EXPRESSION OF TYPE-I AND TYPE-XII COLLAGEN DURING DEVELOPMENT OF THE PERIODONTAL-LIGAMENT IN THE MOUSE

The purpose (of this study) was to determine the temporal and spatial pattern of type XII collagen expression during murine tooth/root devel opment. Using in situ hybridization techniques, expression of type XII collagen was compared with that of type I collagen, the most abundant collagen in periodontal tissues. Mouse first mandibular molars were e xamined at the following developmental periods: pre-root formation, ea rly root formation, initial alignment of the periodontal ligament (PDL ) fibres, and PDL maturation as the tooth erupted and attained occlusa l function. Transcripts for type I collagen were identified in bone ce lls and odontoblasts at all times but not in the dental follicle befor e root formation. As root formation progressed, type I collagen expres sion became apparent within cells of the dental follicle and forming P DL. During early stages of tooth development, signal for type XII coll agen was not observed in any cells/tissues. Type XII collagen expressi on was first detected in the dental follicle/PDL region during tooth e ruption and increased in the PDL as the molar tooth erupted into the m outh and achieved occlusal contact. These findings suggest that type X II expression is timed with the alignment and organization of PDL fibr es and is limited in tooth development to cells within the periodontal ligament. (C) 1998 Elsevier Science Ltd. All rights reserved.