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Dinosaur ancestor's vision possibly nocturnal. Source-Rockefeller University
A recreation of 240-million-year-old protein indicates that the dinosaurÃÂs ancestors may have had nocturnal vision. Researchers at the Howard Hughes Medical Institute at Rockefeller University and Yale University recreated a functional pigment called rhodopsin in a test tube by inferring the animalÃÂs protein sequence. The sequence allowed the archosaurs ("ruling reptiles"), direct ancestors to dinosaurs, to see in dim light.
The findings, published in SeptemberÃÂs issue of Molecular Biology and Evolution, provide a peek into a protein that has been hidden for 240 million years. Consequently, scientists have an opportunity to analyze the evolution of the structure and function of vision pigment, as well as other molecules that are biologically significant. As reported in a Rockefeller University news release, "Visual pigments trigger the critical first step in the biochemical cascade of vision in humans and other animals and obviously were present in now extinct species," says senior author Thomas P. Sakmar, M.D., head of Rockefeller University's Laboratory of Molecular Biology and Biochemistry. "Recreating the inferred visual pigments of the archosaur ancestors in the laboratory should be a first step toward better understanding what they could see -- and not see," adds Sakmar.
The findings indicate that archosaurs may have had a class of visual pigments that would sustain noturnal vision. "This is consistent with the intriguing though controversial possibility that nocturnal, not diurnal, life histories may have been the ancestral state in amniotes, which are birds, reptiles and mammals whose embryos are protected with a fluid-filled sac," Belinda S.W. Chang, Ph.D., first author and research assistant professor at Rockefeller, explained in the news release. "We are doing further biochemical studies on this recreated pigment to clarify this issue."
Using current databases and maximum liklihood phylogenetic statistical methods, Chang was able to infer the DNA sequences most likely for the archosaurÃÂs rhodopsin. "From the databases, we pulled rhodopsin gene sequences for such animals as dogs, rats, cows, birds, teleost fish, eels and amphibians. Then we aligned them,î Chang explained. "Using our knowledge of how these vertebrates are related to each other, the sequence alignment and a model of how often certain types of genetic changes occur over time, we calculated the most likely gene sequence."
The team took the inferred DNA sequence, and reconstructed a gene that was inserted into the tissue cell cultures of a mammal- standard practice for producing rhodopsin in the laboratory. Predictably, the gene directed the cells to produce rhodopsin in the mammalian tissue.
The team next looked at weather the artificially generated rhodopsin resembled ìauthenticî rhodopsin. The proof was in the pudding when the researchers confirmed that it binds to a molecule called 11-cis--retinal, which gives a distinctive absorption spectrum in the visible range and activates in response to light.
Humans have three types of visual receptors, which are sensitive to red, green and blue light- making it possible to see color. However, the fundamental molecule involved in all of these is a type of vitamin A called 11-cis-retinal. "We found it does bind 11-cis-retinal and produces a very beautiful absorption spectrum with a maximal sensitivity at slightly red-shifted wavelengths when compared with our control in the laboratory, which is bovine rhodopsin," explained Chang in the news release. "Although we don't know why the archosaur rhodopsin is shifted toward the red end of the spectrum, it is closest to the spectrum measured for bird rhodopsins."
Finally, the last piece of evidence proving that the team had produced functional rhodopsin showed that the activated form of the pigment interacted with the second messenger called the G protein transducin. "Using a technique that measures the increase of fluorescence in the G protein transducin upon activation, we found, strikingly, that the archosaur rhodopsin activated transducin in a similar time frame as bovine rhodopsin, which is very good at activating transducin," said Chang. "Characteristics of rhodopsin determine characteristics of vision directly, so from this we can infer things about how archosaurs actually saw at night and under dim light conditions," adds Chang. "We can infer that their night vision was, at least on the level of their rhodopsin and its activation of G protein, basically as good as mammalian rhodopsin, which is surprising since mammals went through a nocturnal phase."
