Biology subjects

McDowell, R. J.

Publications and source records attributed to McDowell, R. J..

4 recordsLinked to original sources

bioRxiv2025

Spectral tuning and signaling of diverse and most red sensitive visual rhodopsins that drive high colour discrimination in Mantis Shrimp eyes

Stomatopod crustaceans (mantis shrimps) possess extraordinary eyes with unmatched visual opsin diversity, but their potential for broad colour detection remains unclear. Here, we report that seventeen opsins, mostly from the midband eye region, are involved in colour sensing and signaling via Gq/Gi-coupling and describe the underlying mechanisms of spectral tuning. Two mid-wavelength opsins preferentially absorb blue light and a majority of long-wavelength opsins absorb in the green range, but three absorb light beyond 600 nm, representing exquisite far-red-sensitive animal opsins. Several blue and red opsins exhibit photoreversibility with opposite spectral shifts explained by retinal binding interactions, revealing unrecognised photochemical flexibility in stomatopod photoreception. Row-specific spectral sensitivity results from combining carotenoid filters with multiple individually-tuned rhodopsins, altogether extending broad vision to the far-red spectrum.

biophysics↗

bioRxiv2025

Development of visible light-sensitive human OPN5 via single amino acid substitution

Animal opsins, light-sensitive G-protein-coupled receptors (GPCRs), serve as primary light receptors in animals, supporting vision and providing light-dependent regulation of physiology and behaviour. Animal opsins also show great potential to be used as optogenetic tools that regulate cellular G protein signalling with light. Opn5 is a UV-sensitive "non-visual" opsin that is expressed in a wide range of tissues throughout body. Although Opn5 could be a good template for the development of optogenetic tools applicable to tissues outside of the eye because of its broad expression, its sensitivity to poorly tissue-penetrating UV light poses challenges for its application. In this study, we focused on human OPN5 (hOPN5) to attempt to identify amino acid(s) responsible for the UV sensitivity and to shift the spectral sensitivity to visible light. Sequence alignment across UV-sensitive Opn5s identified a conserved lysine reside (Lys91) at a position implicated in spectral tuning in invertebrate opsins. We applied site-directed mutagenesis to replace this residue with neutral (alanine) or acidic (glutamate or aspartate) amino acids. Heterologous action spectroscopy of these mutants revealed substantial shifts in spectral sensitivity (55-63nm) toward visible wavelengths. Our findings identify Lys91 as a key spectral tuning site in hOPN5 and provide visible-light sensitive versions of this protein as a candidate for optogenetic applications.

biophysics↗

bioRxiv2023

Beyond Lux: Methods for Species and Photoreceptor-Specific Quantification of Ambient Light for Mammals

BackgroundLight is a key environmental regulator of physiology and behaviour. Mistimed or insufficient light disrupts circadian rhythms and is associated with impaired health and well-being across mammals. Appropriate lighting is therefore crucial for indoor housed mammals. The most commonly used measurement for lighting is lux. However, this employs a spectral weighting function based on human perceived brightness and is not suitable for non-visual effects of light or use across species. In humans, a photoreceptor-specific (-opic) metrology system has been proposed as a more appropriate way of measuring light. ResultsHere we establish technology to allow this -opic measurement approach to be readily extended to any mammalian species, accounting for differences in photoreceptor types, photopigment spectral sensitivities, and eye anatomy. Since measuring photopigment spectral sensitivity can be hard to derive for novel animals and photoreceptors, we developed a high-throughput, easy-to-use, method to derive spectral sensitivities for recombinantly expressed melanopsins and use it to establish the spectral sensitivity of melanopsin from 12 non-human mammals. We further address the need for simple measurement strategies for species-specific -opic measures by developing an accessible online toolbox for calculating these units and validating an open hardware, low-cost, multichannel light sensor for point and click measurement. We finally demonstrate that species-specific -opic measurements are superior to photopic lux as predictors of physiological responses to light in mice and allow ecologically relevant comparisons of photosensitivity between species. ConclusionOur study demonstrates that measuring light more accurately using species-specific -opic units is superior to the existing unit of photopic lux and holds the promise of improvements to the health and welfare of animals, scientific research reproducibility, agricultural productivity, and energy usage.

neuroscience↗

bioRxiv2019

Extraocular, rod-like photoreceptors in a flatworm express xenopsin photopigment

Animals detect light using opsin photopigments. One recently classified opsin clade, the xenopsins, found in lophotrochozoans, challenges our views on opsin and photoreceptor evolution. Originally thought to belong to the Gi-coupled ciliary opsins, xenopsins are now understood to have diverged from ciliary opsins in pre-bilaterian times, but little is known about the cells that deploy these proteins, or if they form a photopigment and drive phototransduction. We characterized xenopsin in a flatworm, Maritigrella crozieri, and found that it is expressed in a larval eyespot, and in an abundant extraocular cell type around the adult brain. These distinct cells house hundreds of cilia in an intra-cellular vacuole (a phaosome). Cellular assays show Mc xenopsin forms a photopigment and couples to Gi/o in response to light. These findings reveal a novel photoreceptor cell type and opsin/G-protein couple, and highlight the convergent enclosure of photosensitive cilia in flatworm phaosomes and jawed vertebrate rods.

zoology↗