的组织特异性失活，这也将有助于与该网络中的其他小组合作，他们将研究GC-B在听觉系统和疼痛处理中的功能。将对GC-B杂合子与GC-B KO小鼠的遗传标记神经元进行表达谱分析，以鉴定GC-B阳性神经元和cGMP依赖性转录程序中cGMP信号传导的其他分子组分。这些研究将进一步阐明GC-B在神经元生长和突触整合过程中的作用，并将提高我们对受损cGMP信号传导的神经学后果的理解。

A cGMP signalling pathway triggered by binding of the secreted factor C-type natriuretic peptide (CNP) to its receptor guanylyl cyclase B (GC-B) has been linked to a remarkable variety of physiological functions. Our own investigations demonstrated that the bifurcation of axons from neurons of embryonic dorsaI root ganglia at the dorsal root entry zone of the spinal cord critically depends on a cGMP signalling pathway comprising CNP, GC-B and cGMP-dependent protein kinase I alpha (cGKI alpha). In the first funding period, we established a GC-B-LacZ-reporter mouse line for expression mapping and a GC-B-CreERT2 mouse line that in combination with an appropriate conditional reporter enables the visualization of individual GC-B-expressing neurons. We could demonstrate that, similar to DRG neurons, the CNP/GC-B/cGKI alpha signalling pathway also regulates axon bifurcation of neurons from cranial sensory ganglia at the embryonic hindbrain. The analysis of the expression patterns of CNP and GC-B in the central nervous system utilizing the respective LacZ-reporter mouse lines revealed an interesting distribution of the ligand and its receptor in the hippocampus, a brain structure involved in memory formation and prominent for adult neurogenesis. We determined the neuronal subpopulations that express CNP and GC-B in the hippocampus and the developmental time course of those expression patterns. Thereby, we observed an age-related decrease in the number of GC-B-expressing dentate granule cells (DGCs) in the hippocampal formation. Immunocytochemical studies following the application of BrdU to GC-B-LacZ-reporter mice demonstrated a replenishment of GC-B-positive DGCs in the adult brain. Moreover, we have established a genetic approach for fluorescent labelling of GC-B-positive DGCs with the aim to characterize their electrophysiological properties and connections. Preliminary results suggest a role of GC-B in the control of DGC excitability. These studies will be continued and complemented with behavioural tests. For this purpose, we have generated a conditional GC-B mouse model allowing tissue-specific inactivation of GC-B which will also be instrumental in collaborations with other groups within this network who will study GC-B function in the auditory system and in pain processing. Expression profiling of genetically-labelled neurons from GC-B heterozygous vs GC-B KO mice will be performed to identify further molecular components of cGMP signalling in GC-B-positive neurons and cGMP-dependent transcriptional programmes. These studies will further clarify the role of GC-B in the process of neuronal growth and synaptic integration and will improve our understanding of the neurological consequences of impaired cGMP signalling.