The MaSC-enriched population from Csf1op/opmice yields smaller outgrowths in vivo and has lower clonogenicity in vitro. (a) Wholemounts of fourth mammary glands from eight-week-old wild-type and Csf1op/opmice showing delayed filling of the fat pad and persistence of terminal end buds in mutant animals. (b) Wholemounts of outgrowths following transplantation of CD29hiCD24+ cells from wild-type or Csf1op/opmammary glands into the cleared fat pads of syngeneic wild-type recipients. (c) CD29hiCD24+ cells from Csf1op/opmammary glands exhibit lower clonogenicity and colony size than those from control glands. Histogram (upper panel) showing colony forming capacity of 100 CD29hiCD24+ cells for each genotype. Error bars show standard error of the mean for three independent experiments. Lower panel shows cultures of CD29hiCD24+ cells grown on fibroblast feeder layers. Scale bars = 1 mm. Csf1 = colony stimulating factor 1; MaSC = mammary stem cell.