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Fig. 2. Expression of dkk1 and isl1 and their regulation in early development of Xenopus laevis. A. WMISH shows the spatial expression of isl1 and dkk1 in early cardiogenesis. Both isl1 and dkk1 are present in the cardiac crescent at stage 15 (white arrowhead). At stage 20 (white arrowhead) and stage 24 (black arrowhead), dkk1 is expressed in the middle line where isl1 is absent. At stage 28, dkk1 is expressed in a small expression domain at the ventral midline, whereas isl1 covers a broader expression domain (black arrowheads). White dotted lines indicate the cement gland. Black dotted lines indicate the orientation of the sections shown in B. B. Parasaggital and cross sections reveal co-expression of dkk1 and isl1 in the border of ventral mesoderm (bvm, red arrowhead) and cardiac mesoderm (cm) (green arrowhead). At stages 24 and 28, dkk1 is expressed in the overlying endoderm (yellow arrowhead) in close proximity to the cardiac mesoderm. bvm: border of ventral mesoderm, cg: cement gland, cm: cardiac mesoderm, hm: head mesenchyme, oe: oral evagination, pc: prosencephalon, sha: stomodeal-hypophyseal anlage. C. Isl1 deletion leads to a reduced dkk1 expression at stage 20 (black arrow). Dotted lines indicate the cement gland. Quantification is presented in D. E. At stage 28 dkk1 expression is reduced at the ventral midline upon Isl1 knockdown (white and black arrowheads). Quantitative presentation is shown in F. Mean values with standard errors are given. n = number of independent experiments, N = total number of embryos analyzed. *p < 0.05 with Mann-Whitney rank sum test. |
