Experimental evaluation of the relationship between lethal or non-lethal virulence and transmission success in malaria parasite infections

Background

Theoretical studies suggest that direct and indirect selection have the potential to cause substantial evolutionary change in female mate choice. Similarly, sexual selection is considered a strong force in the evolution of male attractiveness and the exaggeration of secondary sexual traits. Few studies have, however, directly tested how female mate choice and male attractiveness respond to selection. Here we report the results of a selection experiment in which we selected directly on female mating preference for attractive males and, independently, on male attractiveness in the guppy, Poecilia reticulata. We measured the direct and correlated responses of female mate choice and male attractiveness to selection and the correlated responses of male ornamental traits, female fecundity and adult male and female survival.

Results

Surprisingly, neither female mate choice nor male attractiveness responded significantly to direct or to indirect selection. Fecundity did differ significantly among lines in a way that suggests a possible sexually-antagonistic cost to male attractiveness.

Conclusions

The opportunity for evolutionary change in female mate choice and male attractiveness may be much smaller than predicted by current theory, and may thus have important consequences for how we understand the evolution of female mate choice and male attractiveness. We discuss a number of factors that may have constrained the response of female choice and male attractiveness to selection, including low heritabilities, low levels of genetic (co)variation in the multivariate direction of selection, sexually-antagonistic constraint on sexual selection and the "environmental covariance hypothesis".

     

Diverse effects of RacV12 on cell transformation by Raf: partial inhibition of morphological transformation versus deregulation of cell cycle control

Activated Raf kinases and Rac GTPases were shown to cooperate in the oncogenic transformation of fibroblasts, which is characterised by the disassembly of the cellular actin cytoskeleton, a nearly complete loss of focal adhesion complexes and deregulated cell proliferation. This is surprising since the Rac GTPase induces actin structures and the adhesion of suspended cells to extracellular matrix proteins. NIH 3T3 cells expressing a hydroxytamoxifen-inducible oncogenic c-Raf-1-oestrogen receptor fusion protein (c-Raf-1-BxB-ER, N-BxB-ER cells) undergo morphological transformation upon stimulation of the Raf kinase. We show that treatment with the Rac, Rho and Cdc42 activating Escherichia coli toxin CNF1 or coexpression of an activated RacV12 mutant partially inhibits and reverses the disassembly of cellular actin structures and focal adhesion complexes by oncogenic Raf. Activation of the Rac GTPase restores actin structures and focal adhesion complexes at the cellular boundary, leading to spreading of the otherwise spindle-shaped Raf-transformed cells. Actin stress fibres, however, which are regulated by the function of the Rho GTPase, are disassembled by oncogenic Raf even in the presence of activated Rac and Rho. With respect to the RacV12-mediated spreading of Raf-transformed cells, we postulate an anti-oncogenic function of the activated Rac. Another feature of cell transformation is the deregulation of cell cycle control. NIH 3T3 cells expressing high levels of the c-Raf-1-BxB-ER protein undergo a cell cycle arrest upon stimulation of the oncogenic Raf kinase. Our results show that in N-BxB-ER-RacV12 cells the expression of the activated RacV12 mediates cell proliferation in the presence of high-intensity Raf signals and high levels of the Cdk inhibitor p21(Cip1). These results indicate a pro-oncogenic function of the Rac GTPase with respect to the deregulation of cell cycle control.     

Structural changes of tRNA and 5S rRNA induced with magnesium and visualized with synchrotron mediated hydroxyl radical cleavage

The structure of native yeast tRNA^Phe and wheat germ ribosomal 5S RNA induced by different magnesium ion concentrations was studied in solution with a synchrotron mediated hydroxyl radical RNA cleavage reaction. We showed that very small amounts of Mg⁺² can induce significant changes in the hydroxyl radical cleavage pattern of tRNA^Phe. It also turned out that a reactivity of tRNA^Phe towards OH coincides with the strong metal binding sites. Because of the Mg ions are heavily hydrated one can suggest the strong correlation of the observed nucleosides reactivity in vicinity of Mg²⁺ binding sites with availability of water molecules as a source of hydroxyl radical. On the other hand the structure of wheat germ 5S rRNA is less sensitive to the hydroxyl radical reaction than tRNA^Phe although some changes are visible at 4 mM Mg ions. It is probably due to the lack of strong Mg⁺² binding sites in that molecule. The reactivity of nucleotides in loops C and D of 5S rRNA is not effected, what suggests their flexibility or involvement in higher order structure formation. There is different effect of magnesium on tRNA and 5S rRNA folding. We found that nucleotides forming strong binding sites for magnesium are very sensitive to X-ray generated hydroxyl radical and can be mapped with OH. The results show, that guanine nucleotides are preferentially hydrated. X-ray footprinting mediated hydroxyl radical RNA cleavage is a very powerful method and has been applied to studies of stable RNAs for the first time.     

Neurotrophin receptor-interacting mage homologue is an inducible inhibitor of apoptosis protein-interacting protein that augments cell death

The inhibitor of apoptosis proteins (IAPs) have been shown to interact with a growing number of intracellular proteins and pathways to fulfil their anti-apoptotic role. In the search for novel IAP-interacting proteins we identified the neurotrophin receptor-interacting MAGE homologue (NRAGE) as being able to bind to the avian IAP homologue ITA. This interaction requires the RING domain of ITA. NRAGE additionally coimmunoprecipitates with XIAP. When overexpressed in 32D cells NRAGE augments interleukin-3 withdrawal induced apoptosis, possibly through binding endogenous XIAP. Moreover, NRAGE is able to overcome the anti-apoptotic effect of Bcl-2.     

Influenza virus propagation is impaired by inhibition of the Raf/MEK/ERK signalling cascade

Influenza A viruses are important worldwide pathogens in humans and different animal species. The functions of most of the ten different viral proteins of this negative-strand RNA virus have been well elucidated. However, little is known about the virus-induced intracellular signalling events that support viral replication. The Raf/MEK/ERK cascade is the prototype of mitogen-activated protein (MAP) kinase cascades and has an important role in cell growth, differentiation and survival. Investigation of the function of this pathway has been facilitated by the identification of specific inhibitors such as U0126, which blocks the cascade at the level of MAPK/ERK kinase (MEK). Here we show that infection of cells with influenza A virus leads to biphasic activation of the Raf/MEK/ERK cascade. Inhibition of Raf signalling results in nuclear retention of viral ribonucleoprotein complexes (RNPs), impaired function of the nuclear-export protein (NEP/NS2) and concomitant inhibition of virus production. Thus, signalling through the mitogenic cascade seems to be essential for virus production and RNP export from the nucleus during the viral life cycle.