Fig. 1. nlk encodes a protein that is highly homologous to other vertebrate Nlks, and is expressed broadly throughout development. (A) CLUSTAL alignment of zebrafish, Xenopus and human Nlk proteins. Identical amino acids are shaded in dark gray; similar residues are in light gray. All three proteins are extremely highly conserved throughout most of the sequence, but are highly divergent near the N terminus. Overall, zebrafish Nlk is most similar to Xenopus Nlk. (B-F) nlk in situ hybridization. (B) Lateral view of a shield stage embryo, dorsal to the right, showing ubiquitous nlk expression. (C) Dorsal view of a tailbud stage embryo. nlk is broadly expressed, but higher levels are seen in the prospective notochord (arrowhead). (D) Dorsal view of a flat-mounted embryo at 15 somites. nlk is highly expressed throughout the CNS, excluding the developing eyes. (E) Dorsal view of a flattened embryo at 24 hours shows intense staining in the eyes, in addition to continued strong staining elsewhere in the CNS. (F) Ventral view of a 48 hpf embryo. nlk transcripts are localized to the otic vesicles (arrowhead), and in the ganglion cell layer of the retina (arrow).