Lizards are the most closely related vertebrates to mammals with the ability to regenerate an entire appendage as an adult. During the regeneration of the tail appendage, the core contains a growing tube of ependymal cells containing radial glia that help to guide axon regrowth. New muscle groups form surrounding a cartilage endoskeleton, and both motor and sensory innervation to the new muscle groups is established. Skin and scales are reformed, and the entire structure has both motor biomechanical and sensory function. Intriguingly, this capacity can be exhausted through multiple rounds of regeneration, making it a useful model for decreased capacity for repair in aging. Mammals are unable to regenerate the multiple tissue types in a functional appendage like the lizard tail. However, since mammals and reptiles are both amniote vertebrates and have diverged relatively recently compared with other regeneration models (salamander, zebrafish), this means that their gene and regulatory networks are more conserved. While molecular studies have been limited by the lack of genomic data, the 2011 publication of the genome of the green anole lizard, Anolis carolinensis, combined with our research team's genome reannotation based on deep transcriptome sequencing of 21 tissues, including regenerating tail, and microRNA sequencing has built an extensive genomic infrastructure. Differences in regenerative capacity between mammals and reptiles could have arisen either through changes in the cis-regulation of genes at the transcriptional level or through changes in microRNA targets affecting protein levels. Genomic rearrangements and deletions may also have led to the loss of key regeneration genes in mammals. We hypothesize that by connecting the transcriptomic and proteomic profiles of regeneration in the lizard model, we can answer the question of why reptiles are capable of greater regenerative capacity than mammals. Our research team at ASU has been at the forefront of using bioinformatic and statistical tools for comparison of genes between the lizard regenerating tissues and with other model species (Kusumi et al., 2011;Eckalbar et al., 2012). The team also has extensive experience with proteomic analysis, specifically correlating previously uncharacterized peptides derived from splice variants (Antwi et al., 2009;Katchman et al., 2011). The development of this lizard model system and technologies to integrate transcriptomic and proteomic data has great potential for significant impact in regenerative medical research. Specifically, we will carry out 1) transcriptomic analysis of microRNAs and mRNAs in regeneration to examine the effects of age and number of successive regenerative attempts and 2) Connecting the transcriptome and proteome: identifying regulatory interactions and novel genes.
The goal of regenerative therapies is to be able to recreate entire functional units, including muscle groups, tendons, cartilage, motor and sensory nerves, skin, and connective tissue. All of these tissues are regenerated during regrowth of the tail in th lizard, which is the closest animal to humans with this capacity. Building on an extensive genomic infrastructure now available for the lizard, we will work to connect the changes at the transcript level to the protein level to uncover the unique and specifically regulated genes that direct regeneration.
