Mutagenesis of Tbx3: a model of ulnar-mammary syndrome

描述(申请人提供)：T-box基因编码一个转录因子家族，在多个组织中表达，并在发育过程中在不同的遗传途径中发挥作用。人TBX3和TBX5基因突变分别导致常染色体显性遗传、尺乳腺综合征和Holt-Oram综合征，而TBX1缺乏导致22q11综合征的缺失。UMS患者有先天性肢体、大汗腺、牙齿和生殖器异常。破坏DNA结合的TBX3功能缺失突变可能会导致某些UMS病例。其他突变发生在蛋白质-蛋白质相互作用所需的区域，或破坏调节(激活或抑制)功能。在受影响的人中没有检测到基因型和表型的相关性。小鼠TBX3缺失杂合子不表现出UMS表型，大多数纯合子缺失突变体在妊娠中期死亡。因此，要确定TBX3缺乏在发育肢体的不同区域或其他器官中的特定影响，需要对小鼠的TBX3进行条件突变。该项目的目标是建立TBX3基因中断和功能障碍的条件性小鼠模型，并研究TBX3基因突变导致出生缺陷的分子和细胞机制，重点是肢体。我们将有条件地破坏TBX3的功能，并使用重组酶介导盒交换来突变不同的TBX3蛋白功能结构域。将检测基因表达、细胞分化、迁移、增殖和存活的变化。由于外显子7突变的显性负效应，我们已经发现了一种新的表型，并建议分析其转录功能。还可以定义基因型-表型相关性，以指导对患有UMS的人类的新研究。我们提出的灵活的模型系统将是许多器官发育研究的宝贵工具，并有助于更深入地了解人类先天性异常的遗传和分子基础。

DESCRIPTION (provided by applicant): T-box genes encode a family of transcription factors that are expressed in multiple tissues and function in diverse genetic pathways during development. Mutations in humanTBX3 and TBX5 result in autosomal dominant, ulnar-mammary (UMS) and Holt-Oram syndromes, respectively, and TBX1 deficiency contributes to human deletion 22q11 syndromes. Patients with UMS have congenital limb, apocrine gland, tooth, and genital abnormalities. TBX3 loss-of-function mutations that disrupt DNA binding may cause some cases of UMS. Other mutations occur in regions required for protein-protein interactions or disrupt regulatory (activator or repressor) function. No genotype-phenotype correlations have been detected in affected humans. Murine Tbx3 null heterozygotes do not manifest the UMS phenotype and most homozygous null mutants die in midgestation. Thus, determining the specific effects of Tbx3 deficiency in different regions of the developing limb, or in other organs, requires conditional mutation of murine Tbx3. The goal of this project is to generate conditional mouse models of Tbx3 disruption and dysfunction and examine the molecular and cellular mechanisms by which mutations of Tbx3 cause birth defects, with an emphasis on the limb. We will disrupt Tbx3 function conditionally and use recombinase -mediated cassette exchange to mutate distinct Tbx3 protein functional domains. Alterations in gene expression, cellular differentiation, migration, proliferation and survival will be examined. We have already discovered a novel phenotype due to dominant negative effects of an Exon 7 mutation and propose to analyze its transcriptional function. Genotype -phenotype correlations may also be defined to direct new investigations in humans with UMS. The flexible model system we propose will be a valuable tool for developmental studies of many organs and lead to a deeper understanding of the genetic and molecular bases of congenital anomalies in humans.