Developmental mechanism of muscle–tendon–bone complex in the fetal soft palate

摘要

Highlights ? The medial pterygoid process was observed as mesenchymal cell aggregation at embryonic days 14. ? The palatine aponeurosis contacted with the tensor veli palatini muscle at embryonic days 16.5. ? The rapid growth of the pterygoid process was observed embryonic days 16.5 later. Abstract Objective This study was performed to investigate how the palatine aponeurosis, medial pterygoid process (MPP) of the sphenoid bone, and tensor veli palatini (TVP) muscle form the pulley: muscle–tendon–bone complex. Design Mice at embryonic day (ED) 14–17 were used as sample in this study. Azan staining was performed to observe the morphology, and immunohistochemical staining of desmin was performed to closely observe the development of the myotendinous junction. To confirm the bone formation process, immunohistochemical staining of type II collagen (col II), tartrate-resistant acid phosphatase (TRAP), and alkaline phosphatase (ALP) staining were performed. Furthermore, to objectively evaluate bone formation, the major axis and width of the MPP were measured, and osteoclasts that appeared in the MPP were counted. Results At ED 14 and 14.5, ALP showed a reaction throughout the MPP. The col II-positive area expanded until ED 16.5, but it was markedly reduced at ED 17. The TVP initially contacted with the palatine aponeurosis at ED 16.5. The major axis and width of the MPP and the number of TRAP-positive osteoclasts were significantly increased as the TVP and palatine aponeurosis joined. Conclusions Therefore, in addition to the tissue units: muscle, tendon, and bone, the interaction in organogenesis promotes rapid growth of the pulley: muscle–tendon–bone complex.