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Molluscan engrailed expression, serial organization, and shell evolution
Author(s) -
Jacobs David K.,
Wray Charles G.,
Wedeen Cathy J.,
Kostriken Richard,
DeSalle Rob,
Staton Joseph L.,
Gates Ruth D.,
Lindberg David R.
Publication year - 2000
Publication title -
evolution and development
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.651
H-Index - 78
eISSN - 1525-142X
pISSN - 1520-541X
DOI - 10.1046/j.1525-142x.2000.00077.x
Subject(s) - engrailed , biology , evolutionary biology , spicule , phylum , gene , zoology , anatomy , genetics , homeobox , gene expression , sponge spicule
SUMMARY Whether the serial features found in some molluscs are ancestral or derived is considered controversial. Here, in situ hybridization and antibody studies show iterated engrailed ‐gene expression in transverse rows of ectodermal cells bounding plate field development and spicule formation in the chiton, Lepidochitona caverna , as well as in cells surrounding the valves and in the early development of the shell hinge in the clam, Transennella tantilla. Ectodermal expression of engrailed is associated with skeletogenesis across a range of bilaterian phyla, suggesting a single evolutionary origin of invertebrate skeletons. The shared ancestry of bilaterian‐invertebrate skeletons may help explain the sudden appearance of shelly fossils in the Cambrian. Our interpretation departs from the consideration of canonical metameres or segments as units of evolutionary analysis. In this interpretation, the shared ancestry of engrailed ‐gene function in the terminal/posterior addition of serially repeated elements during development explains the iterative expression of engrailed genes in a range of metazoan body plans.