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Cloning, Sequencing, and Expression of the Amelogenin Gene in Two Scincid Lizards

¹ UMR 7138-Systématique, Adaptation, Evolution, Université Paris 6, 7, quai St-Bernard, 75005 Paris, France; and
² EA 1892-Laboratoire du Développement des Tissus Dentaires, Faculté d’Odontologie, Lyon, France

View larger version (39K): [in a new window]   Figure 1. Nucleotide and deduced amino acid sequences of the amelogenin in Chalcides viridanus and C. sexlineatus. The non-coding exon 7 sequence at the 3' end is shown only for C. viridanus. Underlined = 3' region of the signal peptide; boxed = proteolytic sites of TRAP43 and 45; bold = remarkable amino acids; 2|3 = limit between exon 2 and exon 3. (-) = nucleotide/residue identical; (*) = lack of nucleotide/residue.

View larger version (118K): [in a new window]   Figure 2. Amino acid alignments of lizard amelogenin with other amelogenin sequences. (A) Alignment of tetrapod amelogenin sequences. (top to bottom) The putative ancestral amelogenin sequence in mammals (from Delgado et al., 2005a); crocodile, Paleosuchus palpebrosus (GenBank access number, AF118568); ratsnake, Elaphe quadrivirgata (AF095568); lizard, Chalcides viridanus (present work); and three lissamphibians—the pipid frog, Xenopus laevis A, X. laevis B (AF095569; AF095570), and the bullfrog Rana pipiens (from Wang et al., 2005). Amino acid alignment is easy in the N- and C-ter regions, while it is difficult in the central region of exon 6 (in gray), due to numerous amino acid substitutions. Boxed = TRAP proteolytic sites; underlined = remarkable amino acids; 2|3 = limit between exon 2 and exon 3. LRAP = locus of intra-exonic alternative splicing in mammals. (-) = identical amino acid; (*) = either lack or insertion of amino acid. (B–E) Amino acid alignment of the amelogenin sequence of Chalcides viridanus with the snake, crocodile, ancestral mammal, and lissamphibian sequences taken separately. Alignment of the variable region (in gray) is still difficult to obtain, even between the closest species, lizard and snake (B).

View larger version (146K): [in a new window]   Figure 3. Chalcides viridanus. Different steps of amelogenesis during replacement tooth development. Amelogenin gene (amelogenin) expression is revealed by in situ hybridization on sections (dark stippled regions in a,d,f,h,j), with 33P-labeled amelogenin probe. (c,e,g,i) One-µm-thick sections of stages of enamel formation in replacement teeth similar to those shown in d–j (toluidine blue staining). Labial to the right. (a) Low magnification showing 3 tooth positions in the left lower jaw arcade sectioned longitudinally. Anterior to the right. Amelogenin is not expressed in functional teeth, while numerous transcripts are detected in the enamel organ of the replacement teeth below. (b) Negative control for (a), with the sense probe. (c–j) Enamel matrix deposition in replacement teeth, from early deposition (c,d) to the end of enamel maturation (i,j). Transverse sections of the lower jaw. In situ hybridization reveals amelogenin transcripts in the enamel organ (ameloblasts). Transcripts are abundant in the ameloblasts facing the recently deposited immature enamel matrix; they are less numerous in the ameloblasts facing the maturing enamel, and are absent in ameloblasts facing the mature enamel. Scale bars: a,b = 100 µm; c–j = 50 µm. Abbreviations: am, ameloblasts; be, buccal epithelium; d, dentin; db, dentary bone; dej, dentin-enamel junction; e, enamel; eo, enamel organ; ft, functional tooth; od, odontoblasts; ode, outer dental epithelium; pd, predentin; rt, replacement tooth; sr, stellate reticulum.