Expression of zebrafish mpx in adult and embryonic zebrafish by in situ hybridization.

(A-C) Whole-mount in situ hybridization analysis of mpxexpression in adult kidney (A), spleen (B), and gill vasculature (C). Black arrows indicate blue cytoplasmic staining indicating gene expression in heterophils of the adult kidney and spleen but not in erythrocytes in the gill vessels. Control sections with sense riboprobes showed no staining under identical hybridization and development conditions. Scale bar (A-C) = 14 μm. (D-E) Expression of mpx in a 30-hpf embryo (E) as detected by an antisense riboprobe (E, arrow), along with a control embryo hybridized to a sense riboprobe (D). Panels D and E are composite images bringing several focal planes together to demonstrate at higher magnification the typical appearance of the scattered mpx-positive cells indicated by arrows in panels G to K. (F-K) Expression ofmpx in zebrafish embryos from 19 to 72 hpf. Note that expression occurs first diffusely throughout the intermediate cell mass at 19 hpf (F, black arrowhead), but from 24 hpf expression is discrete in cells scattered throughout the embryo, particularly over the surface of the yolk and in relation to the axial vasculature (G-K, black arrowheads).