ABSTRACT: Salamander limb regeneration is dependent upon tissue interactions that are local to the amputation site. Communication among limb epidermis, peripheral nerves, and mesenchyme coordinate cell migration, cell proliferation, and tissue patterning to generate a blastema, a mass of progenitor cells that forms missing limb structures. An outstanding question is how molecular cross-talk between these tissues gives rise to the regeneration blastema. To identify genes associated with epidermis-nerve-mesenchymal interactions during limb regeneration, we examined histological and transcriptional changes during the first week following injury in the wound epidermis and subjacent cells between three injury types; 1) a flank wound on the side of the animal that will not regenerate a limb, 2) a denervated limb that will not regenerate a limb, and 3) an innervated limb that will regenerate a limb. Early, histological and transcriptional changes were highly similar between the three injury types, presumably because a common wound-healing program is employed across anatomical locations. However, we identified transcripts that were enriched in the limb compared to the flank and are associated with vertebrate limb development. Many of these genes were activated before blastema outgrowth and in situ hybridization showed that some of these genes were expressed in specific tissue types including the epidermis, peripheral nerve, and mesenchyme. We also identified a relatively small group of transcripts that were more highly expressed in innervated limbs versus denervated limbs. These transcripts encode for proteins that are associated with myelination of peripheral nerves, epidermal maintenance, and cell proliferation, suggesting that denervation affects myelinating Schwann cells, epidermal cell function, and proliferation of mesenchymal cells. Overall, our study identifies limb-specific and nerve-dependent genes that are upstream of regenerative growth, and thus promising candidates for the regulation of blastema formation. We used microarray analysis to determine the gene expression changes that take place during limb regeneration, flank wound healing, and an denervated amputated limb. Epidermal tissue and cells adhered to the epidermis were collected as samples. Two harvested samples was pooled for each animal. Four biological replicates were collected from uninjured epidermis (D0) and at 1, 3, and 7 days post injury.
