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FIG. 1. 3D modelling of the tadpole head region. The notochord provides an appropriate reference structure for 3D reconstruction of the
developing heart. (A) Whole-mount immunostaining with MZ15 polyclonal antibody demonstrates that the notochord (N) forms an
approximately linear rod above the heart region of the stage 34 tadpole. Episcopic images from a stage 35 embryo yield 3D models (B and
C) which accurately reproduce organ morphology. Brain (magenta), notochord (yellow), eyes (white), heart tube (red), liver primordium
(cyan). Note the spiral shape of the looping heart tube and its extension (as the sinus venosus) over the dorsal surface of the liver. Posterior
bifurcation of the sinus venosus into the Cuverian ducts is also evident.
FIG. 2. Myocardial gene expression precedes overt morphological differentiation. Lateral and ventral views of late tail bud embryos (stage
26/27) after whole-mount in situ hybridisation to detect Nkx2-5 (A), XMLC2a (B), and XMHCa (C) gene expression. Transcripts are
localised in bilateral domains, clearly separated on the ventral midline. Sections through the heart-forming region show bilateral domains
of Nkx2-5 (D) and XMLC2a (E) expression, separated by the ventralmost nonexpressing cells (arrows). Normal, triple-stained sections
through the same region (F) demonstrate that the cardiac mesoderm (m) forms a contiguous layer across the ventral midline, clearly distinct
from the adjacent endoderm (e). |
