Photoreceptor loss causes irreversible blindness in many retinal diseases. Repair of such damage by cell transplantation is one of the most feasible types of central nervous system repair; photoreceptor degeneration initially leaves the inner retinal circuitry intact and new photoreceptors need only make single, short synaptic connections to contribute to the retinotopic map. So far, brain- and retina-derived stem cells transplanted into adult retina have shown little evidence of being able to integrate into the outer nuclear layer and differentiate into new photoreceptors. Furthermore, there has been no demonstration that transplanted cells form functional synaptic connections with other neurons in the recipient retina or restore visual function. This might be because the mature mammalian retina lacks the ability to accept and incorporate stem cells or to promote photoreceptor differentiation. We hypothesized that committed progenitor or precursor cells at later ontogenetic stages might have a higher probability of success upon transplantation. Here we show that donor cells can integrate into the adult or degenerating retina if they are taken from the developing retina at a time coincident with the peak of rod genesis. These transplanted cells integrate, differentiate into rod photoreceptors, form synaptic connections and improve visual function. Furthermore, we use genetically tagged post-mitotic rod precursors expressing the transcription factor Nrl (ref. 6) (neural retina leucine zipper) to show that successfully integrated rod photoreceptors are derived only from immature post-mitotic rod precursors and not from proliferating progenitor or stem cells. These findings define the ontogenetic stage of donor cells for successful rod photoreceptor transplantation.

In the mammalian retina, besides the conventional rod-cone system, a melanopsin-associated photoreceptive system exists that conveys photic information for accessory visual functions such as pupillary light reflex and circadian photo-entrainment [1][2][3][4][5][6][7] . On ablation of the melanopsin gene, retinal ganglion cells that normally express melanopsin are no longer intrinsically photosensitive 8 . Furthermore, pupil reflex 8 , light-induced phase delays of the circadian clock 9,10 and period lengthening of the circadian rhythm in constant light 9,10 are all partially impaired. Here, we investigated whether additional photoreceptive systems participate in these responses. Using mice lacking rods and cones, we measured the action spectrum for phase-shifting the circadian rhythm of locomotor behaviour. This spectrum matches that for the pupillary light reflex in mice of the same genotype 11 , and that for the intrinsic photosensitivity of the melanopsin-expressing retinal ganglion cells 7 . We have also generated mice lacking melanopsin coupled with disabled rod and cone phototransduction mechanisms. These animals have an intact retina but fail to show any significant pupil reflex, to entrain to light/dark cycles, and to show any masking response to light. Thus, the rod-cone and melanopsin systems together seem to provide all of the photic input for these accessory visual functions. © 2003 Nature Publishing GroupCorrespondence and requests for materials should be addressed to K.-W.Y. (kwyau@mail.jhmi.edu). Supplementary Information accompanies the paper on www.nature.com/nature. Competing interests statementThe authors declare that they have no competing financial interests. 8 . In independently produced melanopsin-knockout mice, others have found that the ability of light to phase-delay and lengthen the period of the circadian rhythm is also diminished 9,10 . For the pupil reflex, this photic response can be quantitatively accounted for by a functional complementarity between the rod-cone system and the melanopsin system, without the need to invoke any additional light-detection system 8 . Nonetheless, the proposal has persisted that cryptochromes-flavoproteins reported to have a direct light-detecting role in Drosophila 12,13 -may have the same function in mammals [14][15][16] despite earlier evidence to the contrary 17 . To settle this question, we first examined the action spectrum for phase-shifting the circadian rhythm in mice lacking rod and cone photoreceptors (rd/rd cl) 18 . Next, we generated triple-knockout mice lacking all confirmed photodetection systems-Opn4 −/− Gnat1 −/− Cnga3 −/− (melanopsin (also known as opsin 4), guanine nucleotide-binding protein α-transducin 1 (also known as rod transducin α-subunit, or Trα) and cyclic GMP-gated channel A-subunit 3, respectively)-and tested these animals for pupil reflex, circadian photo-entrainment and the masking response to light. NIH Public AccessIrradiance-response relations for the light-induced phase shifting of the circadian rhythm of l...

This work demonstrates that transgenic mice lacking both rod and cone photoreceptors (rd/rd cl) retain a pupillary light reflex (PLR) that does not rely on local iris photoreceptors. These data, combined with previous reports that rodless and coneless mice show circadian and pineal responses to light, suggest that multiple non-image-forming light responses use non-rod, non-cone ocular photoreceptors in mice. An action spectrum for the PLR in rd/rd cl mice demonstrates that over the range 420-625 nm, this response is driven by a single opsin/vitamin A-based photopigment with peak sensitivity around 479 nm (opsin photopigment/OP479). These data represent the first functional characterization of a non-rod, non-cone photoreceptive system in the mammalian CNS.

No abstract

No abstract