ABROGATION OF TRANSFORMING GROWTH-FACTOR-BETA TYPE-II RECEPTOR STIMULATES EMBRYONIC MOUSE LUNG BRANCHING MORPHOGENESIS IN CULTURE

TGP-beta 1 is a known inhibitor of branching morphogenesis when added exogenously to mouse embryonic lungs in culture. However, the issue of whether endogenous TGF-beta signaling has a function in the process o f lung organogenesis is not completely resolved. We utilized immunoper turbation and antisense oligodeoxynucleotide inhibitory strategies to abrogate TGF-beta type IT receptor function in embryonic mouse lungs u ndergoing branching morphogenesis in serumless explant culture. Antise ra directed against a TGF-beta type II receptor N-terminal peptide tha t perturbs TGF-beta ligand-receptor binding increased branching by 70% . Similarly, antisense TGF-beta type II receptor oligodeoxynucleotides (40 mu M) resulted in a 58% increase in branching, compared to scramb led and mismatched sequence controls, while TGF-beta type II receptor mRNA and its protein expression levels were suppressed by 95 and 84%, respectively. Addition of exogenous TGF-beta 1 did not overcome the st imulatory effects either of TGF-beta type II receptor immunoperturbati on or of antisense oligodeoxynucleotide treatment on lung branching mo rphogenesis. Using in situ hybridization and immunohistochemistry, bot h TGF-beta type II receptor mRNA and protein were localized to the epi thelium lining the developing airways, and to the surrounding mesenchy me, indicating that TGF-beta type II receptor is an important regulato r of epithelial-mesenchymal interaction. Exogenous TGF-beta 1 decrease d cyclin A mRNA levels in control embryonic lung explants, while TGF-b eta type II receptor antisense oligodeoxynucleotides prevented the dow nregulation of cyclin A mRNA expression by exogenous TGF-beta 1. In ad dition, PCNA immunostaining of the primitive bronchial epithelium was increased in the presence of TGF-beta type II receptor antisense oligo deoxynucleotides either alone or together with exogenous TGF-beta 1, w hereas TGF-beta 1 alone decreased PCNA staining. Thus, abrogation of T GF-beta type II receptor expression prevented TGF-beta 1-induced epith elial cell G(1) arrest. These results demonstrate, for the first time, that abrogation of the TGF-beta type II receptor stimulates embryonic lung organogenesis in culture and reverses the negative influence of endogenous TGF-beta signaling upon epithelial cell cycle progression. (C) 1996 Academic Press, Inc.