Abstract: Objective: To observe the effect of type Ⅰbone morphogenetic protein(BMP)receptor activin A receptor type Ⅰ(ACVR1)on the morphology,proliferation and differentiation of the mandibular condylar cartilage (MCC) cells in the postnatal mice, and to provide the reference for the study on etiology and treatment of MCC-related disease. Methods: The C57BL/6J mouse model of conditional deletion of ACVR1 gene was constructed by using the Cre-LoxP system. The female and male mice with Acvr1^fx/fx; RS/RS and Acvr1^+/-; Osterix (+)/(-) genotypes were paired off with each other; the offspring Osterix-Cre (+); Acvr1^fx/-; RS/+ genotype mice were selected as experiment group,and the Osterix-Cre (+); Acvr1^fx/+; RS/+ mice were selected as control group. The newborn (n=3), postnatal day 21(PN21) (n=4) and PN42(n=5) male mice were selected. X-gal staining was used to detect the expressions of Osterix-Cre in MCC tissue of the mice in two groups,micro-CT was used to detect the condylar widths and condylar head lengths of mandible of the mice in two groups,HE and Toluidine blue staining were used to analyze the morphology of MCC cells and the thickness of caritilage in each layer of MCC tissue of the mice in two groups,immunohistochemical (IHC) staining was used to detect the number of proliferating cell nuclear antigen(PCNA)-positive cells and the level of type Ⅹ collagen in MCC tissue of the mice in two groups. Results: The X-gal staining and IHC results showed that the mouse model of ACVR1 gene conditional deletion was successfully constructed. At PN21, compared with control group, the condylar width and the condylar head length of mandible of the mice in experiment group were significantly shortened (P<0.05); the morphology of the MCC cells of the mice in two groups had no significant difference. Compared with control group, the number of PCNA-positive cells in the MCC cells of hypertrophic chondrocyte zone(Hy) and chondroblastic zone(Ch) and single Hy of the mice in experiment group were significantly increased(P<0.05 or P<0.01).At PN42, compared with control group, the shape of parts of the mandibular condylar cartilage cells of the mice in experiment group was abnormal, and the arrangement of some condylar chondrocytes was disordered, the cell thickness of the Ar, Pr and Ch in intermediate part and Hy in anterior part of the condylar cartilage of the mice in experiment group were significantly increased(P<0.05 or P<0.01); compared with control group, the number of PCNA-positive cells in each zone and the level of type Ⅹ collagen in Ch of MCC tissue of the mice in experiment group were incresed. Conclusion: ACVR1 affects the morphology of MCC cells and structure of MCC tissue by inhibiting the proliferation of MCC cells and the differentiation of chondroblasts into hypertrophic chondrocytes.

Key words: activin A receptor type Ⅰ, mandibular condylar cartilage, cell proliferation, cell differentiation, chondroblasts, hypertrophic chondrocytes