EVOLUTION OF INCOMPATIBILITY-INDUCING MICROBES AND THEIR HOSTS

In many insect species, males infected with microbes related to Wolbachia pipientis are “incompatible” with uninfected females. Crosses between infected males and uninfected females produce significantly fewer adult progeny than the other three possible crosses. The incompatibility-inducing microbes are usually maternally transmitted. Thus, incompatibility tends to confer a reproductive advantage on infected females in polymorphic populations, allowing these infections to spread. This paper analyzes selection on parasite and host genes that affect such incompatibility systems. Selection among parasite variants does not act directly on the level of incompatibility with uninfected females. In fact, selection favors rare parasite variants that increase the production of infected progeny by infected mothers, even if these variants reduce incompatibility with uninfected females. However, productivity-reducing parasites that cause partial incompatibility with hosts harboring alternative variants can be favored once they become sufficiently abundant locally. Thus, they may spread spatially by a process analogous to the spread of underdominant chromosome rearrangements. The dynamics of modifier alleles in the host are more difficult to predict, because such alleles will occur in both infected and uninfected individuals. Nevertheless, the relative fecundity of infected females compared to uninfected females, the efficiency of maternal transmission and the mutual compatibility of infected individuals all tend to increase under within-population selection on both host and parasite genes. In addition, selection on host genes favors increased compatibility between infected males and uninfected females. Although vertical transmission tends to harmonize host and parasite evolution, competition among parasite variants will tend to maintain incompatibility.     

Insights into ALS pathomechanisms: from flies to humans

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disease causing the death of motor neurons with consequent muscle atrophy and paralysis. Several neurodegenerative diseases have been modeled in Drosophila and genetic studies on this model organism led to the elucidation of crucial aspects of disease mechanisms. ALS, however, has lagged somewhat behind possibly because of the lack of a suitable genetic model. We were the first to develop a fly model for ALS and over the last few years, we have implemented and used this model for a large scale, unbiased modifier screen. We also report an extensive bioinformatic analysis of the genetic modifiers and we show that most of them are associated in a network of interacting genes controlling known as well as novel cellular processes involved in ALS pathogenesis. A similar analysis for the human homologues of the Drosophila modifiers and the validation of a subset of them in human tissues confirm and expand the significance of the data for the human disease. Finally, we analyze a possible application of the model in the process of therapeutic discovery in ALS and we discuss the importance of novel “non-obvious” models for the disease.     

C-Terminus-Mediated Voltage Gating of Arabidopsis Guard Cell Anion Channel QUAC1

Anion transporters in plants play a fundamental role in volume regulation and signaling. Currently, two plasma membrane-located anion channel familiesmSLAC/SLAH and ALMTmare known. Among the ALMT family, the root-expressed ALuminium-activated Malate Transporter 1 was identified by comparison of aluminum-tolerant and Al3＋-sensitive wheat cultivars and was subsequently shown to mediate voltage-independent malate currents. In con- trast, ALMT12/QUAC1 （QUickly activating Anion Channel1） is expressed in guard cells transporting malate in an Al3＋- insensitive and highly voltage-dependent manner. So far, no information is available about the structure and mechanism of voltage-dependent gating with the QUAC1 channel protein. Here, we analyzed gating of QUACl-type currents in the plasma membrane of guard cells and QUACl-expressing oocytes revealing similar voltage dependencies and activation- deactivation kinetics. In the heterologous expression system, QUAC1 was electrophysiologically characterized at increas- ing extra- and intracellular malate concentrations. Thereby, malate additively stimulated the voltage-dependent QUAC1 activity. In search of structural determinants of the gating process, we could not identify transmembrane domains com- mon for voltage-sensitive channels. However, site-directed mutations and deletions at the C-terminus of QUAC1 resulted in altered voltage-dependent channel activity. Interestingly, the replacement of a single glutamate residue, which is con- served in ALMT channels from different clades, by an alanine disrupted QUAC1 activity. Together with C- and N-terminal tagging, these results indicate that the cytosolic C-terminus is involved in the voltage-dependent gating mechanism of QUAC1.     

