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Figure 2. Changes in endoderm architecture during elongation and epithelial morphogenesis in the Xenopus primitive gut tube. Tadpoles were sectioned and immunohistochemically stained to reveal cell membranes (E-cadherin, green), the basement membrane (laminin, red), and nuclei (DAPI [4 prime ,6-diamidine-2-phenylidole-dihydrochloride], blue). The plane of section is indicated in the yellow embryo diagrams [adapted from Nieuwkoop and Faber ([1994])]. Low magnification (00; A,C,E,G) and high magnification (00; B,D,F,H) views of each section are shown. Scale bar = 100 mu M. Brackets in G indicate the region shown in higher magnification in H. The position of the gut lumen is indicated by white arrowheads. Color coding and circles in B prime , D prime , F prime and H prime highlights representative endoderm cells as in Figure 1. A-B prime : As the gut lumen begins to expand (stage 42), all endoderm cells are radially oriented and the tissue architecture is stratified columnar, with cells arranged in four to five concentric layers. C-D prime : At stage 43-44, radial intercalation has decreased the thickness and number of cell layers in the gut wall, so that only two to three layers of cells line the PGT. Some cells (green cells in D prime ) span the gut wall from the lumen to the basement membrane. E-F prime : By stage 46, epithelial morphogenesis is almost complete; a single-layered, pseudostratified epithelium now lines the narrowed gut tube. G-H prime : Endoderm cells are also interdigitated with anterior and posterior neighbors within the gut walls (stage 41 shown). I: The average ratio of endoderm cell length to width (L:W ratio) is shown for successive stages 32-46, with standard deviations indicated by error bars. duod, duodenum; mg, midgut; st, stomach. |
