THE STUDY OF RHO FAMILY GTPase CASCADES THAT REGULATE NEURONAL MORPHOLOGY

已知Rho家族GTP酶调节细胞的运动和形态。本研究旨在揭示Rho家族GTP酶在神经元发育中的作用。为此，我们将重点放在激活这些GTP酶的鸟核苷酸交换因子(Global)上。在项目期间，我们取得了以下成果：(1)我们以前通过一个运动活性降低的突变表型来鉴定果蝇静物(Sif)基因。该基因主要在神经系统中表达，蛋白质定位于突触。在目前的项目中，我们已经揭示了SIF蛋白是一种在体外激活小鼠RACL的全球环境基金，并定位于神经肌肉连接的周围活动区。我们的基因数据表明，SIF调节突触生长。我们还提出了一个突触结构模型，即周围活动区是一个调控突触发育的膜结构域。(2)我们已经鉴定了Stef基因为小鼠SIF同源基因。该基因在皮质板和成年下丘脑的迁移有丝分裂后细胞中表达，提示Stef调控小鼠神经元运动和突触发育。(3)SIF调控突触生长定位于突触终末，提示可能存在其他GEF控制神经元发育的不同现象。因此，我们利用果蝇数据库搜索了全球环境基金的候选者。一种名为Trio的候选分子被发现在轴突延伸期间在神经系统中表达。我们已经分离了一些三联体突变体，并检查了轴突的分布模式。我们的数据表明，TRIO在轴突延伸的调节中起着关键作用。

Rho family GTPases are known to regulate cellular motility and morphology. This study aimed at revealing the roles for Rho family GTPases in neuronal development. For this purpose, we have focused on guaninenucleotide exchange factors (GEF) that activate these GTPases. During the term of the project, we have obtained the following results.(1) We have previously identified the Drosophila still life (sif) gene by a mutant phenotype of reduced locomotor activity. This gene is predominantly expressed in the nervous system, and the protein is specifically localized at synapses. In the current project, we have revealed that the SIF protein is a GEF that activates mouse Racl in vitro and is localized in the periactive zone in the neuromuscular junction. Our genetic data indicated that SIF regulates synaptic growth. We also propose a model of synaptic structure that the periactive zone is a memebrane domain regulating synaptic development.(2) We have identified the stef gene as a mouse sif orthologue. This gene is exppressed in the migrating postmitotic cells in the cortical plate and also in the adult hypocampus, suggesting that STEF regulates neuronal motility as well as synaptic development in mouse.(3) Our finding that SIF regulating synaptic growth is localized at synaptic terminals suggests that there may be other GEFs that control distinct phenomena of neuronal development. We therefore searched GEF candidates, taking advantage of the Drosophila database. One candidate molecule, named Trio, was found to be expressed in the nervous system during the period of axonal extension. We have isolated a number of trio mutants and examined the axonal distribution patterns. Our data demonstrated that trio has a pivotal role in the regulation of axon extension.