ANALYSIS OF AMELOGENIN MESSENGER-RNA DURING BOVINE TOOTH DEVELOPMENT

The amelogenins are highly conserved enamel-matrix proteins that are e ssential for proper mineral formation. Transcriptionally active genes encoding the bovine amelogenin proteins reside on both the X and Y chr omosomes. Comparison of relative levels of amelogenin mRNAs at various stages of development indicated that the X-chromosomal amelogenin mes sage is at least six fold more abundant than the Y. Alternative splici ng generates at least seven messages, five from the X primary transcri pt, and two from the Y. The two most abundant X-chromosomal amelogenin messages are approx. 850 and 450 nucleotides long, and nearly 10-fold more 850-nucleotide mRNA can be measured than 450 nucleotide, which h as lost most of exon 6 by splicing. The predominant small message enco des leucine-rich amelogenin protein (LRAP), and amounts of LRAP messag e are relatively constant during development. However, the amelogenin message from which exon 3 has been spliced declines approximately 2.3- fold, when compared to total X chromosomal amelogenin transcripts, sug gesting differential regulation of alternative splicing. In addition, a new exon was identified within genomic DNA, which was shown to be ex pressed by the use of reverse transcriptase-polymerase chain reaction, and the exons were renamed accordingly. This new exon-4 sequence is u nusual in that it is not highly conserved between species.