Melanopsin expression in the retinas of owls with different daily activity patterns

Melanopsin is a photopigment found in a subset of retinal ganglion cells that is responsible for generating a series of responses to light in organisms, such as circadian rhythm regulation, pupillary light reflex, and body temperature control. The role of each melanopsin gene in the vertebrate retina is still not fully elucidated and a diversity of expression patterns of this photopigment can be observed in retinas of different vertebrate species. Owls are an excellent model for studying the role of melanopsin due to the diversity of species, which may present diurnal, nocturnal, or cathemeral habits. The purpose of this study was to characterize the expression of melanopsin genes in the retina of four different owl species from the Strigidae family (Athene cunicularia, Asio clamator, Glaucidium brasilianum, and Megascops choliba) through genetic and phylogenetic analysis. The specimens were euthanized, and the retinas were collected for RNA extraction and cDNA transcription. cDNA was used in the polymerase chain reaction (PCR) with subsequent sequencing to identify melanopsin genes expressed in the retina of owls. For the quantitative analysis of gene expression, real-time PCR was performed. The phylogenetic reconstruction was obtained by the maximum likelihood. The results showed that owls express both melanopsin genes, Opn4x and Opn4m, with different patterns of expression among the species. The expression of the Opn4x gene was two times higher in Asio clamator (nocturnal) compared to A. cunicularia (cathemeral), Glaucidium brasilianum (diurnal), and Megascops choliba (nocturnal). On the other hand, the expression of Opn4m was about two times lower in the cathemeral, A. cunicularia compared to the other three species. These results might indicate functional differences of the Opn4x and Opn4m genes among species, related to circadian rhythm regulation. Further investigation in owls at other times of the day will bring light to the circadian pattern of melanopsin expression in these species and its correlation with the different patterns of daily activity.