Phylogenetic relationships of the Wolbachia of nematodes and arthropods

Wolbachia are well known as bacterial symbionts of arthropods, where they are reproductive parasites, but have also been described from nematode hosts, where the symbiotic interaction has features of mutualism. The majority of arthropod Wolbachia belong to clades A and B, while nematode Wolbachia mostly belong to clades C and D, but these relationships have been based on analysis of a small number of genes. To investigate the evolution and relationships of Wolbachia symbionts we have sequenced over 70 kb of the genome of wOvo, a Wolbachia from the human-parasitic nematode Onchocerca volvulus, and compared the genes identified to orthologues in other sequenced Wolbachia genomes. In comparisons of conserved local synteny, we find that wBm, from the nematode Brugia malayi, and wMel, from Drosophila melanogaster, are more similar to each other than either is to wOvo. Phylogenetic analysis of the protein-coding and ribosomal RNA genes on the sequenced fragments supports reciprocal monophyly of nematode and arthropod Wolbachia. The nematode Wolbachia did not arise from within the A clade of arthropod Wolbachia, and the root of the Wolbachia clade lies between the nematode and arthropod symbionts. Using the wOvo sequence, we identified a lateral transfer event whereby segments of the Wolbachia genome were inserted into the Onchocerca nuclear genome. This event predated the separation of the human parasite O. volvulus from its cattle-parasitic sister species, O. ochengi. The long association between filarial nematodes and Wolbachia symbionts may permit more frequent genetic exchange between their genomes

Early smoking initiation and nicotine dependence in a cohort of young adults

We examined the extent to which nicotine dependence and daily smoking might vary by age at first cigarette. The potential confounding effects of sex, race and history of childhood behaviour problems were examined as well. A sample of 1200 was randomly selected from the subset of 21-30-year-old members of a large HMO in the Detroit SMSA; 1007 (84%) agreed to participate. Personal interviews were conducted in respondents' homes, using the NIMH-DIS to elicit information on DSM-III-R diagnoses, including nicotine dependence. Controlling for sex and race, persons who smoked their first cigarette at 14 to 16 years of age were 1.6 times more likely to become dependent than those who initiated smoking at an older age (P = 0.03). The association was unchanged when history of childhood behaviour problems was also controlled. Smoking initiation before age 14 was not associated with increased probability of dependence. Persons who initiated smoking before age 14 had a longer lag time to daily smoking and a lower likelihood of progressing to daily smoking, compared to persons who initiated smoking later on. The findings suggest that, among persons who have ever smoked, there might be two distinct groups in whom the chances of developing dependence are considerably reduced. The first comprises persons who delayed first use until age 17. The second comprises persons who smoked their first cigarette before age 14, a group in whom the progression to daily smoking might be markedly slower than in persons who initiated smoking when they were older.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30589/1/0000226.pd

Examination of a Mineral Specimen from Archaeological Excavations at Quail Creek, Sahuarita, Arizona

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Synteny Comparisons between <i>w</i>Ovo, <i>w</i>Mel, and <i>w</i>Bm

<p>Cartoons represent the conservation of local synteny between the sequenced <i>w</i>Ovo fragments (OW1 to OW5) and the orthologous regions of the genomes of <i>w</i>Bm and <i>w</i>Mel. Genes are shown by small arrowed boxes, but are not drawn to scale. Double diagonal lines show breaks in synteny, and curled arrows show inversions of orientation.</p

A Fragment of a <i>Wolbachia</i> Genome in the O. volvulus Nuclear Genome

<div><p>(A) Sequence alignment of a region upstream of the O. volvulus TATA box–binding protein gene from O. volvulus from Mali (residues 130 to 628 of GenBank accession L13731) and O. volvulus from Ghana (this work), and the orthologous insertion from O. ochengi. These nuclear sequences are aligned to fragments of two different genes from <i>Wolbachia</i> genomes: (1) <i>w</i>Ovo OW4-C (residues 1290 to 1087 of the open reading frame) and the corresponding <i>w</i>Ooc gene, and (2) <i>w</i>Ovo OW2-J (a phosphomannomutase [pmm]; residues 252 to 443 of the open reading frame) and the corresponding fragments from the <i>w</i>Ooc, <i>w</i>Mel, and <i>w</i>Bm orthologues. While <i>w</i>Ovo OW4-C does have homologues in <i>w</i>Mel and <i>w</i>Bm, the region of the <i>w</i>Ovo gene that aligns to the O. volvulus nuclear sequence is very poorly conserved. Inserted gaps are indicated by a dash. Residues identical in >50% of the aligned sequences are shaded.</p><p>(B and C) PCR verification of the presence of the <i>Wolbachia</i>-like gene fragments in O. volvulus and its close relative <i>O. ochengi.</i> Ethidium-bromide-stained gels are shown with lanes M, DNA size markers; 1, 2, 3, and 4, single-primer controls for the primers TATA_Phos, TATA_OW4C, Phos, and OW4C, respectively (see <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.0020094#ppat-0020094-t001" target="_blank">Table 1</a> for primer sequences); 5, PCR product of <i>w</i>Ovo phosphomannomutase (primers TATA_Phos and Phos); 6, PCR product of <i>w</i>Ovo OW4-C (primers TATA_OW4C and OW4C); and 7, PCR product of the <i>Onchocerca</i> genomic insertion (primers TATA_Phos and TATA_OW4C). In (B) the target was O. volvulus genomic DNA, while in (C) the target was O. ochengi genomic DNA.</p></div

A <i>Clp</i>A Pseudogene in <i>w</i>Ovo Has Many Inactivating Mutations

<p>An alignment of the nucleotide sequences of <i>Clp</i>A from <i>w</i>Mel (a functional gene) and <i>w</i>Bm (a pseudogene, inactivated by mutations that generate two in-frame stop codons; otherwise intact), and the partial gene identified from <i>w</i>Ovo from fragment OW5. The <i>w</i>Ovo gene has multiple, independent, inactivating mutations in the 5′ region available for comparison. Yellow shading indicates in-frame indel events, red shading indicates frame-shifting indel events (observed only in <i>w</i>Ovo OW5-K), and violet shading indicates the two in-frame stop codons in <i>w</i>Bm <i>Clp</i>A.</p

Hypotheses of <i>Wolbachia</i> Relationships

<p>While we analysed seven taxa, they can be treated as if they were four: outgroups <i>(Anaplasma</i> and <i>Ehrlichia),</i> clade A <i>Wolbachia</i> (<i>w</i>Mel, <i>w</i>Ana, and <i>w</i>Sim), clade D <i>Wolbachia</i> (<i>w</i>Bm), and clade C <i>Wolbachia</i> (<i>w</i>Ovo). There are thus three possible placements of the root of <i>Wolbachia:</i> (1) Tree 1 [outgroups[A[C,D]]], (2) Tree 2 [outgroups[C[D,A]]], and (3) Tree 3 [outgroups[D[C,A]]]. As clade A included more than one taxon, trees with clade A paraphyletic are also possible. In practice only one such arrangement was found (Tree 4; [outgroups[A′[A′′[C,D]]]]), and may have arisen from analysis of paralogous genes.</p