LIM Homeodomain Factors and Pituitary Gene Expression

总体目标是了解特异性LIM同源结构域（Lhx）转录因子在垂体促甲状腺激素和促性腺激素中糖蛋白激素亚基基因表达中的作用，并确定Lhx因子的作用机制。我们已经证明Lhx2和Lhx3可以与特定的DNA元件PGBE相互作用，激活糖蛋白激素α亚基基因的转录。这些发现提出了Lhx2和Lhx3可能在调节α -亚基基因表达中发挥互换作用的可能性。然而，最近来自本实验室和其他实验室的发现表明Lhx因子作用具有特异性。我们最近进行了一项突变研究，为介导Lhx2和Lhx3转录反应的不同机制提供了证据。个别Lhx因子的不同作用的可能性与最近关于特定Lhx因子在中枢神经系统发育中的作用的研究是一致的。虽然Lhx2和Lhx3基因在小鼠中被破坏，但基因操作导致发育缺陷，因此无法获得成年垂体细胞群。为了解决这些问题，探讨Lhx因子的作用机制，具体目标包括：1)绘制gnrh诱导的Lhx2和Lhx3磷酸化位点，并评价其磷酸化功能。还将评估gnrh诱导SLB磷酸化的可能性。2)使用遗传筛选来识别破坏Lhx3与假定的适配器/共激活子SLB之间相互作用的突变，以检查该复合物在α -亚基基因表达中的结构功能关系。3)在体内直接检测Lhx2、Lhx3和SLB对α -亚基基因表达的需求。4)寻找Lhx2和Lhx3靶基因。这些研究应该明确特定Lhx因子在促性腺激素和促甲状腺激素生物合成中的作用

The overall goal is to understand the roles that specific LIM homeodomain (Lhx) transcription factors play in expression of the glycoprotein hormone subunit genes in thyrotropes and gonadotropes of the pituitary and to determine the mechanism of action of Lhx factors. We have shown that Lhx2 and Lhx3 can interact with a specific DNA element designated the PGBE to activate transcription of the glycoprotein hormone alpha-subunit gene. These findings raise the possibility that Lhx2 and Lhx3 may play an interchangeable role in regulating alpha-subunit gene expression. However, recent findings from this and other laboratories suggest specificity in Lhx factor action. We have recently performed a mutational study that offers evidence for distinct mechanisms mediating transcriptional responses to Lhx2 and Lhx3. The possibility of distinct actions of individual Lhx factors is consistent with recent studies of the role of specific Lhx factors in central nervous system development. Although the Lhx2 and Lhx3 genes have been disrupted in mice, the genetic manipulations result in developmental defects so that adult populations of pituitary cells are not available. To address these issues and explore the mechanism of Lhx factor action the specific aims include: 1) Map the site of GnRH-induced phosphorylation of Lhx2 and Lhx3 and evaluate the function of this phosphorylation. The possibility of GnRH-induced phosphorylation of SLB will also be evaluated. 2) Use a genetic screen to identify mutations that disrupt the interaction between Lhx3 and the putative adapter/coactivator, SLB, to examine structurefunction relationships for this complex in alpha-subunit gene expression. 3) Directly test the requirement for Lhx2, Lhx3 and SLB for alpha-subunit gene expression in vivo. 4) Search for Lhx2 and Lhx3 target genes. These studies should define the role of specific Lhx factors in gonadotropin and thyrotropin biosynthesis as well as provide new insights into more general issues about specificity and mechanisms mediating Lhx actions to regulate gene expression and development.