Very Small Embryonic-Like Cells (VSELs) - A New Type of Ocular Stem Cell?

Abstract

Purpose:: To investigate the presence of very small embryonic-like cells (VSELs) in the mouse retina and if there are differences during development of the retina.

Methods:: Single cells were isolated from both the neurosensory retina (NSR) and retinal pigment epithelium (RPE) from newborn and 3-week-old C57BL/6 adult mice. The tissues were enzymatically digested using papain dissociation system, for the NSR, and dispase + trypsin, for the RPE. Small sized (2~6µm) Sca1⁺Lin^- CD45^- cells were sorted by FACS and the expression of embryonic stem cell markers (i.e. Nanog, Rex1, Rif1, Dppa1, Utf1, Tdgf1) was analyzed by real-time PCR. These cells meet the criteria for VSELs.

Results:: We found small size (2~6 µm) Sca1⁺Lin^- CD45^- cells in both the NSR and RPE from new-born C57BL/6 mice, but mainly in the RPE of 3-week-old C57BL/6 adult mice. The number of these VSELs cells was significantly higher in Sca-1⁺Lin^-CD45^- population than in Sca-1^- Lin^- CD45^- cells. The expression of embryonic cell markers on the Sca-1⁺Lin^- CD45^- cells is similar to VSELs identified in adult mouse bone marrow. Additionally, purified Sca1⁺Lin^- CD45^- cells from the retina expressed Oct-4 mRNA using One Step RT-PCR.

Conclusions:: We have identified VSELs in the developing mouse retina both in the NSR and RPE. VSELs appear to become restrict to the RPE by 3 weeks of age. The latter may serve as resource pool for stem cells in the adult eye and be useful for cell replacement therapy in the ocular disease.

Keywords: retinal culture