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PubMed2004

Sexy sons: a dead end for cytoplasmic genes.

Critics of sexual conflict theory argue that females may gain a net reproductive benefit from mating with manipulative males because the direct costs that they suffer may be offset by the production of sexy, i.e. manipulative, sons. However, this exclusive focus on nuclear gene effects represents an incomplete view of female fitness. Females differ fundamentally from males in transmitting not only nuclear genes but also a wide range of cytoplasmic genetic elements (CGEs) that can have profound effects, from male killing to influencing development of the nervous system and cognitive ability. Maternal transmission of CGEs has two major implications for sexual selection. First, the evolution of male fitness traits, such as sperm competitive ability, may be constrained because response to selection on mitochondrial genomes can occur only through the female line. Second, CGEs bear the direct costs of male manipulation but gain no indirect benefits when females produce sexy sons. This should result in perpetual antagonistic coevolution between nuclear genes involved in male manipulation and CGEs that promote female resistance to male sexually selected traits. Explicit consideration of the consequences of selection acting on CGEs is therefore necessary for a better understanding of the relationship between sexual selection and sexual conflict.

Animals↗
PubMed2006

Outbreeding selects for spiteful cytoplasmic elements.

In addition to their nuclear genome, the vast majority of eukaryotes harbour cytoplasmic genomes, e.g. in mitochondria or chloroplasts. In the majority of cases, these cytoplasmic genomes are transmitted maternally only, leading to selective pressures divergent from those that act on nuclear genes. In particular, cytoplasmic genes, which reduce the fitness of males that carry them, but have no fitness effect in females, are believed to be selectively neutral. Here, we go a step further and argue that in outbreeding populations (i.e. populations with inbreeding avoidance), 'spiteful' cytoplasmic elements that reduce the number of offspring produced by males are in fact selected for. We study this process by means of a stochastic model, analysing both the probability of spread and the impact that such a spiteful cytotype can have on population dynamics. Our results demonstrate that the probability of spread of the spiteful cytotype can be several times higher in outbreeding than in panmictic populations. Spread and fixation of the spiteful cytotype can lead to different qualitative effects on the population dynamics, including extinction, decreased or increased stable population size. We discuss our results in respect to cytoplasmically induced male infertility and cytoplasmic incompatibility.

Animals↗
PubMed1993

Plastid engineering in land plants: a conservative genome is open to change.

We have developed efficient transformation protocols to modify each of the 500-10,000 plastid genome copies in a tobacco cell. The transforming DNA is introduced on the surface of microscopic tungsten particles by the biolistic process. Selection for transplastomes is by spectinomycin resistance based on expression of aminoglycoside-3"-adenyltransferase from a chimeric aadA gene in the transforming DNA. Manipulations that are now feasible include replacement of endogenous plastid genes with DNA sequences modified in vitro, targeted gene disruption, and insertion of reporter genes into the plastid genome. Alternative methods for plastid genome manipulations may be developed utilizing an extrachromosomal element which was identified during the transformation studies. Introduction of foreign genes under control of plastid gene expression elements results in duplication of endogenous regulatory sequences. A sensitive somatic assay to detect deletions via such direct repeats confirmed that these sequence duplications do not result in significant genome instability. The ability to transform plastids will facilitate the study of plastid gene regulation, and the application of genetic engineering to crop improvement.

Base Sequence↗
PubMed1977

Requirement of the bacteriopahge T7 0.7 gene for phage growth in the presence of the Col 1b factor.

A variety of colicinogenic factors were examined for their effect on the growth of phages related to T7. Col B1 and Col B4 inhibited the growth of every phage tested. Col B2, however, did not interfere with T3 and H. Col E2 interfered only with growth of T3, while Col Ib produced abortive infection with some T7 mutants. The abortive infection associated with Col Ib seems to be correlated with the absence of the virus phosphokinase; mixed infection with T7 wild type and a phosphokinase deficient mutant was productive but the phage yield was depressed. The abortively infected cells lysed.

Colicins↗
PubMed1988

Epigenetic control and reintegration of extrachromosomal proviral DNA in HL60 cells chronically infected with human T cell leukaemia virus type 1.

Extrachromosomal human T cell leukaemia virus type 1 (HTLV-I) proviruses are persistently maintained in HTLV-I-infected human promyelocytic leukaemia (HL60) cells even 24 months after viral infection. By successive recloning of these HTLV-I-infected clones, and by Southern blot analysis of their HTLV-I proviruses, we concluded the following. The copy number of extrachromosomal proviruses fluctuated, and this fluctuation was probably dependent on the epigenetic conditions in the host cell, HL60. The transient appearance of a high copy number of extrachromosomal proviruses was followed by an increase in the copy number of integrated proviruses. Persistence of extrachromosomal proviruses appeared to be caused by an intracellular rather than an intercellular mechanism.

DNA, Viral↗
PubMed1992

Extrachromosomal human immunodeficiency virus type 1 DNA forms in fresh peripheral blood lymphocytes and in two interleukin-2-independent T cell lines derived from peripheral blood lymphocytes of an asymptomatic seropositive subject.

Two immature T cell lines (FT1 and FT4) were established after in vitro cloning of peripheral blood lymphocytes (PBLs) from an asymptomatic human immunodeficiency virus type 1 (HIV-1) seropositive, human T cell-lymphotropic virus type 1 seronegative homosexual subject. Although derived from a limiting dilution cell cloning assay, these cell lines were not recloned for this study. Their growth was independent of exogenous interleukin-2. Both cell lines were able to form colonies when cloned in agar, but failed to form solid tumours when injected into nude mice. FT lines belong to the very immature T cell lineage as they exhibit rearranged TCR genes but no expression of T cell membrane antigens, including CD2, CD3, CD4, CD6, CD7 and CD8. They also contain an HIV-1 genome that was detected only in an extra-chromosomal DNA form, even after several passages in vitro. The presence of unintegrated viral DNA was also detected by polymerase chain reaction analysis in the same sample of fresh uncultured PBLs. Furthermore, despite the absence of CD4 expression, both T cell lines were susceptible to CD4-independent HIV-1 superinfection (lack of superinfection inhibition in the presence of OKT4A monoclonal antibodies).

