@entity4664 depletion-mediated effects on XXXX odontogenesis are dependent on tooth developmental stage and culture conditions.

@entity137 @entity5118 @entity19 @entity665 @entity7224 @entity2665 @entity4663 @entity4664 @entity11747 @entity11667
@entity4663 are known to play a central role in processes such as growth and development. Virtually nothing is known about their importance in tooth development, an attractive and frequently used experimental model for studies of developmental processes. A @entity4664 -depleted state was created in tooth cells in an organ culture system. First lower molar germs from 16-and 17.5-day old @entity19 fetuses were used. @entity11747 ( @entity11747 ) and @entity2665 ( @entity2665 ) were used to deplete the cells from their @entity4664 content. @entity4664 interconversion and catabolism were prevented by @entity5118 (AG). In day-16 germs cultured in serum-containing medium, @entity11747 reduced the frequency of cycling cells as shown by @entity665 incorporation, and induced a delay of odontoblast differentiation of about 24 h. Under the same conditions, @entity2665 induced an arrest of histo-morphogenesis, correlated to a significant decrease in the rate of cell proliferation. Addition of @entity4663 prevented @entity11747 - and @entity2665 -induced delay of tooth differentiation. Interestingly, @entity2665 did not delay the terminal differentiation of odontoblasts and ameloblasts in cultured day-17.5 molars; in these, cells at the tip of the cusps are only a few hours before their withdrawal from the cell cycle. In serum-deprived medium, dental cytodifferentiations did not occur. Addition of @entity7224 or @entity11667 to serum-free media, however, allowed for tooth morphogenesis and cytodifferentiation. Tooth explants in a serum-deprived medium reacted to @entity11747 in a cytocidal fashion, whereas @entity2665 showed only a mild @entity137 in some cell types. Addition of @entity7224 to @entity11747 -containing medium prevented its cytotoxic effect. Addition of @entity11667 to @entity2665 -containing medium not only prevented its mild @entity137 but also allowed for predentin secretion by differentiated odontoblasts. The results are discussed with regard to the well-established developmental events of tooth germs cultured in vitro and with respect to present knowledge of @entity4664 metabolism and their involvement in cellular processes.
