Géraudie J et al. (1990), Enhanced c-myc gene expression during forelimb ...

XB-ART-25924

Proc Natl Acad Sci U S A 1990 May 01;8710:3797-801. doi: 10.1073/pnas.87.10.3797.

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Enhanced c-myc gene expression during forelimb regenerative outgrowth in the young Xenopus laevis.

Géraudie J , Hourdry J , Vriz S , Singer M , Méchali M .

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Analysis of the expression of the c-myc protooncogene has been carried out in the forelimb regenerate of the Xenopus laevis froglet. Northern blot hybridization analysis revealed the presence of a 2.5-kilobase c-myc transcript in the regenerate forelimb at a level at least 7-fold more than the one found in nonregenerating forelimbs or stumps of regenerating forelimbs. In situ hybridization analyses confirmed the relative abundance of c-myc RNA in the regenerate forelimb and provided evidence of spatial localization of high levels of c-myc RNA in specific cell layers. The deepest layers of the wound epithelium of epidermal origin showed a strong signal, whereas virtually no c-myc RNA was detected in the outermost layers. Labeling was also observed in mesenchymal cells of the blastema where it was relatively evenly distributed. This pattern of c-myc RNA in the regenerate might indicate that the expression of c-myc plays a role in the regulation of the continued proliferation of specific cells of the regenerate, whereas repression of this gene in the epidermis correlates with terminal differentiation of keratinocytes.

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Species referenced: Xenopus laevis
Genes referenced: cdh2 cdh3 myc wnt8a

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	FIG. 2. Localization of c-myc RNA in the limb regenerate. In situ hybridizations were carried out as described in the text. (A and B) Sections were hybridized with a 35S-labeled mb. antisense c-myc RNA probe. (A) Regenerate under dark-field illumination. A high level of labeling was intermediate layers of the epithelium (star). The signal was much lower in the outermost layers (arrows). A moderate labeling was also detected in the mesenchymal cells (mb). (x 160.) (B) The same regenerate under bright-field illumination. The rim of autoradiographic grains lining the tissue sections is an artifact created during the procedure of autoradiography (drying of the emulsion). (x160.) (C and D) Control sections of the regenerate hybridized with a labeled sense c-myc RNA probe. (C) Dark-field illumination. Labeling is not above background in the epithelum (ep) and in the mesenchyme of the outgrowth (mb). (x200.) (D) Bright-field illumination. (x200.)
	FIG. 3. Localization of c-myc RNA in the limb regenerate and stump. (A and B) Enlarged regions of the regenerate shown in Fig. 2. (x 320.) (C and D) Localization of c-myc RNA in the limb stump after hybridization of sections with a 35S-labeled antisense c-myc probe. (C) Stump under dark-field illumination. Epidermis labeling (ep) is. much weaker than in the regenerate epithelium. Labeling is not above background in the mesenchymal tissue (in). Glands of epidermal origin located in the dermis are not labeled. (x 160.) (D) Bright-field illumination of the same section. (x160.)
	FIG. 4. Ultrastructure of the wound epithelium (EP). The cytoplasmic content is different in the outermost cells rich in cytokeratin tonofilaments (arrow) as compared with the cells located below (star). There, in addition to intermediate filaments, mitochondria and free ribosomes are quite prominent, suggesting high synthetic activity. Note the changes in size and electron density of the nucleus from the basal region toward the surface of the epithelium where c-myc transcription is no longer observed (MB, mesenchymal cells). (x 7360).
	Figure 1. Northern blot analysis of c-myc expression in Xenopus limb regenerates and stumps.Limbs were amputated at the level of the radius-ulna ( A and B) and the distal regions (severed limbs) were kept as control limbs ( sample 1). Four weeks after amputation ( C) the regenerates , considered as the outgrowth about the amputation site, were harvested ( sample 2) as were stump tissues located above the elbow ( sample 3). D. Northern blot analysis of the total mRNA extracted from different tissues. Lane 1control limbs (8ug of RNA); lane 2, regenerates (12ug); lane 3, stumps (13ug); lane 4, 3x10000 Xenopus proliferative cells; lane 5 100000 Xenopus proliferative cells; lane 6, stage II oocytes (5ug). kb, Kilobases.

References [+] :

Blanchard, c-myc gene is transcribed at high rate in G0-arrested fibroblasts and is post-transcriptionally regulated in response to growth factors. , Pubmed