The transfer of intracellular (cytoplasmic) material, as opposed to integration of entire photoreceptor cells, may have a major role in rescuing vision in mice, suggest two separate studies in Nature Communications.
Loss of photoreceptors - rod- and cone-shaped cells that respond to light - results in permanent loss of vision in several retinal diseases. In some instances of photoreceptor degeneration, the inner retinal circuitry remains intact, and in these cases replacement of the photoreceptors in the outer nuclear layer of the retina is needed to restore vision. Previous studies showed that transplantation of rod or cone-like precursor cells in adult mice with degenerating retina improved visual function. However, it was generally assumed that during transplantation of photoreceptors, whole donor photoreceptor cells become integrated into the host retina.
In two separate studies, Rachael Pearson and colleagues and Marius Ader and colleagues genetically labelled host and donor cells with different coloured fluorescent proteins in mice that underwent photoreceptor transplantation. Although the donor label was found in photoreceptors located in the host outer nuclear layer, further experiments to visualise individually transplanted cells did not find evidence for donor nuclear material in these cells or evidence for complete cell fusion. Both groups conclude that the success of photoreceptor transplantation in retinas where some host photoreceptors remain may, in large part, be due to transfer of cellular cytoplasmic material between donor and host photoreceptors.
Although only shown in mice, the finding that cytoplasmic material may be sufficient to mediate transplantation sucess could change current understanding of retinal regeneration.