Localization of EMSP1 expression during tooth formation and cloning of mouse cDNA

Enamel matrix serine proteinase 1 (EMSP1) is a proteolytic enzyme that has been isolated from the developing enamel of pig teeth. Its apparent function is to degrade the organic matrix in preparation for enamel maturation. The expression of EMSP1 has never been investigated in another organism besides the pig, and EMSP1 expression in the enamel organ has never been specifically demonstrated in ameloblasts. Here we report the expression of recombinant pig EMSP 1 (rpEMSP 1), the generation of rabbit polyclonal antibodies against rpEMSP1, the characterization of the antibodies and EMSP1 expression by Western blot and immunohistochemical analyses, the cloning and characterization of a full-length cDNA encoding mouse EMSP1, and the localization of EMSP1 expression in ameloblasts in mouse day 14 first and second molars by in situ hybridization. The full-length mouse EMSP1 cDNA clone has 1,237 nucleotides, excluding the poly(A+) tail, and encodes a preproprotein of 255 amino acids. Mouse EMSP1 shares 75% amino acid identity with pig EMSP1 and has three potential N-linked glycosylation sites, two of which are conserved in the pig homologue. Western blot analysis shows that the polyclonal antibodies are specific for EMSP1 and do not cross-react with trypsin. Immunohistochemistry of pig incisors shows discrete staining in the surface enamel at the earliest part of the maturation stage. In mouse molars, in situ hybridization gives a distinct and specific signal in maturation-stage ameloblasts, and in the junctional epithelium following tooth eruption. We conclude that EMSP1 is expressed by pig and mouse ameloblasts during the early maturation stage of amelogenesis.