The competing countermarks hypothesis: reliable assessment of competitive ability by potential mates

Scent marking on top of (overmarking), or in the vicinity of, a scent mark already present is commonly termed countermarking. Scent marks and countermarks provide a continuous record of competitive challenges between conspecifics, thus providing a reliable advertisement of an individual's ability to dominate or defend an area to other competitors and potential mates. To test the hypothesis that females should prefer males that countermark competing scent marks in their territory over those whose own marks are partially countermarked by a competing male, we manipulated scent marks in the territories of neighbouring male house mice (captive-bred Mus domesticus). As predicted, oestrous females were more strongly attracted to approach territory owners that countermarked the scent mark challenges of competitors than those that had been countermarked, and females themselves deposited more scent marks near the scents of these males. To investigate whether female mice use scent age, overlap or intrinsic qualitative or quantitative differences between scent marks and countermarks to make this discrimination, we redeposited male scent marks artificially as marks and partially overlapping countermarks, with or without a 24-h age difference between them. While the intrinsic quality or quantity of countermarks did not affect discrimination, an age difference between the original mark and subsequent countermark was important for consistent discrimination. The ultimate function of such competitive scent signalling thus may be to provide potential mates with a reliable indicator of the competitive ability of individuals advertising their high status. Since scent marks remain in the environment and are continuously available to challenge and investigation, they may provide a particularly effective and reliable means of dominance advertisement. Copyright 1999 The Association for the Study of Animal Behaviour.     

Expression of mdm-2 oncoprotein in the primary and metastatic sites of mammary tumor (GI-101) implanted athymic nude mice

The expression of mdm-2 oncoprotein (p90) was determined in a human breast tumor xenograft line (GI-101) that was derived from a 57 year old female cancer patient with recurrent, infiltrating ductal adenocarcinoma (Stage IIIa, T3N2MX). Immunoprecipitation coupled western blot analysis of the primary tumors that have been obtained from xenograft implanted athymic nude mice, using mdm-2 (Ab-1) mouse monoclonal antibody, primarily revealed high level expression of a 90 kD full length mdm-2 protein. In the GI-101 tumor the level of full length mdm-2 (p90) protein expression increased with the increase in the size of the tumor (100 to 2,000 mm(3)) and a maximum expression was detected in 2,000 mm(3) size tumors. In addition to the expression in the primary site, a significantly high level expression of mdm-2 protein (p90) was detected in the lung and liver tissues also, which are the known metastatic sites for GI-101 xenograft tumors. However, the level of mdm-2 protein expression was undetectable in the lung and liver tissues obtained from control mice. A cell line (GI-101A) derived from the GI-101 xenograft tumor also showed a high level expression of mdm-2 protein after several generations of cell passage. When the GI-101A cells were treated with DES (Diethylstilbestrol) the mdm-2 protein expression increased after 10 min treatment and reached a peak level at 40 min. Interestingly, DES (10 and 20 microM) treatment increased the total cell number also after 96 hr treatment compared to the non-treated cells. It appears that mdm-2 (p90) may have a significant role in supporting the tumor cell growth as well as the metastatic process of the GI-101A cells.     

How biologically relevant are interaction-based modules in protein networks?

By applying a graph-based algorithm to yeast protein-interaction networks we have extracted modular structures and show that they can be validated using information from the phylogenetic conservation of the network components. We show that the module cores, the parts with the highest intramodular connectivity, are biologically relevant components of the networks. These constituents correlate only weakly with other levels of organization. We also discuss how such structures could be used for finding targets for antimicrobial drugs.     

