Molecular Genetics of Hox Genes and Kidney Development

描述（由申请人提供）：基因的Hox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不明确。靶向基因破坏研究已经证实，这些基因影响前后图案化过程，但单突变动物的表型通常是温和的，多效性的，表现出不完全的突变，并具有可变的表达。由于这些缺陷的性质，关于Hox基因的下游靶点或Hox基因运作的分子途径知之甚少。通过去除Hoxll旁系同源基因的所有六个功能拷贝，我们产生了没有肾脏的动物。后肾胚基在发育早期形成，但没有输尿管芽的诱导发生。这种表型以100%的突变率发生。通过研究这种表型的分子，我们已经能够确定的Hoxll旁系同源基因的下游因素。Six 2是保守的Pax-Eya-Six途径的成员，而Gdnf是负责向沃尔夫管发出信号以启动输尿管芽诱导的诱导配体，在Hoxll旁系同源突变体中不表达。我们的初步数据表明Six 2是Hoxll旁系同源物的直接下游靶标，并且Hoxll旁系同源物直接与Eyal和Pax 2相互作用以调节Six 2表达。由于这些基因中的每一个也参与了GDNF（诱导配体）的调节，因此定义它们的相互作用对于理解肾脏发育的分子基础至关重要。最后，补充的新发现表明，HoxlO旁系同源基因也通过尚未确定的机制在肾发生发育中发挥关键作用。在我们看来，这个系统是理想的识别下游目标的Hox基因和因子与他们调节表达。Hox基因的旁系同源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作为疾病过程的修饰剂。Pax、Eya和Six基因的突变已在鳃-耳-肾综合征以及肾-缺损综合征的人类病例中得到证实。因此，Hox基因很可能影响人类这些综合征的严重程度。使用肾脏作为模型器官系统，我们将研究这些高度保守的组之间的相互作用的发展监管机构和定义以前未描述的Hox基因和Pax-Eya-Six/GDNF调节通路在肾发生之间的分子关系。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Hox在肾脏发育和疾病中的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.