Generation of New Cone and Rod Photoreceptors in the Adult Retina by Transplantation of Crx-Positive Precursor Cells

Abstract

Purpose: : Retinal degenerative conditions result in the irrevocable loss of photoreceptors. Replacing the lost photoreceptor cells may be an appropriate treatment as post mitotic, yet immature, rod precursor cells can efficiently integrate into the diseased murine retina and restore some visual function. As human visual acuity relies mainly on cone photoreceptors, here, we sought to determine the transplantation and integration competency of both cone and rod photoreceptor precursor cells in mice.

Methods: : A Crx.gfp transgenic line was used to fluorescently label and isolate immature cone and rod photoreceptors from the developing mouse retina at embryonic day 12.5, 15.5, 17.5 and post natal days 2 and 3. The Crx.gfp transgene recapitulates the endogenous expression of the cone-rod homeobox gene (Crx) by labeling both immature cones and rods shortly after exit from the cell cycle and maintaining GFP expression in both photoreceptor populations. GFP-positive cells from dissociated neural retinas were transplanted sub-retinally in adult mice. At 3 weeks post-transplantation, the number of integrated rod and cone photoreceptor cells present in the outer nuclear layer (ONL) were analysed. Cones were identified by PNA staining and RXR gamma immunohistochemistry.

Results: : Crx-positive precursor cells from embryonic and early postnatal stages of retinal development can successfully integrate into the adult mouse retina after transplantation into the sub-retinal space. Transplanted Crx.gfp cells migrated into the ONL of the host retina and acquired the morphology of differentiated photoreceptors. The majority of Crx.gfp cells capable of integrating into the ONL generated rod photoreceptors, while a smaller proportion of integrated cells acquired the morphology and correct location of differentiated cone photoreceptors and expressed the cone marker RXR gamma.

Conclusions: : Immature Crx.gfp donor cells develop into cone and rod photoreceptors after transplantation into the adult retina.

Keywords: retina • photoreceptors • transplantation