title: Positional plasticity in regenerating Amybstoma mexicanum limbs is associated with cell proliferation and pathways of cellular differentiation.
abstract: 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.
authors.affiliation: Department of Biology, University of Massachusetts, Boston, MA, 02125, USA. catherine.mccusker@umb.edu.
authors.forename: Catherine D
authors.initials: CD
authors.lastname: McCusker
authors.affiliation: Department of Biology, Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY, 40506, USA. Antony.Athippozhy@uky.edu.
authors.forename: Antony
authors.initials: A
authors.lastname: Athippozhy
authors.affiliation: Department of Developmental and Cellular Biology, University of California, Irvine, CA, 92602, USA. crlsdiazcastillo@gmail.com.
authors.forename: Carlos
authors.initials: C
authors.lastname: Diaz-Castillo
authors.affiliation: Donald Bren School of Information and Computer Science, University of California, Irvine, CA, 92602, USA. fowlkes@ics.uci.edu.
authors.forename: Charless
authors.initials: C
authors.lastname: Fowlkes
authors.affiliation: Department of Developmental and Cellular Biology, University of California, Irvine, CA, 92602, USA. dmgardin@uci.edu.
authors.forename: David M
authors.initials: DM
authors.lastname: Gardiner
authors.affiliation: Department of Biology, Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY, 40506, USA. srvoss@uky.edu.
authors.forename: S Randal
authors.initials: SR
authors.lastname: Voss
mesh_terms: D000558:Ambystoma mexicanum / Q000196:embryology* / Q000235:genetics; D000818:Animals; D002454:Cell Differentiation / Q000235:genetics; D000066670:Cell Plasticity / Q000235:genetics* / Q000502:physiology; D049109:Cell Proliferation / Q000235:genetics; D005121:Extremities / Q000196:embryology*; D018878:Limb Buds / Q000196:embryology* / Q000502:physiology; D012038:Regeneration / Q000235:genetics* / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics