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Fig. 1. The thyroid develops adjacent to the growing ventral aorta in zebrafish
embryos. (A-C) Expression of the thyroid marker nk2.1a
(blue) shows primordial expansion along the AP axis around 55 hpf. Lateral
views, anterior towards the left. (D) An antibody against thyroglobulin
(TG) visualises the lumen of thyroid follicles (brown), surrounded by
follicular cells (blue). (E) The endothelial marker kdr is
expressed in pharyngeal vessels around the thyroid (lumen brown, broken line
around follicle cells), here showing the anterior tip of the ventral aorta on
the level of the heart (arrow) and the first pair of branchial arteries (1st).
(F) Throughout further development, thyroid tissue (follicles in brown)
grows along the ventral aorta (arrows). Ventral view, anterior towards the
left. (G) Schematic drawing summarising thyroid and vessel development.
(H,I) vegf is diffusely expressed in the ventral
pharyngeal area during ventral aorta development. Lateral views, anterior
towards the left. (J,K) kdr is diffusely expressed in
ventral aorta and surrounding mesenchyme (see also E). Lateral views, anterior
towards the left. 1st, first pair of branchial arteries. h, heart; p,
pharynx.