Fig. 7. Effect of periderm cell removal on basal MEE cell viability and shelf fusion. Periderm cells were removed by washing the MEE region after controlled trypsin digestion performed on 14.5 dpc palate shelves before contact. Control palates were also treated with trypsin but washing was not performed. (A) Treated shelves were put in contact and fusion was analyzed 24 hours later by standard Hematoxylin-Eosin staining (HE). Although MES degenerated, proper fusion between `denuded' palate shelves did not occur. Note the absence of epithelial triangles and marked reduction in MES thickness when compared with a control sample (brackets). (B) Isolated halves were cultured for 10 hours and cell death analyzed with the TUNEL technique. More dying MEE cells were detected in `denuded' palates (i.e. without periderm cells). These experiments were repeated more than three times at least in triplicate for each condition. Scale bar: 100 µm.