Histochemical and Ultrastructural Study of Developing Gonial Bone With Reference to Initial Ossification of the Malleus and Reduction of Meckel's Cartilage in Mice

Abstract

Development of mouse gonial bone and initial ossification process of malleus were investigated. Before the formation of the gonial bone, the osteogenic area expressing alkaline phosphatase and Runx2 mRNA was widely recognized inferior to Meckel's cartilage. The gonial bone was first formed within the perichondrium at E16.0 via intramembranous ossification, surrounded the lower part of Meckel's cartilage, and then continued to extend anteriorly and medially until postnatal day (P) 3.0. At P0, multinucleated chondroclasts started to resorb the mineralized cartilage matrix with ruffled borders at the initial ossification site of the malleus (most posterior part of Meckel's cartilage). Almost all CD31-positive capillaries did not run through the gonial bone but entered the cartilage through the site where the gonial bone was not attached, indicating the forms of the initial ossification site of the malleus are similar to those at the secondary ossification center rather than the primary ossification center in the long bone. Then, the reducing process of the posterior part of Meckel's cartilage with extending gonial bone was investigated. Numerous tartrate-resistant acid phosphatase-positive mononuclear cells invaded the reducing Meckel's cartilage, and the continuity between the malleus and Meckel's cartilage was completely lost by P3.5. Both the cartilage matrix and the perichondrium were degraded, and they seemed to be incorporated into the periosteum of the gonial bone. The tensor tympani and tensor veli palatini muscles were attached to the ligament extending from the gonial bone. These findings indicated that the gonial bone has multiple functions and plays important roles in cranial formation.

Calcification and resorption of mouse Meckel’s cartilage analyzed by von Kossa and tartrate-resistant acid phosphatase histochemistry and scanning electron microscopy/energy-dispersive X-ray spectrometry

“…In mandibular bone development, the posterior portion of Meckel's cartilage undergoes endochondral ossification, that is, its resorption is accompanied by vascular invasion of the cartilage. A previous report demonstrated capillary invasion and chondroclastic resorption in the calcified cartilage at the site of future malleus in mice using transmission electron microscopy (TEM) analysis (Shibata et al 2019). In this study, our histological examination did not show obvious capillary invasion into Meckel's cartilage at E17 and E18, where hypertrophic chondrocytes and calcified cartilage were seen.…”

Expression, localization and synthesis of small leucine-rich proteoglycans in developing mouse molar tooth germ

“…In situ hybridization using [ 35 S]-UTP labeled probes was performed as previously described. [31][32][33][34] Following hybridization and RNase treatment, the sections were dipped in emulsion (NTB; Kodak, Rochester, NY, USA) and exposed for 2 weeks at 4°C for autoradiography. Sense probes were used as negative control samples.…”

Diverse Fate of an Enigmatic Structure: 200 Years of Meckel’s Cartilage

“…Here, ossification appears to be a default state if the cartilage matrix can not be degraded. The loss of Meckel’s cartilage at this point has been recently suggested to be linked to the development of the neighbouring gonial bone, with cartilage cells potentially contributing to the periosteum of this bone ( Shibata et al, 2019 ). No apoptotic cell death has been detected in this region in mice, similar to the situation in the intermediate section, however, there is evidence for apoptosis acting in the disconnection of the middle ear and MC in marsupial opossums ( Urban et al, 2017 ).…”