Signaling cascades: a functional characterization of cone arrestin and a differential gene expression analysis of developing retinal ganglion cells

Unrestricted The mature retina is a specialized tissue critical for vision. Individual cell-types that comprise the retina have specialized functional roles mediated by differential gene expression. To identify the contribution of specific genes in defining a cell-type, the function of the cone arrestin protein was analyzed in vivo in photoreceptors and a differential transcript expression profile generated for perinatal developing retinal ganglion cells.; Photoreceptors are responsible for converting photon inputs into neural signals through a process called phototransduction. Rods and cones express unique proteins that enable them to execute this function. The mechanism of rod phototransduction has been well characterized, but little is known about cone phototransduction. Since many homologous components of the rod phototransduction cascade have been identified in cones, it has been suggested that cone phototransduction is similar to rod phototransduction. We hypothesize that CAR functions in cone photoreceptors similar to rod arrestin's role in terminating rod phototransduction.; Using a genetic approach, we expressed cone arrestin (CAR) in rod photoreceptors without rod arrestin to directly compare the functional role of CAR and rod arrestin in terminating the photoresponse. We provide light damage, translocation and membrane association, and single cell electrophysiology evidence that show CAR functions similarly to rod arrestin in the termination of the rod photoresponse in rod photoreceptors in vivo although not as effectively as rod arrestin. These data suggest that the role of CAR in cone phototransduction is akin to rod arrestin's role in quenching rod phototransduction.; In addition to analyzing the specific functional capabilities of CAR, transcripts were screened from perinatal developing retinal ganglion cells (RGCs) for differential expression in order to identify genes that may play a role in developing functional RGCs. We hypothesize that there is uniform coordinated expression of specific transcripts during perinatal RGC maturation that mediate neurite growth loss. High-density microarray analysis of the differentially expressed transcripts from CD90+ RGCs was confirmed by semi-quantitative PCR and in situ hybridization for temporal and spatial expression. Seventy-one transcripts out of ~26,000 genes were identified as differentially expressed (ANOVA corrected p<0.05 with at least a 2^±1.5 fold difference) in RGCs from retinas of mice between embryonic day 16 and postnatal day 5. These data help identify molecular factors that may play a regulatory role in RGC physiology and development.