Genetic Analysis of Forebrain Patterning & Neurogenesis

描述(申请人提供)：我们的大脑半球是我们用来实现最高智力功能的大脑半球。当它们在发育过程中没有正常形成时，破坏性的疾病就会随之而来。最常见的发育性前脑缺陷是全前脑畸形，即两个半球无法分离。尽管大脑半球的发育对正常的大脑功能很重要，但人们对将简单的胚胎神经前体细胞转化为结构复杂的成人大脑半球的机制知之甚少。这项研究的目的是了解两个分泌信号因子家族，BMPs和FGFs，如何在大脑半球的早期发育中发挥作用。具体地说，目的是确定在体内是否需要这些因子来诱导半球的形成，形成它们的侧向和腹侧区域，形成分隔它们的中线，并调节彼此的活动以及在中线形成中必不可少的另一种因子SHH的活动。在小鼠身上，对FGFs和BMPs在体内这些过程中的作用进行直接的遗传学测试一直是困难的，因为这些因子在神经发育开始之前也在胚胎中发挥重要作用。为了绕过这个问题，使用了一种条件遗传方法，即在胚胎大脑半球中特定地删除多个BMP和FGF受体基因，而不影响它们在胚胎其余部分的功能。在人类和小鼠中，SHH基因的突变都会导致大脑中线的丧失，从而导致全前脑畸形。一个悬而未决的问题是，表达在大脑半球腹侧的SHH是如何不仅形成腹中线，而且还形成背中线的。初步证据表明，FGFs和BMPs在形成腹侧、吻侧和背侧中线结构中是必不可少的，并且FGFs在这一过程中作用于SHH的下游。这一证据表明SHH通过成纤维细胞生长因子和BMP信号在从腹侧到背侧中线的信号级联中起作用，并提供了SHH在人类和小鼠中导致全前脑发育的机制。

DESCRIPTION (provided by applicant): Our cerebral hemispheres are what we use for our highest intellectual functions. When they do not form normally during development, devastating disorders ensue. The most common developmental forebrain defect is holoprosencephaly, in which the hemispheres fail to separate. Despite the importance of cerebral hemisphere development to normal brain function, little is known about the mechanisms that transform a simple sheet of embryonic neural precursor cells into the structurally complex adult cerebral hemispheres. The goal of this study is to understand how two families of secreted signaling factors, the BMPs and FGFs, function in early development of the hemispheres. Specifically, the aims are to determine if these factors are required in vivo to induce the formation of the hemispheres, to pattern their lateral and ventral areas, to form the midline that separates them, and to regulate each others activity as well as the activity of another factor essential in midline formation, SHH. In mice, a direct genetic test of the role of FGFs and BMPs in these processes in vivo has previously been difficult because these facotrs also play essential roles in the embryo prior to the onset of neural development. To get around this problem, a conditional genetic approach is used whereby multiple BMP and FGF receptor genes are deleted specifically in the embryonic cerebral hemispheres without affecting their function in the rest of the embryo. In both humans and mice, mutations in the SHH gene cause a loss of the cerebral midline, and hence holoprosencephaly. A question that remains unanswered is how SHH, which is expressed on the ventral side of the hemispheres, is required for forming not only the ventral midline, but also the dorsal midline. Preliminary evidence indicates that FGFs and BMPs are essential in forming ventral, rostral, and dorsal midline structures and that FGFs act downstream of SHH in this process. This evidence suggests that SHH acts in a signaling cascade operating from ventral to dorsal midline through FGF and BMP signaling and provides a mechanism by which SHH in humans and mice leads to holoprosencephaly.