August 1, 1998;
Development of the gut in Xenopus laevis.
The lining of the gut
, together with the pancreas
, gall bladder
, and respiratory system
, is formed from the endoderm
. The gut
also contains smooth muscle
and connective tissue
of mesodermal origin. The amphibian Xenopus laevis is potentially an excellent model organism for studying how the cells of the endoderm
become programmed to produce these internal organs. However, the anatomical complexity of the coiled gut
presents a problem in studying its development. In order to overcome this problem we here present a comprehensive guide to the anatomy and histology of the developing Xenopus gut
. We use a simple dissection to display its anatomy and the expression of four endodermal markers (alkaline phosphatase, IFABP
, and endodermin
). We present schematic diagrams that show how the gut
is arranged in three dimensions and how this organisation changes during development. We also present drawings of histological sections of the gut
which allow any region to be identified and so represent an atlas for working with sections. Finally, we describe the histology of the cells of the various organs of the gut
. This histological identification may be necessary for the identification of parts following experiments in which the normal pattern is disturbed.
[+] show captions
Fig. 1. Anatomy and gene expression in dissected Xenopus guts. A: Dorsal view of a gut from a 3-day-old embryo. B: Ventral view of a gut from a 3-day-old embryo. C: Gut from a 5-day-old embryo. D: Gut from a 7-day-old embryo. E: Stomach region from a 7-day-old gut. F: Boundary between small and large intestine of 7-day-old gut. G: Activity of endogenous alkaline phosphatase in 3-day gut. H: Activity of endogenous alkaline phosphatase in 7-day gut. Inset shows a section through stained gut (arrow highlights alkaline phosphatase staining (blue) in epithelium, arrowhead highlights mesodermal tissue counterstained green). I: Activity of endogenous alkaline phosphatase in stomach region of 7-day gut (1 and 2 show the first and second expression boundaries). J: Ventral view of IFABP expression in 3-day gut. K: Dorsal view of IFABP expression in 3-day gut. L: IFABP expression in 5-day gut. M: IFABP expression in 7-day gut. N: Endodermin expression in 3-day gut. O: Endodermin expression in 5-day gut. P: Endodermin expression in 5-day liver. Q: XlHbox8 expression in 3-day gut (highlighted by bracket). R: XlHbox8 expression in 7-day gut. In C-F the arrows mark the boundary between the stomach and the small intestine, and the arrowheads mark the boundary between the small intestine and the large intestine. st, stomach; si, small intestine; li, large intestine; pr, proctodeum; pa, pancreas; lv, liver; and gb, gall bladder.
fabp2 (fatty acid binding protein 2, intestinal ) gene expression in dissected Xenopus laevis gut, NF stage 41, as assayed by in situ hybridization, ventral view, anterior left.