Lee Alan, Li Wenjun, Xu Kanyan, Bogert Brigitte A, Su Kimmy, Gao Fen-Biao
Gladstone Institute of Neurological Disease, University of California, San Francisco, San Francisco, CA 94141-9100, USA.
Development. 2003 Nov;130(22):5543-52. doi: 10.1242/dev.00792.
Fragile X syndrome is caused by loss-of-function mutations in the fragile X mental retardation 1 gene. How these mutations affect neuronal development and function remains largely elusive. We generated specific point mutations or small deletions in the Drosophila fragile X-related (Fmr1) gene and examined the roles of Fmr1 in dendritic development of dendritic arborization (DA) neurons in Drosophila larvae. We found that Fmr1 could be detected in the cell bodies and proximal dendrites of DA neurons and that Fmr1 loss-of-function mutations increased the number of higher-order dendritic branches. Conversely, overexpression of Fmr1 in DA neurons dramatically decreased dendritic branching. In dissecting the mechanisms underlying Fmr1 function in dendrite development, we found that the mRNA encoding small GTPase Rac1 was present in the Fmr1-messenger ribonucleoprotein complexes in vivo. Mosaic analysis with a repressor cell marker (MARCM) and overexpression studies revealed that Rac1 has a cell-autonomous function in promoting dendritic branching of DA neurons. Furthermore, Fmr1 and Rac1 genetically interact with each other in controlling the formation of fine dendritic branches. These findings demonstrate that Fmr1 affects dendritic development and that Rac1 is partially responsible for mediating this effect.
脆性X综合征由脆性X智力低下1基因的功能丧失突变引起。这些突变如何影响神经元的发育和功能在很大程度上仍不清楚。我们在果蝇脆性X相关（Fmr1）基因中产生了特定的点突变或小缺失，并研究了Fmr1在果蝇幼虫树突状分支（DA）神经元树突发育中的作用。我们发现Fmr1可在DA神经元的细胞体和近端树突中检测到，并且Fmr1功能丧失突变增加了高阶树突分支的数量。相反，在DA神经元中过表达Fmr1会显著减少树突分支。在剖析Fmr1在树突发育中功能的潜在机制时，我们发现编码小GTP酶Rac1的mRNA在体内存在于Fmr1信使核糖核蛋白复合物中。使用阻遏细胞标记（MARCM）的镶嵌分析和过表达研究表明，Rac1在促进DA神经元树突分支方面具有细胞自主功能。此外，Fmr1和Rac1在控制精细树突分支的形成中存在遗传相互作用。这些发现表明Fmr1影响树突发育，并且Rac1部分负责介导这种影响。
