SPECIFIC TRANSFORMING GROWTH-FACTOR-BETA SUBTYPES REGULATE EMBRYONIC MOUSE MECKELS CARTILAGE AND TOOTH DEVELOPMENT

Members of the transforming growth factor-beta (TGF-beta) superfamily have emerged as critical regulators for cell growth and differentiatio n. Whereas the different TGF-beta subtypes are equipotent in the major ity of biological assays using cell lines cultured in vitro, there are indications that in more complex systems involving epithelial-mesench ymal interactions, the TGP-beta subtypes differ in their biological ac tivities. To test the hypothesis that TGF-beta subtypes specifically r egulate either Meckel's cartilage or tooth morphogenesis, we designed experiments to compare loss of function effects of TGF-beta 1, TGF-bet a 2, and TGF-beta 3 subtypes using a serumless, chemically defined med ium to culture embryonic mouse E10 (42-44 somite pairs) mandibular exp lants. The major effect of loss of function resulting from abrogation of TGF-beta 1 using antisense treatment resulted in a 20% increase (P < 0.05) in chondrocyte number, a decrease in extracellular matrix, and dysmorphology of the rostral region of Meckel's cartilage. Exogenous TGF-beta 1 provided indistinguishable recovery to the normal phenotype . TGF-beta 2 antisense treatment produced a threefold enlargement (P < 0.05) of tooth organs and advanced their development to the cap stage . TGF-beta 2 provided recovery to the normal phenotype (e.g., reduced tooth size and development to the bud stage), whereas TGF-beta 1 or TG F-beta 3 polypeptides had no effect. TGF-beta 3 antisense treatment re sulted in a reduction of approximately 15% in the length of Meckel's c artilage. We interpret these results to suggest that TGF-beta 1 functi ons to regulate the number of chondrogenic cells, the amount of extrac ellular matrix, and the rate of developmental assembly of the rostral to posterior segments in forming Meckel's cartilage. TGF-beta 2 appear s to regulate tooth size and stage of development without affecting ca rtilage. TGF-beta 3 appears to regulate Meckel's cartilage size withou t altering tooth size or shape. The results are discussed in terms of the regulatory functions of the TGF-beta subtypes during embryonic cra niofacial morphogenesis. (C) 1994 Academic Press, Inc.