Cloning, characterization and immunolocalization of human ameloblastin

Amelogenesis imperfecta is a broad classification of hereditary enamel defe cts, exhibiting both genetic and clinical diversity. Most amelogenesis impe rfecta cases are autosomal dominant disorders, yet only the local hypoplast ic form has been mapped to human chromosome 4q between D4S2421 and the albu min gene. An enamel protein cDNA, termed ameloblastin (also known as amelin and sheathlin), has been isolated from rat, mouse and pig. Its human homol og has been mapped to chromosome 4q21 between markers D4S409 and D4S400, fl anking the local hypoplastic amelogenesis imperfecta critical region. There fore, ameloblastin is a strong candidate gene for this form of amelogenesis imperfecta. To facilitate genetic studies related to this dental disease, we isolated and characterized a human ameloblastin cDNA. A human third mola r cDNA library was screened and two ameloblastin clones identified. Nucleot ide sequencing of these cDNAs indicated alternative splicing of the putativ e open reading frame, use of different polyadenylation signals, and a high degree of similarity to reported rat, mouse and porcine cDNAs. Immunohistoc hemistry studies on embryonic human teeth using an antibody to recombinant ameloblastin indicated ameloblastin expression by ameloblasts with localiza tion in the enamel matrix associated with the sheath structures.