The spatial and temporal immunolocalization of TGF-beta 1 and bone morphogenetic protein-2/-4 in phallic bone formation in inbred Sprague Dawley male rats.
In male rats and mice, the membranous bone is rapidly formed in the proximal segment (p-segment) of the os penis, and then endochondral ossification proceeds in the proximal half. The spatial and temporal patterns of expression of transforming growth factor-beta 1 (TGF-beta 1) and bone morphogentic protein-2/-4 (BMP-2/-4) were examined immunohistochemically until 14 days after birth and compared. BMP-2/-4 expression was weak in the mesenchymal condensation just at birth, and up-regulated in the membranous bone and cartilage 3 days after birth. BMP-2/-4 was strongly expressed in proliferating and mature chondrocytes 7 days after birth. At birth, TGF-beta 1 expression was diffuse and very strong in mesenchymal condensation. Thereafter, TGF-beta 1 expression was continuously strong in membranous bone and cartilage. Seven days after birth, TGF-beta 1 was actively expressed in proliferating chondrocytes. TGF-beta 1 and BMP-2/-4 seemed to act co-operatively. In particular, TGF-beta 1 appeared to strongly regulate immature stage and BMP-2/-4 may regulate the mature stage.