Identification of two additional exons at the 3′ end of the amelogenin gene

Alternative splicing of the amelogenin gene generates a family of proteins secreted by ameloblasts that are primarily responsible for tooth enamel formation. Here the presence of two additional exons, downstream of exon 7, which are followed by an alternate polyadenylation site, is reported. Long polymerase chain reaction was used with a rat genomic amelogenin template to amplify sequences downstream from the primary polyadenylation site. Within the amplified sequences, two exons of 45 bp (exon 8) and 110 bp (exon 9) were identified. The presence of these additional exons in the human and mouse genome was indicated by Southern blot analysis. Antibodies raised against a synthetic peptide corresponding to a sequence encoded by exon 9 positively stained ameloblasts in sections of developing murine and porcine unerupted teeth. These results suggest that an amelogenin protein(s) that includes sequences derived from exons 8 and 9 is synthesized by the ameloblasts.