Fig. 4. Effects of treatments that alter ectoderm specification on formation and patterning of neurons in the animal plate. (A-D) Antivin-injected embryos (72 hours). (A) SpNk2.1 proteins in the animal plate of injected embryos. Inset is transmitted light image. (B) Ciliary band marker, SpHnf6, is expressed throughout the thickened ectoderm. (C) Serotonergic neurons are detected at the animal plate, but they are not normally patterned. (D) Ciliary band neurons (SpSynB) are scattered throughout lateral ectoderm. (E) Embryos treated with kinase inhibitor SB203580 have supernumerary, unpatterned serotonergic neurons. (F) Embryos treated with the TGFß receptor inhibitor, SB431542, express SpNk2.1 in the animal plate. Inset shows transmitted light image. (G) SB431542-treated embryos have extra serotonergic neurons lacking normal symmetry. (H-J) BMP-injected embryos (72 hours). (H) SpNk2.1 is restricted to the thickened ectoderm at the animal pole. (I) SpHnf6 is also restricted to the animal pole. (J) Serotonergic neurons in the animal plate lack normal patterning. (K-M) Nodal-injected embryos. (K) Distinctive bell-shaped embryos express SpNk2.1 throughout the dome. Inset shows transmitted light image. (L) SpHnf6 is expressed in the central part of the SpNk2.1 domain; thus, the animal plate is restricted to the thickened ectoderm at the pole. Inset shows entire SpHnf6 expression, including the postoral transverse ciliary band. (M) Serotonergic neurons are rarely detected in Nodal-injected embryos. (N) SpNk2.1 expression in Noggin-injected embryo. Inset shows transmitted light image. (O) In Noggin-injected embryos, few serotonergic neurons form in the animal plate. Scale bar: 20 µm.