Kinetics of Rod Photoreceptor Precursor Integration Following Transplantation in the Adult Mouse Retina

PurposeWe have recently demonstrated that adult and wild-type degenerating retina can effectively incorporate rod photoreceptor precursor cells into the ONL. These cells differentiate, form functional synaptic connections with downstream targets in the recipient retina and contribute to visual function (MacLaren et al 2006, Nature 444 (9) 203-207). In this study we have carried out a detailed examination of the kinetics of rod photoreceptor precursor migration, integration and differentiation. MethodsNeural retinas from CBA.GFP or NRl.GFP mice were dissociated enzymatically to a single cell suspension. Cells were transplanted to adult wild type mice. Recipient animals were killed at various time points from 12 hrs to 12 months after transplantation. Eye were fixed and cryosectioned and integrated cells were assessed morphologically and immunohistochemically using confocal microscopy. ResultsPhotoreceptor precursor cells that are at the appropriate ontogenetic stage when transplanted, integrate within 48 hours and appear morphologically differentiated within 7 days of transplantation. Integrated cells survive for at least 12 months. ConclusionsRather than the environment of the mature retina inhibiting photoreceptor maturation, we show that transplantation of precursor cells at a specific ontogenetic stage, defined by activation of the transcription factor Nrl, results in their integration and subsequent differentiation into rod photoreceptors. Conversely, progenitor or stem cells that have not yet begun to express Nrl do not show this property and fail to integrate. Identification of the optimal ontogenetic stage for donor cells might facilitate the generation of appropriate cells for transplantation from either embryonic or adult-derived stem cell whilst evidence for the long term survival of integrated cells provides further support for the strategy of transplanting photoreceptor precursors.