TCF4 and heart failure: Although Osr1 null mutant mice died of heart failure at mid-gestation, Osr2−/− mice indeed showed the deformed and/or fused cartilages in synovial joints.49 Further detailed cell tracing experiments confirmed that Osr1 and Osr2-expressing joint mesenchyme was overlapped in some extent with the muscle connective tissues and tendon progenitors marked by Transcription Factor 4 (Tcf4) and Scx. 50 Therefore, the Cre transgene driven by Osr2 promoter could be activated in tenogenic mesenchyme.