Mouse Dspp frameshift model of human dentinogenesis imperfecta

Non-syndromic inherited defects of tooth dentin are caused by two classes of dominant negative/gain-of-function mutations in dentin sialophosphoprotein (DSPP): 5′ mutations affecting an N-terminal targeting sequence and 3′ mutations that shift translation into the − 1 reading frame. DSPP defects cause an overlapping spectrum of phenotypes classified as dentin dysplasia type II and dentinogenesis imperfecta types II and III. Using CRISPR/Cas9, we generated a Dspp(−1fs) mouse model by introducing a FLAG-tag followed by a single nucleotide deletion that translated 493 extraneous amino acids before termination. Developing incisors and/or molars from this mouse and a Dspp(P19L) mouse were characterized by morphological assessment, bSEM, nanohardness testing, histological analysis, in situ hybridization and immunohistochemistry. Dspp(P19L) dentin contained dentinal tubules but grew slowly and was softer and less mineralized than the wild-type. Dspp(P19L) incisor enamel was softer than normal, while molar enamel showed reduced rod/interrod definition. Dspp(−1fs) dentin formation was analogous to reparative dentin: it lacked dentinal tubules, contained cellular debris, and was significantly softer and thinner than Dspp(+/+) and Dspp(P19L) dentin. The Dspp(−1fs) incisor enamel appeared normal and was comparable to the wild-type in hardness. We conclude that 5′ and 3′ Dspp mutations cause dental malformations through different pathological mechanisms and can be regarded as distinct disorders.