Limb Evolution - "Old" genes

[Luis Azevedo Rodrigues <lmrodrigues@fc.ul.pt>]

Any comments?

Nature 447, 473-476 (24 May 2007)
An autopodial-like pattern of Hox expression in the fins of a basal 
actinopterygian fish
Marcus C. Davis, Randall D. Dahn & Neil H. Shubin
ABSTRACT

Comparative analyses of Hox gene expression and regulation in teleost fish 
and tetrapods support the long-entrenched notion that the distal region of 
tetrapod limbs, containing the wrist, ankle and digits, is an evolutionary 
novelty. Data from fossils support the notion that the unique features of 
tetrapod limbs were assembled over evolutionary time in the paired fins of 
fish. The challenge in linking developmental and palaeontological approaches 
has been that developmental data for fins and limbs compare only highly 
derived teleosts and tetrapods; what is lacking are data from extant taxa 
that retain greater portions of the fin skeletal morphology considered 
primitive to all bony fish. Here, we report on the expression and function 
of genes implicated in the origin of the autopod in a basal actinopterygian, 
Polyodon spathula. Polyodon exhibits a late-phase, inverted collinear 
expression of 5' HoxD genes, a pattern of expression long considered a 
developmental hallmark of the autopod and shown in tetrapods to be 
controlled by a 'digit enhancer' region. These data show that aspects of the 
development of the autopod are primitive to tetrapods and that the origin of 
digits entailed the redeployment of ancient patterns of gene activity.


Luis Azevedo Rodrigues
Museu Nacional de Historia Natural (Mineralogia e Geologia)
Natural History Museum
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e-mail: lmrodrigues@fc.ul.pt
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