title: Isolation and characterization of melanopsin (Opn4) from the Australian marsupial Sminthopsis crassicaudata (fat-tailed dunnart).
abstract: Melanopsin confers photosensitivity to a subset of retinal ganglion cells and is responsible for many non-image-forming tasks, like the detection of light for circadian entrainment. Recently, two melanopsin genes, Opn4m and Opn4x, were described in non-mammalian vertebrates. However, only one form, Opn4m, has been described in the mammals, although studies to date have been limited to the placentals and have not included the marsupials. We report here the isolation and characterization of an Opn4 gene from an Australian marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata), and present evidence which suggests that the Opn4x gene was lost before the placental/marsupial split. In situ hybridization shows that the expression of Opn4 in the dunnart eye is restricted to a subset of ganglion cells, a pattern previously reported for rodents and primates. These Opn4-positive cells are randomly distributed across the dunnart retina. We also undertook a comparative analysis with the South American marsupial, the grey short-tailed opossum (Monodelphis domestica), and two placental mammals, mouse and human. This approach reveals that the two marsupials show a higher sequence identity than that seen between rodents and primates, despite separating at approximately the same point in time, some 65-85 Myr ago.
authors.affiliation: Circadian and Visual Neuroscience, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford OX3 7BN, UK.
authors.forename: Susana S
authors.initials: SS
authors.lastname: Pires
authors.forename: Julia
authors.initials: J
authors.lastname: Shand
authors.forename: James
authors.initials: J
authors.lastname: Bellingham
authors.forename: Catherine
authors.initials: C
authors.lastname: Arrese
authors.forename: Michael
authors.initials: M
authors.lastname: Turton
authors.forename: Stuart
authors.initials: S
authors.lastname: Peirson
authors.forename: Russell G
authors.initials: RG
authors.lastname: Foster
authors.forename: Stephanie
authors.initials: S
authors.lastname: Halford
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001315:Australia; D016678:Genome; D017403:In Situ Hybridization; D008394:Marsupialia / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D012165:Retinal Ganglion Cells / Q000378:metabolism; D017299:Rod Opsins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D000099210:Melanopsin