After removing the ectoderm or endoderm mechanically, 10µl of ECM degrading enzyme Dispase-ii (Roche) was applied to the exposed mesodermal surface for 5 minutes, washed three times using 0.5ml 1XPBS, before preparing the 200mn slices. In parallel, embryo slices were fixed and examined by immunofluorescence in order to assess the degree of digestion of the ECM by the enzyme treatments.