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Mol Biol Evol [journal]
- Insights into the origin of metazoan filopodia and microvilli. [JOURNAL ARTICLE]
- Mol Biol Evol 2013 Jun 14.
Filopodia are fine actin-based cellular projections used for both environmental sensing and cell motility, and they are essential organelles for metazoan cells. In this study we reconstruct the origin of metazoan filopodia and microvilli. We first report on the evolutionary assembly of the filopodial molecular toolkit and show that homologs of many metazoan filopodial components, including fascin and myosin X, were already present in the unicellular or colonial progenitors of metazoans. Furthermore, we find that the actin crosslinking protein fascin localizes to filopodia-like structures and microvilli in the choanoflagellate Salpingoeca rosetta. In addition, homologs of filopodial genes in the holozoan Capsaspora owczarzaki are upregulated in filopodia-bearing cells relative to those that lack them. Therefore, our findings suggest that proteins essential for metazoan filopodia and microvilli are functionally conserved in unicellular and colonial holozoans and that the last common ancestor of metazoans bore a complex and specific filopodial machinery.
- The skeletal proteome of the coral Acropora millepora: the evolution of calcification by cooption and domain shuffling. [JOURNAL ARTICLE]
- Mol Biol Evol 2013 Jun 12.
In corals, biocalcification is a major function that may be drastically affected by Ocean Acidification (OA). Scleractinian corals grow by building up aragonitic exoskeletons that provide support and protection for soft tissues. Although this process has been extensively studied, the molecular basis of biocalcification is poorly understood. Notably lacking is a comprehensive catalogue of the skeleton-occluded proteins - the skeletal organic matrix proteins (SOMPs) that are thought to regulate the mineral deposition.Using a combination of proteomics and transcriptomics, we report the first survey of such proteins in the staghorn coral Acropora millepora. The organic matrix extracted from the coral skeleton was analyzed by mass spectrometry and bioinformatics, enabling the identification of 36 SOMPs. These results provide novel insights into the molecular basis of coral calcification and the macroevolution of metazoan calcifying systems, while establishing a platform for studying the impact of OA at molecular level. Besides secreted proteins, extracellular regions of transmembrane proteins are also present, suggesting a close control of aragonite deposition by the calicoblastic epithelium. In addition to the expected SOMPs (Asp/Glu-rich, galaxins), the skeletal repertoire included several proteins containing known extracellular matrix domains. From an evolutionary perspective, the number of coral-specific proteins is low, many SOMPs having counterparts in the non-calcifying cnidarians. Extending the comparison to the skeletal organic matrix proteomes of other metazoans allowed the identification of a pool of functional domains shared between phyla. The data suggest that cooption and domain shuffling may be general mechanisms by which the trait of calcification has evolved.
- A Phylogenetic Model for the Detection of Epistatic Interactions. [JOURNAL ARTICLE]
- Mol Biol Evol 2013 Jun 6.
Paired epistatic interactions, such as those in the stem regions of RNA, play an important role in many biological processes. However, unlike protein-coding regions, paired epistatic interactions have lacked the appropriate statistical tools for the detection of departures from selective neutrality. Here, a model is presented for the analysis of paired epistatic regions that draws upon the population genetics of the compensatory substitution process to detect the relative strength of natural selection acting against deleterious combinations of alleles. The method is based upon the relative rates of double and single substitution, and can differentiate between nonindependent interactions and negatively epistatic ones. The model is implemented in a fully Bayesian framework for parameter estimation and is demonstrated using a 5S rRNA dataset. In addition to the detection of selection, modeling the double and single substitution processes in this manner inherently accounts for a substantial proportion of rate variation among stem positions.
- Genome-wide analysis reveals origin of transfer RNA genes from tRNA halves. [JOURNAL ARTICLE]
- Mol Biol Evol 2013 Jun 5.
Transfer RNAs (tRNAs) play an important role linking mRNA and amino acids during protein biogenesis. Four types of tRNA genes have been identified in living organisms. However, the evolutionary origin of tRNAs remains largely unknown. In this paper, we conduct a deep sequence analysis of diverse genomes that cover all three domains of life to unveil the evolutionary history of tRNA genes from tRNA halves. tRNA half homologs were detected in diverse organisms, and some of them were expressed in mouse tissues. Continuous tRNA genes have a conserved pattern similar to indels, which is, more closely flanking regions have higher single nucleotide substitution rates, while tRNA half homologs do not have this pattern. In addition, tRNAs tend to break into tRNA halves when tissues are incubated in vitro, the tendency of tRNA to break into tRNA halves may be a "side-effect" of tRNA genes evolving from tRNA halves. These results suggest that modern tRNAs originated from tRNA halves through a repeat element-mediated mechanism. These findings provide insight into the evolutionary origin of tRNA genes.
