Pseudogenization of the tooth gene enamelysin (MMP20) in the common ancestor of extant baleen whales

Proceedings of the Royal Society B: Biological Sciences - Tập 278 Số 1708 - Trang 993-1002 - 2011
Robert W. Meredith1,2, John Gatesy1,3, Joyce Cheng1,4, Mark S. Springer1
1Department of Biology, University of California, Riverside, CA 92521 USA
2Robert W. Meredith Google Scholar Find this author on PubMed
3John Gatesy Google Scholar Find this author on PubMed
4Joyce Cheng Google Scholar Find this author on PubMed

Tóm tắt

Whales in the suborder Mysticeti are filter feeders that use baleen to sift zooplankton and small fish from ocean waters. Adult mysticetes lack teeth, although tooth buds are present in foetal stages. Cladistic analyses suggest that functional teeth were lost in the common ancestor of crown-group Mysticeti. DNA sequences for the tooth-specific genes, ameloblastin (AMBN), enamelin (ENAM) and amelogenin (AMEL), have frameshift mutations and/or stop codons in this taxon, but none of these molecular cavities are shared by all extant mysticetes. Here, we provide the first evidence for pseudogenization of a tooth gene, enamelysin (MMP20), in the common ancestor of living baleen whales. Specifically, pseudogenization resulted from the insertion of a CHR-2 SINE retroposon in exon 2 ofMMP20. Genomic and palaeontological data now provide congruent support for the loss of enamel-capped teeth on the common ancestral branch of crown-group mysticetes. The new data forMMP20also document a polymorphic stop codon in exon 2 of the pygmy sperm whale (Kogia breviceps), which has enamel-less teeth. These results, in conjunction with the evidence for pseudogenization ofMMP20in Hoffmann's two-toed sloth (Choloepus hoffmanni), another enamel-less species, support the hypothesis that the only unique, non-overlapping function of theMMP20gene is in enamel formation.

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Proceedings of the Royal Society B: Biological Sciences

Tập 278 Số 1708

993-1002

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