The role of the notochord in dorsal aortae fusion

Abstract

The paired dorsal aortae are the first prominent vessels to develop in the amniote embryo. The dorsal aortae are kept separate on either side of the midline. This bilaterality of dorsal aortae is induced in part by secretion of BMP antagonists (chordin and noggin) from the notochord that inhibit blood vessel formation and migration into the midline region despite the presence of positive vascular regulators VEGF and Shh. During subsequent development, the paired dorsal aortae fuse at the midline to form a single dorsal aorta. It is not known what causes the paired dorsal aortae to fuse. Here, we show that at the time of dorsal aorta fusion the notochord expresses significantly less BMP‐antagonist while expressing similar levels of VEGF and Shh. This correlative observation is supported by in vivo experimentation where implants of older notochord (not expressing BMP antagonist) exert a positive influence on vascular development. These observations suggest that dorsal aortae fusion is largely regulated by a reduction in BMP‐antagonism at the midline.