Jb. Charrier et al., Defining subregions of Hensen's node essential for caudalward movement, midline development and cell survival, DEVELOPMENT, 126(21), 1999, pp. 4771-4783
Hensen's node, also called the chordoneural hinge in the tail bud, is a gro
up of cells that constitutes the organizer of the avian embryo and that exp
resses the gene HNF-3 beta. During gastrulation and neurulation, it undergo
es a rostral-to-caudal movement as the embryo elongates, Labeling of Hensen
's node by the quail-chick chimera system has shown that, while moving caud
ally, Hensen's node leaves in its wake not only the notochord but also the
floor plate and a longitudinal strand of dorsal endodermal cells. In this w
ork, we demonstrate that the node can be divided into functionally distinct
subregions, Caudalward migration of the node depends on the presence of th
e most posterior region, which is closely apposed to the anterior portion o
f the primitive streak as defined by expression of the T-box gene Ch-Tbx6L,
We call this region the axial-paraxial hinge because it corresponds to the
junction of the presumptive midline axial structures (notochord and floor
plate) and the paraxial mesoderm, We propose that the axial-paraxial hinge
is the equivalent of the neurenteric canal of other vertebrates such as Xen
opus, Blocking the caudal movement of Hensen's node at the 5- to 6-somite s
tage by removing the axial-paraxial hinge deprives the embryo of midline st
ructures caudal to the brachial level, but does not prevent formation of th
e neural tube and mesoderm located posteriorly, However, the whole embryoni
c region generated posterior to the level of Hensen's node arrest undergoes
widespread apoptosis within the next 24 hours. Hensen's node-derived struc
tures (notochord and floor plate) thus appear to produce maintenance factor
(s) that ensures the survival and further development of adjacent tissues.