The fate of duplicated major histocompatibility complex class Ia genes in a dodecaploid amphibian, Xenopus ruwenzoriensis

Sammut, Bénédicte; Marcuz, Anne; Pasquier, Louis Du

doi:10.1002/1521-4141(200206)32:6<1593::aid-immu1593>3.0.co;2-6

Cited by 22 publications

(14 citation statements)

References 39 publications

(50 reference statements)

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“…displays polysomic inheritance and expresses multiple class I paralogs (Sammut et al, 2002). Frogs, in general, show disproportionately high rates of polyploid speciation relative to all vertebrates, with some of the best-known examples occurring in the Hylidae (Haddad et al, 1994;Ptacek et al, 1994), the family to which A. callidryas and S. phaeota belong.…”

Section: Discussionmentioning

confidence: 99%

Genetic diversity of MHC class I loci in six non-model frogs is shaped by positive selection and gene duplication

et al. 2012

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Comparative studies of major histocompatibility complex (MHC) genes across vertebrate species can reveal the evolutionary processes that shape the structure and function of immune regulatory proteins. In this study, we characterized MHC class I sequences from six frog species representing three anuran families (Hylidae, Centrolenidae and Ranidae). Using cDNA from our focal species, we amplified a total of 79 unique sequences spanning exons 2-4 that encode the extracellular domains of the functional alpha chain protein. We compared intra-and interspecific nucleotide and amino-acid divergence, tested for recombination, and identified codon sites under selection by estimating the rate of non-synonymous to synonymous substitutions with multiple codon-based maximum likelihood methods. We determined that positive (diversifying) selection was acting on specific amino-acid sites located within the domains that bind pathogen-derived peptides. We also found significant signals of recombination across the physical distance of the genes. Finally, we determined that all the six species expressed two or three putative classical class I loci, in contrast to the single locus condition of Xenopus laevis. Our results suggest that MHC evolution in anurans is a dynamic process and that variation in numbers of loci and genetic diversity can exist among taxa. Thus, the accumulation of genetic data for more species will be useful in further characterizing the relative importance of processes such as selection, recombination and gene duplication in shaping MHC loci among amphibian lineages.

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Section: Discussionmentioning

confidence: 99%

Genetic diversity of MHC class I loci in six non-model frogs is shaped by positive selection and gene duplication

et al. 2012

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“…These data provide the potential for a more detailed study of the population genetics of genes under balancing selection in tetraploids. The fate of duplicated genes in polyploids has been investigated for the most widely studied vertebrate cell-cell recognition system (the major histocompatibility locus or MHC: Sammut et al, 2002), but similar studies have not been conducted previously on a plant system. In the diploid selfing species A. thaliana, a functional SI response is produced when SRK/SCR genes are introduced from self-incompatible A. lyrata , suggesting that loss of SI is not due to loss of the downstream machinery but is associated with particular haplotypes at the S-locus.…”

Section: Discussionmentioning

confidence: 99%

Inheritance and dominance of self-incompatibility alleles in polyploid Arabidopsis lyrata

2004

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Natural populations of diploid Arabidopsis lyrata exhibit the sporophytic type of self-incompatibility system characteristic of Brassicaceae, in which complicated dominance interactions among alleles in the diploid parent determine selfrecognition phenotypes of both pollen and stigma. The purpose of this study was to investigate how polyploidy affects this already complex system. One tetraploid population (Arabidopsis lyrata ssp kawasakiana from Japan) showed complete self-compatibility and produced viable selfed progeny for at least three generations subsequent to field collection. In contrast, individuals from a second tetraploid population (A. lyrata ssp petraea from Austria) were strongly self-incompatible (SI). Segregation of SI genotypes in this population followed Mendelian patterns based on a tetrasomic model of inheritance, with two to four alleles per individual, independent segregation of alleles, and little evidence of dosage effects of alleles found in multiple copies. Similar to results from diploids, anomalous compatibility patterns involving particular combinations of individuals occurred at a low frequency in the tetraploids, suggesting altered dominance in certain genetic backgrounds that could be due to the influence of a modifier locus. Overall, dominance relationships among S-alleles in self-incompatible tetraploid families were remarkably similar to those in related diploids, suggesting that this very important and complicated locus has not undergone extensive modification subsequent to polyploidization.

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“…S. tropicalis is the only diploid Xenopus species possessing 20 chromosomes, whereas X. laevis with 36 chromosomes, most likely arose by allotetraploidization from its diploid ancestor. The comparison of S. tropicalis and X. laevis genomes provides an ideal model for examining the fate of duplicated genes because the divergence time between the two species is recent and genetic modifications still seem to be ongoing (Sammut et al, 2002; reviewed in Evans, 2008). Recent analysis using genes in the databases estimated that 25–50% of genes are retained as a double-copy in X. laevis after whole genome duplication, and it is proposed that slowly evolving genes are more likely to be retained as subfunctionalized paralogues, whereas fast evolving genes are more likely subjected to purifying selection (i.e., gene loss of one of the duplicates; Hellsten et al, 2007; Sémon and Wolfe, 2008).…”

Section: New Tools To Study Comparative Immunology In Xenopusmentioning

confidence: 99%

“…This rapid diploidization has been best studied for the MHC (Sato et al, 1993; Shum et al, 1993; Kato et al, 1994), RAG (Evans et al, 2005, Evans, 2007), and the Ig heavy chain (Courtet et al, 2001). In the dodecaploid animal, a maximum of four MHC class I genes were detected, having only two loci (Sammut et al, 2002). In these gene loci, accumulated mutations and deletions of parts of the genes were seen in one of the duplicated genes, presumably in the process of gene silencing.…”

Section: New Tools To Study Comparative Immunology In Xenopusmentioning

confidence: 99%

Comparative and developmental study of the immune system inXenopus

Robert

Ohta

2009

Developmental Dynamics

238

253

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Xenopus laevis is the model of choice for evolutionary, comparative, and developmental studies of immunity, and invaluable research tools including MHC-defined clones, inbred strains, cell lines, and monoclonal antibodies are available for these studies. Recent efforts to use Silurana (Xenopus) tropicalis for genetic analyses have led to the sequencing of the whole genome. Ongoing genome mapping and mutagenesis studies will provide a new dimension to the study of immunity. Here we review what is known about the immune system of X. laevis integrated with available genomic information from S. tropicalis. This review provides compelling evidence for the high degree of similarity and evolutionary conservation between Xenopus and mammalian immune systems. We propose to build a powerful and innovative comparative biomedical model based on modern genetic technologies that takes take advantage of X. laevis and S. tropicalis, as well as the whole Xenopus genus.

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The fate of duplicated major histocompatibility complex class Ia genes in a dodecaploid amphibian, Xenopus ruwenzoriensis

Cited by 22 publications

References 39 publications

Genetic diversity of MHC class I loci in six non-model frogs is shaped by positive selection and gene duplication

Genetic diversity of MHC class I loci in six non-model frogs is shaped by positive selection and gene duplication

Inheritance and dominance of self-incompatibility alleles in polyploid Arabidopsis lyrata

Comparative and developmental study of the immune system inXenopus

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