XB-ART-40613Dev Biol February 15, 2010; 338 (2): 117-26.
Gene switching at Xenopus laevis metamorphosis.
During the climax of amphibian metamorphosis many tadpole organs remodel. The different remodeling strategies are controlled by thyroid hormone (TH). The liver, skin, and tail fibroblasts shut off tadpole genes and activate frog genes in the same cell without DNA replication. We refer to this as "gene switching". In contrast, the exocrine pancreas and the intestinal epithelium dedifferentiate to a progenitor state and then redifferentiate to the adult cell type. Tadpole and adult globin are not present in the same cell. Switching from red cells containing tadpole-specific globin to those with frog globin in the liver occurs at a progenitor cell stage of development and is preceded by DNA replication. Red cell switching is the only one of these remodeling strategies that resembles a stem cell mechanism.
PubMed ID: 19896938
Article link: Dev Biol
Genes referenced: adh1c alb cdh1 col11a1 cps1 cyp4b1 fabp1 fetub hbg2 hrg krt62 krt78.6 mmp13 mmp13l trdn
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|Fig. 1. Reprogramming of fibroblasts in the tail notochord. TH induces a change in gene expression in the tail that causes regression of the tail. In situ hybridization of adjacent sections with (A–C) collagen and (D–F) collagenase-3. (A, D) NF55 control; (B, E) 10 nM T3 for 2 days; (C, F) 10 nM T3 for 4 days. (scale bar = 40 μm).|
|Fig. 2. The inhibition of fibroblast reprogramming. In situ hybridization with (A, C) collagen; (B, D) collagenase-3. (A, B) NF55 Col-TRDN transgenic tadpoles treated with 10 nM T3 for 4 days. (C, D) NF55 transgenic for ovine prolactin treated for 4 days with 10 nM T3. (scale bar = 40 μm).|
|Fig. 3. Reprogramming of the skin in cross sections of the limb. In situ hybridization with A, B, C, G, H) tadpole keratin; D, E, F, I, J) adult keratin. Immunocytology with antibodies against (g) tadpole keratin; (i) adult keratin. Keratin is green and Dapi is blue. (A, D) NF55; (B, E) NF59; (C, F) adult frog; (G, g, I, i) NF55 treated with 10 nM T3 for 3 days; (H, J) NF55 treated with 10 nM T3 for 6 days. (g) Scale bar for g and i = 10 μm; for the in situ hybridization panels = 20 μm).|
|Fig. 4. Gene switching in liver parenchymal cells. In situ hybridization with (A–C) fetuin B; (D–F) serum albumin. (A, D) NF55; (B, E) NF60; (C, F) adult frog. Sections from the same stage are consecutive. Transition from larval to adult cell type happens at climax without significant cell replication or cell death. Scale bar = 100 μm.|
|Fig. 5. The liver fatty acid binding protein (L-FABP) promoter from zebra fish expresses GFP specifically in the liver parenchymal cells. (A) Liver fluoresces in a low power ventral abdominal view of a NF55 tadpole transgenic for L-FABP-GFP; (B) section of the liver of the animal shown in (A) showing cytoplasmic expression of GFP in parenchymal cells. (C) Section of a NF55 liver of a tadpole transgenic for the tet inducible L-FABP-TRDN-GFP. This transgene is visualized in the nucleus. B and C are doubly stained with antibodies against E-cadherin (red) and GFP (green). Scale bar is 1 mm for A and 40 μm for B and C.|
|Fig. 6. In situ hybridization of liver sections of control NF55 tadpoles and sibling tadpoles transgenic for the TRDN transgene driven by the L-FABP promoter under control of the tetracycline system. In all panels the tadpoles were incubated for 6 days with the inducer doxycycline followed by 3 days of 10 nM T3. (A, C, E, G) control NF55 tadpoles; (B, D, F, H) L-FABP-TRDN-GFP transgenic tadpoles. (A, B) fetuin B; (C, D) alcohol dehydrogenase; (E, F) CP450; (G, H) CPS. Scale bar = 40 μm.|
|Fig. 8. Labelling of tadpole and adult red cells with BrdU at different times before and after TH treatment. (A–F) BrdU was injected 24 h before the addition of 10 nM T3. Three days later the livers were analyzed. (G–L) BrdU was injected after 48 h of 10 nM T3 treatment. The livers were isolated after another 24 h. (A–C and G–I) tadpole globin; (D–F and J–L) adult globin. (A, D, G, J) in situ hybridization (red). (B, E, H, K) BrdU immunocytology (green) of the adjacent sections; (C, F, I, L) merge of the adjacent two sections. Scale bar = 20 μm.|
|Fig. 7. Switching of globin-containing red blood cells from larval type to adult type occurs at climax in the liver. In situ hybridization with (A–C) tadpole globin; (D–F) adult globin; (G–H) tadpole globin (red) and adult globin (purple). (A, D) NF55; (B, E, G, H) NF62; (C, F) frog liver. There was no co-localization of the two probes (G and H) at climax. Scale bar = 40 μm for A–F; 20 μm for G; 10 μm for H.|