Lmo2 morphants exhibit normal gross morphology but lack hematopoietic gene expression. (A) Genomic structure of the lmo2 gene. Exons (ex) depicted as boxes; atg start and tga stop codons are indicated; intron sizes not to scale; red-shaded regions encode the 2 LIM zinc finger–like domains (the first is split across exons 5 and 6); atgMO binding sites are shown (red lines). (B) Live 30-hpf embryos; lateral views; anterior, left. Lmo2 morphants developed without nonspecific defects. (C-G) Whole-mount embryos; lateral views; anterior, left; inset images in panels E and F show ventral view. (H-I) Whole-mount embryos; lateral view; close-up of trunk/tail region; anterior, left. Numbers of embryos represented in gray. (C-D) Erythroid, βE1, and alas2 expression is abolished in all morphants at 22 hpf. (E-G) In 22-hpf morphants, expression of primitive myeloid genes pu.1, l-plastin, and mpo was severely reduced. Remaining cells were restricted to the heart region (arrows) and, in the case of pu.1, the posterior ICM (arrowhead). (H-I) Expression of HSC markers runx1 and c-myb was significantly down-regulated in the ventral DA of Lmo2-depleted embryos (arrows).