Characterization of the 70S Ribosome from Rhodopseudomonas palustris using an integrated "top-down" and "bottom-up" mass spectrometric approach

We present a comprehensive mass spectrometric approach that integrates intact protein molecular mass measurement ("top-down") and proteolytic fragment identification ("bottom-up") to characterize the 70S ribosome from Rhodopseudomonas palustris. Forty-two intact protein identifications were obtained by the top-down approach and 53 out of the 54 orthologs to Escherichia coli ribosomal proteins were identified from bottom-up analysis. This integrated approach simplified the assignment of post-translational modifications by increasing the confidence of identifications, distinguishing between isoforms, and identifying the amino acid positions at which particular post-translational modifications occurred. Our combined mass spectrometry data also allowed us to check and validate the gene annotations for three ribosomal proteins predicted to possess extended C-termini. In particular, we identified a highly repetitive C-terminal "alanine tail" on L25. This type of low complexity sequence, common to eukaryotic proteins, has previously not been reported in prokaryotic proteins. To our knowledge, this is the most comprehensive protein complex analysis to date that integrates two MS techniques.     

How many species are infected with Wolbachia? Cryptic sex ratio distorters revealed to be common by intensive sampling.

Inherited bacterial symbionts from the genus Wolbachia have attracted much attention by virtue of their ability to manipulate the reproduction of their arthropod hosts. The potential importance of these bacteria has been underlined by surveys, which have estimated that 17% of insect species are infected. We examined whether these surveys have systematically underestimated the proportion of infected species through failing to detect the low-prevalence infections that are expected when Wolbachia distorts the sex ratio. We estimated the proportion of species infected with Wolbachia within Acraea butterflies by testing large collections of each species for infection. Seven out of 24 species of Acraea were infected with Wolbachia. Four of these were infected with Wolbachia at high prevalence, a figure compatible with previous broad-scale surveys, whilst three carried low-prevalence infections that would have had a very low likelihood of being detected by previous sampling methods. This led us to conclude that sex-ratio-distorting Wolbachia may be common in insects that have an ecology and/or genetics that permit the invasion of these parasites and that previous surveys may have seriously underestimated the proportion of species that are infected.     

Local similarity in evolutionary rates extends over whole chromosomes in human-rodent and mouse-rat comparisons: implications for understanding the mechanistic basis of the male mutation bias

The sex chromosomes and autosomes spend different times in the germ line of the two sexes. If cell division is mutagenic and if the sexes differ in number of cell divisions, then we expect that sequences on the X and Y chromosomes and autosomes should mutate at different rates. Tests of this hypothesis for several mammalian species have led to conflicting results. At the same time, recent evidence suggests that the chromosomal location of genes on autosomes affects their rate of evolution at synonymous sites. This suggests a mutagenic source different from germ cell replication. To correctly interpret the previous estimates of male mutation bias, it is crucial to understand the degree and range of this local similarity. With a carefully chosen randomization protocol, local similarity in synonymous rates of evolution can be detected in human-rodent and mouse-rat comparisons. However, the synonymous-site similarity in the mouse-rat comparison remains weak. Simulations suggest that this difference between the mouse-human and the mouse-rat comparisons is not artifactual and that there is therefore a difference between humans and rodents in the local patterns of mutation or selection on synonymous sites (conversely, we show that the previously reported absence of a local similarity in nonsynonymous rates of evolution in the human-rodent comparison was a methodological artifact). We show that linkage effects have a long-range component: not one in a million random genomes shows such levels of autosomal heterogeneity. The heterogeneity is so great that more autosomes than expected by chance have rates of synonymous evolution comparable with that of the X chromosome. As autosomal heterogeneity cannot be owing to different times spent in the germ line, this demonstrates that the dominant determiner of synonymous rates of evolution is not, as has been conjectured, the time spent in the male germ line.     

Wolbachia infection associated with all-female broods in Hypolimnas bolina (Lepidoptera: Nymphalidae): evidence for horizontal transmission of a butterfly male killer

Inherited bacteria that kill male hosts during embryogenesis infect a wide range of insect species. In order to ascertain if there are patterns to host infection, with particular male killing bacteria specialising on particular taxa, we investigated the male killing trait in the butterfly Hypolimnas bolina. All-female broods were first reported in this species in the 1920s. Investigation of this system in the Fiji Islands revealed the causal agent of sex ratio distortion in H. bolina to be a male killing Wolbachia bacterium. This bacterium is identical in wsp and ftsZ sequence to a male killer in the butterfly Acraea encedon in Tanzania, suggesting it has moved between host species, yet retained its phenotype. The prevalence of the Wolbachia was calculated for three different island groups of Fiji, and found to vary significantly across the country. Antibiotics failed to cure either the male killing trait or the Wolbachia infection. The implications of these results are discussed.     

