Homocysteine and NMDA receptor in cardiac neural crest development

神经嵴细胞的形成和迁移是心脏分隔正常发育所必需的。神经嵴消融导致随后的心脏间隔缺损。由于高半胱氨酸引起神经嵴相关的中线闭合缺陷和神经嵴相关的心脏缺陷，高半胱氨酸似乎阻止神经嵴细胞的正常迁移和分化。该假设与体外实验的初步数据一致，因此，该项目的中心假设是同型半胱氨酸通过改变神经嵴起源的心肌细胞的迁移和/或分化导致NGA圆锥干缺陷。基于以下观察，我们进一步假设同型半胱氨酸的作用是由N-甲基-D-天冬氨酸（NMDA）受体介导的。1)NMDA受体拮抗剂引起与同型半胱氨酸相同的神经嵴相关缺陷，2）同型半胱氨酸是NMDA受体拮抗剂，3）NMDA受体在发育期间其他细胞的Ca++依赖性迁移中起关键作用，4）神经嵴细胞显示Ca++依赖性迁移，5）神经嵴细胞表达NMDA受体。下面的实验旨在测试这些假设，并描述该系统的关键组成部分。1.我们将确定同型半胱氨酸暴露是否改变9-12期禽类胚胎神经嵴细胞的形成、迁移和/或迁移。2.同型半胱氨酸对NC细胞的作用是否被NMDA受体试剂和NMDA受体亚基敲除所模拟或阻断？3.我们将鉴定NC细胞中表达的NMDA受体亚型，并确定其直接与同型半胱氨酸相互作用并导致发育缺陷的能力。

Neural crest cell formation and migration is necessary for the normal development of cardiac septation. Neural crest ablation causes subsequent cardiac septation defects. Since homocysteine causes both neural crest- related midline closure defects and the neural crest-related cardiac defects, homocysteine appears to be preventing the normal migration and differentiation of neural crest cells. This hypothesis is consistent with preliminary data from in vitro experimental thus, the central hypothesis for this project is that homocysteine causes NGA conotruncal defects by altering the migration and/or differentiation of cardiac cells of neural crest origin. Based upon the following observations, we further hypothesize that the actions of homocysteine are mediated by an N- methyl-D-aspartate (NMDA) receptor. 1) NMDA receptor antagonists cause the same set of neural crest-related defects as homocysteine, 2) homocysteine is an NMDA receptor antagonist, 3) NMDA receptors play a key role in the Ca++-dependent migration of other cells during development, 4) neural crest cells display Ca++-dependent migration, and 5) neural crest cells express NMDA receptors. The following experiments are designed to test these hypotheses and to describe the key components of this system. 1. We will determine if homocysteine exposure alterations the formation, emigration, and/or migration of neural crest cells in stage 9-12 avian embryos. 2. Are homocysteine's actions on NC cells mimicked, or blocked, by NMDA receptor agents and by NMDA receptor subunit knockout? 3. We will identify the subtype of NMDA receptor that is expressed in NC cells and determine its ability to directly interact with homocysteine and to cause the developmental defects.