HEL cells show a megakaryocytic phenotype on TPA treatment. (A) HEL cells do not form tubule-like structures on collagen. HEL cells (left panel) and Bovine LECs, which served as a positive control (right panel), were grown on collagen gels in the presence of 30 ng/mL of VEGF₁₆₅. Scale bars indicate 200 μm. Microscope: Zeiss Axiovert 25, LD Achrostigmat 20×/0,30; room temperature. Camera: Ricoh single-lens reflex camera; reversal film. (B) TPA treatment induces a polynucleated phenotype in HEL cells. HEL cells were cultivated on a collagen-coated surface in the presence of TPA, ethanol as a solvent control, or left untreated. After 8 days, the cells were fixed and H&E stained. Scale bars indicate 400 μm (controls); 200 μm (TPA treatment). Microscope: Zeiss Axiovert 25, LD Achrostigmat 20×/0,30; room temperature. Camera: Ricoh single-lens reflex camera; reversal film. (C) TPA induces polyploidy in HEL cells. HEL cells were treated or not with TPA for 72 hours, harvested, fixed, and their DNA stained with Draq 5. Ploidy of untreated (left panel) and TPA-treated (right panel) HEL cells was assessed flow cytometrically.