Identification of Heparan-Sulfate Rich Cells in the Loose Connective Tissues of the Axolotl (Ambystoma mexicanum) with the Potential to Mediate Growth Factor Signaling during Regeneration

  • T. Otsuka
  • A. Q. Phan
  • C. T. LaurencinEmail author
  • J. D. Esko
  • S. V. Bryant
  • D. M. GardinerEmail author
Original Research


Limb regeneration is the outcome of a complex sequence of events that are mediated by interactions between cells derived from the tissues of the amputated stump. Early in regeneration, these interactions are mediated by growth factor/morphogen signaling associated with nerves and the wound epithelium. One shared property of these proregenerative signaling molecules is that their activity is dependent on interactions with sulfated glycosaminoglycans (GAGs), heparan sulfate proteoglycan (HSPG) in particular, in the extracellular matrix (ECM). We hypothesized that there are cells in the axolotl that synthesize specific HSPGs that control growth factor signaling in time and space. In this study we have identified a subpopulation of cells within the ECM of axolotl skin that express high levels of sulfated GAGs on their cell surface. These cells are dispersed in a grid-like pattern throughout the dermis as well as the loose connective tissues that surround the tissues of the limb. These cells alter their morphology during regeneration, and are candidates for being a subpopulation of connective tissue cells that function as the cells required for pattern-formation during regeneration. Given their high level of HSPG expression, their stellate morphology, and their distribution throughout the loose connective tissues, we refer to these as the positional information GRID (Groups that are Regenerative, Interspersed and Dendritic) cells. In addition, we have identified cells that stain for high levels of expression of sulfated GAGs in mouse limb connective tissue that could have an equivalent function to GRID cells in the axolotl. The identification of GRID cells may have important implications for work in the area of Regenerative Engineering.


Axolotl Mouse Regeneration Heparan sulfate Morphogens Positional information 



We wish to thank the members of the Bryant/Gardiner Lab for help with and encouragement of the research. Mouse limb skin tissue samples were kindly provided by Dr. David Rowe. Research was supported by an NIH Director’s Pioneer Award, and the National Science Foundation through its support of the Ambystoma Genetic Stock Center at the University of Kentucky, Lexington. Dr. Laurencin was the recipient of the Presidential Faculty Fellow Award from the National Science Foundation.

Author Contributions

SB and DG conceptualized the presence of a positional information GRID; DG, AP, and TO designed the experiments; AP and TO conducted the experiments; DG, AP and TO wrote the draft of the manuscript; and all authors contributed to the final version of the manuscript.

Compliance with Ethical Standards

Competing Interests

None of the authors have competing interests.

Supplementary material

40883_2019_140_MOESM1_ESM.pdf (5.1 mb)
Supplementary Figure 1 Visualization of gels from RT-PCR analysis of expression of axolotl gene that are involved in the synthesis of GAG chains and in modification of their patters of sulfation in axolotl limb skin, as well as blastema tissue during limb regeneration. (PDF 5239 kb)
40883_2019_140_MOESM2_ESM.pdf (11.1 mb)
Supplementary Figure 2 Visualization of gels from RT-PCR analysis of expression of axolotl gene that are involved in the synthesis of GAG chains and in modification of their patters of sulfation in a diversity of tissues. (PDF 11416 kb)
40883_2019_140_MOESM3_ESM.pdf (2.2 mb)
Supplementary Table 1 Results from a search of the axolotl EST database (ref) for genes expected to be involved in both the synthesis of GAG chains and in modification of their patters of sulfation. PCR primers were synthesized as indicated for RT-PCR analysis of expression (Supplemental Fig. 1a, b, and Supplemental Table 2). (PDF 2259 kb)
40883_2019_140_MOESM4_ESM.pdf (58 kb)
Supplemental Table 2 Summary of the relative levels of expression of axolotl genes (RT-PCR analysis illustrated in Supplemental Fig. 1a, b) that are involved in the synthesis of GAG chains and in modification of their patters of sulfation in a diversity of tissues, as well as during limb regeneration. (PDF 57 kb)


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Copyright information

© The Regenerative Engineering Society 2020

Authors and Affiliations

  1. 1.Department of Developmental and Cell Biology, Natural Sciences II Division, 5111 Natural Sciences IIUniversity of California IrvineIrvineUSA
  2. 2.Connecticut Convergence Institute for Translation in Regenerative EngineeringUniversity of Connecticut HealthFarmingtonUSA
  3. 3.Raymond and Beverly Sackler Center for Biological, Physical and Engineering SciencesUniversity of Connecticut HealthFarmingtonUSA
  4. 4.Department of Orthopedic SurgeryUniversity of Connecticut HealthFarmingtonUSA
  5. 5.Department of Biomedical EngineeringUniversity of ConnecticutStorrsUSA
  6. 6.Department of Materials Science and EngineeringUniversity of ConnecticutStorrsUSA
  7. 7.Department of Chemical and Biomolecular EngineeringUniversity of ConnecticutStorrsUSA
  8. 8.Department of Cellular and Molecular MedicineUniversity of California, San DiegoLa JollaUSA
  9. 9.Glycobiology Research and Training CenterUniversity of California, San DiegoLa JollaUSA

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