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Fig. 1 fli-1 and Nkx-2.5 expression in heart precursors. Dorsal views of whole-mounted zebrafish embryos after in situ hybridization, anterior to the left in A–C and to the top in D–F. (A–C) fli-1 expression in precardiac cells at 10 somites (10 s), in bilateral condensations lateral to the midbrain. Expression becomes progressively expanded along the AP axis, extending more posteriorly on the left side (compare arrowheads in B) in the forming heart, flanked anteriorly and posteriorly by narrow bands of expression in the head mesoderm. (D–F) Nkx-2.5 is expressed in the heart at the same stage as fli-1 in bilateral heart fields. (D) Nkx-2.5 expression becomes broader on the left side of the midline at 20 s, as does fli-1 (compare arrowheads in B and D). (E, F) Expression of Nkx-2.5 (E), largely confined to the heart tube, and fli-1 (F) asymmetrically in the tube and in surrounding mesoderm, beneath the pharyngeal arches. Scale bars, 100 μm.
Reprinted from Developmental Biology, 210(2), Schilling, T.F., Concordet, J.-P., and Ingham, P.W., Regulation of left-right asymmetries in the zebrafish by Shh and BMP4, 277-287, Copyright (1999) with permission from Elsevier. Full text @ Dev. Biol.