Cells in the rostolateral PPE undergo medio-lateral intercalating movements. The movie shows an example of an embryo in which a plasmid carrying the photo-convertible Kaede sequence was electroporated at gastrula stage in the rostrolateral PPE domain. After four hours, few kaede-expressing cells positioned in the rostrolateral PPE were hit with a laser beam to photoconvert the kaede to red. The behaviour of red-labelled cells was recorded for the next few hours until the embryo reached stage HH5+/6. Note the medio-lateral movements of the cells.