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      The Genetics of Vitamin C Loss in Vertebrates

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          Abstract

          Vitamin C (ascorbic acid) plays important roles as an anti-oxidant and in collagen synthesis. These important roles, and the relatively large amounts of vitamin C required daily, likely explain why most vertebrate species are able to synthesize this compound. Surprisingly, many species, such as teleost fishes, anthropoid primates, guinea pigs, as well as some bat and Passeriformes bird species, have lost the capacity to synthesize it. Here, we review the genetic bases behind the repeated losses in the ability to synthesize vitamin C as well as their implications. In all cases so far studied, the inability to synthesize vitamin C is due to mutations in the L-gulono-γ-lactone oxidase ( GLO) gene which codes for the enzyme responsible for catalyzing the last step of vitamin C biosynthesis. The bias for mutations in this particular gene is likely due to the fact that losing it only affects vitamin C production. Whereas the GLO gene mutations in fish, anthropoid primates and guinea pigs are irreversible, some of the GLO pseudogenes found in bat species have been shown to be reactivated during evolution. The same phenomenon is thought to have occurred in some Passeriformes bird species. Interestingly, these GLO gene losses and reactivations are unrelated to the diet of the species involved. This suggests that losing the ability to make vitamin C is a neutral trait.

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          Most cited references72

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          Alu repeats and human disease.

          Alu elements have amplified in primate genomes through a RNA-dependent mechanism, termed retroposition, and have reached a copy number in excess of 500,000 copies per human genome. These elements have been proposed to have a number of functions in the human genome, and have certainly had a major impact on genomic architecture. Alu elements continue to amplify at a rate of about one insertion every 200 new births. We have found 16 examples of diseases caused by the insertion of Alu elements, suggesting that they may contribute to about 0.1% of human genetic disorders by this mechanism. The large number of Alu elements within primate genomes also provides abundant opportunities for unequal homologous recombination events. These events often occur intrachromosomally, resulting in deletion or duplication of exons in a gene, but they also can occur interchromosomally, causing more complex chromosomal abnormalities. We have found 33 cases of germ-line genetic diseases and 16 cases of cancer caused by unequal homologous recombination between Alu repeats. We estimate that this mode of mutagenesis accounts for another 0.3% of human genetic diseases. Between these different mechanisms, Alu elements have not only contributed a great deal to the evolution of the genome but also continue to contribute to a significant portion of human genetic diseases. Copyright 1999 Academic Press.
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            Phylogeny and diversification of the largest avian radiation.

            The order Passeriformes ("perching birds") comprises extant species diversity comparable to that of living mammals. For over a decade, a single phylogenetic hypothesis based on DNA-DNA hybridization has provided the primary framework for numerous comparative analyses of passerine ecological and behavioral evolution and for tests of the causal factors accounting for rapid radiations within the group. We report here a strongly supported phylogenetic tree based on two single-copy nuclear gene sequences for the most complete sampling of passerine families to date. This tree is incongruent with that derived from DNA-DNA hybridization, with half of the nodes from the latter in conflict and over a third of the conflicts significant as assessed under maximum likelihood. Our historical framework suggests multiple waves of passerine dispersal from Australasia into Eurasia, Africa, and the New World, commencing as early as the Eocene, essentially reversing the classical scenario of oscine biogeography. The revised history implied by these data will require reassessment of comparative analyses of passerine diversification and adaptation.
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              Cloning and chromosomal mapping of the human nonfunctional gene for L-gulono-gamma-lactone oxidase, the enzyme for L-ascorbic acid biosynthesis missing in man.

              Man is among the exceptional higher animals that are unable to synthesize L-ascorbic acid because of their deficiency in L-gulono-gamma-lactone oxidase, the enzyme catalyzing the terminal step in L-ascorbic acid biosynthesis. In the present study, we isolated a segment of the nonfunctional L-gulono-gamma-lactone oxidase gene from a human genomic library, and mapped it on chromosome 8p21.1 by spot blot hybridization using flow-sorted human chromosomes and fluorescence in situ hybridization. Sequencing analysis indicated that the isolated segment represented a 3'-part of the gene, where the regions corresponding to exons VII, IX, X, and XII of the rat L-gulono-gamma-lactone oxidase gene remain with probable deletion of the regions corresponding to exons VIII and XI. In the identified exon regions were found various anomalous nucleotide changes, such as deletion and insertion of nucleotide(s) and nonconformance to the GT/AG rule at intron/exon boundaries. When the conceptual amino acid sequences deduced from the four exon sequences were compared with the corresponding rat sequences, there were a large number of nonconservative substitutions and also two stop codons. These findings indicate that the human nonfunctional L-gulono-gamma-lactone oxidase gene has accumulated a large number of mutations without selective pressure since it ceased to function during evolution.
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                Author and article information

                Journal
                Curr Genomics
                CG
                Current Genomics
                Bentham Science Publishers Ltd
                1389-2029
                1875-5488
                August 2011
                : 12
                : 5
                : 371-378
                Affiliations
                []Département de Biologie et Centre de Recherche Avancée en Génomique Environnementale, Université d'Ottawa, Ottawa, Ontario, K1N 6N5, Canada
                Author notes
                [* ]Address correspondence to this author at the Département de Biologie, Université d'Ottawa, 30 Marie Curie, Ottawa, Ontario, K1N 6N5, Canada; Tel: (613) 562-5800 ext. 6052; Fax: (613) 562-5486; E-mail: gdrouin@ 123456science.uottawa.ca
                Article
                CG-12-371
                10.2174/138920211796429736
                3145266
                22294879
                36442829-15c5-4f5c-ad23-beccf0525b13
                ©2011 Bentham Science Publishers Ltd.

                This is an open access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.5/), which permits unrestrictive use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 19 April 2011
                : 16 June 2011
                : 24 June 2011
                Categories
                Article

                Genetics
                ascorbic acid,glo gene,vitamin c.,l-gulono-gamma-lactone oxidase,pseudogene,biosynthesis
                Genetics
                ascorbic acid, glo gene, vitamin c., l-gulono-gamma-lactone oxidase, pseudogene, biosynthesis

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