The Retinal Homeobox (Rx) gene is necessary for retinal regeneration in Xenopus laevis tadpoles

The Retinal Homeobox (Rx) gene is essential for retinal development. Rx functions to promote maintenance of retinal progenitor cells (RPCs). Loss of Rx function early in eye development results in impairment in or lack of eye development. In the mature retina, Rx is expressed in photoreceptors and, in lower vertebrates, in RPCs in the ciliary marginal zone at the anterior periphery of the retina. Themature Xenopus retina can regenerate after resection. In the second week after resection, the wound fills with RPCs that are proliferative and express RPC markers, including Rx. To investigate the role of Rx in retinal regeneration,weknockeddownRxexpression using a transgenic shRNA approach. We found that Rx expression was essentially normal at late tailbud/early tadpole stages (st 38) but was decreased by st 41. There was no obvious effect on eye development until st 50 when tadpoles exhibited impaired visual function and photoreceptor degeneration. Rx shRNA tadpoles also exhibited deficits in regeneration when 25% of the retinawas removed at st 44. Thewound did not heal normally and RPCs did not develop normally, if at all, in the wound. Regeneration was rescuedbyexpressionof exogenousRx, suggesting that the impairments in regeneration observed in Rx shRNA transgenic tadpoles were specifically due to knockdown of Rx expression. These results demonstrate that Rx expression is necessary for retinal regeneration. Further, these results suggest that Rx is necessary for RPC development/ recruitment during retinal regeneration.