Fig. 2. Neurons do not differentiate in exogastrulated embryos injected with RNA encoding stabilized ß-catenin (XBC69) or a dominant-negative Gsk3ß (dnGsk). (A) Embryo (72 hours) injected with stabilized ß-catenin RNA. (B,C) Epifluorescent images of embryos labeled with anti-serotonin (B) and anti-synaptotagmin (SpSynB) (C). Neither neural marker is detected in exogastrulae. (D) Embryo injected with RNA encoding dnGsk. Neither serotonin (E) nor synaptotagmin (SpSynB) (F) can be detected in exogastrulae expressing dnGsk. (G-I) Exogastrula prepared by compressing embryos under a coverslip. (G) Exogastrula. (H,I) Epifluorescent images of G. Although the archenteron is not internalized, normal serotonergic neurons form in the apical organ (H, white arrowhead) and anti-synaptotagmin immunoreactive cells (I, yellow arrowhead) in mechanical exogastrula (72 hours). (J) Glycerol injected, control prism at 72 hours. (K,L) Epifluorescent images of J. (K) Serotonergic cells are immunochemically detected at the apical organ (white arrowhead). (L) Anti-synaptotagmin (Sp SynB) immunoreactive cells in the ciliary band (yellow arrowhead). (M-O) SpNk2.1 expression in embryos injected with RNA encoding stabilized ß-catenin. (M) The ectoderm is on the left of image. Neither anti-serotonin immunoreactive cells (N) nor anti-SpNk2.1 immunoreactive cells (O) are detected. SpNk2.1 localizes to the tip of the archenteron (O, asterisk). Scale bars: 20 µm.