Molecular Genetics of Hox Genes and Kidney Development

描述（由申请人提供）：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不明确。靶向基因破坏研究已经证实，这些基因影响前后模式过程，但单突变动物的表型通常是温和的，多效性的，表现出不完全外显性和可变的表达性。由于这些缺陷的性质，对Hox基因的下游靶点或Hox基因运作的分子途径知之甚少。通过移除所有六个Hoxll旁系基因的功能拷贝，我们产生了没有肾脏的动物。后肾胚在发育早期形成，但没有输尿管芽诱导。这种表型的外显率为100%。通过对这种表型的分子检查，我们已经能够确定Hoxll旁系基因下游的因素。Six2（保守的pax - yya - 6通路的成员）和Gdnf（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旁系突变体中不表达。我们的初步数据表明Six2是Hoxll蛋白的直接下游靶点，并且Hoxll蛋白与Eyal和Pax2直接相互作用调控Six2的表达。由于这些基因中的每一个都与诱导配体Gdnf的调控有关，因此确定它们之间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旁系基因在肾形成过程中也发挥着关键作用，但机制尚未明确。在我们看来，该系统是鉴定Hox基因的下游靶标及其调控表达的因子的理想选择。Hox基因的同源性使得这些基因很可能与它们的调控网络中的其他因素一起作为疾病过程的修饰因子。Pax、Eya和Six基因的突变已在人的支气管-耳-肾综合征和肾-结肠综合征病例中得到证实。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发育调节因子组之间的相互作用，并定义先前未描述的Hox基因与pax - yya - 6 /Gdnf调控通路之间的分子关系。我们假设Hox基因与pax - yya - 6调控网络的保守相互作用指定输尿管芽诱导和发育肾脏的模式。相关性：这些研究将为肾脏发育和疾病中Hox调控的分子和机制基础提供关键见解。

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.