ASSIGNMENT OF EARLY CAUDAL IDENTITY TO NEURAL PLATE CELLS BY A SIGNALFROM CAUDAL PARAXIAL MESODERM

The early patterning of the vertebrate central nervous system involves the generation of progenitor cells with distinct fates at rostral and caudal levels of the neuraxis. We provide evidence that the assignmen t of early rostrocaudal differences in progenitor cell properties is e stablished by spatial restrictions in the signaling properties of the paraxial mesoderm and epidermal ectoderm. Caudal level paraxial mesode rm secretes a factor, distinct from retinoic acid or fibroblast growth factors (FGFs), that can impose caudal fates on prospective anterior proencephalic progenitors. The caudalizing activity of the paraxial me soderm can, however, be induced by FGF signaling. The distinct propert ies of cells at rostral and caudal levels of the neural plate appear t o depend, in addition, on the early exclusion of bone morphogenetic pr oteins (BMPs) from rostral lever epidermal ectoderm. Thus, differences in the signaling properties of cell groups that flank the neural plat e appear to contribute to the early rostrocaudal identity of neural ce lls, distinguishing progenitor cells at prospective anterior proenceph alic regions from those at more caudal levels of the neuraxis.