Retinoid Dehydrogenases Involved in Eye Development

描述(申请人提供)：维甲酸(RA)是维生素A(视黄醇)的代谢衍生物，起信号分子的作用。RA对眼睛发育是必不可少的，但人们对它的作用知之甚少。RA信号发生在视黄醇被代谢成RA时，RA是核内RA受体的配体，调节基因的表达。控制胚胎发育期间RA合成的酶目前正在研究中，这些研究为眼睛发育过程中RA的作用机制提供了新的信息。对小鼠胚胎的研究表明，存在三种在眼睛中差异表达的合成RA的视黄醛脱氢酶，即RALDH1、RALDH2和RALDH3。对Raldh1、Raldh2和Raldh3缺失突变小鼠的研究发现了眼睛缺陷，对这些小鼠的进一步研究开始揭示RA的作用机制。由于这三个Raldh基因在小鼠和人类中都是保守的，我们开发的零突变是理解人眼发育过程中RA作用机制的优秀小鼠模型。有证据表明，由于饮食缺乏维生素A而导致的RA缺乏症可能与被称为眼缺损的人类眼睛缺陷有关。这些遗传学研究将为人类眼部疾病的治疗提供相关信息，这些疾病的病因涉及RA合成的遗传缺陷和/或饮食中维生素A的缺乏：我们发现，在眼睛发育过程中，RA合成的位置经历了动态的时空变化，并且RA的作用位置同步变化。Raldh2/Raldh3双突变小鼠胚胎发育出一个视泡，但该结构缺乏RA合成，不能内陷腹侧形成视杯。Raldh3缺失的突变胚胎发育出视杯，但它们在视裂闭合(孔洞)方面显示出缺陷。Raldhl缺失突变胚胎在背部视网膜中缺乏RA合成，但没有观察到眼睛缺陷。然而，Raldh1/Raldh3双突变体表现出视网膜前视周间质的过度侵袭，从而揭示了Raldh1的功能通常由Raldh3补偿(反之亦然)。这些发现导致了一种假设，即RA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视网膜的背腹图案。这个项目的总体目标是确定眼睛发育过程中RA信号的机制，特别是眼睛中受RA调控的基因网络。我们将验证这样的假设，即RA调节视网膜和周围视周间充质的眼睛形态发生运动。这些研究将使用未获救或通过各种遗传或药物方法获救的Raldh复合缺失突变小鼠进行遗传学研究。具体的研究将集中在：(1)视杯形成过程中RA对细胞形态和细胞黏附的控制；(2)视杯形成过程中RA-FGF的拮抗作用；(3)视杯形成后RA对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.