Identification and characterization of amelogenin genes in monotremes, reptiles, and amphibians

Identification and characterization of amelogenin genes in monotremes, reptiles, and amphibians

^*Max-Planck-Institut für Biologie, Abteilung Immungenetik, Corrensstrasse 42, D-72076 Tübingen, Germany

Edited by Susumu Ohno, Beckman Research Institute of the City of Hope, Duarte, CA, and approved August 25, 1998 (received for review June 8, 1998)

Abstract

Two features make the tooth an excellent model in the study of evolutionary innovations: the relative simplicity of its structure and the fact that the major tooth-forming genes have been identified in eutherian mammals. To understand the nature of the innovation at the molecular level, it is necessary to identify the homologs of tooth-forming genes in other vertebrates. As a first step toward this goal, homologs of the eutherian amelogenin gene have been cloned and characterized in selected species of monotremes (platypus and echidna), reptiles (caiman), and amphibians (African clawed toad). Comparisons of the homologs reveal that the amelogenin gene evolves quickly in the repeat region, in which numerous insertions and deletions have obliterated any similarity among the genes, and slowly in other regions. The gene organization, the distribution of hydrophobic and hydrophilic segments in the encoded protein, and several other features have been conserved throughout the evolution of the tetrapod amelogenin gene. Clones corresponding to one locus only were found in caiman, whereas the clawed toad possesses at least two amelogenin-encoding loci.

tooth formation/evolutionary innovations

Footnotes

↵ † Permanent address: Department of Oral Pathology, Osaka University Faculty of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
↵ ‡ To whom reprint requests should be addressed. e-mail: jan.klein{at}tuebingen.mpg.de.
This paper was submitted directly (Track II) to the Proceedings Office.
Data deposition: The sequences reported in this paper have been deposited in the GenBank database [accession nos. AF095566 (platypus), AF095567 (echidna), AF095568 (caiman), AF095569 (toad-1), and AF095570 (toad-2)].
ABBREVIATIONS:

Myr,

million years;

pfu,

plaque-forming units;

UTR,

untranslated region