Patterning of the neural primordium in the avian embryo

Abstract

Abstract The quail-chick chimera system has been used to study two problems related to the patterning of the neural primordium. We first report our analysis of the secondary neurulation as it proceeds in the avian tail bud caudally to the posterior neuropore. We show that the territory located caudally to the primary neural tube and joining it to the caudal end of the notochord, designated as the cordoneural hinge (CNH), can be assimilated to the remainder of the Hensen's node. The CNH undergoes a craniocaudal progression during tail bud development and lays down the notocord and floor plate which thus originate from closely related progenitor cells. We show that the floor plate material becomes inserted within the neurectoderm thus forming the neural plate. The second part of this article is devoted to the hindbrain development. We show that transposition of the presumptive territory of anterior rhombomeres (r1 to r6) at the level of r7–r8 results in their phenotypic posteriorization which is preceded by their expression of posterior Hox genes characteristic to the AP level at which they are transplanted and hence that there are inductive signals within the neural epithelium itself.