The role of the GPI anchor in Cripto signaling and forebrain specification

描述(由申请人提供)：无前脑畸形(HPE)是一种前脑发育缺陷，每250例妊娠中就有1例发生。HPE的特征是前脑截断或前脑间隔失败以及其他各种中线缺陷。在发育中的小鼠胚胎中，前脑在原肠形成过程中首先由前内脏内胚层(AVE)指定，AVE是胚胎外的组织。AVE通过阻止来自原始条纹的信号来指定潜在胚胎组织中的前脑，原始条纹为组织提供后部特征。随着发育的进行，AVE被前终末内胚层(ADE)取代，ADE也具有前脑规范活动。CRIPTO在原肠胚的后部表达，在AVE迁移和ADE规范中起关键作用。克里普托缺陷型胚胎有严重的原肠发育缺陷，而克里普托亚型胚胎有HPE。 我已经分离出一种小鼠品系GONZO，它也表现出原肠形成和HPE表型。此外，我已经将导致这种突变的基因定位到1号染色体的一个小区域，并在GPI生物合成酶Pig-N中发现了一个突变。由于Cripto和Gonzo突变体的表型惊人地相似，并且Cripto是一种GPI锚定蛋白，我将检验以下假设：首先，HPE是由AVE迁移缺陷或未能指定ADE引起的。其次，Pig-N突变是HPE表型的原因。第三，Cripto的GPI异常修饰干扰了Cripto信号转导，是HPE表型的致病因素。在这项建议中，我将完成以下目标： 目的1：我将进一步描述HPE的表型，并通过检测已知的与头部形态发生有关的分子标记来明确AVE和ADE的特征。 目的2：证实猪N基因突变与HPE表型有关，并确定其对猪N蛋白的稳定性、定位和活性的影响。 目的3：我将在刚佐胚胎中检测Cripto的活性，并试图通过人为地将Cripto定位到其激活位置来挽救表型。 全前脑畸形(250例中有1例发生)以前脑缺陷为特征；最严重的病例会导致一只单眼，睫状视。我已经在老鼠身上发现了一种新的基因，当它发生突变时，会导致全前脑畸形。这项建议将确定该基因的正常功能，从而更好地理解无前脑畸形的原因。

DESCRIPTION (provided by applicant): Holoprosencephaly (HPE) is a developmental defect of the forebrain, which occurs in 1 out of 250 pregnancies. HPE is characterized by either forebrain truncation or failure of forebrain septation and various other midline defects. In the developing mouse embryo, the forebrain is first specified during gastrulation by the anterior visceral endoderm (AVE), an extra-embryonic tissue. The AVE specifies forebrain in the underlying embryonic tissue by blocking the signals from the primitive streak that provide posterior character to the tissue. As development proceeds, the AVE is displaced by the anterior definitive endoderm (ADE), which also has forebrain specification activity. Cripto, which is expressed in the posterior aspect of the gastrulating embryo, is critically involved in AVE migration and ADE specification. Cripto null embryos have severe gastrulation defects, whereas Cripto hypomorphs have HPE. I have isolated a mouse line, gonzo, that also displays gastrulation and HPE phenotypes. Furthermore, I have mapped the gene responsible for this mutation to a small region of chromosome 1, and have identified a mutation in Pig-N, a GPI-biosynthesis enzyme. Because the phenotypes of Cripto and gonzo mutants are strikingly similar, and because Cripto is a GPI-anchored protein, I will test the following hypotheses: First, HPE results from either an AVE migration defect or failure to specify the ADE. Second, the Pig-N mutation is responsible for the HPE phenotype. Third, aberrant GPI modification of Cripto disrupts Cripto signaling - and is the causative factor for the HPE phenotype. In this proposal I will complete the following aims: Aim 1: I will further characterize the HPE phenotype, and specifically look at specification of the AVE and ADE by examining molecular markers known to be involved in head morphogenesis. Aim 2: I will confirm that the mutation in Pig-N is responsible for the HPE phenotype and determine its effect on Pig-N stability, localization and activity. Aim 3: I will determine Cripto activity in gonzo embryos, and will attempt to rescue the phenotype by artificially targeting Cripto to its site of activation. Holoprosencephaly (which occurs in 1 out of 250 pregnancies) is characterized by forebrain defects; the most severe cases result in a single, cyclopic eye. I have identified a new gene in the mouse that results in holoprosencephaly when it is mutated. This proposal will identify the normal function of this gene thus leading to a better understanding of the causes of holoprosencephaly.