Ultrastructural and Molecular Changes in the Developing Small Intestine of the Toad Bufo regularis

Figure 4

Electron micrographs of the anterior portion of the small intestine of the metamorphic stage 63 ((a)–(h)) showing the following (a): apoptotic nucleus (AN) and lysosomes. (b): degenerating cell with AN. Although the plasma membrane is disrupted, the mitochondria (Mi) retain normal morphological structure. (c): degenerating epithelial cell with AN characterized by chromatin condensation and irregular nuclear envelop. The rough endoplasmic reticulum (rER) was evidently degenerated (arrow heads) and the Mi were swollen (arrows). (d): an intraepithelial macrophage (Mac) with numerous large vacuoles (Vac) and pseudopodium-like processes. (e): phagocytic Mac possessing large Vac in the connective tissue (Ct). F: adult epithelial-connective tissue interface. Epithelial cell contains Mi and numerous rER. The basal lamina (BL) is thick. (g): coexistence of larval (LE) and adult epithelia (AE) at stage 63. Vac are localized in the LE. (h): adult epithelial primordia (P-AE) replace the LE, where AN are detected at stage 63. Scale bar = 1 μm.