Spatial and temporal localisation of bone morphogenetic protein-3 (osteogenin) in the developing rat submandibular gland.

Submandibular gland morphogenesis is a highly regulated process modulated by epithelio-mesenchymal interactions. Bone morphogenetic proteins (BMPs), members of the transforming growth factor-beta (TGF-beta) superfamily, are known to be soluble mediators of epithelio-mesenchymal interactions during the development of certain organs. The aim of this study was to localise bone morphogenetic protein-3 (BMP-3 or osteogenin), spatially and temporally in the developing rat submandibular gland. Immunocytochemistry was performed on sections of the developing submandibular gland (gestation ages E14.5-E19.5). BMP-3 was localised in the extra-cellular matrix of the mesenchyme of the gland in all the stages examined. Intense staining of BMP-3 was observed in the epithelial cells of the developing end-buds between stages E14.5 and E16.5. As cytodifferentiation progressed (stage E17.5 onwards) the number of epithelial cells in the developing acini in which BMP-3 was present became markedly reduced. Similarly, the number of cells containing BMP-3 in the developing ducts decreased as duct development progressed. By stage E19.5, BMP-3 was located mainly in the immature ducts. While the effects of BMP-3 on matrix macromolecules could not be deduced from this study, its spatial and temporal location within the developing glands may indicate a role in the co-ordinated regulation of branching morphogenesis.