Fig. 2

Whole mount zebrafish embryos stained by in situ hybridization using gene-specific antisense RNA probes. Blue –violet staining indicates the presence of the cognate gene transcripts. (A–H) nkx2.5 staining at 12 (A), 13.5 (B), 18 (C), 19 (D), 20 (E), 22 (F), 24 (G), and 26 (H) hpf showing the progression from paired cardiac primordia (white arrows) to fused heart tube (ht). Noncardiac regions of staining are indicated (black arrows). (I-P) nkx2.7 at 10.5 (I), 13.5 (J), 18 (K), 19 (L), 20 (M), 24 (N), 36 (O), and 48 (P) hpf showing the earliest staining in the postgastrulation hypoblast (black arrows); white arrows indicate consolidations of apparent precardiac mesoderm. (Q –S) nkx2.3 at 24 (Q), 36 (R), and 48 (S) hpf. Specimens are viewed dorsolaterally with the rostral end of the embryo to the left and the dorsal axis up, except I, which is a head-on view (dorsal up), and A, C, M, O, and R, which are true dorsal projections. Brown pigment is endogenous melanin that appears after 24 hpf. Faint staining of neural structures was not reproducible. Labels: h, head; t, tailbud; y, yolk; ht, heart; g, gut; md, mandibular; hy, hyoid, and 1, 2, 3, 4, first through fourth branchial clefts; *, artifact. Numbers in lower left corner indicate hpf. Scale bars indicate 250 μm.