I agree with RPE65, BEST1 and INSYN2B. The trailing edge that expresses TMEM40 contains cells expressing HBG- hemoglobin gamma which is expressed in fetal cell including fetal RPE, plus other choroid fetal lineages. If there are stem cells in RPE then HBG +adults RPE cells may link to the 1 in 1000 RPE cells that express MKI67.