Lineage & Development of the Midbrain & Hindbrain

描述（由申请人提供）：脊椎动物的大脑来源于吻侧神经管，其最初表现为一系列被称为神经粒的形态学收缩，描绘了大脑的主要细分。神经粒的组织特异性模式导致成人高度专业化的解剖和功能单位。完成这些显著发育事件的一种方法是结合模式的组合机制，该机制涉及谱系限制边界的形成，同时伴随着指示相邻组织的特定位置信息和命运的“组织者”的出现。这一机制已经在果蝇的翅膀想象盘以及小鸡和老鼠的肢体上得到证实，但还没有在大脑上得到证实。中脑（mesencephalon, mes）和中脑（metencephalon, met）彼此相对，具有明显不同的形态结构。在发育早期，表达Otx2和Wnt1的mes和表达Gbx2和Fgf8的met沿着被定义为峡部的前后轴并置于一个明确的收缩处。差异表达的mes/met基因指定区域身份，并可能将两个细胞群体隔离到假定的区室中。有趣的是，经典移植研究表明，地峡是一个组织者，似乎通过由形态因子Fgf8启动的复杂遗传级联介导教学事件。分泌因子Wnt1可能在维持mes/met边界完整性方面发挥作用，尽管这一机制尚未得到深入研究。本研究将探讨mes/met并置是否是一个谱系限制边界，并探讨Wnt1在mes/met边界形成或维持中的作用。我建议通过使用两种可诱导的Cre/loxP系统对mes的Wnt1表达细胞和met的gbx2表达细胞进行遗传标记和命运定位来解决这些问题。为了解决Wnt1是否在建立和/或维持mes/met界面中发挥作用，我将生成一个条件Wnt1突变等位基因，并评估Wnt1功能丧失在不同发育阶段的表型后果。

DESCRIPTION (provided by applicant): The vertebrate brain is derived from the rostral neural tube, which first appears as a series of morphological constrictions termed neuromeres that delineate the major subdivisions of the brain. Tissue specific patterning of neuromeres results in highly specialized anatomical and functional units in the adult. One method to accomplish these remarkable developmental events is with a combinatorial mechanism of patterning that involves the formation of a lineage restriction boundary concomitant with the emergence of an 'organizer' that instructs specific positional information and fates on adjacent tissue. This mechanism has been shown to pattern Drosophila wing imaginal disks as well as chick and mouse limb but not as of yet brain. The mesencephalon (mes) and metencephalon (met) are opposed to each other and are clearly distinct morphological structures. During early development the mes, which expresses Otx2 and Wnt1, and the met, which expresses Gbx2 and Fgf8, are juxtaposed at a well-defined constriction along the anteroposterior axis defined as the isthmus. The differentially expressed mes/met genes specify regional identity and potentially segregate two populations of cells into presumptive compartments. Interestingly, the isthmus has been shown to be an organizer using classical transplantation studies and appears to mediate instructional events through a complex genetic cascade initiated by the morphogen Fgf8. The secreted factor Wnt1 may play a role in maintaining mes/met boundary integrity, though this mechanism has not been closely studied. This proposal will investigate whether the mes/met juxtaposition is a lineage restriction boundary and addresses the role of Wnt1 in mes/met boundary formation or maintenance. I propose to address these questions by genetically marking and fate mapping Wnt1 expressing cells of the mes and Gbx2-expressing cells of the met using two inducible Cre/loxP systems. To address whether Wnt1 plays a role in establishing and/or maintaining the mes/met interface, I will generate a conditional Wnt1 mutant allele and assess the phenotypic consequences of loss of Wnt1 function at different developmental stages.