A recreation of 240-million-year-old protein indicates that the dinosaurÃÂs ancestors may have had nocturnal vision. Researchers at the Howard Hughes Medical Institute at Rockefeller University and Yale University recreated a functional pigment called rhodopsin in a test tube by inferring the animalÃÂs protein sequence. The sequence allowed the archosaurs ("ruling reptiles"), direct ancestors to dinosaurs, to see in dim light.
The findings, published in SeptemberÃÂs issue of Molecular Biology and Evolution, provide a peek into a protein that has been hidden for 240 million years. Consequently, scientists have an opportunity to analyze the evolution of the structure and function of vision pigment, as well as other molecules that are biologically significant. As reported in a Rockefeller University news release, "Visual pigments trigger the critical first step in the biochemical cascade of vision in humans and other animals and obviously were present in now extinct species," says senior author Thomas P. Sakmar, M.D., head of Rockefeller University's Laboratory of Molecular Biology and Biochemistry. "Recreating the inferred visual pigments of the archosaur ancestors in the laboratory should be a first step toward better understanding what they could see -- and not see," adds Sakmar.
The findings indicate that archosaurs may have had a class of visual pigments that would sustain noturnal vision. "This is consistent with the intriguing though controversial possibility that nocturnal, not diurnal, life histories may have been the ancestral state in amniotes, which are birds, reptiles and mammals whose embryos are protected with a fluid-filled sac," Belinda S.W. Chang, Ph.D., first author and research assistant professor at Rockefeller, explained in the news release. "We are doing further biochemical studies on this recreated pigment to clarify this issue."
Using current databases and maximum liklihood phylogenetic statistical methods, Chang was able to infer the DNA sequences most likely for the archosaurÃÂs rhodopsin. "From the databases, we pulled rhodopsin gene sequences for such animals as dogs, rats, cows, birds, teleost fish, eels and amphibians. Then we aligned them,î Chang explained. "Using our knowledge of how these vertebrates are related to each other, the sequence alignment and a model of how often certain types of genetic changes occur over time, we calculated the most likely gene sequence."
The team took the inferred DNA sequence, and reconstructed a gene that was inserted into the tissue cell cultures of a mammal- standard practice for producing rhodopsin in the laboratory. Predictably, the gene directed the cells to produce rhodopsin in the mammalian tissue.
The team next looked at weather the artificially generated rhodopsin resembled ìauthenticî rhodopsin. The proof was in the pudding when the researchers confirmed that it binds to a molecule called 11-cis--retinal, which gives a distinctive absorption spectrum in the visible range and activates in response to light.
Humans have three types of visual receptors, which are sensitive to red, green and blue light- making it possible to see color. However, the fundamental molecule involved in all of these is a type of vitamin A called 11-cis-retinal. "We found it does bind 11-cis-retinal and produces a very beautiful absorption spectrum with a maximal sensitivity at slightly red-shifted wavelengths when compared with our control in the laboratory, which is bovine rhodopsin," explained Chang in the news release. "Although we don't know why the archosaur rhodopsin is shifted toward the red end of the spectrum, it is closest to the spectrum measured for bird rhodopsins."
Finally, the last piece of evidence proving that the team had produced functional rhodopsin showed that the activated form of the pigment interacted with the second messenger called the G protein transducin. "Using a technique that measures the increase of fluorescence in the G protein transducin upon activation, we found, strikingly, that the archosaur rhodopsin activated transducin in a similar time frame as bovine rhodopsin, which is very good at activating transducin," said Chang. "Characteristics of rhodopsin determine characteristics of vision directly, so from this we can infer things about how archosaurs actually saw at night and under dim light conditions," adds Chang. "We can infer that their night vision was, at least on the level of their rhodopsin and its activation of G protein, basically as good as mammalian rhodopsin, which is surprising since mammals went through a nocturnal phase."
