A SINGLE MORPHOGENETIC FIELD GIVES RISE TO 2 RETINA PRIMORDIA UNDER THE INFLUENCE OF THE PRECHORDAL PLATE

Two bilaterally symmetric eyes arise from the anterior neural plate in vertebrate embryos. An interesting question is whether both eyes shar e a common developmental origin or they originate separately. We repor t here that the expression pattern of a new gene ET reveals that there is a single retina field which resolves into two separate primordia, a suggestion supported by the expression pattern of the Xenopus Pax-6 gene. Lineage tracing experiments demonstrate that retina field resolu tion is not due to migration of cells in the median region to the late ral parts of the field. Removal of the prechordal mesoderm led to form ation of a single retina both in chick embryos and in Xenopus explants . Transplantation experiments in chick embryos indicate that the prech ordal plate is able to suppress Pax-6 expression. Our results provide direct evidence for the existence of a single retina field, indicate t hat the retina field is resolved by suppression of retina formation in the median region of the field, and demonstrate that the prechordal p late plays a primary signaling role in retina field resolution.