Fig. 2

Normal precardiac mesoderm and aberrant LPM development in han^s6 mutants. (A,B) Dorsal views at the 10-somite stage (14 hpf), anterior to the top. Wild-type (A) and han^s6 mutant (B) siblings have indistinguishable nkx2.5 expression. (C-G) Dorsal views, anterior to the top, of gata4 expression at the 5-somite stage (approximately 12 hpf) (C), 15-somite stage (D,E) and 24 hpf (F,G). (C) Expression of gata4 in the anterior LPM begins in narrow bilateral stripes of cells that fuse medially by the 20-somite stage. (D) Before cardiac fusion begins, the gata4 expression domain has become much wider mediolaterally in wild-type embryos. (E) However, in hans6 mutants, gata4 expression remains as narrow bilateral stripes. (G) gata4 expression is maintained in the LPM and myocardia (arrowheads) of hans6 mutants. (F) The mutant LPM is narrow and dysmorphic in comparison to the broad sheet of gata4-expressing LPM in wild-type siblings (arrowhead indicates heart tube). We have obtained similar results with all other LPM markers, including gata5, gata6 and tbx5; that is, the expression domains of these genes expand in wild-type embryos but not in han^{s6 mutants.}