Localization of Transforming Growth Factor-β Type I and Type II Receptors in Mouse Development

We have investigated the localization pattern of the transforming growth factor-β (TGF-β) receptors type I (TβR-I) and type II (TβR-II) during mouse organogenesis by immunohistochemical analysis. Staining of both receptors was found in many developing organs, e.g., bone, teeth, Meckel's cartilage, and neural tissues, where the expression of their ligands has been previously reported. During the investigated stages, expression of TβR-I was more ubiquitous than that of TβR-II. TβR-II preferentially localized in the undifferentiated mesenchymal cells which subsequently differentiated into bone. There was no staining of TβR-II in the central nervous system, while intense TβR-I staining was found specifically in nervous tissues. Expression of TβR-I and TβR-II was mostly coincident with that of their ligands, suggesting that TGF-βs act as multiple mediators during organogenesis. In addition, colocalization of both receptors in the epithelia of the tooth bud and submandibular gland, which were actively invaginating into the mesenchyme, leads us to speculate that both receptors may be necessary for dynamic epithelial morphogenesis.