Department of Biological Sciences, University of Toledo, Toledo, Ohio 43606, USA.
Genetics. 2011 Sep;189(1):137-51. doi: 10.1534/genetics.111.131227. Epub 2011 Jul 12.
Rho-family GTPases play regulatory roles in many fundamental cellular processes. Caenorhabditis elegans UNC-73 RhoGEF isoforms function in axon guidance, cell migration, muscle arm extension, phagocytosis, and neurotransmission by activating either Rac or Rho GTPase subfamilies. Multiple differentially expressed UNC-73 isoforms contain a Rac-specific RhoGEF-1 domain, a Rho-specific RhoGEF-2 domain, or both domains. The UNC-73E RhoGEF-2 isoform is activated by the G-protein subunit Gαq and is required for normal rates of locomotion; however, mechanisms of UNC-73 and Rho pathway regulation of locomotion are not clear. To better define UNC-73 function in the regulation of motility we used cell-specific and inducible promoters to examine the temporal and spatial requirements of UNC-73 RhoGEF-2 isoform function in mutant rescue experiments. We found that UNC-73E acts within peptidergic neurons of mature animals to regulate locomotion rate. Although unc-73 RhoGEF-2 mutants have grossly normal synaptic morphology and weak resistance to the acetylcholinesterase inhibitor aldicarb, they are significantly hypersensitive to the acetylcholine receptor agonist levamisole, indicating alterations in acetylcholine neurotransmitter signaling. Consistent with peptidergic neuron function, unc-73 RhoGEF-2 mutants exhibit a decreased level of neuropeptide release from motor neuron dense core vesicles (DCVs). The unc-73 locomotory phenotype is similar to those of rab-2 and unc-31, genes with distinct roles in the DCV-mediated secretory pathway. We observed that constitutively active Gαs pathway mutations, which compensate for DCV-mediated signaling defects, rescue unc-73 RhoGEF-2 and rab-2 lethargic movement phenotypes. Together, these data suggest UNC-73 RhoGEF-2 isoforms are required for proper neurotransmitter signaling and may function in the DCV-mediated neuromodulatory regulation of locomotion rate.
Rho 家族 GTPases 在许多基本的细胞过程中发挥调节作用。秀丽隐杆线虫 UNC-73 RhoGEF 同工型通过激活 Rac 或 Rho GTPase 亚家族，在轴突导向、细胞迁移、肌肉臂伸展、吞噬作用和神经传递中发挥作用。多个差异表达的 UNC-73 同工型包含 Rac 特异性 RhoGEF-1 结构域、Rho 特异性 RhoGEF-2 结构域或这两个结构域。UNC-73E RhoGEF-2 同工型被 G 蛋白亚基 Gαq 激活，并且是正常运动速度所必需的；然而，UNC-73 和 Rho 通路调节运动的机制尚不清楚。为了更好地定义 UNC-73 在调节运动中的功能，我们使用细胞特异性和诱导性启动子来检查 UNC-73 RhoGEF-2 同工型在突变体拯救实验中的时空要求。我们发现 UNC-73E 在成熟动物的肽能神经元中发挥作用，以调节运动速度。尽管 unc-73 RhoGEF-2 突变体具有大体上正常的突触形态和对乙酰胆碱酯酶抑制剂 aldicarb 的弱抗性，但它们对乙酰胆碱受体激动剂左旋咪唑非常敏感，表明乙酰胆碱神经递质信号发生改变。与肽能神经元功能一致，unc-73 RhoGEF-2 突变体表现出从运动神经元致密核心囊泡 (DCV) 释放的神经肽水平降低。unc-73 运动表型与 rab-2 和 unc-31 相似，rab-2 和 unc-31 基因在 DCV 介导的分泌途径中具有不同的作用。我们观察到，组成型激活的 Gαs 途径突变可以补偿 DCV 介导的信号缺陷，从而拯救 unc-73 RhoGEF-2 和 rab-2 运动迟缓表型。这些数据表明 UNC-73 RhoGEF-2 同工型是正常神经递质信号所必需的，并且可能在 DCV 介导的运动速度神经调节调节中发挥作用。
