The Relation Between Scale and the Completeness of Pattern in Vertebrate Embryogenesis: Models and Experiments

Abstract

SYNOPSIS. The distinctive features of the theory of positional information for pattern formation are described, as applied to early vertebrate development. The results that follow two experimental challenges to the pattern control mechanism in the amphibian gastrula and neurula are presented, together with a discussion of the problems they present for most models that have been proposed for the generation of positional signal gradients. An alternative model which is related to the positional information idea, but which departs significantly from it in explaining the proportioning of patterns, is given in outline. Finally, differences between the behaviour of the antero-posterior patterning system of the chick limb-bud and that of the gastrular axial pattern are described and the concept is introduced that features of the limb pattern, namely its repetitive elements, may require the introduction of a growth control system to regulate tissue size in the rudiment in relation to the forming pattern.