Dataset Information

Visual pigments in a palaeognath bird, the emu Dromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision.

ABSTRACT: A comprehensive description of the spectral characteristics of retinal photoreceptors in palaeognaths is lacking. Moreover, controversy exists with respect to the spectral sensitivity of the short-wavelength-sensitive-1 (SWS1) opsin-based visual pigment expressed in one type of single cone: previous microspectrophotometric (MSP) measurements in the ostrich (Struthio camelus) suggested a violet-sensitive (VS) SWS1 pigment, but all palaeognath SWS1 opsin sequences obtained to date (including the ostrich) imply that the visual pigment is ultraviolet-sensitive (UVS). In this study, MSP was used to measure the spectral properties of visual pigments and oil droplets in the retinal photoreceptors of the emu (Dromaius novaehollandiae). Results show that the emu resembles most other bird species in possessing four spectrally distinct single cones, as well as double cones and rods. Four cone and a single rod opsin are expressed, each an orthologue of a previously identified pigment. The SWS1 pigment is clearly UVS (wavelength of maximum absorbance [?max] = 376 nm), with key tuning sites (Phe86 and Cys90) consistent with other vertebrate UVS SWS1 pigments. Palaeognaths would appear, therefore, to have UVS SWS1 pigments. As they are considered to be basal in avian evolution, this suggests that UVS is the most likely ancestral state for birds. The functional significance of a dedicated UVS cone type in the emu is discussed.

SUBMITTER: Hart NS

PROVIDER: S-EPMC4947894 | biostudies-literature | 2016 Jul

REPOSITORIES: biostudies-literature

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Publications

Visual pigments in a palaeognath bird, the emu Dromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision.

Hart Nathan S NS Mountford Jessica K JK Davies Wayne I L WI Collin Shaun P SP Hunt David M DM

Proceedings. Biological sciences 20160701 1834

A comprehensive description of the spectral characteristics of retinal photoreceptors in palaeognaths is lacking. Moreover, controversy exists with respect to the spectral sensitivity of the short-wavelength-sensitive-1 (SWS1) opsin-based visual pigment expressed in one type of single cone: previous microspectrophotometric (MSP) measurements in the ostrich (Struthio camelus) suggested a violet-sensitive (VS) SWS1 pigment, but all palaeognath SWS1 opsin sequences obtained to date (including the o ...[more]

PMID: 27383819

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Project description:The evolutionary origin of powered flight was fundamental to the establishment and radiation of the avian clade, and it remains a salient feature of modern birds. However, flight has been lost multiple times throughout the evolution of the avian lineage. Ratites (flightless palaeognaths, including the emu, ostrich and other well-known groups) are perhaps the most notable flightless birds, and their convergent losses of flight often coincide with adaptations to a cursorial lifestyle, including robust legs, digit loss, and reduced wings. Although there is a wealth of comparative anatomical knowledge for several ratites, the underlying genetic mechanisms producing these changes remain debated. Here we use a multidisciplinary approach employing embryological, genetic, and genomic techniques to interrogate the mechanisms underlying the delay in forelimb development contributing to the diminution of the forelimb in emu embryos. We show that the epithelial to mesenchymal transition (EMT) in the lateral plate mesoderm (LPM) and muscle precursor migration, the initiating events of limb formation, occur at equivalent stages in the emu and chick. However, the early emu forelimb fails to proliferate at HH18. The unique emu forelimb expression of Nkx2.5, previously associated with diminished wing development, does not initiate until after this stage, concomitant with migration of myoblasts into the limb bud, and hence would not appear to be the proximal cause of limb reduction in this species. In contrast, RNA-sequencing of HH18 limb tissues reveals significantly lower Fgf10 expression in the emu forelimb. Artificially increasing mesenchymal Fgf10 expression to the nascent emu wing induces ectodermal Fgf8 expression and results in a proliferative limb bud. Analyzing open chromatin reveals differentially active regulatory elements near Fgf10 and Sall-1 in the emu wing compared to emu hindlimb and both chicken limbs. Additionally, we show that the Sall-1 enhancer activity is dependent on an Ets transcription factor-binding site likely mediated by Fgf-signaling. Taken together, our results support a model where regulatory changes result in lower expression of Fgf10 and a concomitant failure to induce the genes required for limb proliferation in the early emu wing bud at HH18.

Dataset Information

Visual pigments in a palaeognath bird, the emu Dromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision.

Publications

Visual pigments in a palaeognath bird, the emu Dromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision.

Similar Datasets

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