- Contrasting patterns of evolution of 45S and 5S rDNA families uncover new aspects in the genome constitution of the agronomically important grass Thinopyrum intermedium (Triticeae). [JOURNAL ARTICLE]
- Mol Biol Evol 2013 Jun 4.
We employed sequencing of clones and in situ hybridization (GISH, rDNA-FISH) to characterize both the sequence variation and genomic organization of 45S (herein ITS1-5.8SITS2 region) and 5S (5S gene + non-transcribed spacer) rDNA families in the allohexaploid grass Thinopyrum intermedium. Both rDNA families are organized within several rDNA loci within all three subgenomes of the allohexaploid species. Both families have undergone different patterns of evolution. The 45S rDNA family has evolved in a concerted manner: ITS sequences residing within the arrays of two subgenomes out of three got homogenized towards one major ribotype, while the third subgenome contained a minor proportion of distinct unhomogenized copies. Homogenization mechanisms such as unequal crossover and/or gene conversion were coupled with the loss of certain 45S rDNA loci. Unlike in the 45S family, the data suggest that neither interlocus homogenization among homeologous chromosomes nor locus loss occurred in 5S rDNA. Consistently with other Triticeae, the 5S rDNA family in intermediate wheatgrass comprised two distinct array types - the long- and short-spacer unit classes. Within the long and short units, we distinguished five and three different types, respectively, likely representing homeologous unit classes donated by putative parental species. While the major ITS ribotype corresponds in our phylogenetic analysis to the E-genome species, the minor ribotype corresponds to Dasypyrum. 5S sequences suggested the contributions from Pseudoroegneria, Dasypyrum and Aegilops. The contribution from Aegilops to the intermediate wheatgrass' genome is a new finding with implications in wheat improvement. We discuss rDNA evolution and potential origin of intermediate wheatgrass.
- The evolutionary history of Plasmodium vivax as inferred from mitochondrial genomes: parasite genetic diversity in the Americas. [JOURNAL ARTICLE]
- Mol Biol Evol 2013 Jun 2.
Plasmodium vivax is the most prevalent human malaria parasite in the Americas. Previous studies have contrasted the genetic diversity of parasite populations in the Americas with those in Asia and Oceania, concluding that New World populations exhibit low genetic diversity consistent with a recent introduction. Here we used an expanded sample of complete mitochondrial genome sequences to investigate the diversity of P. vivax in the Americas as well as in other continental populations. We show that the diversity of P. vivax in the Americas is comparable to that in Asia and Oceania, and we identify several divergent clades circulating in South America that may have resulted from independent introductions. In particular, we show that several haplotypes sampled in Venezuela and northeastern Brazil belong to a clade that diverged from the other P. vivax lineages at least 30,000 years ago, albeit not necessarily in the Americas. We propose that, unlike in Asia where human migration increases local genetic diversity, the combined effects of the geographical structure and the low incidence of vivax malaria in the Americas has resulted in patterns of low local, but high regional genetic diversity. This could explain previous views that P. vivax in the Americas has low genetic diversity because these were based on studies carried out in limited areas. Further elucidation of the complex geographical pattern of P. vivax variation will be important both for diversity assessments of genes encoding candidate vaccine antigens and in the formulation of control and surveillance measures aimed at malaria elimination.
- The linkage method: a novel approach for SNP detection and haplotype reconstruction from a single diploid individual using next generation sequence data. [JOURNAL ARTICLE]
- Mol Biol Evol 2013 May 31.
When we sequence a diploid individual, the output actually comprises two genomes: one from the paternal parent and the other from the maternal parent. In this study, we introduce a novel heuristic algorithm for distinguishing SNPs from the two parents and phasing them into haplotypes. The algorithm is unique because it simultaneously performs SNP calling and haplotype phasing. This approach can exploit the linkage information of nearby SNPs, which facilitates the efficient removal of haplotypes that originate from incorrectly mapped short reads. Using simulated data, we demonstrated that our approach increased the accuracy of SNP calls. The haplotype reconstruction performance depended largely on the density of SNPs. Using current next generation sequence technology with a relatively short read length, reasonable performance is expected when this approach is applied to species with an average of five heterozygous sites per 1 kb. The algorithm was implemented as the program "linkSNPs."
