Abstract
Bone morphogenetic protein 1 (BMP1) and tolloid-like 1 (TLL1) belong to the BMP1/tolloid-like proteinase family, which cleaves secretory proteins. The constitutive deletion of the Bmp1 or Tll1 genes causes perinatal or embryonic lethality in mice. In this study, we first studied the β-galactosidase activity in mice in which an IRES-lacZ-Neo cassette was inserted in the intron of either the Bmp1 or the Tll1 gene; the β-galactosidase activities were used to reflect the expression of endogenous Bmp1 and Tll1, respectively. Our X-gal staining results showed that the odontoblasts in the tooth and cells in the periodontal ligament express both Bmp1 and Tll1. We then created Bmp1 (flox/flox) and Tll1 (flox/flox) mice by removing the IRES-lacZ-Neo cassette. By breeding 2.3 kb Col1a1-Cre mice with the Bmp1 (flox/flox) and Tll1 (flox/flox) mice, we further generated Col1a1-Cre;Bmp1 (flox/flox) ;Tll1 (flox/flox) mice in which both Bmp1 and Tll1 were inactivated in the Type I collagen-expressing cells. We employed X-ray radiography, histology and immunohistochemistry approaches to characterize the Col1a1-Cre;Bmp1 (flox/flox) ;Tll1 (flox/flox) mice. Our results showed that the molars of the Col1a1-Cre;Bmp1 (flox/flox) ;Tll1 (flox/flox) mice had wider predentin, thinner dentin and larger pulp chambers than those of the normal controls. The dentinal tubules of the molars in the Col1a1-Cre;Bmp1 (flox/flox) ;Tll1 (flox/flox) mice appeared disorganized. The level of dentin sialophosphoprotein in the molars of the 6-week-old Col1a1-Cre;Bmp1 (flox/flox) ;Tll1 (flox/flox) mice was lower than in the normal controls. The periodontal ligaments of the Col1a1-Cre;Bmp1 (flox/flox) ;Tll1 (flox/flox) mice were disorganized and had less fibrillin-1. Our findings indicate that the proteinases encoded by Bmp1 and Tll1 genes play essential roles in the development and maintenance of mouse dentin and periodontal ligaments.