Expression analysis of grn1, grn2, hybrid grn, and ASgrn1-2 in the 5 day-old zebrafish larva by mRNA in situ hybridization. Panels A–C: grn1 is expressed in the intestine (arrow), swim bladder, and more abundantly in the head kidneys (arrowheads) than in the pronephric ducts. Panels D–F: grn2 is expressed similarly to grn1 in the head kidneys (arrowheads) and pronephric ducts, but is undetected in the intestine. In contrast, grn2 is strongly expressed in the brain and the branchial jaw region (compare A with D, and C with F), is distributed in a punctuate pattern along the ventral region of the animal in presumed myeloid progenitors (asterisks in D), and often found in randomly dispersed leukocytes (large cells in F). Panel G: Hybrid grn is found exclusively in the proctodeum. Panel H: The sense riboprobe to ASgrn1-2 (devoid of the tzf sequence) recapitulates the combined expression patterns for grn1 and grn2. Panels (I–N): Sense riboprobes to grn1 (I,J) or grn2 (K,L), but not hybrid grn (M), show that antisense transcription occurs in the jaw region (arrows in I and K), the swim bladder, and in the mid-region of the intestine, in a pattern identical to that observed for the antisense probe corresponding to ASgrn1-2 (N). B, E: dorsal views; C, F, I, K: ventral views. For each target mRNA, the use of corresponding sense and antisense (AS) riboprobes is indicated. OC, presumed ossification center; HK, head kidney; PD, pronephric duct; SB, swim bladder.