(A) Experimental design for B-E. Dox was administered to timed pregnant dams starting at E11.5. At E13.5, cochlear tissue from FST overexpressing embryos (R26-FST) and wild type littermates were cultured for 48 hr with or without Activin A (500 ng/ml). (B–E) Atoh1-GFP reporter expression (GFP, gray) marks nascent hair cells. Asterisks indicate hair cells within vestibular sacculus. Yellow arrows mark nascent cochlear hair cells. Scale bar, 100 μm. (F) The length of the GFP positive sensory epithelium was used to quantify the extent of hair cell differentiation in wild type (WT) and FST overexpressing (FST) cochlear explants cultured with and without Activin A. Data expressed as mean ± SEM (n = 5–8 cochlear explants per group, *p≤0.05, **p<0.01, ***p<0.001, student’s t-test). Two independent experiments were conducted and data compiled.