Fig. 4. Extra-embryonic apoptosis in internal follicle cells at mid-tailbud stage (12 hpf). (A) Confocal optical section showing the superposition of TUNEL and WGA labeling in a mid-tailbud embryo. Apoptotic nuclei of internal follicle cell appear in green, cytoplasm in red. No apoptosis is seen in the head (H) or in the tail (T) of the future tadpole. (B) Optical section at a different focal plane of the embryo shown in (A). Note the accumulation of apoptotic internal follicle cells between the head and the tail (arrow). (C,D) Apoptotic internal follicle cells observed by TEM at mid-tailbud stage (12 hpf). The nuclear membrane disappears when apoptosis progresses to result in a rounded condensed chromatin (cc), while a new membrane system encloses narrow regions of the cytosol (arrow). Scale bars: 85 µm in A,B; 1.4 µm in C; 1.2 µm in D.