Periostin (POSTN)

By screening human placenta and osteosarcoma cDNA libraries with mouse Postn as probe, they cloned 2 variants of human POSTN. One variant encodes a deduced 779-amino acid protein with an apparent molecular mass of 87.0 kD, and the other encodes a deduced 836-amino acid protein with an apparent molecular mass of 93.3 kD. POSTN contains a typical signal sequence, followed by a cysteine-rich domain, a 4-fold repeat structure of about 150 amino acids, and a C-terminal domain. Mouse and human POSTN share 89.2% amino acid identity overall and 90.1% identity in their mature forms. Northern blot analysis of a mouse osteoblastic cell line detected a 3.4-kb Postn transcript. RNA dot blot analysis detected expression of Postn in primary mouse osteoblasts and in lung, but not in any other tissues examined.