Donor T cell activation initiates small bowel allograft rejection through an IFN-gamma-inducible protein-10-dependent mechanism

The poor success in controlling small bowel (SB) allograft rejection is partially attributed to the unique immune environment in the donor intestine. We hypothesized that Ag-induced activation of donor-derived T cells contributes to the initiation of SB allograft rejection. To address the role of donor T cell activation in SB transplantation, SB grafts from DO11.10 TCR transgenic mice (BALB/c, H-2L(d+)) were transplanted into BALB/c (isografts), or single class I MHC-mismatched (L(d)-deficient) BALB/c H-2(dm2) (dm2, H-2L(d-)) mutant mice (allografts). Graft survival was followed after injection of control or antigenic OVA(323-339) peptide. Eighty percent of SB allografts developed severe rejection in mice treated with antigenic peptide, whereas <20% of allografts were rejected in mice treated with control peptide (p < 0.05). Isografts survived >30 days regardless of OVA(323-339) administration. Activation of donor T cells increased intragraft expression of proinflammatory cytokine (IFN-gamma) and CXC chemokine IFN-gamma-inducible protein-10 mRNA and enhanced activation and accumulation of host NK and T cells in SB allografts. Treatment of mice with neutralizing anti-IFN-gamma-inducible protein-10 mAb increased SB allograft survival in Ag-treated mice (67%; p < 0.05) and reduced accumulation of host T cells and NK cells in the lamina propria but not mesenteric lymph nodes. These results suggest that activation of donor T cells after SB allotransplantation induces production of a Th1-like profile of cytokines and CXC chemokines that enhance infiltration of host T cells and NK cells in SB allografts. Blocking this pathway may be of therapeutic value in controlling SB allograft rejection.     

Hydrogen peroxide and nitric oxide as signalling molecules in plants

It is now clear that hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) function as signalling molecules in plants. A wide range of abiotic and biotic stresses results in H(2)O(2) generation, from a variety of sources. H(2)O(2) is removed from cells via a number of antioxidant mechanisms, both enzymatic and non-enzymatic. Both biotic and abiotic stresses can induce NO synthesis, but the biosynthetic origins of NO in plants have not yet been resolved. Cellular responses to H(2)O(2) and NO are complex, with considerable cross-talk between responses to several stimuli. In this review the potential roles of H(2)O(2) and NO during various stresses and the signalling pathways they activate are discussed. Key signalling components that might provide targets for enhancing crop production are also identified.     

Which way to manipulate host reproduction? Wolbachia that cause cytoplasmic incompatibility are easily invaded by sex ratio-distorting mutants

The bacterium Wolbachia manipulates its hosts by inducing cytoplasmic incompatibility (CI), where zygotes formed from crosses between uninfected mothers and infected fathers die. In addition, it distorts the host's sex ratio via male killing, parthenogenesis induction, or feminization. Here, we model transitions between these states, examining the evolution of mutants of CI strains that retain both the ability to induce and resist CI but, in addition, cause sex ratio distortion. The model shows that CI strains are highly susceptible to invasion and subsequent elimination by these mutants. For all three types of sex ratio distortion, there is some parameter space in which the strain showing sex ratio distortion becomes extinct following exclusion of the progenitor CI strain, leaving the population uninfected. Extinction of the new Wolbachia strain is common for the case of male killing but rarer for parthenogenesis induction and feminization. Our models predict that CI strains of Wolbachia will occur most commonly in hosts that are male heterogametic, where there is little interaction between siblings because these hosts are unlikely to favor the spread of male killing, feminization, or parthenogenesis induction. The models raise the question of why CI strains apparently predominate in nature, and it is suggested that this is a result of either fewer restrictions on CI strains spreading through novel host populations or restrictions to the mutability of Wolbachia strains.