Multipotent and Stem Cells in the Developing, Definitive, and Regenerating Vertebrate Eye

This is a review of the experimental studies on the vertebrate retina neurogenesis. Data are provided on the distribution and localization of multipotent and stem cells in the developing, definitive, and regenerating eye. At the early stages of retina development, the neuroepithelial cells divide synchronously, thus leading to the accumulation of a certain number of the retinal rudiment cells. Synchronous divisions precede the asynchronous ones, when the differentiation of the retinal cells is initiated. The neuroepithelial cells are multipotent: the neuroblast is a source of the cells of different types, for example, neurons and glial cells. The proliferating multipotent cells are preserved in the ciliary-terminal zone of the retina of amphibians, fish, and chickens during their entire life. The differentiated pigment epithelium cells also proliferate in this area of the eye. The multipotent cells of the retinal ciliary-terminal zone and cells of the pigment epithelium in the eye periphery provide for the growth of amphibian and fish eyes during the entire life of these animals. In adult mammals, clonable and self-renewable cells were found among the pigmented differentiated cells in the ciliary folds. In a culture, the stem cells form spheroids consisting of depigmented and proliferating cells. Upon transdifferentiation, the cells of spheroids form rods, bipolar cells, and ganglion and glial cells, thus suggesting the possible regenerative potencies of the stem cells in the ciliary body of the mammalian eye. The main event of retinal regeneration in newts is the transdifferentiation of the pigment epithelium cells. The results of comparative analysis suggest that the stem cells of the ciliary body in the mammalian eye and pigment epithelium cells in lower vertebrates exhibit similar potencies and use similar mechanisms during the formation of the cells of the neural series.