Generation of Retinoid Signals during Development

描述（由申请人提供）：当维生素A转化为视黄酸（RA）时，类维生素A信号传导启动，视黄酸作为核RA受体的配体，在包括肢芽、神经管和心脏在内的多种器官发育期间调节基因表达和模式形成。通过发现在小鼠和人类中保守的三种将视网膜代谢为RA的视黄醇醛脱氢酶（RALDH 1，RALDH 2和RALDH 3），我们对RA产生如何调节的理解得到了改善。小鼠Raldh 2的突变几乎完全消除了RA的合成，并导致妊娠中期致死性心脏和后脑缺陷。有条件救援的Raldh 2突变体有限的母体RA管理允许发展进行（除了前肢芽），并导致建立额外的网站RA合成连接到Raldh 1在背侧视网膜的表达和Raldh 3在腹侧视网膜，嗅窝，输尿管芽的表达。出乎意料的是，有条件的RA拯救Raldh 2突变体也具有新的网站的RA合成在后脑，脊髓，和心脏，不对应于Raldh 1 -3的表达。因此，额外的酶在神经管和心脏中进行RA合成，加上后肢芽从未知来源接收RA。给予RA不仅直接挽救Raldh 2突变体的发展，而且还通过刺激额外的组织特异性RA生成酶，在需要的地方局部产生RA。我们只是在学习胚胎组织如何调节RA产生的过程的开始，特别是需要确定其他酶。这些信息对于开发基于干细胞的疾病治疗方法至关重要。为了诱导器官从干细胞发育，我们需要彻底了解胚胎如何执行这项任务。我们假设，胚胎类维生素A信号需要组织特异性的局部RA的合成，一些组织利用一种以上的酶，每个独特的时空表达模式，以实现这一目标。我们将使用遗传学方法来检测胚胎组织中的RA，并检查潜在的RA产生酶的功能。在我们完全理解RA信号传导的影响之前，我们需要鉴定所有产生RA的酶，清楚地定义它们在胚胎组织中何时何地起作用，并使用无效突变体来定义它们丢失的形态学后果以及对下游靶基因的影响。具体而言，条件性RA拯救的Raldh 2突变体将用于鉴定依赖于RALDH 2或依赖于其他酶的肢芽、后脑和脊髓中的发育过程。此外，我们将确定在神经管和心脏中表达的新型RA生成酶，并开始对它们进行遗传研究。

DESCRIPTION (provided by applicant): Retinoid signaling initiates when vitamin A is converted to retinoic acid (RA) which serves as a ligand for nuclear RA receptors that regulate gene expression and pattern formation during development of diverse organs including the limb buds, neural tube, and heart. Our understanding of how RA generation is regulated has been improved by discovery of three retinaldehyde dehydrogenases conserved in mouse and human that metabolize retinal to RA (RALDH1, RALDH2, and RALDH3). Null mutations of mouse Raldh2 almost totally eliminate RA synthesis and result in midgestation lethality with defects in the heart and hindbrain. Conditional rescue of Raldh2 mutants by limited maternal RA administration allows development to proceed (except for the forelimb buds) and results in the establishment of additional sites of RA synthesis linked to Raldh1 expression in the dorsal retina and to Raldh3 expression in the ventral retina, olfactory pit, and ureteric bud. Unexpectedly, conditionally RA-rescued Raldh2 mutants also possess novel sites of RA synthesis in the hindbrain, spinal cord, and heart that do not correspond to expression of Raldh1-3. Thus, additional enzymes perform RA synthesis in the neural tube and heart, plus the hindlimb bud receives RA from an unknown source. Administered RA rescues development of Raldh2 mutants not only directly, but also by stimulating additional tissue-specific RA generating enzymes that produce RA locally where it is needed. We are only at the beginning of the process in learning how embryonic tissues regulate the generation of RA, especially as additional enzymes need to be identified. Such information will be essential for development of stem cell-based treatments for disease. In order to induce organs to develop from stem cells, we need to have a thorough understanding of how the embryo performs this task. We hypothesize that embryonic retinoid signaling requires tissue-specific local RA synthesis and that some tissues utilize more than one enzyme, each with unique spatiotemporal expression patterns, to achieve this goal. We will use genetic approaches to detect RA in embryonic tissues and to examine the functions of potential RA generating enzymes. Before we can fully understand the impact of RA signaling we need to identify all the RA generating enzymes, clearly define when and where they function in embryonic tissues, and use null mutants to define the morphological consequences of their loss and the effect on downstream target genes. Specifically, conditionally RA-rescued Raldh2 mutants will be used to identify developmental processes in the limb buds, hindbrain, and spinal cord dependent upon RALDH2 or dependent upon other enzymes. Also, we will identify the novel RA-generating enzymes expressed in the neural tube and heart and begin genetic studies on them.