BACKGROUND: The endogenous ability to dedifferentiate, re-pattern, and re-differentiate adult cells to repair or replace damaged or missing structures is exclusive to only a few tetrapod species. The Mexican axolotl is one example of these species, having the capacity to regenerate multiple adult structures including their limbs by generating a group of progenitor cells, known as the blastema, which acquire pattern and differentiate into the missing tissues. The formation of a limb regenerate is dependent on cells in the connective tissues that retain memory of their original position in the limb, and use this information to generate the pattern of the missing structure. Observations from recent and historic studies suggest that blastema cells vary in their potential to pattern distal structures during the regeneration process; some cells are plastic and can be reprogrammed to obtain new positional information while others are stable. Our previous studies showed that positional information has temporal and spatial components of variation; early bud (EB) and apical late bud (LB) blastema cells are plastic while basal-LB cells are stable. To identify the potential cellular and molecular basis of this variation, we compared these three cell populations using histological and transcriptional approaches.

RESULTS: Histologically, the basal-LB sample showed greater tissue organization than the EB and apical-LB samples. We also observed that cell proliferation was more abundant in EB and apical-LB tissue when compared to basal-LB and mature stump tissue. Lastly, we found that genes associated with cellular differentiation were expressed more highly in the basal-LB samples.

CONCLUSIONS: Our results characterize histological and transcriptional differences between EB and apical-LB tissue compared to basal-LB tissue. Combined with our results from a previous study, we hypothesize that the stability of positional information is associated with tissue organization, cell proliferation, and pathways of cellular differentiation.

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Published in BMC Developmental Biology, v. 15, article 45, p. 1-17.

© 2015 McCusker et al.

Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Catherine McCusker was supported by a Postdoctoral Fellowship, PF-12–145–01-DDC, from the American Cancer Society. Charless Fowlkes was supported by a grant from the National Science Foundation, NSF IIS-1253538. Additional support was provided by the US Army Research Office Multidisciplinary University Research Initiative (MURI), NIH R24OD010435, and NIH (P40OD019794) through its support of the Ambystoma Genetic Stock Center at the University of Kentucky, Lexington, KY. This work was made possible, in part, through access to the confocal facility of the optical biology shared resource of the Cancer Center Support Grant (CA-62203) at the University of California, Irvine.

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Additional file 1: Table S1.

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Additional file 2: Figure S1.

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Additional file 3: Figure S3.

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Additional file 4: Table S2.

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Additional file 5: Figure S2.

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