Fig. 7.

Competence to generate a secondary heart is maintained until the onset of cardiac differentiation. GATA4-injected animal cap reaggregates (CAG-GFP) were transplanted at stage 13 (A, A′), 24 (B, B′), 26 (C, C′) and 28 (D, D′) in the ventral side of host embryos at stage 20 (CAG-GFP) and were analysed at stage 39–40 for cardiac GFP expression and for lineage tracing (rhodamine-dextran). (E–G′) Patterned expression of myl7 and myl3 was found in reaggregates transplanted at stage 20 and 24. Overlapping expression is indicated by black arrowheads and myl7-only expression by white arrowheads. (H) Summary of frequency of GFP expression and beating activity. The capacity to generate a beating structure declines with the increasing age of the transplants. (I) Data summarised the number of embryos positive to the gene expression of myl7 and myl3 in double WMISH. h, heart; t, transplant. The scale bar corresponds to 100 μm.