VERTEBRATE LIMB BUD DEVELOPMENT AND REGEN ERATION

The ability of higher Vertebrates such as Birds or Mammals to regenera te amputated extremities is quite nonexistent. However, limb buds and limb regeneration blastemas can be easily compared. In this paper, we describe the vertebrate limb bud development. Epithelial caps were kno wn to maintain subapical cells in a loose mesenchymal state and were t hought to synthesize factors which can induce cell proliferation withi n mesodermal cores. Here, we summarize the previous observations that led to these hypothesis and report recent data related to the establis hment of the different polarities within embryonic members. Indeed, nu merous studies concerned with molecular aspects of epithelio-mesenchym al signalling are now available and we present evidence that both grow th factors and peculiar gene expressions elicit the limb bud outgrowth and its subsequent development.