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Recent Loss of Vitamin C Biosynthesis Ability in Bats
Jie Cui, Xinpu Yuan, Lina Wang, Gareth Jones,Shuyi Zhang mail
Published: November 01, 2011
DOI: 10.1371/journal.pone.00271
Abstract
The traditional assumption that bats cannot synthesize vitamin C (Vc) has been challenged recently. We have previously shown that two Old World bat species (Rousettus leschenaultii and Hipposideros armiger) have functional L-gulonolactone oxidase (GULO), an enzyme that catalyzes the last step of Vc biosynthesis de novo. Given the uncertainties surrounding when and how bats lost GULO function, exploration of gene evolutionary patterns is needed. We therefore sequenced GULO genes from 16 bat species in 5 families, aiming to establish their evolutionary histories. In five cases we identified pseudogenes for the first time, including two cases in the genus Pteropus (P. pumilus and P. conspicillatus) and three in family Hipposideridae (Coelops frithi, Hipposideros speoris, and H. bicolor). Evolutionary analysis shows that the Pteropus clade has the highest ω ratio and has been subjected to relaxed selection for less than 3 million years. Purifying selection acting on the pseudogenized GULO genes of roundleaf bats (family Hipposideridae) suggests they have lost the ability to synthesize Vc recently. Limited mutations in the reconstructed GULO sequence of the ancestor of all bats contrasts with the many mutations in the ancestral sequence of recently emerged Pteropus bats. We identified at least five mutational steps that were then related to clade origination times. Together, our results suggest that bats lost the ability to biosynthesize vitamin C recently by exhibiting stepwise mutation patterns during GULO evolution that can ultimately lead to pseudogenization.
Citation: Cui J, Yuan X, Wang L, Jones G, Zhang S (2011) Recent Loss of Vitamin C Biosynthesis Ability in Bats. PLoS ONE 6(11): e27114. doi:10.1371/journal.pone.0027114
Editor: Brock Fenton, University of Western Ontario, Canada
Received: July 21, 2011; Accepted: October 10, 2011; Published: November 1, 2011
Copyright: ? 2011 Cui et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by the Chinese National Science Foundation (Grant No. 31172077) to S.Z., the PhD Program Scholarship Fund of East China Normal University (2010044) to J.C., and a Biotechnology and Biological Sciences Research Council China Partnering Award to G.J. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Vitamin C (Vc), or L-ascorbic acid is a water-soluble vitamin that is an essential nutrient impotant in animal metabolism. Vc is involved in tissue growth and repair, and also functions as an antioxidant to block damage caused by free radicals. It is also a cofactor in enzymatic reactions that are catalyzed by Cu+-dependent monooxygenases and Fe2+-dependent dioxygenases [1]. Vc is required in the diet of all vertebrates in order to sustain good health [2], and Vc deficiency can lead to potentially fatal scurvy in humans. Most vertebrates can satisfy their Vc requirements by synthesizing it de novo with glucose [3]. However, some mammals, including haplorhine primates and guinea pigs, have lost this ability, and thus have to obtain Vc from their diet [4]. The ability to synthesize Vc has been reported in many ancestral vertebrate lineages [5], [6], suggesting the ability for de novo synthesis is ancient. Moreover, there is an apparent transition of the organs used for the biosynthesis of Vc during evolution, from the kidney of reptiles to the liver of mammals [7].
The ability to synthesize Vc has been lost independently several times in vertebrates e.g. in some fishes [5], in some passeriform birds [7], in some bats [8], in guinea pigs [10] and in primates of the suborder Haplorrhini (e.g. monkeys, apes and humans) [7], [9]?[10]. All of these species lack activity of L-Gulonolactone oxidase (GULO) in their livers (or kidneys) to catalyze the last step of the Vc synthesis pathway so that they need to compensate by obtaining Vc from their food [8]?[10]. The gene encoding GULO in guinea pigs and humans has become a pseudogene [11], [12].
Our recent research has challenged the traditional opinion that bats cannot synthesize Vc [8], [13] by showing that GULO genes in two species (Rousettus leschenaultii and Hipposideros armiger) are still in their intact forms and can produce functional proteins [14]. Bats are perhaps in the process of large-scale loss of Vc biosynthesis ability [14], and show varying degrees of lack of GULO function. For example, the genera Pteropus and Rousettus belong to the same chiropteran family (Pteropodidae), and although the former has lost the ability to synthesize Vc, the latter retains it [14].
Our previous study on Vc synthesis in bats raises the question-what is the evolutionary pattern that shapes bat GULO evolution in bats? Given the uncertainty of when and how bats lost GULO gene function, it is important to sequence GULO genes of more bat to explore patterns of GULO evolution. In this study, we therefore sequenced the GULO genes of 16 bat species and aimed to reconstruct bat GULO evolutionary history. Using ancestral reconstructions, we infer stepwise mutation patterns showing how bats may have lost GULO function.
