Initiation of granulopoiesis in zebrafish embryos.

(A-E) Whole-mount myeloperoxidase histochemistry of zebrafish embryos at 26 (A), 31 (B), and 48 (C) hpf, showing discrete histochemically positive myeloperoxidase reactive cells over the yolk sac and in the ventral venous plexus (B-E, black arrows). Discrete cellular staining is shown at higher power under Nomarski illumination in the ventral venous plexus of 48-hpf embryos (D, E). Diffuse, less intense staining over the surface of the yolk (arrowhead B, C) is believed to be nonspecific staining in pooled erythrocytes. (F, G) Comparison of histochemical staining for myeloperoxidase (F) ando-dianisidine staining (G) for hemoglobin in the head and gill region of 6-dpf embryos. Myeloperoxidase-positive cells are scattered and discrete, whereas hemoglobin-positive cells are pooled in large blood vessels. (H-K) Comparison of histochemical staining for myeloperoxidase (J, K) and o-dianisidine staining (H, I) for hemoglobin in wild-type (H, J) and cloche (I, K) 3-dpf (H, I) and 2-dpf (J, K) embryos. Cloche (clo) embryos retain some globin expression in the ventral vein region (H, I, arrowhead). Myeloperoxidase-positive cells were fewer and more sparsely scattered and were generally located in the posterior ICM immediately caudal of the tip of the yolk sac extension (K, arrow). (L, M) Myeloperoxidase histochemical staining of a 48-hpf spadetail(spt) embryo (M) and age-matched sibling wild-type embryo (L), showing myeloperoxidase-positive cells (arrows) scattered throughout the spt embryo.