A new model of vasculogenesis and angiogenesis in vitro as compared with vascular growth in the avian area vasculosa

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Abstract
In cultures of dissociated quail epiblast the basic constituents of the vascular system, blood cells and endothelial cells can be induced by basic fibroblast growth factor (Flamme and Risau, Development, 116:435–439, 1992). As we show here, in those cultures three types of vascular plexus differentiate spontaneously under different culture conditions: At the 3rd day a vascular plexus appears in situ closely resembling the vascular plexus of the quail area opaca vasculosa (vasculogenesis). Vascular sprouts are formed, extending long filopodia at their tips. Such filopodia are shown to build the first intervascular bridges in the growing vascular plexus of the area vasculosa at embryonic day 3. Connections of filopodia turn out to be precursors of new capillaries interconnecting pre‐existing blood vessels (angiogenesis). Two further types of in vitro capillary plexus differentiate in long term endothelial cell cultures derived from induced angioblasts. Whereas one closely resembles so‐called angiogenesis in vitro, the third type comprises mainly multinucleated giant endothelial cells lining loop like capillaries and represents a differentiation of aging endothelial cell culture. Thus, the present in vitro model is an approach to the sequence of angioblast induction, vasculogenesis, and angiogenesis.