FOXD1 and infection: High expression levels of YAP and FOXD1 were detectable by RT-qPCR (Fig 6B and 6C); immunohistochemical analysis of the flag-tagged Luc, YAP, and FOXD1 further verified the persistent infection of the lentiviruses and expression of indicated proteins primarily in the superficial zone of articular cartilage (S8B Fig).