Dataset Information

Reevaluating Emx gene phylogeny: homopolymeric amino acid tracts as a potential factor obscuring orthology signals in cyclostome genes.

ABSTRACT: BACKGROUND: Vertebrate Emx genes, retained as multiple copies, are expressed in a nested pattern in the early embryonic forebrain and required for its regionalization. This pattern seems to have originated in a vertebrate common ancestor; however, a previous analysis, reporting two lamprey Emx genes, claimed independent Emx gene duplications in both cyclostome (extant jawless fish) and gnathostome (jawed vertebrate) lineages after their divergence. This scenario is neither parsimonious nor consistent with the hypothesis that genome expansion occurred before the cyclostome-gnathostome split, which is supported by recent genome-wide analyses. RESULTS: We isolated and sequenced cDNA of two hagfish Emx genes and performed intensive molecular phylogenetic analyses, including the hagfish and/or lamprey Emx genes. The lamprey genes tended to attract each other in inferred phylogenetic trees, an effect that tended to be relaxed on inclusion of the hagfish genes. The results of these analyses suggest that cyclostome EmxB is orthologous to gnathostome Emx2, which was also supported by conserved synteny. Homopolymeric amino acid (HPAA) tracts represent a remarkable feature of the lamprey Emx sequences, and a comparative genome-wide scan revealed that lamprey proteins exhibit a unique pattern of HPAA tract accumulation. CONCLUSIONS: Our analysis, including hagfish Emx genes, suggests that gene duplications gave rise to Emx1, -2 and -3 before the cyclostome-gnathostome split. We propose that independent HPAA tract accumulations in multiple ancient duplicates, as identified in lamprey Emx gene products, may have led to erroneous identification of gene duplication in the lamprey lineage. Overall, our reanalysis favors the scenario that the nested Emx expression pattern in mouse and lamprey shares a common origin.

SUBMITTER: Noro M

PROVIDER: S-EPMC4464114 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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Reevaluating Emx gene phylogeny: homopolymeric amino acid tracts as a potential factor obscuring orthology signals in cyclostome genes.

Noro Miyuki M Sugahara Fumiaki F Kuraku Shigehiro S

BMC evolutionary biology 20150504

<h4>Background</h4>Vertebrate Emx genes, retained as multiple copies, are expressed in a nested pattern in the early embryonic forebrain and required for its regionalization. This pattern seems to have originated in a vertebrate common ancestor; however, a previous analysis, reporting two lamprey Emx genes, claimed independent Emx gene duplications in both cyclostome (extant jawless fish) and gnathostome (jawed vertebrate) lineages after their divergence. This scenario is neither parsimonious no ...[more]

PMID: 25935411

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Project description:BACKGROUND:Bordetella pertussis, the causative agent of whooping cough, is a highly clonal pathogen of the respiratory tract. Its lack of genetic diversity, relative to many bacterial pathogens, could limit its ability to adapt to a hostile and changing host environment. This limitation might be overcome by phase variation, as observed for other mucosal pathogens. One of the most common mechanisms of phase variation is reversible expansion or contraction of homopolymeric tracts (HPTs). RESULTS:The genomes of B. pertussis and the two closely related species, B. bronchiseptica and B. parapertussis, were screened for homopolymeric tracts longer than expected on the basis of chance, given their nucleotide compositions. Sixty-nine such HPTs were found in total among the three genomes, 74% of which were polymorphic among the three species. Nine HPTs were genotyped in a collection of 90 geographically and temporally diverse B. pertussis strains using the polymerase chain reaction/ligase detection reaction (PCR/LDR) assay. Six HPTs were polymorphic in this collection of B. pertussis strains. Of note, one of these polymorphic HPTs was found in the fimX promoter, where a single base insertion variant was present in seven strains, all of which were isolated prior to introduction of the pertussis vaccine. Transcript abundance of fimX was found to be 3.8-fold lower in strains carrying the longer allele. HPTs in three other genes, tcfA, bapC, and BP3651, varied widely in composition across the strain collection and displayed allelic polymorphism within single cultures. CONCLUSION:Allelic polymorphism at homopolymeric tracts is common within the B. pertussis genome. Phase variability may be an important mechanism in B. pertussis for evasion of the immune system and adaptation to different niches in the human host. High sensitivity and specificity make the PCR/LDR assay a powerful tool for investigating allelic variation at HPTs. Using this method, allelic diversity and phase variation were demonstrated at several B. pertussis loci.

Project description:Homopolymeric amino acids repeats (AARs), which are widespread in proteomes, have often been viewed simply as spacers between protein domains, or even as "junk" sequences with no obvious function but with a potential to cause harm upon expansion as in genetic diseases associated with polyglutamine or polyalanine expansions, including Huntington disease and cleidocranial dysplasia. A growing body of evidence indicates however that at least some AARs can form organized, functional protein structures, and can regulate protein function. In particular, certain AARs can mediate protein-protein interactions, either through homotypic AAR-AAR contacts or through heterotypic contacts with other protein domains. It is still unclear however, whether AARs may have a generalized, proteome-wide role in shaping protein-protein interaction networks. Therefore, we have undertaken here a bioinformatics screening of the human proteome and interactome in search of quantitative evidence of such a role. We first identified the sets of proteins that contain repeats of any one of the 20 amino acids, as well as control sets of proteins chosen at random in the proteome. We then analyzed the connectivity between the proteins of the AAR-containing protein sets and we compared it with that observed in the corresponding control networks. We find evidence for different degrees of connectivity in the different AAR-containing protein networks. Indeed, networks of proteins containing polyglutamine, polyglutamate, polyproline, and other AARs show significantly increased levels of connectivity, whereas networks containing polyleucine and other hydrophobic repeats show lower degrees of connectivity. Furthermore, we observed that numerous protein-protein, -nucleic acid, and -lipid interaction domains are significantly enriched in specific AAR protein groups. These findings support the notion of a generalized, combinatorial role of AARs, together with conventional protein interaction domains, in shaping the interaction networks of the human proteome, and define proteome-wide knowledge that may guide the informed biological exploration of the role of AARs in protein interactions.

Dataset Information

Reevaluating Emx gene phylogeny: homopolymeric amino acid tracts as a potential factor obscuring orthology signals in cyclostome genes.

Publications

Reevaluating Emx gene phylogeny: homopolymeric amino acid tracts as a potential factor obscuring orthology signals in cyclostome genes.

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