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Visual pigments in a living fossil, the Australian lungfish Neoceratodus forsteri.

Bailes HJ, Davies WL, Trezise AE, Collin SP - BMC Evol. Biol. (2007)

Bottom Line: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri.Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes.However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biomedical Sciences, University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. helena.bailes@manchester.ac.uk

ABSTRACT

Background: One of the greatest challenges facing the early land vertebrates was the need to effectively interpret a terrestrial environment. Interpretation was based on ocular adaptations evolved for an aquatic environment millions of years earlier. The Australian lungfish Neoceratodus forsteri is thought to be the closest living relative to the first terrestrial vertebrate, and yet nothing is known about the visual pigments present in lungfish or the early tetrapods.

Results: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri. Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes. However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

Conclusion: The presence of four cone pigments in Australian lungfish suggests that the earliest tetrapods would have had a colorful view of their terrestrial environment.

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Related in: MedlinePlus

Multiple transcripts of rh1 occur in the Australian lungfish retina. A) 3' RACE PCR products from lungfish rh1 cDNA. Arrows point to two potential transcripts differing in size in lane 2 (a third, faint band is also visible above these two but was not successfully sequenced), while lane 3 contained no template cDNA. The vertical grey line indicates where an irrelevant region of gel was removed using Photoshop 6.0 (Adobe). B) The 3' UTR of lungfish rh1. Two sequenced polyA signals are present (bold and italicised), both of which can induce polyadenylation producing two differently sized Rh1 transcripts.
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Figure 2: Multiple transcripts of rh1 occur in the Australian lungfish retina. A) 3' RACE PCR products from lungfish rh1 cDNA. Arrows point to two potential transcripts differing in size in lane 2 (a third, faint band is also visible above these two but was not successfully sequenced), while lane 3 contained no template cDNA. The vertical grey line indicates where an irrelevant region of gel was removed using Photoshop 6.0 (Adobe). B) The 3' UTR of lungfish rh1. Two sequenced polyA signals are present (bold and italicised), both of which can induce polyadenylation producing two differently sized Rh1 transcripts.

Mentions: Two rh1 polyA transcripts were successfully sequenced from Neoceratodus forsteri (a third, faint band was also visible but not sequenced, fig. 2) and sequence analysis shows that the two polyA signals are present in a tandem array within the 3' UTR. This finding adds to increasing evidence that multiple transcripts arising from tandem polyA signals are a common, yet little studied, feature of rh1 genes [28-31]. The longer lungfish rh1 transcript shows a more intense band than the shorter transcripts (Fig. 2A), which could be a result of differential stability of the transcripts. There is evidence that some genes contain regulatory elements between polyA sites, which influence the stability of the longer mRNA transcript [32]. rh1 transcript levels in mice change according to circadian rhythms, possibly due to inherent transcript stability or even a circadian variation in competing mRNA processing factors and therefore site preference [33]. The use of alternative polyA transcripts as a mechanism of rh1 gene regulation therefore evolved early in vertebrate evolution and has been selectively maintained in mammals.


Visual pigments in a living fossil, the Australian lungfish Neoceratodus forsteri.

Bailes HJ, Davies WL, Trezise AE, Collin SP - BMC Evol. Biol. (2007)

Multiple transcripts of rh1 occur in the Australian lungfish retina. A) 3' RACE PCR products from lungfish rh1 cDNA. Arrows point to two potential transcripts differing in size in lane 2 (a third, faint band is also visible above these two but was not successfully sequenced), while lane 3 contained no template cDNA. The vertical grey line indicates where an irrelevant region of gel was removed using Photoshop 6.0 (Adobe). B) The 3' UTR of lungfish rh1. Two sequenced polyA signals are present (bold and italicised), both of which can induce polyadenylation producing two differently sized Rh1 transcripts.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2194722&req=5

Figure 2: Multiple transcripts of rh1 occur in the Australian lungfish retina. A) 3' RACE PCR products from lungfish rh1 cDNA. Arrows point to two potential transcripts differing in size in lane 2 (a third, faint band is also visible above these two but was not successfully sequenced), while lane 3 contained no template cDNA. The vertical grey line indicates where an irrelevant region of gel was removed using Photoshop 6.0 (Adobe). B) The 3' UTR of lungfish rh1. Two sequenced polyA signals are present (bold and italicised), both of which can induce polyadenylation producing two differently sized Rh1 transcripts.
Mentions: Two rh1 polyA transcripts were successfully sequenced from Neoceratodus forsteri (a third, faint band was also visible but not sequenced, fig. 2) and sequence analysis shows that the two polyA signals are present in a tandem array within the 3' UTR. This finding adds to increasing evidence that multiple transcripts arising from tandem polyA signals are a common, yet little studied, feature of rh1 genes [28-31]. The longer lungfish rh1 transcript shows a more intense band than the shorter transcripts (Fig. 2A), which could be a result of differential stability of the transcripts. There is evidence that some genes contain regulatory elements between polyA sites, which influence the stability of the longer mRNA transcript [32]. rh1 transcript levels in mice change according to circadian rhythms, possibly due to inherent transcript stability or even a circadian variation in competing mRNA processing factors and therefore site preference [33]. The use of alternative polyA transcripts as a mechanism of rh1 gene regulation therefore evolved early in vertebrate evolution and has been selectively maintained in mammals.

Bottom Line: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri.Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes.However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biomedical Sciences, University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. helena.bailes@manchester.ac.uk

ABSTRACT

Background: One of the greatest challenges facing the early land vertebrates was the need to effectively interpret a terrestrial environment. Interpretation was based on ocular adaptations evolved for an aquatic environment millions of years earlier. The Australian lungfish Neoceratodus forsteri is thought to be the closest living relative to the first terrestrial vertebrate, and yet nothing is known about the visual pigments present in lungfish or the early tetrapods.

Results: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri. Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes. However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

Conclusion: The presence of four cone pigments in Australian lungfish suggests that the earliest tetrapods would have had a colorful view of their terrestrial environment.

Show MeSH
Related in: MedlinePlus