Remodeling of the intestine during metamorphosis of Xenopus laevis

Abstract

Thyroid hormone controls remodeling of the tadpole intestine during the climax of amphibian metamorphosis. In 8 days, the Xenopus laevis tadpole intestine shortens in length by 75%. Simultaneously, the longitudinal muscle fibers contract by about the same extent. The radial muscle fibers also shorten as the diameter narrows. Many radial fibers undergo programmed cell death. We conclude that muscle remodeling and contraction play key roles in the shortening process. Shortening is accompanied by a temporary ''heaping'' of the epithelial cells into many layers at climax. Cells that face the lumen undergo apoptosis. By the end of metamorphosis, when the epithelium is folded into crypts and villi, the epithelium is a single-cell layer once again. Throughout this remodeling, DNA replication occurs uniformly throughout the epithelium, as do changes in gene expression. The larval epithelial cells as a whole, rather than a subpopulation of stem cells, are the progenitors of the adult epithelial cells.BrdUrd ͉ caspase-3 ͉ smooth muscle ͉ epithelium ͉ thyroid hormone

Regulation of adult intestinal epithelial stem cell development by thyroid hormone during Xenopus laevis metamorphosis

“…It is possible that the stem cells (1) originated from a pool of predetermined undifferentiated cells (Bonneville, 1963), (2) were transformed from differentiated larval epithelial cells (Marshall and Dixon, 1978b), or (3) migrated from the surrounding tissues. Although there is a growing body of circumstantial evidence that the stem cells originate from at least "partially" differentiated cells Schreiber et al, 2005), it still remains uncertain from what cells the stem cells are actually derived. The ability to manipulate intestinal metamorphosis both in vivo and in vitro makes it an ideal system to investigate the origin and the mechanism for adult intestinal stem cell development.…”

Shh/BMP‐4 signaling pathway is essential for intestinal epithelial development during Xenopus larval‐to‐adult remodeling

“…On the other hand, a small number of undifferentiated cells appear as islets (adult primordia) between the larval epithelium and the connective tissue (McAvoy and Dixon, 1977). The adult primordia are of unknown origin, although there is a growing body of circumstantial evidence that they are transformed from differentiated larval epithelial cells (Marshall and Dixon, 1978;Schreiber et al, 2005). The adult primordia include stem cells that are analogous to those in the mammalian intestine (Ishizuya-Oka et al, 2003), rapidly grow in size by active cell proliferation, and then differentiate into the intestinal absorptive epithelium similar to the mammalian counterpart (Hourdry and Dauca, 1977;Shi and Ishizuya-Oka, 1996).…”

Thyroid hormones and the control of cell proliferation or cell differentiation: Paradox or duality?

“…From this stage onward, the epithelium is constantly renewed along the trough-crest axis (Ishizuya-Oka and Shi, 2005), which strongly resembles the mammalian intestine ( Figure 2F). It is worth noting that for a long time, the origin of the adult epithelial progenitor cells or stem cells was not clearly defined (Ishizuya-Oka et al, 2003;Schreiber et al, 2005). Interestingly, a recent study has now demonstrated that they arise from dedifferentiated larval epithelial cells under the influence of the THs (Ishizuya-Oka et al, 2009).…”