Adult↗
PubMed1993

Unusual structure of the double-stranded RNA associated with the '447' cytoplasmic male sterility in Vicia faba.

The 16.7 kbp dsRNA specific to the '447' cytoplasmic male sterility (CMS) line of Vicia faba was labelled in vitro with [alpha-32P]ATP and poly(A) polymerase, and by T4 RNA ligase-mediated addition of [32P]pCp. Analysis of the reaction products under denaturing conditions revealed in both cases extensive labelling of a 4.5 kb ssRNA, already detected in previous experiments in which the RNA-dependent RNA polymerase associated with the dsRNA was allowed to pursue RNA synthesis on preinitiated complexes. Mobility shift analysis of total pCp-labelled dsRNA revealed not two but three different 3' termini. The most prominent sequencing pattern corresponded to the 4.5 kb ssRNA, indicating that this RNA species has a preferentially accessible, free 3' OH extremity. Northern blot analysis of the denatured dsRNA confirmed that the 4.5 kb ssRNA is a subgenomic mRNA and detected its counterpart of about 12 kb. Nearly all 16.7 kbp dsRNA molecules featured an interrupted positive-sense strand, indicating a marked prevalence of transcription over replication complexes. This unusual strategy of transcription by a strand displacement mechanism, following initiation at an internal discontinuity, is compared with that of other dsRNA viruses or defective viruses, and is discussed in relation to the expression of the CMS trait.

Base Sequence↗
PubMed1980

Distribution of genes for trimethoprim and gentamicin resistance in bacteria and their plasmids in a general hospital.

The incidence of trimethoprim resistance in enterobacteria causing infection in a London hospital increased from 5.6% in 1970 to 16% in 1979. The proportion of gentamicin-resistant aerobic Gram-negative bacilli had risen to 6.5% by 1979. During a 5-month period in 1977, during which no epidemic was recognized, all isolates resistant to either trimethoprim, gentamicin, tobramycin or amikacin were studied. The proportion of enterobacteria resistant to both trimethoprim and gentamicin (3.8% of the total) was significantly higher than expected assuming no correlation between acquisition of resistance characters. The resistance was transferable in 23% of trimethoprim-resistant and 76% of gentamicin-resistant strains. Trimethoprim resistance was carried by plasmids of seven different incompatibility groups and in at least four instances was part of a transposon. Gentamicin resistance was determined by plasmids of three groups - IncC, IncFII and IncW. Transposition of gentamicin resistance was not shown, though this may have been the means of evolution of the gentamicin R plasmids of InW, which determined aminoglycoside acetyltransferase, AAC(3). Some bacterial strains with their plasmids were endemic. There was evidence for these plasmids (i) acquiring new resistance genes by transposition, (ii) losing resistance genes by deletion and (iii) being transferred between bacterial species in the hospital.

Amikacin↗
PubMed1996

Mycobacterium xenopi IS1395, a novel insertion sequence expanding the IS256 family.

An insertion sequence (IS) of Mycobacterium xenopi has been isolated and sequenced. This 1323 bp element, designated IS1395, is present in up to 18 copies in the M. xenopi genome and may be harboured in an M. xenopi extrachromosomal element. It encodes a putative transposase of 415 amino acids which displays sequence homology to the Staphylococcus aureus IS256 family. Members of this class of elements have been described in the genus Mycobacterium-for example IS1081 is present in the M. tuberculosis complex, IS1245-IS1311 in M. avium, and IS6120 in M. smegmatis; these elements exhibit an 89%, 45% and 16% amino acid identity with IS1395, respectively. Investigation of the host range of IS1395 by Southern blot analysis revealed additional IS1395-related repeated sequences in M. gordonae and M. celatum. Moreover, IS1395 represents a useful epidemiological tool for M. xenopi strain typing as it provides a diversity of restriction fragment length polymorphism patterns.

Amino Acid Sequence↗
PubMed1997

Diversity and differential distribution of IS231, IS232 and IS240 among Bacillus cereus, Bacillus thuringiensis and Bacillus mycoides.

Bacillus cereus, Bacillus thuringiensis and Bacillus mycoides are very closely related bacteria, generally considered as subspecies of B. cereus sensu lato. Different transposable elements have been isolated from B. thuringiensis, including IS231, IS232 and IS240 and their variants. The distribution of these three insertion sequences (IS) within the B. cereus group has been investigated in 90 strains of B. thuringiensis (representing 61 serovars), in 30 reference strains of B. cereus and in 33 strains of B. mycoides. Since these IS elements are delimited by well-conserved and specific inverted repeats, the use of primers corresponding to these ends allowed their amplification by PCR. The results showed that IS231 is the most abundant element in the three taxa, whereas IS232 is apparently exclusively associated with B. thuringiensis. Hybridization and Dral RFLP analysis of the PCR products confirmed and extended knowledge of the heterogeneity previously observed among iso-IS231 elements. Moreover, a similar diversity was observed among iso-IS240 elements. This contrasted with the relative homogeneity displayed by iso-IS232 elements. No specific association appeared to exist between any particular iso-element and a specific strain or serotype.

Bacillus↗