Classification of the stages required for HSC emergence. Whole-mount in situ hybridization for flk1 and efrinb2a transcripts in wild-type, hdac, plcg1, and tbx16 mutant animals. (A-H) Lateral views, anterior left; 24 to 28 hpf; low magnification (original magnification ×10) and higher magnification (original magnification ×40) of the trunk region. (Column 1) flk1 gene expression in the dorsal aorta is indicated by black arrowheads, and intersomitic vessels are marked with green arrowheads. (Column 2) efrinb2a transcripts are highlighted with red arrowheads. (I) Stages required for HSC induction with the genes listed under each arrow that are needed for the transition to occur.