Toki S, Kawasaki H, Tashiro N, Housman D E, Graybiel A M
Pharmaceutical Research Institute, Kyowa Hakko Kogyo Company, Ltd., Shizuoka 411-8731, Japan.
J Comp Neurol. 2001 Sep 3;437(4):398-407. doi: 10.1002/cne.1291.
CalDAG-GEFI and CalDAG-GEFII (identical to RasGRP) are novel, brain-enriched guanine nucleotide exchange factors (GEFs) that can be stimulated by calcium and diacylglycerol and that can activate small GTPases, including Ras and Rap1, molecules increasingly recognized as having signaling functions in neurons. Here, we show that CalDAG-GEFI and CalDAG-GEFII mRNAs, detected by in situ hybridization analysis, have sharply contrasting forebrain-predominant distributions in the mature brain: CalDAG-GEFI is expressed mainly in the striatum and olfactory structures and deep cortical layers, whereas CalDAG-GEFII is expressed widely in the forebrain. Within the striatum, however, the two CalDAG-GEF mRNAs have nearly identical distributions: they are coexpressed in striatal projection neurons that give rise to the direct and indirect pathways of the basal ganglia. Subcellular fractionation analysis of the substantia nigra with monoclonal antibodies against CalDAG-GEFI suggests that CalDAG-GEFI protein is present not only in the cell bodies of striatal projection neurons but also in their axons and axon terminals. These results suggest that the CalDAG-GEFs may be key intracellular regulators whereby calcium and diacylglycerol signals can regulate cellular functions through small GTPases in the basal ganglia circuits.
钙依赖性鸟嘌呤核苷酸交换因子I（CalDAG-GEFI）和钙依赖性鸟嘌呤核苷酸交换因子II（与Ras鸟嘌呤核苷酸释放蛋白相同）是新型的、在脑中大量表达的鸟嘌呤核苷酸交换因子（GEFs），它们可被钙和二酰基甘油激活，并能激活小GTP酶，包括Ras和Rap1，这些分子在神经元中的信号传导功能日益受到认可。在此，我们通过原位杂交分析发现，CalDAG-GEFI和CalDAG-GEFII mRNA在成熟脑中的前脑分布形成鲜明对比：CalDAG-GEFI主要表达于纹状体、嗅觉结构和皮质深层，而CalDAG-GEFII在前脑广泛表达。然而，在纹状体内，这两种CalDAG-GEF mRNA的分布几乎相同：它们在产生基底神经节直接和间接通路的纹状体投射神经元中共表达。用抗CalDAG-GEFI单克隆抗体对黑质进行亚细胞分级分离分析表明，CalDAG-GEFI蛋白不仅存在于纹状体投射神经元的细胞体中，还存在于其轴突和轴突终末。这些结果表明，CalDAG-GEFs可能是关键的细胞内调节因子，通过它们钙和二酰基甘油信号可在基底神经节回路中通过小GTP酶调节细胞功能。
