The goal of the proposed research is to use the fruit fly, Drosophila melanogaster, as an animal model to unravel the molecular mechanisms underlying the biosynthesis, turnover and non-classical functions of rhodopsins. Rhodopsin is comprised of an opsin protein and a vitamin A-derived chromophore, which senses light. Among the most common forms of retinal degeneration are those that result from defects in the visual cycle (retinoid cycle)-an enzymatic pathway required for regeneration of the chromophore. Until recently it was thought that flies do not employ a visual cycle, since the chromophore does not normally release from photoactivated rhodopsin. However, some rhodopsin is internalized and the opsin gets degraded, thereby releasing the chromophore. During the last funding period, we made the discovery that flies use a visual cycle to regenerate the released chromophore. The experiments proposed in aim 1 are designed to differentiate between competing hypotheses to explain the basis for the retinal degeneration that results from defects in this enzymatic pathway. We also propose experiments to test hypotheses predicted by the newly formulated model for the invertebrate cycle. Since the mammalian opsin (melanopsin) that functions in the intrinsically photosensitive retinal ganglion cells appears to be more akin to Drosophila rhodopsins than to rod and cone photopigments, these studies also suggest that a visual cycle might function to regenerate the chromophore used by melanopsin. Although some rhodopsin is normally internalized, excessive internalization and degradation of rhodopsin occurs in a variety of flies with mutations that hyperactivate the phototransduction cascade. This appears to be a feedback mechanism to limit excessive signaling.
The second aim addresses a new hypothesis that would explain how uncontrolled activity of the heterotrimeric G-protein leads to excessive turnover of rhodopsin. Although rhodopsins that function in the retina are among the best-characterized receptor proteins, in the past few years it has become clear that some opsins are expressed outside the retina. However, their extra-retinal roles are understood poorly.
Aims 3 and 4 of the proposed research will characterize the roles of two opsins that are expressed in neurons in the olfactory system and central brain and that have not been associated with a light response. We propose to test the contributions of these rhodopsins to animal behaviors. The proposed experiments raise intriguing possibilities as to the potential roles for mammalian extra-retinal opsins, such as Opn3 and Opn5, which have not been subjected to genetic analysis. To accomplish our goals, we propose to employ a multidisciplinary approach using a combination of genetic, cell biological, electrophysiological, molecular and biochemical techniques. The long-term goals of these studies are to 1) uncover mechanisms underlying the retinal degenerations that result from defects in the visual cycle with the ultimate goal of discovering new therapeutic approaches, and 2) uncover the roles of the enigmatic extra-retinal opsins.

Public Health Relevance

Rhodopsin is the receptor that is critically important for detecting light, and mutations affecting rhodopsin lead to common forms of retinal degeneration. The focus of the proposed work is to exploit the great technical advantages of the fruit fly as an animal model to uncover mechanisms underlying the retinal degeneration resulting from impairments in rhodopsins, and to identify roles for opsins that are expressed in cells that are not known to function in light reception.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
2R01EY008117-24
Application #
8294154
Study Section
Biology and Diseases of the Posterior Eye Study Section (BDPE)
Program Officer
Neuhold, Lisa
Project Start
1989-04-01
Project End
2013-04-30
Budget Start
2012-05-01
Budget End
2013-04-30
Support Year
24
Fiscal Year
2012
Total Cost
$405,000
Indirect Cost
$155,000
Name
Johns Hopkins University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Walker, Marquis T; Montell, Craig (2016) Suppression of the motor deficit in a mucolipidosis type IV mouse model by bone marrow transplantation. Hum Mol Genet 25:2752-2761
Hofmann, Lukas; Tsybovsky, Yaroslav; Alexander, Nathan S et al. (2016) Structural Insights into the Drosophila melanogaster Retinol Dehydrogenase, a Member of the Short-Chain Dehydrogenase/Reductase Family. Biochemistry 55:6545-6557
Sokabe, Takaaki; Chen, Hsiang-Chin; Luo, Junjie et al. (2016) A Switch in Thermal Preference in Drosophila Larvae Depends on Multiple Rhodopsins. Cell Rep 17:336-344
Walker, Marquis T; Rupp, Alan; Elsaesser, Rebecca et al. (2015) RdgB2 is required for dim-light input into intrinsically photosensitive retinal ganglion cells. Mol Biol Cell 26:3671-8
Akitake, Bradley; Ren, Qiuting; Boiko, Nina et al. (2015) Coordination and fine motor control depend on Drosophila TRPγ. Nat Commun 6:7288
Liu, Chao; Montell, Craig (2015) Forcing open TRP channels: Mechanical gating as a unifying activation mechanism. Biochem Biophys Res Commun 460:22-5
Chen, Zijing; Chen, Hsiang-Chin; Montell, Craig (2015) TRP and Rhodopsin Transport Depends on Dual XPORT ER Chaperones Encoded by an Operon. Cell Rep 13:573-84
Liman, Emily R; Zhang, Yali V; Montell, Craig (2014) Peripheral coding of taste. Neuron 81:984-1000
Venkatachalam, Kartik; Luo, Junjie; Montell, Craig (2014) Evolutionarily conserved, multitasking TRP channels: lessons from worms and flies. Handb Exp Pharmacol 223:937-62
Montell, Craig (2012) Drosophila visual transduction. Trends Neurosci 35:356-63

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