High levels of c-kit RNA are expressed in parental TF-1 cells in absence of stroma and low levels in stroma-dependent TF-1S clones. To determine c-kit expression, RNA (15 μg) from cell line TF-1 and stroma-dependent clones (TF-1S #MB6 and TF-1S #MB8) was subjected to Northern analysis. Absence of MS-5 stroma cells for 1 day is indicated by “−MS5” (lanes 4 and 5).