| bioproject id |
PRJNA292033
to NCBI
|
| key word |
baseline;phototransduction;rhodopsin;transducin;phosphodiesterase;cyclic nucleotide-gated channel;VISUAL PIGMENTS;GAF DOMAINS;ROD;PHOTORECEPTORS;SENSITIVITY;VISION;OPSINS;GENES;DUPLICATION;DETERMINANT |
| experiment type |
baseline |
| publication |
Lamb, T. D. , and D. M. Hunt . "Evolution of the vertebrate phototransduction cascade activation steps." Developmental Biology (2017):S0012160616308326. |
| description |
Vertebrate phototransduction represents the best understood example of response activation in a G protein cascade. Not only have the protein components been characterised comprehensively, but in addition the molecular mechanisms that mediate high amplification and rapid response kinetics are understood in sufficient detail to predict the onset phase of the response to light absorption. Although the phylogeny of the phototransduction proteins has been studied extensively in jawed vertebrates (gnathostomes), there is a paucity of information about the corresponding proteins in the jawless branch of vertebrates (agnathans), from which gnathostomes diverged around 500 million years ago. The only surviving jawless vertebrates are lampreys (around 40 species) and hagfish (around 80 species). We have applied high-throughput sequencing to eye tissue from one species of hagfish, two species of lamprey and five species of gnathostome fish, to obtain mRNA sequences for the components of the phototransduction cascade |
| abstract |
We applied high-throughput sequencing to eye tissue from several species of basal vertebrates (a hagfish, two species of lamprey, and five species of gnathostome fish), and we analyzed the mRNA sequences for the proteins underlying activation of the phototransduction cascade. The molecular phylogenies that we constructed from these sequences are consistent with the 2R WGDmodel of two rounds of whole genome duplication. Our analysis suggests that agnathans retain an additional representative (that has been lost in gnathostomes) in each of the gene families we studied; the evidence is strong for the G-protein a subunit (GNAT) and the cGMP phosphodiesterase (PDE6), and indicative for the cyclic nucleotide-gated channels (CNGA and CNGB). Two of the species (the hagfish Eptatretus cirrhatus and the lamprey Mordacia mordax) possess only a single class of photoreceptor, simplifying deductions about the composition of cascade protein isoforms utilized in their photoreceptors. For the other lamprey, Geotria australis, analysis of the ratios of transcript levels in downstream and upstream migrant animals permits tentative conclusions to be drawn about the isoforms used in four ofthe five spectral classes of photoreceptor. Overall, our results suggest that agnathan rod-like photoreceptors utilize the same GNAT1 as gnathostomes, together with a homodimeric PDE6 that may be agnathanspecific, whereas agnathan cone-like photoreceptors utilize a GNAT that may be agnathan-specific, together with the same PDE6C as gnathostomes. These findings help elucidate the evolution of the vertebrate phototransduction cascade from an ancestral chordate phototransduction cascade that existed prior to the vertebrate radiation. |
Gene
RNA