We have compared the expression of the genes encoding transforming growth factors β1, β2 and β3 during mouse embryogenesis from 9.5 to 16.5 days p.c. using in situ hybridisation to cellular RNAs. Each gene has a different expression pattern, which gives some indication of possible biological function in vivo.

All three genes appear to be involved in chondro ossification, though each is expressed in a different cell type. Transcripts of each gene are also present in embryonic epithelia. Epithelial expression of TGF β1, β2 and β3 RNA is associated with regions of active morphogenesis involving epithelial-mesenchymal inter actions. In addition, widespread epithelial expression of TGF β2 RNA can be correlated with epithelial differentiation per se. The localisation of TGF β2 RNA in neuronal tissue might also be correlated with differentiation. Finally both TGF β1 and β2 transcripts are seen in regions actively undergoing cardiac septation and valve formation, suggesting some interaction of these growth factors in this developmental process.