AXONAL GUIDANCE FROM RETINA TO TECTUM IN EMBRYONIC XENOPUS

This chapter describes the early development of the retinotectal system of the African clawed frog Xenopus laevis. Early work on the Xenopus retinotectal projection was done by manipulating the embryo and assaying the effects after metamorphosis, but, over the past decade, attention has shifted to embryonic assays. Embryonic experiments have the practical advantage of taking days instead of months, and they also have a great conceptual advantage. Postmetamorphic studies show the distant shadows of initial development. Embryonic experiments, on the other hand, allow direct observation of the processes of initial development. Amphibians have long been favored for embryological studies because their external fertilization and development make them easy to observe and manipulate. Xenopus are especially useful because they are easily raised in captivity, can be induced to breed by hormonal injection, produce hundreds of embryos per mating, and develop very quickly during embryonic stages. © 1994 Academic Press Inc.