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Fig. 3. Ectopic endothelial cells can influence thyroid morphology cell
non-autonomously. Lateral views (A,B) and cross-sections (C-I) through the
head region. (A,C) In wild-type embryos, bilateral groups of
kdr domains (arrowheads) mark part of the anterior (head) lateral
plate mesoderm that give rise to vascular structures. (B,D)
Co-injection of scl and lmo2 mRNA leads to massive
upregulation of kdr in the head mesenchyme of zebrafish embryos.
(E) Experimental procedure: donor cells from scl and
lmo2 co-injected embryos were grafted into wild-type embryos.
(F,G) Donor cells have all developed into endothelial cells when
found in the head mesenchyme of host embryos. Arrows indicate kdr
expression (blue) overlapping with the cell marker biotin (brown) present in
grafted cells. Endogenous kdr expression (arrowhead in F) is variably
visible on sections, depending on the exact level of sectioning (compare with
A). (H) At 55 hpf, grafted scl+lmo2 cells (brown, arrows) have
caused the thyroid primordium (blue) to expand laterally. One of the four
embryos where grafted cells were detected adjacent to the thyroid primordium.
(I) An embryo where gfp injected donor cells are found close
to the thyroid, which is not expanded towards the grafted cell. In H and I,
care was taken to chose the section through the median level of the thyroid,
and diameters were measured on the base of these sections. In I, nuclei in the
thyroid appear more prominent than in H, so that the cytoplasmic
nk2.1a signal looks slightly weaker on this median section. Broken
lines indicate the border of the neural tube (nt) in C,F,G, and the midline in
H,I. 12 ss, 12 somite stage.
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