Some species are endowed with unique physiology and provide new paradigms for both basic and applied biology. For example, adult newts can regenerate body parts, including lens, limb, tail, jaw, small intestine, brain, and heart. This regenerative ability is the highest even among amphibians, including axolotls and frogs [1
]. It is well known that lens regeneration is mediated by dedifferentiation and transdifferentiation of terminally differentiated pigmented epithelial cells (PECs). After lens removal, PECs in dorsal irises undergo dedifferentiation where PECs exclude pigment granules and lose their cellular identity, proliferate, and then differentiate into lens cells. Although lens regeneration never occurs from the ventral iris, dedifferentiation events, depigmentation, proliferation, and gene expression are observed in ventral iris PECs [2
]. Transdifferentiation of PECs has been directly demonstrated by clonal culture experiments [3
For cells to change their identity and assume a new fate, a considerable degree of gene regulation must take place. It has been shown that nucleostemin, a stem cell-specific nucleolar protein found in mammals [5
], accumulates in nucleoli as PECs dedifferentiate during lens regeneration [6
]. We have also recently reported that mammalian stem cell pluripotency-maintaining factors cellular myelocytomatosis oncogene, sex determining region Y box 2, and kruppel-like factor 4 are expressed and regulated during lens regeneration as well [7
]. These data suggest that a PEC is reprogrammed to a stem cell-like cell during dedifferentiation. However, information about molecular events during dedifferentiation is not well elucidated.
To understand the process of dedifferentiation, analysis of global gene expression during dedifferentiation is needed. Although more than 34,000 cDNA sequences for the axolotl Ambystoma mexicanum
, 677,000 cDNAs for the African clawed frog Xenopus laevis
, and 1,271,000 cDNAs for the western clawed frog Xenopus tropicalis
are available [8
], cDNA resources are lacking in the newt field. Here, we generated expression sequence tags (ESTs; 1,368 contigs and 3,357 singlets) from the iris undergoing dedifferentiation during the process of lens regeneration and analyzed their expression profiles.