Time-course And Characterisation Of Transplanted Photoreceptor Precursor Migration And Maturation

Purpose: : Transplantation of photoreceptors offers a potential therapy for irreversible retinal degenerations, a leading cause of blindness in the developed world. Transplanted rod photoreceptor precursors have been shown to integrate robustly into recipient retinas, adopt a mature rod phenotype and contribute to scotopic vision. Here, we aim to elucidate the time-course and mechanisms of donor cell migration, integration and maturation within the recipient retina and to compare these processes with the same integration-competent population during normal development. Understanding such mechanisms will allow refinement of strategies to improve transplanted photoreceptor integration efficiency, ultimately aiding progress towards clinical utility and facilitate adaptation of the approach to different cell types and systems. Methods: : Neonatal Nrl.GFP mouse retinas were dissociated enzymatically. Nrl.GFP+ve rod precursors were FACS-sorted and injected subretinally into adult wild-type mice. Recipients were sacrificed between 24 hrs and 3 weeks post-transplantation. Eyes were cryosectioned, immuno-stained and confocally imaged. Maturation and migration of Nrl.GFP+ve rod precursors during normal development were assessed using immunohistochemistry and time-lapse 2-photon microscopy, respectively. Results: : Numbers of integrated Nrl.GFP+ve donor cells peaked during the first week post-transplantation. Cells were observed to integrate into recipient retinas through a sequence of events involving polarized neurite extension and somatic translocation. Immunostaining for phototransduction cascade proteins indicated a polarization of cellular specializations during migration, with segment formation preceding synaptogenesis. Expression of rod-specific markers in integrated cells took place in a time frame similar to that of normal development. Differentiation of nuclear architecture was significantly accelerated in transplanted rods. Conclusions: : Transplanted rod precursors simultaneously undergo a morphological transition from amorphous to rod-like and a spatial translocation from the subretinal space, through the outer/inner segment region into the recipient ONL. Analysis of the same cell population during normal development reveals migratory behavior and similar timing of rod marker expression