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Participant: PROMISE AGEP Research Symposium, 2014
Juan Valdez-Lopez
Department: Biological Sciences
Institution: University of Maryland, Baltimore County (UMBC)
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ABSTRACT
Exploring the molecular and structural basis of melanopsin signaling
The visual pigment melanopsin is expressed in a subset of retinal ganglion cells (ipRGCs). These cells are intrinsically photosensitive and their axons project to brain regions such as the suprachiasmatic nucleus (SCN) and the olivary pretectal nucleus (OPN). These regions regulate non-image forming functions such as circadian photoentrainment and the pupillary eye reflex. Therefore, melanopsin is unique compared to visual opsins, such as cone opsins and rhodopsin, due to its role in regulating non-image forming functions. Melanopsin is also unique at the molecular level; the most distinctive feature being its long intracellular c-tail. Previous work has shown that there are several residues on the intracellular tail that are necessary for deactivation of melanopsin. However, it’s not clear if the tail mediates the activation portion of signaling. We hypothesize that residues 377, 380, and 382 on the proximal portion of the intracellular tail are interacting with residues on intracellular loop 3 via hydrogen bonds. This would result in a physical interaction that is necessary for proper activation of melanopsin. To test this, a mutant mouse melanopsin (3X mutant) was constructed with sites 377, 380, and 382 on the c-tail altered to prolines to disrupt the hypothesized interaction with intracellular loop 3. This 3X mutant was transiently expressed in human embryonic kidney (HEK) cells to test its response to light via calcium imaging assay. Using this assay, we observed a deficit in activation in the 3X mutant, suggesting that the tail is important for proper activation of melanopsin.
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BIOGRAPHICAL SKETCH
Hailing from Washington DC, Juan has always been a curious young man. His curiosity led to a fascination with science from a young age, particularly after his experience dissecting frogs during middle school. He graduated from Paint Branch High in Burtonsville, MD in 2008, and then obtained his B.S. in Biological Sciences from UMBC in 2012. He recently obtained his M.S. in Applied Molecular Biology from UMBC in 2013. He is now in the PhD program in Biological Sciences at UMBC.
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GENERAL SUMMARY OF GRADUATE RESEARCH
During his time in the Applied Molecular Biology M.S. program at UMBC, he worked on a project in Dr. Tom Cronin’s lab that involved isolating and sequencing various visual opsin genes from the stomatopod Squilla empusa. It was interesting that many distinct opsin sequences were isolated from S.empusa since microspectrophotometry data suggests that its vision is monochromatic. Using the sequence data, expression of opsin transcripts were analyzed via in situ hybridization of riboprobes. He is currently rotating in Dr. Phyllis Robinson’s lab where is exploring the molecular and structural basis of melanopsin signaling, focusing on activation. In this project, he is confirming that there are important sites on the intracellular c-tail that hydrogen-bond with sites on intracellular loop 3, forming a physical interaction that is necessary for proper activation of melanopsin.
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PROMISE: Maryland's AGEP 2003-2018 
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