SITE-SPECIFIC EXPRESSION OF COLLAGEN I AND COLLAGEN XII MESSENGER-RNAS IN THE RAT PERIODONTAL-LIGAMENT AT 2 DEVELOPMENTAL STAGES

In mammals, the periodontal ligament (PDL) is a highly specialized tissue which facilitates tooth eruption and lends mechanical support to the tooth once in occlusion. The PDL extracellular matrix fibers play a major role in such functions. During its development, the spatial arrangement of the PDL extracellular matrix undergoes rapid changes. So that it could be determined whether the structural alteration in the PDL is associated with changes in the expression of collagenous proteins with different functional properties, the transcriptional patterns of collagens I and XII were examined. The maxillary dento-alveolar segments, each containing three molars, from 25-day-old and 40-day-old Sprague-Dawley rats were selected as being representative of developing and matured tissues, respectively. Rat alpha-2(I) collagen cDNA and rat alpha-1(XII) collagen cDNA were used as molecular probes for identification of the corresponding mRNAs by RNA transfer blot analysis, RNase protection assay, and in situ hybridization. The results showed that alpha-2(I) collagen mRNA was expressed in both developing and matured tissues. However, the level of expression decreased with maturity. In contrast, the expression of alpha-1(XII) collagen was increased in the matured tissue as compared with the developing tissue. In situ hybridization in these tissues indicated that the expression of alpha-1(XII) collagen mRNA was limited to the mature stage of PDL development. It is suggested that collagen fibril arrangement during PDL development may be related to the expression of collagen XII.