Role of migrating cells for morphogenesis

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Meckel's cartilage (MC) disappears during development. However, the precise mechanisms of the process of MC disappearance have been still uncertain. In this study, we observed a morphological changes of MC with development and analyzed the factors which might participated in this process. MCs of ICR strain mice from 14 to 19 days gestation (E14-E19) were used in this study. MC matrix was strongly stained with hematoxylin in E14. During the development, the staining pattern of the matrix changed from hematoxylin to eosin. The immunohistochemical staining indicated that only type II collagen was detected in the matrix of E14. However, in accordance with the change of H-E staining pattern, type I collagen was detected in the cartilage matrix with development. Chondrocytes also expressed high acid phosphatase activities at these stages. Organ culture study indicated the disappearance of Meckel's cartilage of E17 but E14. Immunohistochemical examination showed the massive penetration of macrophages into perichondrium at E16. RT-PCR analysis indicated the expression of interleukin-1β, type I collagen at E17 but not at E14. These results indicated the dynamic matrix changes of Meckel's cartilage during development. Colocalization of type I and type II collagens in the matrix strongly suggested the functional changes of chondrocytes to synthesize type I collagen during the development. The results of organ culture suggested the signal to disappear was informed between E14 and E17, and interleukin-1β and macrophages penetrating into perichondrium might be the candidate molecule and cells for this process.