Cranial Vasculature in Zebrafish Forms By Angioblast Cluster-Derived Angiogenesis.
Proulx K, Lu A, Sumanas S.
Dev Biol. 2010 Sep 8
Article in Press, Accepted Manuscript doi:10.1016/j.ydbio.2010.08.036
Figure 10. A diagram of cranial vasculature formation and myelopoiesis prior to the initiation of circulation as observed in etsrp:GFP and kdrl:mCherry transgenic embryos. Dorsal view of the anterior region, anterior is up. 8-12 somite stages, endothelial and myeloid precursors coalesce into two bilaterally located organizing centers within the anterior lateral plate mesoderm (ALPM), the Midbrain Organizing Center (MOC), located adjacent to the midbrain, and the Rostral Organizing Center (ROC), located more rostrally adjacent to the forebrain. 12-16 somite stages, first angiogenic extensions are apparent at the ROC and the MOC. At the same time, myeloid cell (mc) precursors emerge from the MOC and MOC-derived endocardial precursors (end) migrate to the midline. 16-somite-24 hpf stages, kdrl:mCherry+ arterial vessels and etsrp:GFP+ venous vessels extend in the anterior and posterior directions from the MOC. The anterior vessels merge with their counterparts that migrate posteriorly from the ROC and form the venous primordial midbrain channel (pmbc) and the primitive internal carotid artery (pica). The posteriorly migrating MOC-derived vessels join with their counterparts that emerge from the anterior / posterior cardinal vein (acv/pcv) and the dorsal aorta (da) and form the venous primordial hindbrain channel (phbc) and the lateral dorsal aorta (lda). At the same time, branches extend from the ROC to form the caudal division of the internal carotid artery (cadi), the cranial division of internal carotid artery (crdi) that connects to the MOC-derived pmbc, and the nasal ciliary artery (nca) which does not make connections until later stages. A subset of etsrp:GFP; kdrl:mCherry+ cells that migrate to the midline form aortic arches (aa) which join both bilateral ldas. Green, GFP expressing cells; Red, mCherry expression; orange, coexpression of both transgenes; light green, strong GFP, weak mCherry expression.
Formation of embryonic vasculature involves vasculogenesis as endothelial cells differentiate and aggregate into vascular cords and angiogenesis which includes branching from the existing vessels. In the zebrafish which has emerged as an advantageous model to study vasculogenesis, cranial vasculature is thought to originate by a combination of vasculogenesis and angiogenesis, but how these processes are coordinated is not well understood. To determine how angioblasts assemble into cranial vasculature, we generated an etsrp:GFP transgenic line in which GFP reporter is expressed under the promoter control of an early regulator of vascular and myeloid development, etsrp/etv2. By utilizing time-lapse imaging we show that cranial vessels originate by angiogenesis from angioblast clusters, which themselves form by the mechanism of vasculogenesis. The two major pairs of bilateral clusters include the rostral organizing center (ROC) which gives rise to the most rostral cranial vessels and the midbrain organizing center (MOC) which gives rise to the posterior cranial vessels and to the myeloid and endocardial lineages. In Etsrp knockdown embryos initial cranial vasculogenesis proceeds normally but endothelial and myeloid progenitors fail to initiate differentiation, migration and angiogenesis. Such angioblast cluster-derived angiogenesis is likely to be involved during vasculature formation in other vertebrate systems as well.