LONGITUDINAL ORGANIZATION OF THE ANTERIOR NEURAL PLATE AND NEURAL-TUBE

Over the last century, several morphological models of forebrain organ ization have been proposed that hypothesize alternative topological so lutions for the relationships of the histogenic primordia, Central to all of these models are their definitions of the longitudinal axis and the longitudinal organization of the neural plate and neural tube, To understand the longitudinal organization of the anterior brain, we ha ve sought to identify molecular properties that are continuous along t he entire longitudinal axis of the embryonic CNS, In this essay, we de scribe studies of the expression of several genes in the mouse between 7.5 (presomite stage) and 10.5 days post coitum (dpc) that provide ev idence for the trajectory of the anterior-posterior axis and the longi tudinal organization of the anterior CNS. Specifically, we report that the expression of noggin, sonic hedgehog and Nkx-2.2 define longitudi nal columns of cells that are present along the entire CNS axis. Withi n the forebrain, the expression of these genes, as well as that of Nkx -2.1 and BF-1, are in distinct longitudinal regions in the neural plat e and tube. We demonstrate that the earliest longitudinal axon pathway s of the forebrain are spatially correlated with the longitudinal doma in defined by Nkx-2.2, Finally, expression of the former genes, and Ot x-1 and Emx-2, suggests that the cephalic neural plate is organized in to molecularly distinct domains delimited by longitudinal and transver se borders; these results provide a foundation for defining the mechan isms that pattern the neural plate.