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Fig. 2. Overexpression of XNkx-2.3 and XNkx-2.5 in heart progenitors results in enlarged cardiac structures. Embryos injected with lineage tracer plus water, control Mix.2 RNA, XNkx-2.3 RNA or XNkx-2.5 RNA are shown. (A) Fluorescence micrograph of an embryo injected with fluoresceinated dextran in water into the dorsal vegetal blastomere at the 8-cell stage. The heart region is indicated by an arrowhead. (B) Embryo injected as in A into the ventral vegetal blastomere. These embryos are labeled primarily in the posterior gut and ventral mesoderm. (C-K) In situ hybridization depicting cardiac troponin I expression (blue stain) in stage 37 embryos that were injected into the dorsal vegetal blastomere as in A. (C,K) Water injected (D) Mix.2 injected (E,G,I) XNkx-2.3 injected (F,H,J) XNkx-2.5 injected (L) XNkx-2.5 injected embryo stained by in situ hybridization with XMLC2 probe. The heart is enlarged in XNkx-2.3 and XNkx-2.5 injected embryos (E,F,G,H,I,J,L), but not in water or Mix.2 injected embryos (C,D,K). This is not a non-specific effect of overexpressing homeobox sequences since Mix.2 injected embryos have normal size or small hearts (D). No ectopic cardiac differentiation is detected by in situ hybridization with either XTnIc or XMLC2 probe (I,J,L). Embryos in C-H were photographed at 0 magnification and embryos in I-L were photographed at 0 magnification. The brown color in all embryos is natural pigmentation. |
