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

描述（由申请人提供）：前脑无裂畸形（HPE）是前脑发育缺陷，250例妊娠中有1例发生。HPE的特征是前脑截断或前脑分隔失败和各种其他中线缺陷。在发育中的小鼠胚胎中，前脑首先在原肠胚形成期间由前内脏内胚层（AVE）（一种胚外组织）指定。AVE通过阻断来自原始条纹的信号来指定底层胚胎组织中的前脑，原始条纹为组织提供后部特征。随着发育的进行，AVE被前定形内胚层（ADE）取代，ADE也具有前脑特化活性。Cripto在原肠胚的后部表达，与AVE迁移和ADE特化密切相关。Cripto null胚胎有严重的原肠胚形成缺陷，而Cripto hypomorphs有HPE。 我已经分离出一个小鼠品系，gonzo，也显示原肠胚形成和HPE表型。此外，我已经将导致这种突变的基因定位在1号染色体的一个小区域，并确定了Pig-N（一种GPI生物合成酶）中的突变。因为Cripto和gonzo突变体的表型惊人地相似，并且因为Cripto是GPI锚定蛋白，所以我将测试以下假设：首先，HPE是由AVE迁移缺陷或未能指定ADE引起的。第二，Pig-N突变是HPE表型的原因。第三，Cripto的异常GPI修饰破坏Cripto信号传导-并且是HPE表型的致病因素。在本提案中，我将完成以下目标： 目标1：我将进一步表征HPE表型，并通过检查已知参与头部形态发生的分子标记物来具体研究AVE和ADE的规格。 目标二：我将确认Pig-N中的突变是HPE表型的原因，并确定其对Pig-N稳定性、定位和活性的影响。 目标3：我将确定奇普托在gonzo胚胎中的活性，并试图通过人工将奇普托靶向其激活位点来拯救表型。 前脑无裂畸形（每250例妊娠中发生1例）的特征是前脑缺陷;最严重的病例会导致单眼独眼。我在老鼠身上发现了一种新基因，当它突变时会导致前脑无裂畸形。这项建议将确定该基因的正常功能，从而导致更好地了解前脑无裂畸形的原因。

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.