Formation of the sphenomandibular ligament by Meckel's cartilage in the mouse: possible involvement of epidermal growth factor as revealed by studies in vivo and in vitro

Abstract

In mammals, the midportion of the soft tissue of Meckel's cartilage at the degenerating stage forms a ligament known as the sphenomandibular ligament. To clarify the mechanism of formation of this ligament by Meckel's cartilage in mouse, we examined the effects of epidermal growth factor (EGF) on the chondrocytes in terms of the proliferation and differentiation of cells and calcification of the matrix in vivo and in vitro. The effects of EGF were examined by immunohistochemical staining, with EGF-soaked beads, by electron microscopy, and by general histochemical analysis of proteoglycans and calcification. Analysis of labeling with bromodeoxyuridine (BrdU) and the rate of cell growth revealed that EGF enhanced DNA synthesis and the proliferation of Meckel's chondrocytes. Histological findings in organ culture and in cell culture, with and without the application of EGF-soaked beads, revealed that EGF inhibited the differentiation of cells to chondrocytes and induced phenotypic changes in fibroblastic cells. The inhibition of alkaline phosphatase activity that resulted from exposure to EGF was accompanied by prolonged calcification of the matrix. Whole-mount staining revealed that subcutaneous injection of EGF enhanced the disappearance of Meckel's cartilage. Our results suggest a possible mechanism whereby the midportion of Meckel's cartilage remains uncalcified and is rapidly transformed into the sphenomandibular ligament.

Autophagy Prior to Chondrocyte Cell Death During the Degeneration of Meckel's Cartilage

“…The posterior part of the central portion of Meckel's cartilage is located in soft tissues and eventually becomes the sphenomandibular ligament. However, the anterior part of the central portion of Meckel's cartilage is located in the mandible and disappears almost immediately after birth (Bhaskar et al, 1953;Ishizeki et al, 2001).…”

Differentiation Status-dependent Regulation of Cyclooxygenase-2 Expression and Prostaglandin E2 Production by Epidermal Growth Factor via Mitogen-activated Protein Kinase in Articular Chondrocytes

“…Cartilage Explant Culture and Immunohistochemistry-Rabbit joint cartilage explants (ϳ125 mm 3 ) were fixed in 4% paraformaldehyde for 24 h at 4°C, dehydrated with graded ethanol, embedded in paraffin, and sectioned into 4-m slices as described previously (31). The sections were stained by standard procedures using Alcian blue or antibody against type II collagen or COX-2 and visualized by developing with a kit purchased from DAKO (Carpinteria, CA).…”

gp130 is important for the normal morphogenesis of Meckel's cartilage and subsequent mandibular development

“…As in other developmental events, epithelial-mesenchymal interactions are required to initiate chondrogenesis of Meckel's cartilage and osteogenesis of the jaw bone. Meckel's cartilage is derived from cranial neural crest cells of the first branchial arch (Ishizeki et al, 2001). The proper development of Meckel's cartilage is critical for craniofacial skeletogenesis, and particularly for mandibular morphogenesis, because Meckel's cartilage serves as the primordium of the mandible and guides its early morphogenesis (Macdonald and Hall, 2001).…”

“…A derivative of the cranial crest, Meckel's cartilage is regarded as the prominent first skeletal component of the developing mandible (Tomo et al, 1997;Ishizeki et al, 2001). A variety of growth factors, such as EGF (Shum et al, 1993), fibroblast growth factor (FGF) (Wilson and Tucker, 2004), TGF (Ito et al, 2002) and hepatocyte growth factor (HGF) (Amano et al, 1999), and a complicated BMP-Msx-FGF signaling network participate in the initiation and maintenance of chondrogenesis of Meckel's cartilage and osteogenesis of the mandible (Macdonald and Hall, 2001;Wilson and Tucker, 2004).…”

“…The rostral and auricular ends of Meckel's cartilage support the mandibular development and give rise to the inner-ear ossicles, the malleus, and the incus, respectively, through endochondral-type ossification. In contrast, the midportion of Meckel's cartilage transforms into noncartilagenous tissue and forms the sphenomandibular ligament soon after birth (Yamazaki et al, 1997;Ishizeki et al, 2001). However, its direct role in embryonic mandibular development has not yet been well elucidated.…”