Role of RAD52 Epistasis Group Genes in Homologous Recombination and Double-Strand Break Repair

The process of homologous recombination is a major DNA repair pathway that operates on DNA double-strand breaks, and possibly other kinds of DNA lesions, to promote error-free repair. Central to the process of homologous recombination are the RAD52 group genes (RAD50, RAD51, RAD52, RAD54, RDH54/TID1, RAD55, RAD57, RAD59, MRE11, and XRS2), most of which were identified by their requirement for the repair of ionizing-radiation-induced DNA damage in Saccharomyces cerevisiae. The Rad52 group proteins are highly conserved among eukaryotes, and Rad51, Mre11, and Rad50 are also conserved in prokaryotes and archaea. Recent studies showing defects in homologous recombination and double-strand break repair in several human cancer-prone syndromes have emphasized the importance of this repair pathway in maintaining genome integrity. Although sensitivity to ionizing radiation is a universal feature of rad52 group mutants, the mutants show considerable heterogeneity in different assays for recombinational repair of double-strand breaks and spontaneous mitotic recombination. Herein, I provide an overview of recent biochemical and structural analyses of the Rad52 group proteins and discuss how this information can be incorporated into genetic studies of recombination.     

Cytomegalovirus Vaccine Strain Towne-Derived Dense Bodies Induce Broad Cellular Immune Responses and Neutralizing Antibodies That Prevent Infection of Fibroblasts and Epithelial Cells

Human cytomegalovirus (HCMV), a betaherpesvirus, can cause severe disease in immunosuppressed patients and following congenital infection. A vaccine that induces both humoral and cellular immunity may be required to prevent congenital infection. Dense bodies (DBs) are complex, noninfectious particles produced by HCMV-infected cells and may represent a vaccine option. As knowledge of the antigenicity and immunogenicity of DB is incomplete, we explored characterization methods and defined DB production methods, followed by systematic evaluation of neutralization and cell-mediated immune responses to the DB material in BALB/c mice. DBs purified from Towne-infected cultures treated with the viral terminase inhibitor 2-bromo-5,6-dichloro-1-beta-d-ribofuranosyl benzimidazole riboside (BDCRB) were characterized by nanoparticle tracking analysis (NTA), two-dimensional fluorescence difference gel electrophoresis (2D-DIGE), immunoblotting, quantitative enzyme-linked immunosorbent assay, and other methods. The humoral and cellular immune responses to DBs were compared to the immunogenicity of glycoprotein B (gB) administered with the adjuvant AddaVax (gB/AddaVax). DBs induced neutralizing antibodies that prevented viral infection of cultured fibroblasts and epithelial cells and robust cell-mediated immune responses to multiple viral proteins, including pp65, gB, and UL48. In contrast, gB/AddaVax failed to induce neutralizing antibodies that prevented infection of epithelial cells, highlighting a critical difference in the humoral responses induced by these vaccine candidates. Our data advance the potential for the DB vaccine approach, demonstrate important immunogenicity properties, and strongly support the further evaluation of DBs as a CMV vaccine candidate.     

Terpenoid aldehyde formation and lysigenous gland storage sites in cotton: variant with mature glands but suppressed levels of terpenoid aldehydes

A new cotton variant with reduced levels of terpenoid aldehydes (sesquiterpenoids and sesterterpenoids (heliocides)) was isolated from the progeny of hemizygous cotton (Gossypium hirsutum cv. Coker 312) transformed with antisense (+)-delta-cadinene synthase cDNA. Southern analysis of leaf DNA digested with HindIII, Pst or KpnI restriction endonucleases did not detect any antisense cdn1-C1 DNA in the genome of the variant. The gossypol content in the seed of the variant was markedly lower than in the seed of T1 antisense plants. Eighty-nine percent of the variant seed had a 71.1% reduction in gossypol and the foliage of the variant plants showed a 70% reduction in gossypol and a 31% reduction in heliocides. Compared to non-transformed plants there was no reduction in the number of lysigenous glands in the seed of the variant. The cotton variant shows uncoupling of terpenoid aldehyde synthesis and gland formation. The cotton variant may have resulted from somaclonal variation occurring in the callus tissue during the transformation-regeneration process.     

Fixed vs. Random Temporal Predictability of Predation Risk: An Extension of the Risk Allocation Hypothesis

Predation is a strong selective force acting on prey animals. Predation is by nature highly variable in time; however, this aspect of predation risk has traditionally been overlooked by behavioural ecologists. Lima and Bednekoff proposed the predation risk allocation hypothesis (RAH), predicting how temporal variation in predation risk drives prey antipredator behaviours. This model is based on the concept that prey adaptively allocate their foraging and antipredator efforts across high‐ and low‐risk situations, depending on the duration of high‐ vs. low‐risk situations and the relative risk associated with each of them. An unstudied extension of the RAH is the effect of predictability of predation risk. A predictable risk should lead to prey displaying minimal vigilance behaviours during predictable low‐risk periods and the strongest antipredator behaviours during risky periods. Conversely, an unpredictable predation risk should result in prey displaying constant vigilance behaviour, with suboptimal foraging rates during periods of safety but antipredator behaviours of lower intensity during periods of risk. We tested this extension of the RAH using convict cichlids exposed to high‐risk alarm cues at two frequencies of risk (1× vs. 3×) per day, on either a fixed or random schedule for 5 d. We then tested the fish for a response to high‐risk cues (alarm cues) and to low‐risk cues (disturbance resulting from the introduction of distilled water). Our study supports previous results on the effects of risk frequency and cue intensity on cichlid behaviour. We failed to show an effect of risk predictability on the behavioural responses of cichlids to high‐risk alarm cues, but predictability did influence responses to low‐risk cues. We encourage further studies to test the effect of predictability in other systems.     

