srp54^+/− and srp54^−/− fish display neutropenia but no overt pancreatic defects. (A) Structure of the human SRP54 NG domain. The cartoon shows the domain organization of SRP54, the sites of CN-relevant single-acid mutations (T115A, T117Δ, G226E [encircled]) and the truncation product of the srp54^sa11820 variant in our zebrafish mutant (N-terminal 14 residues in blue). A nonhydrolyzable GTP-analog (GNP) taken from the SRP54/SRα structure is shown superposed (sticks) in the active site of the SRP54 G domain. (B) Representative images of srp54^+/−, srp54^−/−, and WT siblings. Fish were mounted in methylcellulose, and photographs were taken with a Zeiss SteREO Discovery.V20 microscope. (C) Kaplan-Meier survival analysis of genotyped fish (at least 45 embryos per condition from 3 biological replicates). (D) Representative images of WT and srp54^−/− embryos after 54 hpf. Note that srp54^−/− embryos are still inside the chorion. (E-F) Assessment of neutrophil counts in genotyped srp54^+/−, srp54^−/−, and WT siblings using WISH for (E) mpo or (F) lyz. Representative images are shown. Numbers below the representative images indicate the sum of embryos with the respective phenotype per total number of embryos analyzed in all replication experiments for the respective condition. (↓) Indicates downregulation. Shown are data from 3 biological replicates with at least 3 to 10 larvae per replicate. (G) Representative images after WISH for trypsin in srp54^+/− and WT siblings at 96 hpf (left) and corresponding tissue slices (right). Student t test was used for statistical analysis. **P < .01; ***P < .005; ****P < .0001. Horizontal lines in the graphs represent the mean value of the replicates. Error bars indicate the standard deviation of the mean.