Browsing by Author "Algrain, Haya"
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Item EXPLORING MELANOPSIN FUNCTION IN MAMMALS WITH DIVERSE PHOTORECEPTOR ARCHITECTURE(2023-01-01) Algrain, Haya; Robinson, Phyllis R; Biological Sciences; Biological SciencesThe properties of visual pigments and retinal architecture in mammals are adapted to suit diverse light environments. Intrinsically photosensitive retinal ganglion cells (ipRGCs), which express the visual pigment melanopsin, integrate both their intrinsic photoresponse and input from rods and cones to mediate both image and non-image forming visual functions. Molecular modeling and genetic analyses suggest that the absorption spectra of all mammalian melanopsins are nearly identical. However, melanopsin expression varies significantly among mammals with different photoreceptor architectures, suggesting potential variability in melanopsin signaling kinetics and melanopsin-mediated behavior. This study investigates the impact of the evolutionary gain or loss of cone photoreceptor types on melanopsin signaling kinetics. This study also investigates the expression of melanopsin the nine-banded armadillo, a terrestrial monochromat. Detailed analysis of phosphorylation at the C-terminus of mouse melanopsin has identified key residues that are important for the kinetics of ipRGC-regulated behavior. Using an in vitro fluorescent calcium signaling assay, our results demonstrate a correlation between delayed melanopsin activation and deactivation kinetics in rod monochromats. Furthermore, mammals with activity patterns during the day (trichromats and dichromats) have similar or faster melanopsin signaling kinetics than wildtype mouse melanopsin. In addition, we confirmed the expression of melanopsin in the nine-banded armadillo. These findings suggest that the presence or absence of photopic vision (i.e., the possession of cone opsins) is a key evolutionary factor driving rapid melanopsin signaling in ipRGCs.?Item Spectral tuning and deactivation kinetics of marine mammal melanopsins(PLOS, 2021-10-15) Fasick, Jeffry I.; Algrain, Haya; Samuels, Courtland; Mahadevan, Padmanabhan; Schweikert, Lorian E.; Naffaa, Zaid J.; Robinson, Phyllis R.In mammals, the photopigment melanopsin (Opn4) is found in a subset of retinal ganglion cells that serve light detection for circadian photoentrainment and pupil constriction (i.e., mydriasis). For a given species, the efficiency of photoentrainment and length of time that mydriasis occurs is determined by the spectral sensitivity and deactivation kinetics of melanopsin, respectively, and to date, neither of these properties have been described in marine mammals. Previous work has indicated that the absorbance maxima (λmax) of marine mammal rhodopsins (Rh1) have diversified to match the available light spectra at foraging depths. However, similar to the melanopsin λmax of terrestrial mammals (~480 nm), the melanopsins of marine mammals may be conserved, with λmax values tuned to the spectrum of solar irradiance at the water’s surface. Here, we investigated the Opn4 pigments of 17 marine mammal species inhabiting diverse photic environments including the Infraorder Cetacea, as well as the Orders Sirenia and Carnivora. Both genomic and cDNA sequences were used to deduce amino acid sequences to identify substitutions most likely involved in spectral tuning and deactivation kinetics of the Opn4 pigments. Our results show that there appears to be no amino acid substitutions in marine mammal Opn4 opsins that would result in any significant change in λmax values relative to their terrestrial counterparts. We also found some marine mammal species to lack several phosphorylation sites in the carboxyl terminal domain of their Opn4 pigments that result in significantly slower deactivation kinetics, and thus longer mydriasis, compared to terrestrial controls. This finding was restricted to cetacean species previously found to lack cone photoreceptor opsins, a condition known as rod monochromacy. These results suggest that the rod monochromat whales rely on extended pupillary constriction to prevent photobleaching of the highly photosensitive all-rod retina when moving between photopic and scotopic conditions.