Knockdown of npm1a and npm1b leads to loss of myeloid cells. (A-L) WISH for mpx in 48-hpf embryos, lateral view, anterior to the left, dorsal upwards. (A,D,G,J,M) Knockdown of npm1 genes results in loss of mpx-expressing myeloid cells. A significant difference is seen in myeloid cell numbers when each gene is knocked-down individually (npm1a in panel D and npm1b in panel G, quantified in panel M); this effect is at least additive in the double knockdown (npm1a + npm1b in panel J, quantified in panel M). (B,E,H,K,N) mpx expression is reduced upon npm1 knockdown compared with controls in both the p53^wt/wt (B,E) and p53^m/m (H,K) backgrounds (quantified in panel N). (C,F,I,L,O) Loss of mpx expression by knockdown of npm1 (F) can be rescued completely (I) or partially (L) by NPM1 RNA injection (10 pg). No differential expression of mpx is observed when 10 pg NPM1 or 10 pg control RNA (C) are injected with a control MO (quantified in panel O). npm1a MO indicates 5′UTR MO (1.4 ng); npm1b MO, 5′UTR MO (1.4 ng); npm1(a+b), npm1a MO + npm1b MO (1.4 ng each); control MO, npm1a 5-bp mismatch + npm1b 5-bp mismatch at 1.4 ng each. Error bars represent SEM. ns indicates not significant; *P < .02; **P < .01; ***P < .001 (Student t test). Complete rescue in panel I is defined as mpx⁺ cell numbers per embryo greater than the lower limit of the 95% confidence interval of the control RNA/control MO-injected embryos. Partial rescue in panel L is defined as mpx⁺ cells/embryos greater than the upper limit of the 95% confidence interval of the npm1(a+b) MO but below the lower limit of the 95% confidence interval of the control RNA/control MO-injected embryos.