Ephrin reverse signaling induces mouse palatal fusion without TGFβ3 signaling (921.4)

Abstract

Orofacial clefts are the most prevalent craniofacial birth defects. The secondary palate forms from mesenchymal shelves covered with epithelium which adheres to form the midline epithelial seam (MES). MES cells then proceed through epithelial to mesenchymal transition (EMT) forming a fused palate. TGF‐β3 is essential for the disintegration of the palatal MES. Eph receptor tyrosine kinases and their ephrin ligands are responsible for many developmental processes. Binding of ephrins causes receptor activation in Eph‐bearing cells (forward signaling), and intracellular signaling inside ephrin‐bearing cells (reverse signaling). We asked if activation of ephrin reverse signaling is sufficient to fuse mouse palates if we blocked TGFβ receptors. We cultured E13.5 mouse palatal shelves in different conditions: Control IgG Fc; anti‐TGF‐β3 with or without clustered recombinant EphB2/Fc protein; TGF‐β RI kinase inhibitor (SB 431542) with or without EphB2/Fc. Palatal fusion was quantified and analyzed with a mean fusion score (MFS) in anterior, medial and posterior regions. Palates treated with anti‐TGF‐β3 or (SB 431542) did not fuse while those treated with SB 431542 and EphB2/Fc and those treated with anti‐TGF‐β3 and EphB2/Fc were partially fused. Palates from the control groups fused. These results demonstrate that ephrin reverse signaling induces fusion of the mammalian palate without TGF‐β3 signaling.Grant Funding Source: Biomedical Sciences Department, baylor College of Dentistry, Baylor Oral Health Foundation