Fig. 6

Latent Cardiac Potential in Rostral ALPM Is Revealed by Inhibition of Vasculogenesis and Myelopoiesis (A–H) In situ hybridization depicts expression of hand2 (A–D) and cmlc2 (E–H) in wild-type (A, E, and G) and MO-injected (B–D, F, and H) embryos. The scale bars represent 100 μm. (A–F) Dorsal views, anterior to the top, at the 7 somite (A–D) and 20 somite (E and F) stages. (G and H) Frontal views, dorsal to the top, at 48 hpf. (A–D) hand2 is ectopically expressed in the rostral ALPM of embryos when scl and etsrp are knocked down. Injections of anti-scl (B) or anti-etsrp (C) MOs caused weak expression of hand2 in rostral ALPM (arrows; anti-scl MOs, n = 6/10; anti-etsrp MOs, n = 6/12). Rostral hand2 expression was not observed in control sibling embryos (n = 0/24). Injection of anti-scl+etsrp MOs (D) caused robust expression of hand2 in rostral ALPM (arrows; strong expression, n = 10/17; weak expression, n = 7/17). Thus, injection of anti-scl+etsrp MOs phenocopies a loss of clo function. (E and F) Injection of anti-scl+etsrp MOs causes a rostral extension of cmlc2 expression (arrows; injected embryos, n = 25/31; control siblings, n = 0/33). (G and H) Injection of anti-scl+etsrp MOs results in cardiac chamber morphology resembling that of clo mutants (injected embryos, n = 8/10; control siblings, n = 0/15). (I) Hearts of anti-scl+etsrp MO-injected embryos contain too many cardiomyocytes. Counting of cardiomyocyte nuclei reveals statistically significant increases (asterisks) in the total number of cardiomyocytes and the number of atrial cardiomyocytes in MO-injected embryos (p < 0.0002, Student's t test; n = 13 uninjected controls and 15 injected embryos). The bar graph indicates mean and standard error of each data set.