Abstract
Purpose: :
The isolation of subsets of retinal cells such as retinal progenitors is one of the strategies being used to achieve neural retina regeneration by transplantation. However, these cell populations have not yet been adequately characterized. This is due, in part, to a lack of markers that can be used to identify the distinct stages and lineages of retinal cells. Surface antigens permit the isolation of a specific subset of cells from a cell mixture without damaging the cells. We screened the mouse retina at various developmental stages for reactivities with a panel of antibodies directed against cell-surface antigens and obtained unique expression patterns for more than 30 antigens. Among these, SSEA-1 and c-kit have been shown previously to represent the early and late retinal progenitor cells, respectively. In this work, we aimed to identify markers for photoreceptor and Mueller glia cells.
Methods: :
Among 30 antibodies, which showed positive signals with retinal cells in the previous screening, we focused on CD73 and CD44 for more detailed analyses. Retinal cells expressing CD73 or CD44 were purified by a cell sorter, and characterization of the cells were done by in vitro reaggregation culture. Furthermore, singlings regulating differentiation of these sub-populations of retina were examined by gain- and loss-of-function analyses and knockout mice. The expression of the antigens in common marmoset retina was examined.
Results: :
Mouse retinal subpopulations that expressed CD73 first appeared around birth and subsequently increased dramatically in number, eventually representing more than 90% of the retinal cells in the adult. In the adult retina, most of these cells expressed rhodopsin but not s-opsin. Results of re-aggregation cultures, supports the idea that CD73 is an early photoreceptor lineage marker. Ectopic expression in retinal cells of Nrl and Crx, both of which are known to be expressed in photoreceptor lineage, suggests that CD73 is downstream of Crx. Adult retina of common marmoset also showed the expression of CD73 in rods. CD44 is known to be expressed in mature Mueller glia, and we found its expression in a part of c-kit positive progenitor cells at around birth. Purified CD44/c-kit double positive cells differentiate exclusively into Mueller glia cell in re-aggregation culture. Involvement of Notch for differentiation of c-kit+ progenitor cells to glial lineage, and role of CD44 and BMP signals for terminal differentiation of Mueller glia cells were suggested by gain- and loss-of-function analyses of signalings in vitro retinal cultures.
Conclusions: :
We identified CD73 and CD44 as markers for photorecptor- and Mueller glia-precursors, respectively.
Keywords: retinal development • flow cytometry • signal transduction