ShRNA constructs for ROBO1 silencing were ordered from Dharmacon, Thermo Scientific (the RNAi Consortium (TRC) Lentiviral shRNA). Mature antisense sequences can be found in Supplemental Methods. shRNA4 was chosen for initial experiments based on best KD efficiency. shRNA5 was subsequently used to confirm data. Lentiviral transduction was performed as previously described.(16 (link)) Cells were selected in puromycin-containing media for up to 7 days. ROBO1 KD was confirmed using western blotting of cells harvested 3 days post puromycin. Aliquots of cells were collected 3, 5, and 7 days post puromycin selection to assess for apoptosis via flow cytometry for annexin V-propidium iodine staining (PI) as described in supplemental methods. Scrambled-transfected cells were used as controls for procedure-related toxicity.