Degradation of the dental basement membrane during mouse tooth development in vitro.

During tooth development, the basement membrane is degraded at the late bell stage, but the developmental significance of this event is not known. Organ culture offers a method where developmental processes can be manipulated in controlled conditions. We cultured bell-stage tooth germs either in a chemically defined or a serum-containing medium and analyzed the degradation of the basement membrane by different methods. Type IV collagen was present throughout the dental basement membranes at the epithelial-mesenchymal interface at the onset of culture. After 10 days of culture, irrespective of the medium used, type IV collagen and laminin had disappeared from the cuspal areas but were present at the cervical loop. As was the case in vivo, the expression of 72 kDa type IV collagenase gene was intense in the differentiating preodontoblasts and in the odontoblasts during secretion of the first predentin matrix near the cuspal tips. Ultrastructural observations showed that the basal lamina had been removed in all cultured tooth organs. Also, the breakdown of the basement membrane occurred irrespective of the presence of mineral in the dentin matrix. Our observations suggest in contrast to earlier observations, that there are no major differences in basic events leading to dentino- and amelogenesis, when tooth organs are cultured in the presence or absence of serum.