Molecular Genetics of Hox Genes and Kidney Development

描述(申请人提供)：HOX基因复合体影响发育和疾病，但HOX转录因子调节下游靶基因的途径在很大程度上仍未确定。有针对性的基因干扰研究已经证实，这些基因影响前后图案化过程，但单个突变动物的表型通常是温和的、多效性的，表现出不完全外显，并具有可变的表达能力。由于这些缺陷的性质，对HOX基因下游靶点或HOX基因作用的分子途径知之甚少。通过移除Hoxll近亲基因的所有六个功能副本，我们产生了没有肾脏的动物。后肾胚泡形成于发育的早期，但没有输尿管芽的诱导。这种表型以100%的外显率出现。通过分子检测这种表型，我们已经能够确定Hoxll类似基因下游的因素。SIX2是保守的Pax-Eya-Six途径的成员，GDNF是负责向Wolffian管发出信号以启动输尿管芽诱导的诱导配体，在Hoxll近缘突变体中没有表达。我们的初步数据表明，SIX2是Hoxll对虾的直接下游靶标，Hoxll对虾直接与EYAL和Pax2相互作用来调节SIX2的表达。由于这些基因中的每一个都参与了诱导配体GDNF的调节，因此定义它们的相互作用对于了解肾脏发育的分子基础至关重要。最后，值得称赞的新发现表明，HoxlO类似基因也在肾脏发育中发挥关键作用，其机制尚不明确。在我们看来，这个系统是识别HOX基因下游靶点和调节其表达的因子的理想方法。HOX基因的相似性质使得这些基因很可能与其调控网络中的其他因素一起充当疾病过程的修饰者。在Branchio-Oto-Renal综合征和肾缺损综合征的人类病例中，已经发现了Pax、Eya和六个基因的突变。因此，HOX基因很可能影响人类这些综合征的严重程度。以肾脏为模型器官系统，我们将研究这些高度保守的发育调节基因之间的相互作用，并确定之前未描述的HOX基因与Pax-Eya-Six/GDNF调控通路在肾脏发生中的分子关系。我们假设，HOX基因与Pax-Eya-Six调控网络的保守相互作用指定了输尿管芽诱导和发育中的肾脏模式。相关性：这些研究将为肾脏发育和疾病中HOX调节的分子和机制基础提供关键的见解。

DESCRIPTION (provided by applicant): The Hox complex of genes affects both development and disease, but the pathways by which Hox transcription factors regulate downstream target genes remain largely undefined. Targeted gene disruption studies have confirmed that these genes affect anteroposterior patterning processes, but phenotypes of single mutant animals are generally mild, pleiotropic, demonstrate incomplete penetrance and have variable expressivities. Because of the nature of these defects, very little is known regarding downstream targets of Hox genes or the molecular pathways in which Hox genes operate. By removing all six functional copies of the Hoxll paralogous genes, we generated animals that have no kidneys. The metanephric blastema forms early in development, but no ureteric bud induction occurs. This phenotype occurs with 100% penetrance. By examining this phenotype molecularly, we have been able to identify factors downstream of the Hoxll paralogous genes. Six2 a member of the conserved Pax-Eya-Six pathway, and Gdnf, the inducing ligand responsible for signaling to the Wolffian duct to initiate ureteric bud induction, are not expressed in the Hoxll paralogous mutants. Our preliminary data indicate that Six2 is a direct downstream target of the Hoxll paralogs, and that Hoxll paralogs directly interact with Eyal and Pax2 to regulate Six2 expression. As each of these genes has also been implicated in the regulation of Gdnf, the inducing ligand, defining their interactions is critical to understanding the molecular basis of kidney development. Finally, complimentary new findings indicate that HoxlO paralogous genes also play a critical role in nephrogenic development by as yet undefined mechanisms. In our view, this system is ideal for identifying downstream targets of Hox genes and factors with which they regulate expression. The paralogous nature of the Hox genes make it very likely that these genes act as modifiers of disease proccesses in conjunction with other factors in their regulatory network. Mutations in Pax, Eya and Six genes have been demonstrated in human cases of Branchio-Oto-Renal Syndrome as well as Renal- Coloboma Syndrome. It is thus very likely that Hox genes influence the severity of these syndromes in humans. Using the kidney as a model organ system, we will examine the interaction between these highly conserved groups of developmental regulators and define the previously undescribed molecular relationships between Hox genes and the Pax-Eya-Six/Gdnf regulatory pathway in nephrogenesis. We hypothesize that a conserved interaction of Hox genes with the Pax-Eya-Six regulatory network specifies ureteric bud induction and patterns the developing kidney. Relevance: These studies will provide key insights into the molecular and mechanistic basis of Hox regulation in kidney development and disease.