Figure 1.
Characterization of hdc−/− zebrafish. A, Alignment of Hdc protein sequences from human (Hs, ENSG00000140287), mouse (Mm, ENSMUSG00000027360), zebrafish WT (Dr, ENSDARG00000075454), and zebrafish 10-bp deletion mutant (Dr d10). The red box indicates an amino acid required for the activity of human Hdc (Komori et al., 2012a). Amino acids are colored to indicate residues with similar properties. B, Phylogenetic tree of human, mouse, and zebrafish Hdc. Values indicate the number of amino acid substitutions per 100 residues. C, D, Ventral views of 5 dpf larval brains in which histaminergic neurons are labeled using IHC with a histamine-specific antibody (C) or ISH using an hdc-specific riboprobe (D) are shown for hdc+/+, hdc+/−, and hdc−/− siblings. Histamine is reduced in hdc+/− larvae and undetectable in hdc−/− larvae (C), but the number of hdc-expressing neurons is only slightly reduced in hdc−/− larvae compared with their hdc+/+ and hdc+/− siblings (D). Boxed region in schematic diagram (lower left) indicates region shown in (C, D), with the TMN shaded magenta. Scale bars: 20 µm. E, Histamine concentration assayed by ELISA from WT and hdc−/− adult brains. Little or no histamine was detected in hdc−/− fish. Histamine detected in hdc−/− animals is below the level of assay sensitivity and precision. ***p < 0.001 by Student’s t test.