Molecular genetic studies on mammalian brain morphogenesis

肌醇1,4,5 -三磷酸（IP_3）是在激素、神经递质和生长因子的生理作用下，通过激活磷酸肌肽（PI）而产生的，是细胞内的第二信使。IP_3与特定的IP_3受体结合，从细胞内储存部位（如内质网）释放Ca^<2+>。[Ca^<2+>] i的增加可能调节各种Ca_<2+>1相关蛋白的功能，导致细胞对细胞外刺激的各种反应。IP_3受体最初被鉴定为正常小鼠小脑中存在的糖基化和磷酸化蛋白P400，而在小脑浦肯病细胞缺陷突变小鼠中不存在。我们从小鼠小脑中纯化该蛋白，制备单克隆抗体，并将受体亚细胞定位于浦肯野细胞内质网。目前通过重组计划脂双分子层中纯化受体的记录实验表明，该受体具有ip_3诱导的阳离子选择性离子通道活性，在ATP存在下活性增强。我们从小脑cDNA文库中分离到了该cDNA。IP_3受体cDNA的结构分析和功能表达表明，功能性IP_3受体复合物是一个同源四聚体：其前聚体（2749个氨基酸）具有一个大的n端细胞质区（83%）与配体（IP_3）结合位点（n端650个氨基酸）和camp依赖性磷酸化和atp结合的调节位点，以及一个短的c -末端跨膜区，参与形成Ca^<2+>通道孔。这种特征结构在最近克隆的果蝇受体同源物中也得到了很好的保存。我们将从IP_3受体的区域分布出发，讨论IP_3/Ca^<2+>信号在中枢神经系统中的功能作用。

Inositol 1, 4, 5-trisphosphate (IP_3) is Produced through the activation of phosphoinositide (PI) tumover by the physiological action of hormones, neurotransmitters and growth factors, and functions as an intracellular second messenger. IP_3 binds to a specific IP_3 receptor that releases Ca^<2+> from intracellular store sites such as the endoplasmic reticulum (ER). The increase in [Ca^<2+>]_i probably modulates functions of various Ca_<2+>1-associated proteins, leading to a variety of cellular responses to extracellular stimuli.The IP_3 receptor was originally identified as the glycosylated and phosphorylated protein P400 present in the cerebellum from normal mice but not from cerebellar Purkinje-celldeficient mutant mice. We purified the protein from mouse cerebellum, prepared monoclonal antibodies, and subcellularly localized the receptor mostly at the ER of Purkinje cells. Current recording experiments by reconstitution of the purified receptors in planner lipid bilayer represented that the receptor has an IP_3-induced cation selective ion channel activity that is enhanced in the presence of ATP. We isolated the cDNA from a cerebellar cDNA library. The structural analysis and functional expression of the IP_3 receptor cDNA indicated that the functional IP_3 receptor complex is a homotetramer : the pretomer (2749 amino acids) has a large N-terminal cytoplasmic region (83%) with a ligand (IP_3) -binding site (N-terminal 650 amino acids) and modulation sites for cAMP-dependent phosphorylation and ATP-binding, and a short C-teffninal transmembrane region involved in forming a Ca^<2+> channel pore. This characteristic structure is well-conserved in the recently-cloned Drosophila receptor homologue, as well. From regional distribution of the IP_3 receptor, we will discuss the functional role of IP_3/Ca^<2+> signalling in the central nervous system.