A, Schematic of HA tagged-Foxf1 conditional allele (Foxf1f-HA-Foxf1/f-HA-Foxf1). B, Schematic and representative immunofluorescence images of Kit (green), HA-Foxf1 (red), and DAPI (nuclei, blue in the merged image) in the large intestine of a mouse harbouring the Foxf1f-HA-Foxf1/f-HA-Foxf1 conditional allele. Scale bar: 25μm. White dotted line marks the border of longitudinal muscle and circular muscle. M: mucusa; CM: circular muscle layer; LM: longitudinal muscle layer; ICC-SMP: submucosal ICCs; ICC-IM: intramuscular ICCs; ICC-MY: myenteric ICCs. C, Representative immunofluorescence images of Kit (green), HA-Foxf1 (red) and DAPI (nuclei, blue in the merged image) of GIST-like tumor from mice with KitV558Δ/+; Foxf1f-HA-Foxf1/f-HA-Foxf1; Rosa26Cre-ERT2 genotype with either coil oil control or tamoxifen treatment (TAM). Scale bar: 25μm. D–F, Comparison of tumor weight (D), proliferation index by percent of Ki67 IHC (E), and number of cleaved-caspase 3 (#Cl-Caspase 3)/20 high power fields (HPF) (F) from age-matched (~5 week old) KitV558Δ/+; Foxf1f-HA-Foxf1/f-HA-Foxf1; Rosa26Cre-ERT2 mice tumors with either corn oil control or tamoxifen treatment (TAM). Error bars: Mean ± SD. n=3 for each cohort (Corn Oil or TAM). All P values are as indicated and significant by two-tailed and unpaired t test. G, Immunoblots of the indicated proteins in mouse cecal GIST-like tumors derived from KitV558Δ/+; Foxf1f-HA-Foxf1/f-HA-Foxf1; Rosa26Cre-ERT2 mice with either coil oil control or tamoxifen treatment (TAM). H, Representative images of H&E, IHC of indicated markers and trichrome staining of mouse GIST tumor derived from KitV558Δ/+; Foxf1f-HA-Foxf1/f-HA-Foxf1; Rosa26Cre-ERT2 treated with either corn oil control or TAM. Scale bar: 50 μm.