MARCKS-Like Protein Immunolocalization in Healing Appendages of Amphibians Suggests Its Involvement in Regeneration

The present study reveals the immunolocalization of the MARCKS-like protein in two urodeles and an anuran during the initial stages of appendage regeneration. This acidic protein of 22-32 kDa interacts with the dynamic cytoskeleton of activated keratinocytes and blastema cells and is believed to be among the initial signaling factors stimulating limb regeneration in the axolotl. Bioinformatics controls indicate presence of homologous MARCKS-like proteins also in other amphibian species. The present study aims to generalize the presence of this protein during the first 2-8 days of appendage regeneration in amphibians. In the wound epidermis of the axolotl, the protein is prevalently localized in pale Leydig cells, a mucous cell type described in amphibian epidermis, many of which are present in the regenerating epidermis. A lower immunolabeling is found in the newt wound epidermis but is high in regenerating nerves. In the regenerating tail of frog tadpoles MARCKS-like immunolabeling is present in the wound epidermis, regenerating spinal cord, ganglia and nerves but also with lower intensity in myotubes and in the external layer of notochord. Low to absent MARCKS-like immunoreactivity is instead observed in the normal epidermis and in the wound epidermis of the non-regenerating tadpole limb. Although mainly cytoplasmic, also some nuclear labeling is detected in immunoreactive cells of different tissues, especially in the spinal cord, suggesting the activation of nuclear transcriptional process. The protein is present in tissues with high proliferative activity, but is low to absent in most blastema cells and connective tissues during regeneration. The study indicates that the presence of MARCKS-like protein is a general reaction that favors regeneration in amphibians and possibly also in other vertebrates.