jak2a expression and effects of jak2a knock-down. (A,B,E) Whole-mount ISH for jak2a mRNA showing specific expression in the ICM (black arrows) of 18 hpf (A,B) and 24 hpf embryos (F). (C,D,F) Increased jak2a expression in the expanded ICM (white arrows) of the chordin morphant. (G-J) Knock-down of jak2a by jak2a^UTR-MO had no effects on embryonic development at 24 hpf (G,H) and 48 hpf (I,J). (K-N) O-dianisidine staining (black arrows) in 48-hpf embryos showing reduced hematopoiesis by MOs against jak2a (L,M) and a soluble jak2a inhibitor AG490 (N). (O,P) MOs against an intron-exon junction in jak2a resulting in reduced levels of jak2a mRNA shown by Q-RT-PCR. Chd indicates chordin morphant; jak2a^UTR and jak2a^SS, embryos injected with jak2a^UTR and jak2a^SS MOs; CTL, embryos injected with random sequence MOs (“Materials and methods, Zebrafish and modulation of jak2a”). (A-N) Representative pictures from at least 3 separate experiments containing 10 (A-J) and 20 (K-N) embryos per experiment. The columns in panel P represent mean values of 3 separate experiments using around 20 embryos per experiment. Comparison was made between uninjected embryos and those injected with jak2a^UTR MOs. (*P < .05). Error bars are SEM.