...
Discussion
As GULO is present in all major vertebrate lineages except some bats (most of these being New World species) [8], anthropoid primates [12], [26], guinea pigs [11], some passerine birds [27], and some fishes [5], such loss-of-function is neither related to broad phylogenetic affiliations nor to diet [28]. Some researchers have even proposed that the loss of Vc synthesis is associated with higher speciation rates because of higher mutation rates [29], which seems unlikely and which has not been tested formally.
Having successfully cloned bat GULO genes from 16 species, we carried out detailed evolutionary analyses. Our results show a range of forms of the GULO gene in bats. Combined with our earlier functional studies [14], we identify the following conditions: 1) pseudogenes that will have lost function, as seen in some Pteropus and hipposiderid species, 2) intact genes that functional studies showed loss of function in Vc synthesis (e.g. Pteropus vampyrus), 3) intact genes that maintain some ability to synthesize Vc (Rousettus leschenaultii and Hipposdieros armiger). We found that strong purifying selection has shaped non-Pteropus bat pseudogenes, suggesting these bats are in early stages of loss in their ability to synthesize Vc. In the family Hipposideridae some species possess pseudogenes that show only small changes from the intact and functional genes of their close relatives. Together with the evidence for puryifying selection our results suggest that Vc function has been lost recently in hipposiderid species showing pseudogenized GULO. Relaxed selection acting on Pteropus bat GULO suggests that bats in this genus lost the ability to synthesize Vc within the past 3 mya [25]. Thus we infer that pseudogenization of bat GULO evolved recently.
Ancestral reconstruction clearly shows a stepwise accumulating mutation pattern during bat GULO evolution. By mapping each mutation step with theorigination times of each clade (figure 4), we surprisingly found that the more ancient the species are, the less mutations they had accumulated; conversely, more recently evolved bats often accumulated many mutations, which supports our hypothesis that Vc synthesis involving GULO is gradually becoming less important in bats. The ancestral bats were therefore presumably able to biosynthesize Vc, and during evolution, GULO gene function is gradually becoming redundant.
In conclusion, our study shows that bats are beginning to lose their ability to biosynthesis vitamin C and some have lost this ability in no more than 3 mya. During gene degeneration, stepwise mutation patterns are evident and these are important mechanisms leading eventually to pseudogenization...
Jie Cui, Xinpu Yuan, Lina Wang, Gareth Jones,Shuyi Zhang mail
Published: November 01, 2011
DOI: 10.1371/journal.pone.00271
Abstract
The traditional assumption that bats cannot synthesize vitamin C (Vc) has been challenged recently. We have previously shown that two Old World bat species (Rousettus leschenaultii and Hipposideros armiger) have functional L-gulonolactone oxidase (GULO), an enzyme that catalyzes the last step of Vc biosynthesis de novo. Given the uncertainties surrounding when and how bats lost GULO function, exploration of gene evolutionary patterns is needed. We therefore sequenced GULO genes from 16 bat species in 5 families, aiming to establish their evolutionary histories. In five cases we identified pseudogenes for the first time, including two cases in the genus Pteropus (P. pumilus and P. conspicillatus) and three in family Hipposideridae (Coelops frithi, Hipposideros speoris, and H. bicolor). Evolutionary analysis shows that the Pteropus clade has the highest ω ratio and has been subjected to relaxed selection for less than 3 million years. Purifying selection acting on the pseudogenized GULO genes of roundleaf bats (family Hipposideridae) suggests they have lost the ability to synthesize Vc recently. Limited mutations in the reconstructed GULO sequence of the ancestor of all bats contrasts with the many mutations in the ancestral sequence of recently emerged Pteropus bats. We identified at least five mutational steps that were then related to clade origination times. Together, our results suggest that bats lost the ability to biosynthesize vitamin C recently by exhibiting stepwise mutation patterns during GULO evolution that can ultimately lead to pseudogenization.
