RESEARCH ARTICLE Plasticity for axolotl lens regeneration is associated with age-related changes in gene expression Konstantinos Sousounis1, Antony T. Athippozhy2, S. Randal Voss2 & Panagiotis A. Tsonis1 1Department of Biology and Center for Tissue Regeneration and Engineering, University of Dayton, Dayton OH, USA 2Department of Biology and Spinal Cord and Brain Injury Research Center, University of Kentucky, Lexington, KY 40503, USA
Correspondence Abstract Panagiotis A. Tsonis, Department of Biology Mexican axolotls lose potential for lens regeneration 2 weeks after hatching. We and Center for Tissue Regeneration and used microarrays to identify differently expressed genes before and after this critical Engineering, University of Dayton, Day- time, using RNA isolated from iris. Over 3700 genes were identified as differentially ton, Ohio, United States of America. expressed in response to lentectomy between young (7 days post-hatching) and old Tel: 937 229 2579; Fax: 937 229 2021; E-mail: (3 months post-hatching) axolotl larvae. Strikingly, many of the genes were only [email protected] expressed in the early or late iris. Genes that were highly expressed in young Received: 6 June 2014; Revised: 10 August iris significantly enriched electron transport chain, transcription, metabolism, and 2014; Accepted: 3 September 2014 cell cycle gene ontologies, all of which are associated with lens regeneration. In contrast, genes associated with cellular differentiation and tissue maturation doi: 10.1002/reg2.25 were uniquely expressed in old iris. Many of these expression differences strongly suggest that young and old iris samples were collected before and after the spleen became developmentally competent to produce and secrete cells with humoral and innate immunity functions. Our study establishes the axolotl as a powerful model to investigate age-related cellular differentiation and immune system ontogeny within the context of tissue regeneration.
Keywords Axolotl, lens, microarray, newt, regeneration
Introduction et al. 2012). In contrast, progenitor cells that regenerate lens after lentectomy derive from the iris, which has a neural Regenerative ability varies across organs, developmental origin (Fuhrmann 2010; Graw 2010). Thus, transdifferen- stages, and species. However, one generality that has been tiation refers to a special type of regeneration where pro- noted for highly and lowly regenerative vertebrates is that genitor cells from a different tissue are the source of the regenerative ability tends to decrease with age (Sousounis regenerate. et al. 2014). Fetal and larval forms tend to possess an abil- The adult red-spotted newt (Notophthalmus viridescens) ity to regenerate tissue in a scar-free manner while adults, has long served as the primary salamander model for stud- and especially mammals, show minimal potential for regen- ies of transdifferentiation and lens regeneration. Soon af- eration. These patterns suggest that regenerative ability is ter lentectomy, pigment epithelial cells (PECs) of the dorsal associated with age-related changes in cells that form tissues and ventral iris dedifferentiate; however, only PECs from and organs, as well as maturation of systems that broadly the dorsal iris contribute progenitors for lens regeneration regulate development and physiology (Seifert & Voss 2013). (Sato 1940). For many years, the axolotl (Ambystoma mex- Exceptions include lens regeneration in adult newts (Eguchi icanum) was thought to lack the newt’s lens regenerative et al. 2011) and fin regeneration in zebrafish (Itou et al. 2012). potential; however, it was recently shown that axolotls can Some amphibians are capable of regenerating their lens in fact regenerate lens from dorsal and ventral iris PECs dur- through a process called transdifferentiation. During embry- ing early larval development (Suetsugu-Maki et al. 2012). onic development of salamanders, the lens is formed by in- But, after approximately 28 days of post-hatching devel- vagination of the surface ectoderm, which later differentiates opment, axolotl larvae lose the ability to regenerate lens. into cornea (Wolff 1895; Freeman 1963; Suetsugu-Maki Thus, the axolotl provides an important new model to