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. 2012 Aug 17;12:148.
doi: 10.1186/1471-2148-12-148.

Multiple Functionally Divergent and Conserved Copies of Alpha Tubulin in Bdelloid Rotifers

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Free PMC article

Multiple Functionally Divergent and Conserved Copies of Alpha Tubulin in Bdelloid Rotifers

Isobel Eyres et al. BMC Evol Biol. .
Free PMC article

Abstract

Background: Bdelloid rotifers are microscopic animals that have apparently survived without sex for millions of years and are able to survive desiccation at all life stages through a process called anhydrobiosis. Both of these characteristics are believed to have played a role in shaping several unusual features of bdelloid genomes discovered in recent years. Studies into the impact of asexuality and anhydrobiosis on bdelloid genomes have focused on understanding gene copy number. Here we investigate copy number and sequence divergence in alpha tubulin. Alpha tubulin is conserved and normally present in low copy numbers in animals, but multiplication of alpha tubulin copies has occurred in animals adapted to extreme environments, such as cold-adapted Antarctic fish. Using cloning and sequencing we compared alpha tubulin copy variation in four species of bdelloid rotifers and four species of monogonont rotifers, which are facultatively sexual and cannot survive desiccation as adults. Results were verified using transcriptome data from one bdelloid species, Adineta ricciae.

Results: In common with the typical pattern for animals, monogonont rotifers contain either one or two copies of alpha tubulin, but bdelloid species contain between 11 and 13 different copies, distributed across five classes. Approximately half of the copies form a highly conserved group that vary by only 1.1% amino acid pairwise divergence with each other and with the monogonont copies. The other copies have divergent amino acid sequences that evolved significantly faster between classes than within them, relative to synonymous changes, and vary in predicted biochemical properties. Copies of each class were expressed under the laboratory conditions used to construct the transcriptome.

Conclusions: Our findings are consistent with recent evidence that bdelloids are degenerate tetraploids and that functional divergence of ancestral copies of genes has occurred, but show how further duplication events in the ancestor of bdelloids led to proliferation in both conserved and functionally divergent copies of this gene.

Figures

Figure 1
Figure 1
Saturation curves comparing sampling effort (number of clones sequenced) with number of unique sequences identified.
Figure 2
Figure 2
Alignment of the five major copy types of alpha tubulin in bdelloid rotifers. Classes based on intron presence/absence. Black block = exon, grey block = intron, line = gap. Copy classes 4, 5 and 3 contained variants with introns indicated by a, b and c respectively that were absent in copies otherwise sharing the same intron structure. Numbers of copies in each species are shown: A. ricciae (Ar), A. vaga (Av), M. quadricornifera (Mq) and P. flaviceps (Pf).
Figure 3
Figure 3
Phylogenetic relationships among alpha tubulin copies based on bayesian analysis of the exon nucleotide alignment. Classes defined by intron structure in Figure 2 are indicated by labels on branches. Species are indicated by colours: monogonont outgroups = grey; A. ricciae = red; A. vaga = green; M. quadricornifera = magenta; P. flaviceps = blue. Putative copies homogenized by gene conversion are indicated by curly brackets.
Figure 4
Figure 4
Phylogenetic relationships among alpha tubulin copies based on maximum likelihood analysis of amino acid sequences. Classes defined by intron structure in Figure 2 are indicated by labels on branches. Species are indicated by colours: monogonont outgroups = grey; A. ricciae = red; A. vaga = green; M. quadricornifera = magenta; P. flaviceps = blue.
Figure 5
Figure 5
Variation in indices of predicted protein biochemistry among all alpha tubulin copies, arranged by class. Top = grand average of hydropathy (GRAVY), middle = Instability Index, bottom = isoelectric point (pI).

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References

    1. Poinar GO, Ricci C. Bdelloid Rotifers in Dominican Amber - Evidence for Parthenogenetic Continuity. Experientia. 1992;48(4):408–410.
    1. Segers H. Annotated checklist of the rotifers (Phylum Rotifera), with notes on nomenclature, taxonomy and distribution. Zootaxa. 2007;1564(1564):1–104.
    1. Mark Welch JL, Mark Welch DB, Meselson M. Cytogenetic evidence for asexual evolution of bdelloid rotifers. Proc Natl Acad Sci USA. 2004;101(6):1618–1621. - PMC - PubMed
    1. Ricci C. Anhydrobiotic capabilities of bdelloid rotifers. Hydrobiologia. 1998;388:321–326.
    1. Gladyshev EA, Arkhipova IR. Genome structure of bdelloid rotifers: shaped by asexuality or desiccation? J Hered. 2010;101(Suppl 1):S85–93. - PubMed

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