The significance of call duration in howler monkeys

The “loud” calls of forest primates consist of repeated sounds that elicit a response from other members of the species. Recent studies suggest that these calls are often displays by the males that permit them to assess the strength of their opponents. Previous research on red howler monkeys supported the hypothesis that howling functions in assessment of competing individuals, as an alternative to energetically expensive chases and fights. As the second step in the attempt to understand the evolution of howling in genus Alouatta,one aspect—call duration — was compared in two species,the mantled howler (Alouatta palliata)and the red howler (A. seniculus).In A. palliatathe median howl duration was 3.5 sec and the interhowl interval was 20.0 sec, while in A. seniculusthe median howl duration was 19.0 sec and the interhowl interval was 3.0 sec. During the dawn chorus, the total duration of calling in A. seniculusmay be 10 or more times greater than that in A. palliata.The latter species appears to be limited in the duration of howls it can produce, so it increases the amount of calling by reducing the interhowl interval. At least four factors may be important in the evolution of the observed differences in call structure: constraints of the acoustic environment, alternate forms of display used by A. palliata,the presence or absence of competing males within the troop, and the effect of female calls on male howling. The observations suggest that the use of the male loud call may reflect differences in the nature of male-male competition and female support more than it reflects the constraints of the acoustic environment.     

Resistance of fast- and slow-growing subalpine fir to pheromone-induced attack by western balsam bark beetle (Coleoptera: Scolytinae)

Abstract 1 We investigated the resistance of fast‐ and slow‐growing subalpine fir to pheromone‐induced attack by western balsam bark beetle at two sites in the interior of British Columbia, Canada. 2 Attack success by the beetle and subsequent tree mortality were higher in slow‐growing trees than in fast‐growing trees. 3 Fast‐growing trees were more likely to produce secondary resin, and in greater quantities, than slow‐growing trees after attack. 4 Host vigour (indicated by recent radial growth) was positively related to the induced defense response and resistance of subalpine fir to bark beetle attack. These results are discussed in the context of plant defense and plant–herbivore interaction hypotheses. 5 Given the preference of western balsam bark beetle for weakened trees, as well as the reduced defenses and increased mortality rates in less vigorous trees, effective management tactics for this beetle may include strategies that increase the growth and vigour of its subalpine fir host.     

Detectable serum flagellin and lipopolysaccharide and upregulated anti-flagellin and lipopolysaccharide immunoglobulins in human short bowel syndrome

Gut barrier dysfunction may occur in short bowel syndrome (SBS). We hypothesized that systemic exposure to flagellin and lipopolysaccharide (LPS) in SBS might regulate specific immune responses. We analyzed serial serum samples obtained from parenteral nutrition (PN)-dependent patients with SBS versus non-SBS control serum. Serum from 23 adult SBS patients was obtained at baseline and 4, 8, 12, 16, 20, and 24 wk in a trial of modified diet with or without growth hormone. Control serum was obtained from 48 healthy adults and 37 adults requiring PN during critical illness. Serum flagellin was detected by an ELISA recognizing an array of gram-negative flagellins, and LPS was detected by limulus assay. Serum flagellin- and LPS-specific immunoglobulin levels (IgM, IgA, and IgG) were determined by ELISA. Serum flagellin and LPS were undetectable in control subjects. In contrast, serum flagellin, LPS, or both were detected in 14 SBS patients (61%) during one or more time points [flagellin alone, 5/23 (22%); LPS alone, 6/23 (26%); or flagellin + LPS, 3/23 (13%)]. Flagellin-specific serum IgM, IgA, and IgG levels were markedly increased in SBS patients compared with both control populations and remained elevated during the 6-mo study period. LPS-specific IgA was significantly higher in SBS patients compared with healthy controls; LPS-specific IgM, IgA, and IgG levels each decreased over time in association with PN weaning. We conclude that adults with PN-dependent SBS are systemically exposed to flagellin and LPS, presumably from the gut lumen. This likely regulates innate and adaptive immune responses to these specific bacterial products.     

Degradation of chemical alarm cues and assessment of risk throughout the day

The use of chemical information in assessment of predation risk is pervasive across animal taxa. However, by its very nature, chemical information can be temporally unreliable. Chemical cues persist for some period of time after they are released into the environment. Yet, we know surprisingly little about the rate of degradation of chemical cues under natural conditions and hence little about how they function in temporal risk assessment under natural conditions. Here, we conducted an experiment to identify a concentration of fresh alarm cues that evoke a strong antipredator response in coral reef damselfish, Pomacentrus ambonensis. We then tested the rate at which these alarm cues degraded under natural conditions in ocean water, paying attention to whether the rate of degradation varied throughout the day and whether the temporal pattern correlated with physicochemical factors that could influence the rate of degradation. Fresh alarm cues released into ocean water evoke strong avoidance responses in juvenile fish, while those aged for 30 min no longer evoke antipredator responses. Fish exposed to cues aged for 10 or 20 min show intermediate avoidance responses. We found a marked temporal pattern of response throughout the day, with much faster degradation in early to mid‐afternoon, the time of day when solar radiation, temperature, dissolved oxygen, and pH are nearing their peak. Ecologists have spent considerable effort elucidating the role of chemical information in mediating predator–prey interactions, yet we know almost nothing about the temporal dynamics of risk assessment using chemical information. We are in dire need of additional comparative field experiments on the rate of breakdown of chemical cues, particularly given that global change in UV radiation, temperature, and water chemistry could be altering the rates of degradation and the potential use of this information in risk assessment.