Encephalopsin (OPN3) is required for normal refractive development and the GO/GROW response to induced myopia.

Purpose: Myopia, or nearsightedness, is the most common form of refractive error and is increasing in prevalence. While significant efforts have been made to identify genetic variants that predispose individuals to myopia, these variants are believed to account for only a small portion of the myopia prevalence, leading to a feedback theory of emmetropization, which depends on the active perception of environmental visual cues. Consequently, there has been renewed interest in studying myopia in the context of light perception, beginning with the opsin family of G-protein coupled receptors (GPCRs). Refractive phenotypes have been characterized in every opsin signaling pathway studied, leaving only Opsin 3 (OPN3), the most widely expressed and blue-light sensing noncanonical opsin, to be investigated for function in the eye and refraction. Methods: Opn3 expression was assessed in various ocular tissues using an Opn3eGFP reporter. Weekly refractive development in Opn3 retinal and germline mutants from 3 to 9 weeks of age was measured using an infrared photorefractor and spectral domain optical coherence tomography (SD-OCT). Susceptibility to lens-induced myopia was then assessed using skull-mounted goggles with a -30 diopter experimental and a 0 diopter control lens. Mouse eye biometry was similarly tracked from 3 to 6 weeks. A myopia gene expression signature was assessed 24 h after lens induction for germline mutants to further assess myopia-induced changes. Results: Opn3 was found to be expressed in a subset of retinal ganglion cells and a limited number of choroidal cells. Based on an assessment of Opn3 mutants, the OPN3 germline, but not retina conditional Opn3 knockout, exhibits a refractive myopia phenotype, which manifests in decreased lens thickness, shallower aqueous compartment depth, and shorter axial length, atypical of traditional axial myopias. Despite the short axial length, Opn3 null eyes demonstrate normal axial elongation in response to myopia induction and mild changes in choroidal thinning and myopic shift, suggesting that susceptibility to lens-induced myopia is largely unchanged. Additionally, the Opn3 null retinal gene expression signature in response to induced myopia after 24 h is distinct, with opposing Ctgf, Cx43, and Egr1 polarity compared to controls. Conclusions: The data suggest that an OPN3 expression domain outside the retina can control lens shape and thus the refractive performance of the eye. Prior to this study, the role of Opn3 in the eye had not been investigated. This work adds OPN3 to the list of opsin family GPCRs that are implicated in emmetropization and myopia. Further, the work to exclude retinal OPN3 as the contributing domain in this refractive phenotype is unique and suggests a distinct mechanism when compared to other opsins.

Violet-light suppression of thermogenesis by opsin 5 hypothalamic neurons.

The opsin family of G-protein-coupled receptors are used as light detectors in animals. Opsin 5 (also known as neuropsin or OPN5) is a highly conserved opsin that is sensitive to visible violet light1,2. In mice, OPN5 is a known photoreceptor in the retina3 and skin4 but is also expressed in the hypothalamic preoptic area (POA)5. Here we describe a light-sensing pathway in which POA neurons that express Opn5 regulate thermogenesis in brown adipose tissue (BAT). We show that Opn5 is expressed in glutamatergic warm-sensing POA neurons that receive synaptic input from several thermoregulatory nuclei. We further show that Opn5 POA neurons project to BAT and decrease its activity under chemogenetic stimulation. Opn5-null mice show overactive BAT, increased body temperature, and exaggerated thermogenesis when cold-challenged. Moreover, violet photostimulation during cold exposure acutely suppresses BAT temperature in wild-type mice but not in Opn5-null mice. Direct measurements of intracellular cAMP ex vivo show that Opn5 POA neurons increase cAMP when stimulated with violet light. This analysis thus identifies a violet light-sensitive deep brain photoreceptor that normally suppresses BAT thermogenesis.

Crx-L253X Mutation Produces Dominant Photoreceptor Defects in TVRM65 Mice.

Purpose: The cone-rod homeobox (CRX) transcription factor is essential for photoreceptor gene expression, differentiation, and survival. Human CRX mutations can cause dominant retinopathies of varying onset and phenotype severity. In animal models, dominant frameshift Crx mutations introduce a premature termination codon (PTC), producing inactive truncated proteins that interfere with normal CRX function. Previously, a mutant mouse, TVRM65, was reported to carry a recessive late PTC mutation, Crx-L253X. More detailed phenotype analysis of the pathogenicity of Crx-L253X sheds new light on the variability of CRX-linked diseases. Methods: Homozygous (L253X/X); heterozygous (L253X/+); Crx-/- and control C57BL/6J (WT) mice were analyzed at various ages for changes in retinal function (ERG), morphology (histology) and photoreceptor gene expression (qRT-PCR). Results: At 1 month, L253X/X mice lack visual function, show greater reductions in retinal thickness, and distinct gene expression changes relative to Crx-/-, suggesting that the phenotype of L253X/X is more severe than Crx-/-. L253X/+ mice have reduced rod/cone function, but normal retinal morphology at all ages tested. qRT-PCR assays described a complex phenotype in which both developing and mature photoreceptors are unable to maintain proper gene expression. L253X mRNA/protein is overexpressed relative to normal Crx, suggesting a pathogenic mechanism similar to early PTC mutations. However, the overexpression is less pronounced, correlating with a relatively mild dominant phenotype. Conclusions: The L253X mouse provides a valuable model for CRX-associated retinopathy. The pathogenicity of CRX frameshift mutations depends on the position of the PTC, which in turn determines the degree of mutant mRNA/protein overproduction.