Identification and characterization of a cDNA for mouse ameloblastin

Ameloblastin was first identified as one of the most abundant novel transcr ipts from a random screening of a rat incisor cDNA library. In situ hybridi zation experiments have shown ameloblastin expression to be specific to ame loblasts, with highest levels in secretory and maturation stage ameloblasts and cells of the epithelial root sheath. Ameloblastin has been identified as a candidate gene for the local hypoplastic form of autosomal dominant am elogenesis imperfecta, by virtue of it's location within the critical disea se locus. The purpose of this study was to isolate a full length mouse amel oblastin cDNA and determine its temporal expression pattern during odontoge nesis. A newborn mouse molar cDNA library was screened using a rat amelobla stin cDNA probe, Positive clones were confirmed by PCR analysis with amelob lastin-specific primers, and their size determined with vector-specific pri mers. Phage clones were rescued to phagemid using Exassist helper phage and the nucleotide sequence determined. We report here the identification of t wo clones, exhibiting alternative splicing of the putative open reading fra me, and use of multiple polyadenylation signals. Nucleotide sequence analys is indicated a high degree of similarity to rat ameloblastin, rat amelin 1 and 2 and porcine sheathlin, Reverse transcriptase-PCR analysis using mouse first and second mandibular molar mRNA indicated initial expression at E-1 4. This is one day after the initial expression of tuftelin (E-13) and one day prior to that of amelogenin (E-15).