WT bone marrow cells (BMCs) were seeded on top of confluent WT, Fanca−/− and Fancc−/− MSCs in 35 mm culture dish (BD Falcon, Tewksbury, MA) and allow the precursor cells forming hematopoietic clones under the stromal layers [19 (link), 32 (link)]. The cells were cocultured in 37°C incubator supplemented with 5% CO2 and fed weekly by half medium change. Phase-dark hematopoietic clone was imaged under phase contrast images were taken at 20× objective. The identified area was analyzed with ImageJ software (NIH).