LIM-HD Transcription Factors in Forebrain Patterning

描述（由申请人提供）：成年哺乳动物前脑的解剖学和功能组织的基本原理是新皮质形成不同区域的图案，以及丘脑背侧（dTh）包裹成核。新皮层进入区域的发育模式，即实现的过程，受到两种内在机制的控制，在这里定义为指定皮质神经元位置或区域身份的调节基因，以及外在影响，主要被认为是区域特异性丘脑皮质轴突（TCA）输入，或由其传递的信息，这些信息来自于d核，部分由新皮层固有的遗传框架建立。在过去的几年里，关于实现的内在遗传调控的证据才开始出现，到目前为止，已经涉及到同源结构域转录因子EMX2和配对盒转录因子PAX6控制实现。关于将dTh形成细胞核并指定细胞核独特性质的遗传机制，我们所知甚少。基于LIM-HD基因的已知功能、LHX2在新皮层中的独特分级表达以及LHX2和LHX9在dTh核亚群中的组合表达，我们推测LIM-HD转录因子LHX2和LHX9通过直接机制指定了皮层中的区域身份和dTh核中的细胞核身份。我们还提出，它们通过控制dTh进入细胞核的模式和指定dTh投射神经元自主的特性来间接但关键地影响新皮层的实现，这些特性决定了它们的TCA投射到特定新皮层区域的发展，这反过来又影响皮层模式。为了研究LHX2和LHX9的这些作用，我们将采用一系列方法，包括使用组织特异性转基因表达和靶向基因失活的条件功能增益和功能丧失分析，这些方法被设计用于存活到成年的小鼠。我们将分析皮层和dTh神经元的区域和核特异性表型，包括身份标记的表达，特定的输入和输出投影，以及新皮层进入区域和dTh进入细胞核的组织。提出的多层次分析和替代策略将有助于规避与更有限的方法相关的潜在问题，为支持解释提供补充发现，并有助于建立前脑模式调节的层次结构。

DESCRIPTION (provided by applicant): A fundamental principle that underlies the anatomical and functional organization of the adult mammalian forebrain is the patterning of the neocortex into distinct areas and the parcellation of the dorsal thalamus (dTh) into nuclei. The developmental patterning of the neocortex into areas, i.e. the process of arealization, is controlled by both intrinsic mechanisms, defined here as regulatory genes that specify positional or area identities of cortical neurons, and extrinsic influences, mainly considered to be area-specific thalamocortical axon (TCA) input, or the information being relayed by it, that arises from dTh nuclei and is established in part by the genetic framework intrinsic to the neocortex. Evidence for the intrinsic genetic regulation of arealization has only begun to emerge over the past few years and thus far has implicated the homeodomain transcription factor EMX2 and the paired-box transcription factor PAX6 in controlling arealization. Less is known about the genetic mechanisms that pattern the dTh into nuclei and specify nuclei-unique properties. We hypothesize that the LIM-homeodomain (LIM-HD) transcription factors LHX2 and LHX9 specify area identities in the cortex and nuclei identities in the dTh through a direct mechanism, based on the known functions of LIM-HD genes, the uniquely graded expression of LHX2 in the neocortex, and the combinatorial expression of LHX2 and LHX9 in subsets of dTh nuclei. We also propose that they indirectly, but critically, influence neocortical arealization by controlling patterning of the dTh into nuclei and specifying properties autonomous to dTh projection neurons that determine the development of their TCA projections to specific neocortical areas, which in turn influence cortical patterning. To study these roles for LHX2 and LHX9, we will employ a range of approaches including conditional gain- and loss-of-function analyses using tissue specific transgene expression and targeted gene inactivation in mice designed to survive to adulthood. We will analyze area- and nuclei-specific phenotypes of cortical and dTh neurons, including expression of markers of identity, specific input and output projections, and the organization of neocortex into areas and dTh into nuclei. The multilevel analyses and alternative strategies proposed will help circumvent potential problems associated with more limited approaches, provide complementary findings to support interpretations, and help establish a hierarchy of regulation of forebrain patterning.