Local change of an exogastrula-inducing peptide (EGIP) in the pluteus larva of the sea urchin Anthocidaris crassispina

Immunofluorescence staining of cryosections of pluteus larvae of the sea urchin Anthocidaris crassispina was performed with an antiserum raised in rabbit against exogastrula-inducing peptide D (EGIP-D). The apical side of the ectoderm and gut of pluteus larvae that had been cultured for 36 hr was stained. However, the gut of pluteus larvae that had been cultured for 38 hr was only partially stained and the gut of larvae that had been cultured for 40 hr was not stained at all. By contrast, the ectoderm of the 38-hr and 40-hr pluteus larvae remained stainable. These results suggest that EGIP-D is present in the gut of pluteus larvae 36 hr after fertilization, but it begins to disappear from the gut at 38 hr and is lost at all from the gut at 40 hr. The significance of the disappearance of EGIP-D from the gut of the pluteus larva is discussed in relation to the differentiation of the gut.