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Regulation, spectral tuning and evolution of visual pigment genes in fish

Cowing, Jill Alison; (2001) Regulation, spectral tuning and evolution of visual pigment genes in fish. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The opsin genes of mammals have been the subject of a number of studies. As a useful comparison and to increase our understanding of gene regulation, spectral tuning and evolution, I have studied the visual pigment genes of goldfish (Carassius auratus) and a number of species of cottoid fish from Lake Baikal in Eastern Siberia. An unusual feature of the goldfish is that, due to tetraploidy, many of its genes are present as duplicate copies and both may be expressed. This is seen with the green cone opsin genes. The level of expression and localisation to particular cone cells of the two green genes was assessed. It was found that green 2 was expressed at a higher level than green 1, although it is thought that both opsins are expressed within the same subset of cone cells. Regulation of the rod and two green cone opsin genes in goldfish has also been studied by the sequencing of the promoter regions and comparing them to each other and to those of mammals, chicken and Xenopus. A number of regions of homology were identified, many of which were known cis-acting elements. Additionally, an eight base pair motif, which has not been identified before, was found to be conserved between species. The wavelength of maximum absorption (?max) of a visual pigment is determined by the structure of the opsin; changes in the amino acid composition at critical sites can significantly affect the ?max. The species flock of cottoid fish living in Lake Baikal are known to have visual pigments whose ?max is short-wave shifted with increasing depth of habitat. In order to identify amino acid substitutions responsible for these spectral shifts, the blue opsin gene of a representative subset of these fish has been sequenced. Three potential spectral tuning sites were identified at positions 118, 215 and 269. Mutations at these sites were then generated by site-directed mutagenisis and the mutant opsins expressed in 293T cells. After isolation and regeneration with 11-cis retinal, the resulting pigments were analysed spectrophotometrically. Evolution of the blue visual pigment genes in the cottoid fish has also been investigated by phylogenetic analysis of the blue opsin sequences.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Regulation, spectral tuning and evolution of visual pigment genes in fish
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences; Opsin
URI: https://discovery.ucl.ac.uk/id/eprint/10100507
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