Retinoid Dehydrogenases Involved in Eye Development

视黄酸（RA）是维生素a（视黄醇）的代谢衍生物，在脊椎动物发育过程中对眼睛的轴向模式至关重要。当视黄醇被代谢为视网膜，然后作为核类视黄醇受体的配体调节基因表达时，类视黄醇信号就会发生。妊娠期维生素A缺乏或类视黄酮受体零突变导致的类视黄酮信号中断可导致眼的背腹轴发育异常。眼内局部类风湿性关节炎的产生机制以及类风湿性关节炎如何调节眼的背腹侧模式的机制尚不清楚。我们对视黄醇如何被生理激活形成RA的理解仍然模糊，但通过发现在眼睛中表达的三种类视黄醇脱氢酶，即RALDH1， RALDH2和RALDH3，它们都是醛脱氢酶（ALDH）酶家族的成员，将视网膜代谢为RA，已经有所改善。本实验室和另一个实验室产生的Raldh2零突变小鼠在妊娠中期显示出致命的表型，躯干和前肢发育缺陷巨大，后脑模式异常，但未观察到视神经囊泡缺陷。母体给药可以挽救Raldh2突变体中的许多缺陷，从而可以通过条件挽救进行进一步分析。本实验室最近产生的Raldh1零突变小鼠是可以存活的，但胚胎在背视网膜中缺乏RA合成，这表明在进一步的分析中会发现视网膜缺陷。目前还没有关于Raldh3基因的研究报道。对raldh的进一步分析应提供了解人类发育性眼缺陷所需的关键信息。本项目的总体目标是利用零突变小鼠确定RALDH1、RALDH2和RALDH3在眼部RA合成中的作用，并以这些突变小鼠为工具进一步研究类视黄醛信号在眼部发育中的作用机制。突变小鼠将在组织学上检查发育性眼缺陷，并通过原位杂交检测眼组织中中断的基因表达。携带RARE-lacZ标记基因的小鼠将用于检测突变胚胎中的内源性RA。本项目的具体目标如下：(1)利用Raldh1突变体研究背侧视网膜缺乏RA对视网膜发育和视网膜投射轴突寻路的影响；(2)通过比较RALDH2和RALDH1 - RALDH2双突变体，研究RALDH1和RALDH2对RA合成的贡献；(3)生成Raldh3零突变小鼠，检测该基因在眼睛发育中的作用。

Retinoic acid (RA), a metabolic derivative of vitamin A (retinol), is essential for axial patterning of the eye during vertebrate development. Retinoid signaling occurs when retinol is metabolized to retinal and then to RA which serves as a ligand for nuclear retinoid receptors that regulate gene expression. Disruption of retinoid signaling either by gestational vitamin A deficiency or by creation of retinoid receptor null mutations results in abnormal dorsoventral axial development of the eye. The mechanism for generation of RA locally in the eye as well as the mechanism for how RA regulates dorsoventral patterning of the eye are not yet understood. Our understanding of how retinol is physiologically activated to form RA is still vague, but has been improved by discovery of three retinoid dehydrogenases expressed in the eye that metabolize retinal to RA, i.e. RALDH1, RALDH2, and RALDH3, all members of the aldehyde dehydrogenase (ALDH) enzyme family. Raldh2 null mutant mice generated in this laboratory and another have revealed phenotypes that are lethal at midgestation with massive trunk and forelimb developmental defects plus abnormal hindbrain patterning, but no optic vesicle defects were observed. Maternal RA administration rescues many defects in Raldh2 mutants, thus allowing further analysis by conditional rescue. Raldh1 null mutant mice recently generated in this laboratory are viable, but embryos suffer a lack of RA synthesis in the dorsal retina suggesting that retinal defects will be discovered upon further analysis. There have been no genetic studies reported on Raldh3. Further analysis of RALDHs should provide key information needed to understand human developmental eye defects. The overall goals of this project are to use null mutant mice to establish roles for RALDH1, RALDH2, and RALDH3 in eye RA synthesis, plus use these mutant mice as tools to further examine the mechanism of retinoid signaling in eye development. Mutant mice will be examined for developmental eye defects histologically and by in situ hybridization to detect disrupted gene expression in eye tissues. Mice carrying the RARE-lacZ marker gene will be used to detect endogenous RA in mutant embryos. Specific goals for this project will be as follows: (1) Use Raldh1 mutants to examine the effect of a lack of RA in the dorsal retina on retinal development and axonal pathfinding for retinofugal projections; (2) Examine the contribution of RALDH1 and RALDH2 to RA synthesis for eye development by comparison of conditionally RA-rescued Raldh2 mutants and Raldh1-Raldh2 double mutants; (3) Generate Raldh3 null mutant mice to examine the role of this gene in eye development.