Abstract
Until now the developmental process of masticatory muscle (derived from the branchial arches) is not well documented. Thus, in order to clarify the developmental process of murine masseter muscle, Hepatocyte Growth Factor (HGF), Insulin-like Growth Factor-1 (IGF-1) and Myosin Heavy Chain (MyHC) were evaluated by histological examination, western blotting and RT-PCR analyses on embryonic days 14 (E14), 16 (E16) and 18 (E18). E14 showed that the mandibular bone development is initiated by the appearance of the ossification centre in the peripheral zone of Meckel cartilage. Whereas, E16 demonstrated presence of developing masseter muscle at the lower part of the mandible composed of immature bone. On the contrary, E18 showed larger masseter muscle and more mature mandibular than E16. Interestingly, both IGF and HGF proteins and genes increased at initial stage of masseter muscle development, and decreased with the time. A significant change in composition of MyHC was detected in E18 compared with E14 and E16. This result indicate that murine masseter muscle develops in accordance with the surrounding tissue, where IGF-1 and HGF could be an important modulator of stem cell-derived myoblast proliferation and myogenic differentiation, and MyHC-2a and 2d are strongly expressed by mature muscle fibres during the developmental process of the masseter muscle.
