Genes Involved in the Retinal Development Are Also Expressed in the Retinal Regeneration

Abstract

Newts can regenerate the functional retina from retinal pigment epithelial (RPE) cells. We examined here whether genes expressed in early retinal development are also expressed in this regeneration system. RNA samples were prepared from eye cups at selected days after surgical removal of the neural retina, and gene expressions during retinal regeneration were examined by reverse transcriptase-polymerase chain reaction. Pax-6 genes were the so-called master control gene for eye development. Their expressions were detected around 10 days after surgery when RPE cells start cell division, and increased as regeneration progressed. Delta-Notch signaling negatively regulates the neuronal determination and contributes to keep neural stem cells in the developing retina. Notch-1 was abruptly expressed, at the maximal level, around 20 days after surgery when one to two layers of retinal progenitor cells appeared. On the other hand, a Notch ligand and effector, Delta-1 and Hes-1,were expressed at day 0 (i.e., normal eye cups without neural retina). Delta-1 expression suddenly rose around 20 days after surgery and was sustained until at least 23 days. Hes-1 expression slightly increased around 10 days and reached the maximum around 20 days. Expressions of these genes were down-regulated as the retina fully regenerated. Neurogenin (Ngn) is a positive regulator for neurogenesis. Expression of Ngn was detected at day 0. The expression level slightly increased around 10 days after surgery, reached the maximum around 23 days, and decreased as the retina fully regenerated. Correlating with the Ngn increase, neural markers such as N-CAM or voltage-gated Na⁺ channel genes were expressed around 23 days. These observations may suggest that common molecular mechanisms are involved in retinal development and regeneration.