A study showed that FBS(Fetal Bovine Serum) was added to activate hippo target genes (Wang et al, 2019, Nucleic Acids Research). And, I found that both cell density and culture medium (contained FBS) affected the core protein YAP expression of hippo signaling pathway. However, The YAP1 expression showed fluctuation in cancer cell with shRNA treatment. I am confused about this. I want to identify the effect of gene X or FBS on hippo signaling pathway. So, could some body give me some tips about this?