TRANSPORT MEDIATED REGULATION OF CELLULAR MYOINOSITOL

肌醇是哺乳动物细胞的重要组成部分。除了 作为膜磷酸肌醇的前体，在 涉及钙和蛋白激酶C的信号转导过程， 这种环状多元醇化合物在细胞增殖调节中起关键作用。 肌醇是“自发渗透压物质”或有机渗透剂， 在高渗状态下在脑组织中积累。在大多数细胞中， 肌醇水平通过能量依赖性转运来维持。期间 适应高渗应激，这是调节的数量， 通过Vmax测量证明的质膜转运蛋白， 确定细胞内肌醇水平的新设定点。的 反过来，转运蛋白的合成在基因 至少在一些哺乳动物的肾脏、大脑和眼睛中， 细胞我们最近克隆了人β-淀粉样蛋白调节Na+/肌醇 协同转运蛋白（SMIT）基因。这种基因在许多人体组织中都有表达 包括大脑。我们已经将该基因定位于 21号染色体的长臂唐氏综合症患者可能有 在胎儿或出生后任何细胞中肌醇水平升高 如果细胞不能抑制3个基因拷贝的表达， 这将是适当的2。SMIT基因可能在 唐氏综合症的发病机制，特别是神经系统 功能障碍在这项研究中，我们建议完成测序的 使用两个新分离的噬菌体P1克隆的人SMIT基因; 通过免疫组织化学方法，描述SMIT基因在不同组织中的表达 原位杂交和免疫组化;测量肌- 唐氏症患者脑内肌醇和交替渗透调节物质的变化 综合征和对照组，并将组织水平与 SMIT基因的表达，并确定高渗或 低渗应力对正常和三体21培养的成纤维细胞， 评估生存力、渗透压水平和SMIT mRNA水平。

Myo-inositol is a critical constituent of mammalian cells. In addition to serving as the precursor of membrane phosphoinositides, important in the signal transduction processes which involve calcium and protein kinase C, this cyclic polyol compound plays a key role in cellular osmoregulation. Myo-inositol is "the idiogenic osmole" or organic osmolyte which accumulates in brain tissue during hyperosmolar states. In most cells, myo-inositol levels are maintained by energy -dependent transport. During adaptation to hypertonic stress, it is the regulation of the number of plasma membrane transporters as evidenced by Vmax measurements which determine the new set point for intracellular myo-inositol levels. The synthesis of the transporter protein, in turn, is exerted at the gene transcriptional level at least in some mammalian kidney, brain and ocular cells. We have recently cloned the human osmoregulatory Na+/myo-inositol cotransporter (SMIT) gene. The gene is expressed in many human tissues including the brain. We have localized the gene to the distal portion of the long arm of chromosome 21. Patients with Down Syndrome may have increased levels of myo-inositol in any cell, during fetal or post-natal life, if the cell is unable to dampen the expression of 3 gene copies to that which would be appropriate for 2. The SMIT gene may play a role in the pathogenesis of Down Syndrome, especially the neurological dysfunction. In this study, we propose to complete the sequencing of the human SMIT gene using two newly isolated bacteriophage PI clones; delineate the expression of SMIT gene in different human tissues via in situ hybridization and immunohistochemistry; measure the level of myo- inositol and alternate osmolytes in the brain of patients with Down Syndrome and control subjects, and correlate the tissue levels with the expression of the SMIT genes and determine the effect of hypertonic or hypotonic stress on the normal and trisomic 21 cultured fibroblasts by assessing viability, osmolyte levels and SMIT mRNA levels.