GJA1 and neoplasm: Preloading dye transfer studies to assess whether Cx43 is being assembled into functional gap junctions at tumor/endothelial cell interfaces revealed that dye spread extensively from Cx43 expressing HBL100 cells to endothelial cells (Fig. 3i), whereas dye failed to spread from control HBL100v cells to endothelial cells (Fig. 3f).