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，类维甲酸信号启动，视黄酸作为核RA受体的配体，在包括肢体芽、神经管和心脏在内的多种器官的发育过程中调节基因表达和模式形成。通过发现小鼠和人类中保存的三种将视网膜代谢为RA的视黄醛脱氢酶（RALDH1， RALDH2和RALDH3），我们对RA的产生是如何调节的理解得到了提高。小鼠Raldh2的零突变几乎完全消除RA合成，导致妊娠中期死亡，心脏和后脑缺陷。通过有限的母体给药，Raldh2突变体的有条件拯救允许发育继续进行（前肢芽除外），并导致与背视网膜中Raldh1表达和腹侧视网膜、嗅窝和输尿管芽中Raldh3表达相关的其他RA合成位点的建立。出乎意料的是，条件性RA拯救的Raldh2突变体在后脑、脊髓和心脏中也具有新的RA合成位点，这些位点与Raldh1-3的表达不一致。因此，额外的酶在神经管和心脏中进行RA合成，再加上后肢芽从未知来源接收RA。给药的RA不仅可以直接挽救Raldh2突变体的发展，还可以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。在了解胚胎组织如何调节类风湿性关节炎的产生这一过程中，我们才刚刚开始，特别是在需要确定其他酶的情况下。这些信息对于开发基于干细胞的疾病治疗方法至关重要。为了从干细胞诱导器官发育，我们需要彻底了解胚胎是如何完成这一任务的。我们假设胚胎类视黄醇信号需要组织特异性的局部RA合成，并且一些组织使用多种酶，每种酶具有独特的时空表达模式，以实现这一目标。我们将使用遗传方法检测胚胎组织中的类风湿性关节炎，并检查潜在的类风湿性关节炎生成酶的功能。在我们能够完全理解RA信号的影响之前，我们需要识别所有产生RA的酶，清楚地确定它们在胚胎组织中的作用时间和位置，并使用零突变体来确定它们丢失的形态学后果以及对下游靶基因的影响。具体来说，有条件ra拯救的Raldh2突变体将用于鉴定依赖于Raldh2或其他酶的肢体芽、后脑和脊髓的发育过程。此外，我们将确定在神经管和心脏中表达的新的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.