Spatial aspects of neural induction in Xenopus laevis

A monoclonal antibody, 2G9, has been identified and characterised as a marker of neural differentiation in Xenopus. The epitope is present throughout the adult central nervous system and in peripheral nerves. Stain-ing is first detected in embryos at stage 21 in the thoracic region. By stage 29 it stains the whole central nervous system, except the tail tip. The epitope is present in a 65K Mr protein, and includes sialic acid. The antibody also reacts with neural tissue in mice and axolotls and newts. 2G9 was used to show that both notochord and somites are capable of neural induction, and the stimu-lus is present as late as stage 22. Attempts to demon-strate the induction of nervous system by developing nervous system (homoiogenetic induction) were unsuc-cessful. The view that the lateral extent of the nervous system might be determined by that of the inductive stimulus is discussed. Neural induction was detected as early as stage 10 and occurs in embryos without gastru-lation and without cell division from stage 7i. Key words: Xenopus laevis, neural induction, monoclonal antibody, central nervous system, peripheral nervous system