- Substrate ambiguous enzymes within the Escherichia coli proteome offer different evolutionary solutions to the same problem. [JOURNAL ARTICLE]
- Mol Biol Evol 2013 May 31.
Many enzymes exhibit some catalytic promiscuity or substrate ambiguity. These weak activities do not affect the fitness of the organism under ordinary circumstances, but can serve as potential evolutionary precursors of new catalytic functions. We wondered whether different proteins with the same substrate ambiguous activity evolve differently under identical selection conditions. Patrick et al. previously showed that three multicopy suppressors, gph, hisB and ytjC, rescue ΔserB Escherichia coli cells from starvation on minimal media. We directed the evolution of variants of Gph, HisB and YtjC that complemented ΔserB more efficiently, and characterized the effects of the amino acid changes, alone and in combination, upon the evolved phosphoserine phosphatase (PSP) activity. Gph and HisB are members of the HAD superfamily of hydrolases, but they adapted through different, kinetically distinguishable, biochemical mechanisms. All of the selected mutations, except N102T in YtjC, proved to be beneficial in isolation. They exhibited a pattern of antagonistic epistasis, as their effects in combination upon the kinetic parameters of the three proteins in reactions with phosphoserine were non-multiplicative. The N102T mutation exhibited sign epistasis, as it was deleterious in isolation but beneficial in the context of other mutations. We also showed that the D57N mutation in the chromosomal copy of hisB is sufficient to suppress the ΔserB deletion. These results in combination show that proteomes can offer multiple mechanistic solutions to a molecular recognition problem.
- "APE-type Non-LTR Retrotransposons of Multicellular Organisms Encode Virus-Like 2A Oligopeptide Sequences Which Mediate Translational Recoding During Protein Synthesis". [JOURNAL ARTICLE]
- Mol Biol Evol 2013 May 31.
2A oligopeptide sequences ('2As') mediate a co-translational recoding event termed 'ribosome skipping'.Previously we demonstrated the activity of 2As (and "2A-like sequences") within a wide range of animal RNA virus genomes and non-LTR retrotransposons (non-LTRs) in the genomes of the unicellular organisms Trypanosoma brucei (Ingi) and T. cruzi (L1Tc). Here we report the presence of 2A-like sequences in the genomes of a wide range of multicellular organisms and, as in the trypanosome genomes, within non-LTRs - clustering in the Rex1, Crack, L2, L2A, CR1 clades, in addition to Ingi. These 2A-like sequences were tested for translational recoding activity and highly active sequences were found within the Rex1, L2, CR1 and Ingi clades. The presence of 2A-like sequences within non-LTRs may represent a method of controlling protein biogenesis, but also shows some correlation with such APE-type non-LTRs encoding one, rather than two, open reading frames (ORFs). Interestingly, such non-LTRs cluster with closely related elements lacking 2A-like recoding elements, but retaining ORF1. Taken together, these observations suggest that acquisition of 2A-like translational recoding sequences may have played a role in the evolution of these elements.
- Timing and consequences of recurrent polyploidy in meadow-rues (Thalictrum, Ranunculaceae). [JOURNAL ARTICLE]
- Mol Biol Evol 2013 May 31.
The discovery of ancient whole genome duplications in eukaryotic lineages has renewed the interest in polyploidy and its effects on the diversification of organisms. Polyploidy has large-scale effects on both genotype and phenotype, and has been linked to the evolution of genome size, dioecy, and changes in ecological interactions, such as pollinator visitation. Here, we take a molecular systematics approach to examine the evolution of polyploidy in the plant genus Thalictrum (Ranunculaceae) and test its correlation to changes in genome size, sexual system and pollination mode. Thalictrum is an ideal study system due to its extensive ploidy range and floral diversity. Phylogenetic analyses were used for character reconstructions, correlation tests, and dating estimates. Our results suggest that polyploidization occurred frequently and recently in the evolution of Thalictrum, mostly within the last 10.6-5.8 my, coinciding with the diversification of particular clades. In spite of an overall trend of genomic downsizing accompanying polyploidy in angiosperms and proportional increases observed at finer scales, our genome size estimates for Thalictrum show no correlation with chromosome number. Instead, we observe genomic expansion in diploids and genomic contraction in polyploids with increased age. Additionally, polyploidy is not correlated with dioecy in Thalictrum; therefore, other factors must have influenced the evolution of separate sexes in this group. A novel finding from our study is the association of polyploidy with shifts to wind pollination, in particular, during a time period of global cooling and mountain uplift in the Americas.