VA-derived cell clusters are viable and express hematopoietic markers. (A) VE-cadherin Cre fate mapped endothelial and HCs in green (crossed to a R26R EYFP Cre reporter) were costained with proliferation marker phospho-histone H3 (pH3, top panel in red) and apoptosis marker cleaved caspase-3 (bottom panel in red). Some proliferation within the cell clusters is noted (arrows, top panel), although no apoptosis is detected. There is one cell outside of the cluster found to be positive for caspase-3 (arrows). (B) CD41 (top panel in red), a marker of HSCs and hemogenic endothelium, is expressed within EYFP⁺ cell clusters (arrows) and in circulating HCs in an adjacent vessel (arrowheads). Ikaros (bottom panel in red), a gene expressed by HSCs and lymphoid progenitors, exhibits a similar expression pattern (arrows and arrowheads). (C) The Runx1-LacZ knock-in mouse line exhibits early Runx-1 (blue) endothelial expression within the VA (arrows, left panels), and later within the artery associated cell clusters (arrows, right panels). (A-C) Scale bars as labeled per row.