Molecular targets underlying SUMO‐mediated neuroprotection in brain ischemia

SUMOylation (small ubiquitin‐like modifier conjugation) is an important post‐translational modification which is becoming increasingly implicated in the altered protein dynamics associated with brain ischemia. The function of SUMOylation in cells undergoing ischemic stress and the identity of small ubiquitin‐like modifier (SUMO) targets remain in most cases unknown. However, the emerging consensus is that SUMOylation of certain proteins might be part of an endogenous neuroprotective response. This review brings together the current understanding of the underlying mechanisms and downstream effects of SUMOylation in brain ischemia, including processes such as autophagy, mitophagy and oxidative stress. We focus on recent advances and controversies regarding key central nervous system proteins, including those associated with the nucleus, cytoplasm and plasma membrane, such as glucose transporters (GLUT1, GLUT4), excitatory amino acid transporter 2 glutamate transporters, K⁺ channels (K2P1, K_v1.5, K_v2.1), GluK2 kainate receptors, mGluR8 glutamate receptors and CB1 cannabinoid receptors, which are reported to be SUMO‐modified. A discussion of the roles of these molecular targets for SUMOylation could play following an ischemic event, particularly with respect to their potential neuroprotective impact in brain ischemia, is proposed.     

Genetics and selective breeding of variation in wing truncation in a flightless aphid control agent

Augmentative biological control by predaceous ladybird beetles can be improved by using flightless morphs, which have longer residence times on the host plants. The two‐spot ladybird beetle, Adalia bipunctata (L.) (Coleoptera: Coccinellidae), is used for the biological control of aphids in greenhouses and on urban trees. Flightlessness due to truncated wings occurs at very low frequency in some natural populations of A. bipunctata. Pure‐breeding strains of this 'wingless' genotype of A. bipunctata can easily be obtained in the laboratory. Such strains have not been commercialized yet due to concerns about their reduced fitness compared to wild‐type strains, which renders mass production more expensive. Wingless strains exhibit, however, wide intra‐population phenotypic variation in the extent of wing truncation which is related to fitness traits. We here use classical quantitative genetic techniques to study the heritability and genetic architecture of variation in wing truncation in a wingless strain of A. bipunctata. Split‐families reared at one of two temperatures revealed strong family‐by‐temperature interaction: heritability was estimated as 0.64 ± 0.09 at 19 °C and 0.29 ± 0.06 at 29 °C. Artificial selection in opposite directions at 21 °C demonstrated that the degree of wing truncation can be altered within a few generations resulting in wingless phenotypes without any wing tissue (realized h² = 0.72), as well as those with minimal truncations (realized h² = 0.61) in two replicates. The latter lines produced more than twice as many individuals. This indicates that selective breeding of wing truncation may be exploited to improve mass rearing of flightless strains of A. bipunctata for commercial biological control. Our work illustrates that cryptic variation can also be a source for the selective breeding of natural enemies.     

Quantitative control of gene expression by nucleocytoplasmic interactions in early mouse embryos: Consequence for reprogrammation by nuclear transfer

HSP 70.1 is one of the first genes to be expressed in the mouse embryo at the time of zygotic genome activation. We studied the regulation of this gene, using a transgene associating HSP 70.1 promoter and the firefly luciferase reporter gene, which allows the precise quantification of HSP 70.1 level of expression on individual embryos. In the present work, we show first that the level of HSP 70.1 expression at the two-cell stage is significantly higher (around two-fold) in embryos whose maternal cytoplasm is from C3H strain than with BALB/c strain. We verified that this difference is not an artefact of the use of transgenic embryos, of the time of first cleavage, or of in vitro culture. This regulation of HSP 70.1 level of expression is controlled by strain-specific maternal modifiers and is independent of replication, syngamy, and mitosis. Following nuclear transfer, reactivation of HSP 70.1 is also subjected to the same epigenetic influence. Only the strain-of-origin of the recipient cytoplast modulates the level of HSP 70.1 reprogrammation; the origin of donor nucleus is not significant, demonstrating the reversibility of this strain effect. These results point out the importance of the quality of recipient cytoplast in the intensity of gene reprogrammation, which may be of importance for nuclear transfer efficiency. © 1996 Wiley-Liss, Inc.     

Solution structure of Phrixotoxin 1, a specific peptide inhibitor of Kv4 potassium channels from the venom of the theraphosid spider Phrixotrichus auratus

Animal toxins block voltage-dependent potassium channels (Kv) either by occluding the conduction pore (pore blockers) or by modifying the channel gating properties (gating modifiers). Gating modifiers of Kv channels bind to four equivalent extracellular sites near the S3 and S4 segments, close to the voltage sensor. Phrixotoxins are gating modifiers that bind preferentially to the closed state of the channel and fold into the Inhibitory Cystine Knot structural motif. We have solved the solution structure of Phrixotoxin 1, a gating modifier of Kv4 potassium channels. Analysis of the molecular surface and the electrostatic anisotropy of Phrixotoxin 1 and of other toxins acting on voltage-dependent potassium channels allowed us to propose a toxin interacting surface that encompasses both the surface from which the dipole moment emerges and a neighboring hydrophobic surface rich in aromatic residues.