Microarray analysis and functional genomics identify novel components of melanopsin signaling.
BACKGROUND
Within the mammalian retina, there exists a third photoreceptive system based upon a population of melanopsin (Opn4) expressing photosensitive retinal ganglion cells (pRGCs; also termed ipRGCs or intrinsically photosensitive RGCs). Here, we use a microarray-based approach, which we term transcriptional recalibration, coupled with functional genomics to identify downstream targets of melanopsin signaling.


RESULTS
In a mouse with genetically ablated rods and cones (rd/rd cl), approximately 30% of the ocular transcriptome is transiently regulated in response to nocturnal light exposure (3112 genes). A total of 163 of these genes were associated with the "intracellular signaling" gene ontology term. On the basis of their similarity to invertebrate phototransduction genes, 14 were selected for further study. Laser capture microdissection demonstrated that eight of these genes (Gnas, Gnb2l1, Gnaq, Prkcz, Pik3r1, Inadl, Slc9a3r1, and Drd1a) colocalized with melanopsin. The impact of genetic ablation of one of these genes, protein kinase C zeta (Prkcz), was assessed. Prkcz-/- animals show attenuated phase-shifting responses to light, reduced period lengthening under constant light, and attenuated pupillary responses at high irradiances, as well as impaired light-induced gene expression in the suprachiasmatic nuclei (SCN). These attenuated responses are indistinguishable from the deficits observed in melanopsin knockout mice.


CONCLUSIONS
Here, we show that (1) Prkcz plays an as yet unidentified role in melanopsin signaling, (2) the proteins of seven further light-regulated genes emerge as strong candidates in melanopsin signaling, and (3) transcriptional recalibration may provide a powerful new approach for dissecting unmapped signaling pathways.
Peirson
Stuart N
SN
Circadian and Visual Neuroscience Group, University of Oxford, Wellcome Trust Centre for Human Genetics, Roosevelt Drive, Oxford OX3 7BN, United Kingdom.
Oster
Henrik
H
Jones
Sarah L
SL
Leitges
Michael
M
Hankins
Mark W
MW
Foster
Russell G
RG
D000818:Animals; D020869:Gene Expression Profiling; D008027:Light; D055537:Light Signal Transduction; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D046228:Microarray Analysis; D020419:Photoreceptor Cells, Vertebrate / Q000378:metabolism*; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D012165:Retinal Ganglion Cells / Q000378:metabolism*; D017299:Rod Opsins / Q000378:metabolism*; D013493:Suprachiasmatic Nucleus / Q000378:metabolism; D014158:Transcription, Genetic; D000099221:Protein Kinase C zeta; D000099210:Melanopsin
D011493:Protein Kinase C; D017299:Rod Opsins; D000099221:Protein Kinase C zeta; D000099210:Melanopsin