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. Author manuscript; available in PMC: 2016 Jan 31.
Published in final edited form as: Biochim Biophys Acta. 2014 Aug 15;1849(2):94–111. doi: 10.1016/j.bbagrm.2014.08.003

Figure 4. Multiple functions of retinoic acid (RA) signalling in posterior, sino-atrial, cardiac precursors.

Figure 4

A) The RA produced by ALDH1A2 was suggested to establish the posterior limit of a population of cardiac progenitors that expresses Isl-1 and/or FGF-8 (a.k.a. the Second Heart Field, or SHF), but not Tbx-5 (a.k.a. First Heart Field, or FHF). Primary data from [171, 172]. Diagram adapted from [173]. B) RA produced by ALDH1A2 was previously suggested to provide clues for the specification of inflow (sino-atrial) fates to posterior cells of the Tbx-5-expressing progenitor field (FHF). The red rectangle highlights the overlap between Tbx-5 and ALDH1A2 expression [40]. C) Double Tbx-5 in situ hybridization/beta galactosidase stain in a 7.5 d.p.c. (days post coitum) mouse embryo. The red rectangle highlights the overlap between Tbx-5 expression and beta galactosidase activity. This result indicates that cells in the caudal domain of the Tbx-5-expressing cardiac progenitor population (or FHF) activate RA signalling in response to local concentrations of the retinoid produced by ALDH1A2 [40]. D) Chicken cardiac fate map performed in the presence of DMSO (control). Cardiac outflow (ventricular and outflow tract) progenitors (green) and inflow (sino-atrial) progenitors (in yellow) are well separated in the anterior-posterior axis. Note that no outflow progenitors were mapped below line “F” [40]. E) Chicken cardiac fate map performed in the presence of the RAR pan-antagonist BMS493. The limits between outflow and inflow progenitors are blurred. Note that after RA signalling inhibition cardiac outflow progenitors are now mapped well below their usual domain, in line “H” [40]. F) Diagram representing unilateral (right side only) treatment of chicken embryos with agar cylinders containing BMS493 at HH6. G) Results of the experiment represented in F. Local inhibition of RA signalling in the embryonic domain occupied by the ALDH1A2 caudal to rostral wave prevents expression of the inflow marker AMHC1 in the treated side. This results indicates that the RA produced in response to the ALDH1A2 caudal to rostral wave is instructive to posterior cardiac progenitors [40]