Retinoid Dehydrogenases Involved in Eye Development

描述（由申请人提供）：视黄酸（RA）是维生素a（视黄醇）的代谢衍生物，作为信号分子发挥作用。类风湿性关节炎对眼睛发育至关重要，但人们对其作用知之甚少。当视黄醇代谢为RA时，RA信号就会发生，RA作为核RA受体的配体，调节基因表达。在胚胎发生过程中控制RA合成的酶目前正在研究中，这些研究为RA在眼睛发育过程中的作用机制提供了新的信息。对小鼠胚胎的研究表明，眼内存在三种合成RA的异表达视黄醛脱氢酶，即RALDH1、RALDH2和RALDH3。对Raldh1、Raldh2和Raldh3零突变小鼠的研究已经发现了眼睛缺陷，对这些小鼠的进一步研究开始揭示RA作用的机制。由于三个Raldh基因在小鼠和人类中都是保守的，因此我们开发的零突变体是了解人类眼睛发育过程中RA作用机制的良好小鼠模型。有证据表明，由膳食维生素A缺乏引起的类风湿性关节炎缺乏症可能与人眼缺陷（称为眼结肠瘤）有关。提出的遗传学研究将为治疗病因涉及RA合成遗传缺陷和/或膳食维生素A缺乏的人类眼病提供相关信息：我们发现，RA合成的位置在眼睛发育过程中经历了动态的时空变化，RA作用的位置同步变化。Raldh2/Raldh3双突变小鼠胚胎发育视神经囊泡，但这种结构缺乏RA合成，不能腹侧内陷形成视神经杯。Raldh3零突变胚胎发育视神经杯，但视神经裂隙闭合缺陷（coloboma）。Raldhl零突变胚胎在背视网膜缺乏RA合成，但未观察到眼睛缺陷。然而，Raldh1/Raldh3双突变体表现出过度侵犯视网膜前的视周间质，从而揭示了Raldhl通常由Raldh3代偿的功能（反之亦然）。这些发现导致了一种假设，即类风湿性关节炎控制着眼睛的形态发生运动，而不是像之前认为的那样控制着视网膜的背腹侧模式。本项目的总体目标是确定RA在眼睛发育过程中的信号传导机制，特别是RA在眼睛中调控的基因网络。我们将测试RA调节视网膜和周围视周间质的眼形态发生运动的假设。这些研究将在遗传学上使用未获救或通过各种遗传或药理学方法获救的Raldh化合物零突变小鼠进行。具体研究将集中在：(1)RA对视杯形成过程中细胞形状和细胞粘附的控制；(2)视杯形成过程中RA-FGF的拮抗作用；(3) RA对视杯形成后视周间质侵袭的控制。

DESCRIPTION (provided by applicant): Retinoic acid (RA) is a metabolic derivative of vitamin A (retinol) that functions as a signaling molecule. RA is essential for eye development, but its action is poorly understood. RA signaling occurs when retinol is metabolized to RA which serves as a ligand for nuclear RA receptors that regulate gene expression. The enzymes controlling synthesis of RA during embryogenesis are now under investigation and such studies are providing new information on the mechanism of RA action during eye development. Studies on mouse embryos have demonstrated the existence of three retinaldehyde dehydrogenases differentially expressed in the eye that synthesize RA, i.e. RALDH1, RALDH2, and RALDH3. Investigations of Raldh1, Raldh2, and Raldh3 null mutant mice have uncovered eye defects, and further studies of these mice are beginning to reveal the mechanism of RA action. As the three Raldh genes are conserved in mice and humans, the null mutants we have developed are excellent mouse models for understanding the mechanism of RA action during human eye development. Evidence exists suggesting that RA deficiency caused by dietary vitamin A deficiency may be linked to the human eye defect known as ocular coloboma. The genetic studies proposed will provide information relevant to treatment of human eye diseases whose etiology involves genetic deficiency in RA synthesis and/or dietary vitamin A deficiency: We have found that the location of RA synthesis undergoes dynamic spatiotemporal changes during eye development, and that the location of RA action changes in synchrony. Raldh2/Raldh3 double mutant mouse embryos develop an optic vesicle, but this structure lacks RA synthesis and fails to invaginate ventrally to form the optic cup. Raldh3 null mutant embryos develop an optic cup but they display defects in closure of the optic fissure (coloboma). Raldhl null mutant embryos lack RA synthesis in the dorsal retina, but eye defects are not observed. However, Raldh1/Raldh3 double mutants display excessive invasion of perioptic mesenchyme anterior to the retina, thus revealing a function for Raldhl that is normally compensated by Raldh3 (and vice-versa). These findings have led to the hypothesis that RA controls eye morphogenetic movements rather than dorsoventral patterning of the retina as previously thought. The overall goal of this project is to determine the mechanism of RA signaling during eye development, particularly the gene networks regulated by RA in the eye. We will test the hypothesis that RA regulates eye morphogenetic movements of both the retina and the surrounding perioptic mesenchyme. These studies will be performed genetically using Raldh compound null mutant mice that are unrescued or rescued by various genetic or pharmacological methods. Specific investigations will focus upon: (1) RA control of cell shape and cell adhesion during optic cup formation; (2) RA-FGF antagonism during optic cup formation; (3) RA control of perioptic mesenchyme invasion following optic cup formation.