LIM Homeodomain Factors and Pituitary Gene Expression

总体目标是了解特定的LIM同源域（Lhx）转录因子在垂体促甲状腺细胞和促性腺细胞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。我们已经表明，Lhx 2和Lhx 3可以与一个特定的DNA元件指定的PGBE激活糖蛋白激素α亚基基因的转录。这些发现提出了Lhx 2和Lhx 3在调节α亚基基因表达中可能发挥可互换作用的可能性。然而，本实验室和其他实验室最近的研究结果表明Lhx因子作用的特异性。我们最近进行了一项突变研究，为介导Lhx 2和Lhx 3转录反应的不同机制提供了证据。个别Lhx因素的不同行动的可能性是一致的，与最近的研究特定的Lhx因素在中枢神经系统发育中的作用。虽然Lhx 2和Lhx 3基因在小鼠中被破坏，但遗传操作导致发育缺陷，使得不能获得垂体细胞的成年群体。为了解决这些问题，并探讨Lhx因子的作用机制，具体的目标包括：1）定位GnRH诱导的Lhx 2和Lhx 3磷酸化的位点，并评估这种磷酸化的功能。还将评估GnRH诱导的SLB磷酸化的可能性。2)使用遗传筛选，以确定突变，破坏Lhx 3和假定的适配器/辅激活因子，SLB之间的相互作用，检查结构功能关系，为这个复杂的α-亚基基因表达。3)直接检测体内α亚基基因表达对Lhx 2、Lhx 3和SLB的需求。4)寻找Lhx 2和Lhx 3靶基因。这些研究应该明确促性腺激素和促甲状腺激素生物合成中特定Lhx因子的作用 以及提供新的见解更普遍的问题，特异性和机制介导的Lhx行动，以调节基因的表达和发展。

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.