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Branching, segmentation and the metapterygial axis: pattern versus process in the vertebrate limb
Author(s) -
Cohn M.J.,
Lovejoy C.O.,
Wolpert L.,
Coates M.I.
Publication year - 2002
Publication title -
bioessays
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.175
H-Index - 184
eISSN - 1521-1878
pISSN - 0265-9247
DOI - 10.1002/bies.10088
Subject(s) - hox gene , limb development , vertebrate , limb bud , biology , anatomy , segmentation , evolutionary developmental biology , fish fin , branching (polymer chemistry) , numerical digit , process (computing) , forelimb , zone of polarizing activity , evolutionary biology , fin , embryonic stem cell , embryo , gene , computer science , gene expression , fish <actinopterygii> , genetics , mesoderm , artificial intelligence , materials science , arithmetic , mathematics , fishery , composite material , operating system
Explanations of the patterns of vertebrate fin and limb evolution are improving as specific hypotheses based on molecular and developmental data are proposed and tested. Comparative analyses of gene expression patterns and functions in developing limbs, and morphological patterns in embryonic, adult and fossil limbs point to digit specification as a key developmental innovation associated with the origin of tetrapods. Digit development during the fin‐to‐limb transition involved sustained proximodistal outgrowth and a new phase of Hox gene expression in the distal fin bud. These patterning changes in the distal limb have been explained by the linked concepts of the metapterygial axis and the digital arch. These have been proposed to account for the generation of limb pattern by sequential branching and segmentation of precartilagenous elements along the proximodistal axis of the limb. While these ideas have been very fruitful, they have become increasingly difficult to reconcile with experimental and comparative studies of fin and limb development. Here we argue that limb development does not involve a branching mechanism, and reassess the concept of a metapterygial axis in limb development and evolution. BioEssays 24:460–465, 2002. © 2002 Wiley Periodicals, Inc.