Lysosomal trafficking of transferrin in erythroid progenitors. (A) Fluorescence microscopy of human erythroid and granulocytic progenitors undergoing pHrodo Red-transferrin uptake (confocal image obtained with 20× objective). (B) Fluorescence microscopy at higher magnification of erythroid progenitors undergoing pHrodo Red-transferrin uptake (confocal image with 63× objective; arrows denote perinuclear clustered vesicles). (C) Fluorescence microscopy for colocalization of Alexa Fluor 594-transferrin with endogenous Lamp1 in erythroid progenitors (confocal image with 63× oil objective). Yellow denotes merge between separate red and green channels. (D) Transmission electron microscopy of erythroid progenitors undergoing 10 nm gold-conjugated transferrin uptake, with boxed regions expanded to highlight MVB/lysosomal accumulation of transferrin particles (arrows denote representative gold-conjugated transferrin particles).