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

Robert W. Meredith, John Gatesy, Joyce Cheng, Mark S. Springer

Research output: Contribution to journalArticle

57 Scopus citations

Abstract

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 of MMP20. 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 for MMP20 also 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 of MMP20 in Hoffmann's two-toed sloth (Choloepus hoffmanni), another enamel-less species, support the hypothesis that the only unique, non-overlapping function of the MMP20 gene is in enamel formation.

Original languageEnglish
Pages (from-to)993-1002
Number of pages10
JournalProceedings of the Royal Society B: Biological Sciences
Volume278
Issue number1708
DOIs
StatePublished - 1 Jan 2011

Keywords

  • Baleen whale
  • Enamel
  • Enamelysin
  • Macroevolution
  • Pseudogene
  • Teeth

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