Abstract
Retinal diseases often cause the loss of photoreceptor cells and, consequently, impairment of vision. To date, several cell populations are known as potential endogenous retinal regeneration cell sources (RRCSs): the eye ciliary zone, the retinal pigment epithelium, the iris, and Müller glia. Factors that can activate the regenerative responses of RRCSs are currently under investigation. The present review considers accumulated data on the relationship between the progenitor properties of RRCSs and the features determining their differentiation. Specialized RRCSs (all except the ciliary zone in low vertebrates), despite their differences, appear to be partially “prepared” to exhibit their plasticity and be reprogrammed into retinal neurons due to the specific gene expression and epigenetic landscape. The “developmental” characteristics of RRCS gene expression are predefined by the pathway by which these cell populations form during eye morphogenesis; the epigenetic features responsible for chromatin organization in RRCSs are under intracellular regulation. Such genetic and epigenetic readiness is manifested in vivo in lower vertebrates and in vitro in higher ones under conditions permissive for cell phenotype transformation. Current studies on gene expression in RRCSs and changes in their epigenetic landscape help find experimental approaches to replacing dead cells through recruiting cells from endogenous resources in vertebrates and humans.
Highlights
Disorders that affect the structure and functions of the retina, usually associated with ageing or diseases, may eventually result in the partial or complete loss of vision
Biomedicines 2020, 8, 208 recent advances in biology that contribute to the understanding of the tissue regeneration processes, the identification of endogenous cell sources for regeneration, and to the development of methods for inducing the differentiation of pluripotent stem cells provide a broad range of opportunities for regenerative medicine
A number of retinal degenerative diseases result in the death of retinal neurons, leading to reduced vision and, in extreme cases, blindness
Summary
Disorders that affect the structure and functions of the retina, usually associated with ageing or diseases, may eventually result in the partial or complete loss of vision. Biomedicines 2020, 8, 208 recent advances in biology that contribute to the understanding of the tissue regeneration processes, the identification of endogenous cell sources for regeneration, and to the development of methods for inducing the differentiation of pluripotent stem cells provide a broad range of opportunities for regenerative medicine These opportunities should be used for the medical treatment of a retina that has been damaged by diseases or has an age-related or other pathology. Along with undifferentiated RRCSs in the circumferential ciliary zone of the eye in lower vertebrates, the latent but differentiated RRCSs, including the retinal pigment epithelium (RPE), the iris, the ciliary body (CB), and Müller glial (MG) cells, show the expression of genes that provide their clear specialization and functioning in the retina (see below). Special attention in the review is paid to the currently available relevant information on the extent to which RRCSs are advanced towards differentiation in adult vertebrates of different classes and humans and to what extent they have retained the progenitor properties in terms of gene expression and epigenetics
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