Ephrin reverse signaling controls palate fusion through a PI3 Kinase dependant mechanism

Secondary palate fusion requires adhesion and epithelial to mesenchymal transition (EMT) of the epithelial layers on palate shelves. EMT requires transforming growth factor β3 (TgFβ3), and its failure results in cleft palate. Eph receptor tyrosine kinases and their membrane‐bound ligands, the ephrins, are involved in the proliferation, differentiation, apoptosis and migration of cranial neural crest cells that contribute to secondary palate. Both Eph and ephrin can function as signal transducing receptors (termed “forward” and “reverse” signaling, respectively). We cultured E8 chicken palates with TGFβ3 and or recombinant ephrin‐B2 or EphB2. Another set of the same groups was used adding PI3 Kinase Inhibitor (LY 294002 10μM). Tissues were processed for histology and scored for fusion from anterior to posterior on our 1 to 5 scale and assigned a Mean Fusion Score (MFS). Palates treated with TgFβ3 +IgG‐Fc or EphB2 showed extensive palatal fusion (MFS: 3.39 n=18; MFS: 3.05 n=16 respectively). Treatment with the PI3 Kinase inhibitor prevented fusion even in the presence of TgFβ3 (MFS: 1.81 n=19) or EphB2 (MFS: 2.30 n=18). We concluded that ephrin reverse signaling in chicken palates induced fusion through a PI‐3 Kinase dependent mechanism in the absence of TgFβ3. These data describe a novel role for ephrins in palate morphogenesis. Grant Funding Source : March of Dimes (FY06‐321)