Xenbase Image ID: 132234

FIG. 6. Differential regulation of contractile gene expression by dorsal tissue. (A–C) Explants were isolated at stage 22, cultured, and subsequently assayed for gene expression and beating (see Materials and Methods). Contractile protein mRNA expression is represented by the bars in the histogram. The beating frequency is indicated by the dashed horizontal line. XNkx2.5 is normally expressed in the LHF region in intact embryos (Figs. 1–3) and is likewise expressed in the corresponding tissue when explanted either with (A) or without (B) dorsal tissues (neural tube and dorsal mesoderm). Contractile protein genes are not normally expressed in LHF cells (Figs. 1–3). Absence of ventral (prospective myocardial) tissue caused expression of contractile protein genes ectopically in the LHF region (LHF-N explants, A), suggesting that signals from the prospective myocardium suppress myocardial genes in the lateral portion of the heart field. Note that the fraction of explants expressing Tn-Ic and cardiac actin transcripts exceeded beating incidence, while the fraction expressing XMLC-2a coincided with beating incidence. Removal of neural and dorsal mesodermal tissue in LHF explants (B) increased the incidence of expression of genes (XTn-Tc, XMHCa, and XMLC-2a) such that all markers were expressed in a large proportion of the explants. Beating incidence also increased. (C) Control explants of prospective myocardium (VHF) generally beat and expressed all markers. Expression of all markers, with the exception of cardiac actin, was in the LHF region (see Fig. 7). For cardiac actin, only heart and not somitic expression was scored. Results are statistically significant (P , 0.05). Image published in: Raffin M et al. (2000) Copyright © 2000. Image reproduced with permission of the Publisher, Elsevier B. V. Larger Image Printer Friendly View

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