Defective degradation and accumulation of TUNEL-positive nucleic material in Mekk1^ΔKD fetal livers. Histochemical analysis of FLs. Nucleic material in wt and Mekk1^ΔKD FLs, as shown by TUNEL stain (green). Note the large amount of abnormal apoptotic foci in the Mekk1^ΔKD fetal liver B, and in higher magnification D. A, B: bar = 75 μm; C, D: bar = 100 μm.