Expression of SOX 9 and type II collagen in the spheno-occipital synchondrosis

Abstract

AIM: Cranial base synchondroses are important growth centres of the craniofacial skeleton, especially the spheno-occipital synchondrosis because of its late ossifi cation and major contribution to post-natal cranial base growth. It develops from a cartilaginous template that is eventually replaced by bone through endochondral ossifi cation. Endochondral ossifi cation is modulated by a cascade of events from various factors. SOX 9 is a key transcription factor in governing chondrocyte differentiation. It also directly activates the expression of type II collagen that acts as an early main marker of the chondrocytes and forms the framework of the cartilage matrix. Therefore, it is important to understand the mechanism of SOX 9 and type II collagen in the development of synchondroses. The aim of this research was to establish the temporal pattern of SOX 9 and type II collagen expression, with or without tensile stress, in order to understand the role of these factors in the growth of cartilage in the spheno-occipital synchondrosis. MATERIALS AND METHOD: Sixty, 1-day-old, male balb/c mice were randomly divided into experimental and control groups. Each group was subdivided again into fi ve different time frames; 6, 24, 48, 72 and 168 hours. Each subgroup consisted of fi ve mice. Each mouse was sacrifi ced using an intraperitoneal injection of overdose chemical anaesthetic, pentobarbitone sodium (150-200 mg/kg). The spheno-occipital synchondrosis was aseptically removed and incubated in a 24-well plate, with or without tensile stress, in tissue culture at 37ºC and 5 per cent CO2. Tissue sections were subjected to immunohistochemical staining for quantitative analysis of SOX 9 and type II collagen expression. RESULTS: There was a signifi cant increase (57%; P < 0.001) in the expression of SOX 9 between control and experimental groups at 24 hours. This was followed by a signifi cant increase (44.4%; P < 0.001) of type II collagen expression in the experimental groups at 72 hours compared with the control groups in the same time frame. CONCLUSION: Tensile stress increases the expression of SOX 9 and type II collagen synthesis in the spheno-occipital synchondrosis. SOX 9 is an essential factor for early differentiation of chondrocytes, and for type II collagen synthesis during cartilage growth in spheno-occipital synchondrosis.