Citation: Cui J, Yuan X, Wang L, Jones G, Zhang S (2011) Recent Loss of Vitamin C Biosynthesis Ability in Bats. PLoS ONE 6(11): e27114. doi:10.1371/journal.pone.0027114
Editor: Brock Fenton, University of Western Ontario, Canada
Received: July 21, 2011; Accepted: October 10, 2011; Published: November 1, 2011
Copyright: ? 2011 Cui et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was supported by the Chinese National Science Foundation (Grant No. 31172077) to S.Z., the PhD Program Scholarship Fund of East China Normal University (2010044) to J.C., and a Biotechnology and Biological Sciences Research Council China Partnering Award to G.J. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Introduction
Vitamin C (Vc), or L-ascorbic acid is a water-soluble vitamin that is an essential nutrient impotant in animal metabolism. Vc is involved in tissue growth and repair, and also functions as an antioxidant to block damage caused by free radicals. It is also a cofactor in enzymatic reactions that are catalyzed by Cu+-dependent monooxygenases and Fe2+-dependent dioxygenases [1]. Vc is required in the diet of all vertebrates in order to sustain good health [2], and Vc deficiency can lead to potentially fatal scurvy in humans. Most vertebrates can satisfy their Vc requirements by synthesizing it de novo with glucose [3]. However, some mammals, including haplorhine primates and guinea pigs, have lost this ability, and thus have to obtain Vc from their diet [4]. The ability to synthesize Vc has been reported in many ancestral vertebrate lineages [5], [6], suggesting the ability for de novo synthesis is ancient. Moreover, there is an apparent transition of the organs used for the biosynthesis of Vc during evolution, from the kidney of reptiles to the liver of mammals [7].
The ability to synthesize Vc has been lost independently several times in vertebrates e.g. in some fishes [5], in some passeriform birds [7], in some bats [8], in guinea pigs [10] and in primates of the suborder Haplorrhini (e.g. monkeys, apes and humans) [7], [9]?[10]. All of these species lack activity of L-Gulonolactone oxidase (GULO) in their livers (or kidneys) to catalyze the last step of the Vc synthesis pathway so that they need to compensate by obtaining Vc from their food [8]?[10]. The gene encoding GULO in guinea pigs and humans has become a pseudogene [11], [12].
Our recent research has challenged the traditional opinion that bats cannot synthesize Vc [8], [13] by showing that GULO genes in two species (Rousettus leschenaultii and Hipposideros armiger) are still in their intact forms and can produce functional proteins [14]. Bats are perhaps in the process of large-scale loss of Vc biosynthesis ability [14], and show varying degrees of lack of GULO function. For example, the genera Pteropus and Rousettus belong to the same chiropteran family (Pteropodidae), and although the former has lost the ability to synthesize Vc, the latter retains it [14].
Our previous study on Vc synthesis in bats raises the question-what is the evolutionary pattern that shapes bat GULO evolution in bats? Given the uncertainty of when and how bats lost GULO gene function, it is important to sequence GULO genes of more bat to explore patterns of GULO evolution. In this study, we therefore sequenced the GULO genes of 16 bat species and aimed to reconstruct bat GULO evolutionary history. Using ancestral reconstructions, we infer stepwise mutation patterns showing how bats may have lost GULO function.
...
Discussion
As GULO is present in all major vertebrate lineages except some bats (most of these being New World species) [8], anthropoid primates [12], [26], guinea pigs [11], some passerine birds [27], and some fishes [5], such loss-of-function is neither related to broad phylogenetic affiliations nor to diet [28]. Some researchers have even proposed that the loss of Vc synthesis is associated with higher speciation rates because of higher mutation rates [29], which seems unlikely and which has not been tested formally.
Having successfully cloned bat GULO genes from 16 species, we carried out detailed evolutionary analyses. Our results show a range of forms of the GULO gene in bats. Combined with our earlier functional studies [14], we identify the following conditions: 1) pseudogenes that will have lost function, as seen in some Pteropus and hipposiderid species, 2) intact genes that functional studies showed loss of function in Vc synthesis (e.g. Pteropus vampyrus), 3) intact genes that maintain some ability to synthesize Vc (Rousettus leschenaultii and Hipposdieros armiger). We found that strong purifying selection has shaped non-Pteropus bat pseudogenes, suggesting these bats are in early stages of loss in their ability to synthesize Vc. In the family Hipposideridae some species possess pseudogenes that show only small changes from the intact and functional genes of their close relatives. Together with the evidence for puryifying selection our results suggest that Vc function has been lost recently in hipposiderid species showing pseudogenized GULO. Relaxed selection acting on Pteropus bat GULO suggests that bats in this genus lost the ability to synthesize Vc within the past 3 mya [25]. Thus we infer that pseudogenization of bat GULO evolved recently.
Ancestral reconstruction clearly shows a stepwise accumulating mutation pattern during bat GULO evolution. By mapping each mutation step with theorigination times of each clade (figure 4), we surprisingly found that the more ancient the species are, the less mutations they had accumulated; conversely, more recently evolved bats often accumulated many mutations, which supports our hypothesis that Vc synthesis involving GULO is gradually becoming less important in bats. The ancestral bats were therefore presumably able to biosynthesize Vc, and during evolution, GULO gene function is gradually becoming redundant.
In conclusion, our study shows that bats are beginning to lose their ability to biosynthesis vitamin C and some have lost this ability in no more than 3 mya. During gene degeneration, stepwise mutation patterns are evident and these are important mechanisms leading eventually to pseudogenization...
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