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FIG. 1. GATA-4/5/6 transcription is not inhibited by RA treatment, which blocks myocardial differentiation. (a) Whole-mount in situ
hybridization was performed using probes specific to transcripts for cardiac troponin I, Nkx2.5, or GATA-4/5/6, as indicated on the right.
Embryos are oriented with anterior to the left, dorsal to the top. RA was added at stage 23 and embryos were allowed to develop until stage
35. Examples of control embryos, treated with DMSO alone, are shown on the left; examples of RA-treated embryos are on the right. The
arrow and arrowheads in the two upper right images indicate the small patch of differentiated myocardium that remains in these embryos,
at the most ventral position of the presumptive heart-forming region. Note that the pharyngeal endoderm, which does not express
GATA-4/5/6, remains positive for Nkx2.5 following RA treatment. The Nkx2.5 levels appear increased in pharyngeal endoderm of this
RA-treated embryo due to extended staining in order to observe the weak signal in the residual heart region. However, enhanced levels of
Nkx2.5 RNA are not observed generally in pharyngeal endoderm of RA-treated embryos (Drysdale et al., 1997). (b) An example of an
RA-treated embryo analyzed for xGATA-6 RNA to illustrate the induction of a posterior domain of transcription (arrow). A similar
activation is seen for GATA-5 but not for GATA-4. Our previous work implicated GATA-6 in the regulation of progenitor cells of the gut
(Gao et al., 1998), and so this domain is likely to correspond to the presumptive hindgut. |
