Meckel's cartilage is known to be involved in formation of the prenatal mandible. However, the relationship between Meckel's cartilage and the embryonic mylohyoid muscle during growth and development has been investigated only rarely. This study examined the expression of intermediate filaments in Meckel's cartilage and the embryonic mylohyoid muscle in fetal mice during morphological development. Specimens of E12-16 ICR mice sectioned in the frontal direction were subjected to immunohistochemistry for vimentin and desmin. Hematoxylin and eosin sections showed that the immature mylohyoid muscle began to grow along Meckel's cartilage during fetal development. Weak vimentin expression was detected in the mylohyoid muscle and surrounding tissues at E12. Desmin expression was detected specifically in the mylohyoid, and strong expression was evident after E13, and increased with age. It was inferred that the mylohyoid muscle is one the tissues developing from Meckel's cartilage, the latter exerting a continuous influence on the growth of the former. In the early stage, the surrounding mesenchymal tissues expressing vimentin formed a scaffold for the developing mylohyoid muscle. Muscle attachment at E13 showed steady desmin expression, which continued until maturity. This study suggested the possibility that Meckel's cartilage has an influence not only on the mandibular bone, but also on the development of the mylohyoid muscle attached to the mandibular bone. Furthermore, it revealed a stage of the developmental process of the mylohyoid muscle in which the expression of vimentin, which is a common protein in the surrounding tissue such as muscle and bone, induces the morphological formation of the mylohyoid muscle, cooperating with the surrounding structures.

Fibroblasts exist in the interstices of various organs as a component of connective tissue and are one of several types of somatic cells that have been well established in culture. They have been reported to undergo myogenic conversion and to induce the expression of genes associated with pluripotency. However, their own plasticity with regard to direct differentiation has scarcely been described. Here, we show that human fibroblasts are able to differentiate directly to all three germ layer derivatives. The results indicate that human dermal fibroblasts have more plasticity than has been generally thought and that fibroblasts have potential utility as a source for cell therapy.

： In recent years, the expression of desmin intermediate filament in muscle and tendon attachment brought about mechanical stress has been reported. Mastication and swallowing exercises can stimulate the growth of the tongue through functional load. However, the expression of intermediate filaments during development has not been investigated. Moreover, the relevance of the surrounding tissues to the development of the tongue is still unknown. Therefore, the expression of desmin in embryonic mouse tongue during development and the expression of vimentin in mesenchymal tissues were investigated by immunohistochemistry and Western Blot. Results revealed that at E11, there was no distinction between the tongue and mandible. Vimentin expression was detected in the entire tissue at E11 and the expression spread to the surrounding tissues over time. Desmin was not detected at E11 however, at E12, desmin expression was observed at the attachment of genioglossus and intrinsic muscle of the tongue which then became more intense and spread throughout the surrounding tissues. The IHC results coincided with Western Blot analysis. The results suggest that desmin expression at the site of intense mechanical loading plays an important function in mastication and swallowing.

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