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.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
Project #
Application #
Study Section
Biology and Diseases of the Posterior Eye Study Section (BDPE)
Program Officer
Neuhold, Lisa
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Johns Hopkins University
Schools of Medicine
United States
Zip Code
Liman, Emily R; Zhang, Yali V; Montell, Craig (2014) Peripheral coding of taste. Neuron 81:984-1000
Wang, Xiaoyue; Wang, Tao; Ni, Jinfei D et al. (2012) The Drosophila visual cycle and de novo chromophore synthesis depends on rdhB. J Neurosci 32:3485-91
Kottgen, Michael; Hofherr, Alexis; Li, Weizhe et al. (2011) Drosophila sperm swim backwards in the female reproductive tract and are activated via TRPP2 ion channels. PLoS One 6:e20031
Venkatachalam, Kartik; Wasserman, David; Wang, Xiaoyue et al. (2010) Dependence on a retinophilin/myosin complex for stability of PKC and INAD and termination of phototransduction. J Neurosci 30:11337-45
Wang, Xiaoyue; Wang, Tao; Jiao, Yuchen et al. (2010) Requirement for an enzymatic visual cycle in Drosophila. Curr Biol 20:93-102
Liu, Zhaohui; Wang, Xiaoyue; Yu, Yi et al. (2008) A Drosophila model for LRRK2-linked parkinsonism. Proc Natl Acad Sci U S A 105:2693-8
Wang, Tao; Wang, Xiaoyue; Xie, Qiang et al. (2008) The SOCS box protein STOPS is required for phototransduction through its effects on phospholipase C. Neuron 57:56-68
Venkatachalam, Kartik; Long, A Ashleigh; Elsaesser, Rebecca et al. (2008) Motor deficit in a Drosophila model of mucolipidosis type IV due to defective clearance of apoptotic cells. Cell 135:838-51
Wang, Tao; Jiao, Yuchen; Montell, Craig (2007) Dissection of the pathway required for generation of vitamin A and for Drosophila phototransduction. J Cell Biol 177:305-16
Wang, Tao; Montell, Craig (2006) A phosphoinositide synthase required for a sustained light response. J Neurosci 26:12816-25

Showing the most recent 10 out of 34 publications