Interactions between TGF-β1 and TGF-β3 and their role in medial edge epithelium cell death and palatal fusion in vitro

In recent decades, studies have shown that both TGF-β1 and TGF-β3 play an important role in the induction of medial edge epithelium (MEE) cell death and palatal fusion. Many of these experiments involved the addition or blockage of one of these growth factors in wild-type (WT) mouse palate cultures, where both TGF-β1 and TGF-β3 are present. Few studies have addressed the existence of interactions between TGF-β1 and TGF-β3, which could modify their individual roles in MEE cell death during palatal fusion. We carried out several experiments to test this possibility, and to investigate how this could influence TGF-β1 and TGF-β3 actions on MEE cell death and palatal shelf fusion. We double-immunolabelled developing mouse palates with anti-TGF-β1 or anti-TGF-β3 antibodies and TUNEL, added rhTGF-β1 or rhTGF-β3 or blocked the TGF-β1 and TGF-β3 action at different concentrations to WT or Tgf-β3 null mutant palate cultures, performed in situ hybridizations with Tgf-β1 or Tgf-β3 riboprobes, and measured the presence of TUNEL-positive midline epithelial seam (MES) cells and MES disappearance (palatal shelf fusion) in the different in vitro conditions. By combining all these experiments, we demonstrate great interaction between TGF-β1 and TGF-β3 in the developing palate and confirm that TGF-β3 has a more active role in MES cell death than TGF-β1, although both are major inductors of MES disappearance. Finally, the co-localization of TGF-β1, but not TGF-β3, with TUNEL in the MES allows us to suggest a possible role for TGF-β1 in MES apoptotic clearance.