Fig. 6

ltbp3 morphant embryos develop distinct vascular and thyroid defects. tg(tg:mCherry;kdrl:EGFP) embryos injected with a control morpholino (CTRL-MO) or a morpholino targetting ltbp3 (ltbp3-MO) were stained by IF for mCherry (red), GFP (green) and cardiac troponin T (white) and were analyzed by confocal microscopy for thyroid and vessel defects at 55, 80 and 100 hpf. ((A)-(C)). Embryos injected with a CTRL-MO displayed normal development of the pharyngeal vasculature and thyroid tissue. Note that the compact mass of thyroid cells at 55 hpf was tightly invested by endothelial cells of the forming hypobranchial artery (HA). Later, control embryos displayed the characteristic expansion of thyroid tissue along the pharyngeal midline closely apposed to the ventral aorta (VA) and the caudally running paired HA. ((D)-(F)) The majority of ltbp3 morphants (group I) displayed a thyroid phenotype that was characterized by a lateral expansion of thyroid tissue in the vicinity of the heart outflow tract (OFT). Note that lateral expansion was evident as early as 55 hpf (D) and was associated with the presence of dysplastic HA. The HA was absent at later stages and a VA was never formed ((E) and (F)). ((G)-(I)) The other distinct thyroid phenotype observed in ltbp3 morphants (group II) was characterized by a single compact mass of thyroid cells in the vicinity of the OFT. In ltbp3 morphants of group II, formation of the HA was never observed and the thyroid showed neither a rostral expansion along the midline nor a lateral expansion. All panels show ventral views and anterior is to the left. aa1, aa3, aortic arch artery 1 and 3; ba, bulbus arteriosus. Scale bar: 50 μM.