Formation of Flk1⁺ and c-kit⁺ cell populations is accelerated and enhanced in response to mMix. FACS analysis of cell surface Flk1 and c-kit protein expression in i-Mix EBs cultured in the presence or absence of DOX for 3 or 5 days (DOX added on day 1). Single-cell suspensions were labeled with anti-Flk1 and –c-kit sera and analyzed by FACS. Parental (wild-type) ES and uninduced (–DOX) i-Mix cells produced comparable numbers of Flk⁺, c-kit^hi, and Flk⁺ckit⁺ double-positive cells (not shown). This experiment was repeated 3 times with similar results.