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Media type:
E-Article
Title:
Degenerate Evolution of the Hedgehog Gene in a Hemichordate Lineage
Contributor:
Sato, Atsuko;
White-Cooper, Helen;
Doggett, Karen;
Holland, Peter W. H.;
Carroll, Sean B.
Published:
National Academy of Sciences, 2009
Published in:
Proceedings of the National Academy of Sciences of the United States of America, 106 (2009) 18, Seite 7491-7494
Language:
English
ISSN:
0027-8424
Origination:
Footnote:
Description:
The discovery of a set of highly conserved genes implicated in patterning during animal development represents one of the most striking findings from the field of evolutionary developmental biology. Existence of these "developmental toolkit" genes in diverse taxa, however, does not necessarily imply that they always perform the same functions. Here, we demonstrate functional evolution in a major toolkit gene, hedgehog (hh) encodes a protein that undergoes autocatalytic cleavage, releasing a signaling molecule involved in major developmental processes, notably neural patterning. We find that the hh gene of a colonial pterobranch hemichordate, Rhabdopleura compacts, is expressed in a dramatically different pattern to its ortholog in a harrimaniid enteropneust hemichordate, Saccoglossus kowalevskii. These represent two of the three major hemichordate lineages, the third being the indirect developing ptychoderid enteropneusts. We also show that the normally well-conserved amino acid sequence of the autoproteolytic cleavage site has a derived change in S. kowalevskii. Using ectopic expression in Drosophila, we find that this amino acid substitution reduces the efficiency of Hh autocatalytic cleavage and its signaling function. We conclude that the Hh sequence and expression in S. kowalevskii represent the derived state for deuterostomes, and we argue that functional evolution accompanied secondary reduction of the central nervous system in harrimaniids.