TAIL BUD DETERMINATION IN THE VERTEBRATE EMBRYO

Background: Although as humans we lose our tails in the second month o f embryonic development, a persistent tail is a prominent structural f eature of most adult vertebrates. Indeed, the post-anal tail is part o f the definition of a chordate. The internal organization of the devel oping tail - with neural tube, notochord and paired somites - is the s ame as that of the main body axis, so it can be expected that the mech anism of tail formation has a close relationship to that of the verteb rate body plan as a whole. Despite this, almost nothing is known about how tails arise. Results: We present evidence to show that the tail b ud of Xenopus laevis arises as the result of interactions between dist inct zones of tissue at the posterior of the embryo at the neurula sta ge. These tissue interactions were demonstrated by manipulations of ex ogastrulae, which normally form no tail, and by transplantation experi ments performed on the neural plate of stage 13 neurulae, whereby embr yos with supernumary tails were produced. Conclusions: We propose a ne w model of tail bud determination, termed the NMC model, to explain th e results we have obtained. In this model, the tail bud is initiated b y an interaction between two territories in the neural plate and a pos terior mesodermal territory.