Bacteriophage Mu-induced modification of DNA is dependent upon a host function.

The DNA of bacteriophage Mu, extracted from induced lysates, is partially resistant to digestion by the endonuclease BalI. This modification of DNA is controlled by the Mu modification function (mom), which acts in conjunction with the dam (DNA-adenine methylation) function of Escherichia coli. Since the BalI recognition site is apparently different from the dam recognition site, these results imply that either the specificity of the dam function is changed by the mom function or the mom function requires the dam function for its activity.     

Wolbachia-mediated antibacterial protection and immune gene regulation in Drosophila

The outcome of microbial infection of insects is dependent not only on interactions between the host and pathogen, but also on the interactions between microbes that co-infect the host. Recently the maternally inherited endosymbiotic bacteria Wolbachia has been shown to protect insects from a range of microbial and eukaryotic pathogens. Mosquitoes experimentally infected with Wolbachia have upregulated immune responses and are protected from a number of pathogens including viruses, bacteria, Plasmodium and filarial nematodes. It has been hypothesised that immune upregulation underpins Wolbachia-mediated protection. Drosophila is a strong model for understanding host-Wolbachia-pathogen interactions. Wolbachia-mediated antiviral protection in Drosophila has been demonstrated for a number of different Wolbachia strains. In this study we investigate whether Wolbachia-infected flies are also protected against pathogenic bacteria. Drosophila simulans lines infected with five different Wolbachia strains were challenged with the pathogenic bacteria Pseudomonas aeruginosa PA01, Serratia marcescens and Erwinia carotovora and mortality compared to paired lines without Wolbachia. No difference in mortality was observed in the flies with or without Wolbachia. Similarly no antibacterial protection was observed for D. melanogaster infected with Wolbachia. Interestingly, D. melanogaster Oregon RC flies which are naturally infected with Wolbachia showed no upregulation of the antibacterial immune genes TepIV, Defensin, Diptericin B, PGRP-SD, Cecropin A1 and Attacin D compared to paired flies without Wolbachia. Taken together these results indicate that Wolbachia-mediated antibacterial protection is not ubiquitous in insects and furthermore that the mechanisms of antibacterial and antiviral protection are independent. We suggest that the immune priming and antibacterial protection observed in Wolbachia-infected mosquitoes may be a consequence of the recent artificial introduction of the symbiont into insects that normally do not carry Wolbachia and that antibacterial protection is unlikely to be found in insects carrying long-term Wolbachia infections.     

Circadian rhythm of homocysteine is hCLOCK genotype dependent

Homocysteine (Hcy) is known to be a prognostic marker for neurological, cardiovascular and cerebrovascular diseases and several other pathophysiological conditions. A sudden surge in Hcy can increase cardiovascular events. Hemodynamic modulations are known to be associated with individual’s chronotype. Therefore, precise monitoring of Hcy is crucial for evaluating its impact on risk. The aim of the present study was to investigate the rhythmicity of Hcy under controlled dietary conditions and whether this rhythmicity is under the genetic control of circadian rhythm. Five subjects were selected from 200 Malayalam speaking healthy ethnic individuals who were screened for functionally critical variants of MTHFR and hCLOCK genes. MTHFR is the rate-limiting enzyme in the methionine cycle and critical for regulating Hcy levels while hCLOCK is a critical gene responsible in regulating the day and night cycles. Rhythmicity in Hcy levels were observed in all the subjects with a consensus on a morning nadir and an evening peak. Gender specific stratification of Hcy levels were observed among similar genotypes of MTHFR and hCLOCK genes. Variations from the conventional rhythmicity of Hcy were observed among similar genotypes of MTHFR and dissimilar hCLOCK genotypes. A reduced plasma Hcy in hCLOCK rs1801260 CC genotype individuals were observed in contrast to CT genotype individuals. The study tends to suggest that Hcy and body time are genetically interdependent and throws light on some of the previously unexplained reasons for variability in Hcy levels. A population specific variation of MTHFR and hCLOCK genes also highlights ethnicity specific risk management.     

Mycorrhizal colonization in cowpea is host dependent and heritable

Cowpea genotypes (101) of diverse origin were evaluated for their endomycorrhizal colonization under natural field conditions in an alfisol soil. There was considerable variation in colonization ranging from 0 to 28.6%. The genetic coefficient of variability was high (55.9), heritability moderate (46.2) with high genetic advance (78.3) revealing that mycorrhizal colonization is not only host dependent but heritable.     

A specific primed immune response in Drosophila is dependent on phagocytes

Drosophila melanogaster, like other invertebrates, relies solely on its innate immune response to fight invading microbes; by definition, innate immunity lacks adaptive characteristics. However, we show here that priming Drosophila with a sublethal dose of Streptococcus pneumoniae protects against an otherwise-lethal second challenge of S. pneumoniae. This protective effect exhibits coarse specificity for S. pneumoniae and persists for the life of the fly. Although not all microbial challenges induced this specific primed response, we find that a similar specific protection can be elicited by Beauveria bassiana, a natural fly pathogen. To characterize this primed response, we focused on S. pneumoniae-induced protection. The mechanism underlying this protective effect requires phagocytes and the Toll pathway. However, activation of the Toll pathway is not sufficient for priming-induced protection. This work contradicts the paradigm that insect immune responses cannot adapt and will promote the search for similar responses overlooked in organisms with an adaptive immune response.     

High-frequency P element loss in Drosophila is homolog dependent

P transposable elements in Drosophila melanogaster can undergo precise loss at a rate exceeding 13% per generation. The process is similar to gene conversion in its requirement for a homolog that is wild type at the insertion site and in its reduced frequency when pairing between the homologs is inhibited. However, it differs from classical gene conversion by its high frequency, its requirement for P transposase, its unidirectionality, and its occurrence in somatic and premeiotic cells. Our results suggest a model of P element transposition in which jumps occur by a "cut-and-paste" mechanism but are followed by double-strand gap repair to restore the P element at the donor site. The results also suggest a technique for site-directed mutagenesis in Drosophila.     

RhoA biological activity is dependent on prenylation but independent of specific isoprenoid modification.

Recent studies showed that specific isoprenoid modification may be critical for RhoB subcellular location and function. Therefore, we determined whether the function of the highly related RhoA protein is also critically dependent on specific isoprenoid modification: (a) in contrast to observations with RhoB or Ras proteins, where farnesylated and geranylgeranylated versions showed differences in subcellular location, both prenylated versions of RhoA showed the same plasma membrane and cytosolic location; (b) a farnesylated version of activated RhoA(63L) retained the same diverse functions as the normally geranylgeranylated RhoA(63L) protein, and both proteins show indistinguishable abilities to stimulate gene expression, cause growth transformation of NIH 3T3 mouse fibroblasts, to stimulate the motility of T47D human breast epithelial cells, and to block HIV-1 viral replication and gene expression; and (c) cells expressing farnesylated RhoA retained sensitivity to the growth inhibition caused by inhibition of geranylgeranyltransferase I, indicating that other proteins are critical targets for inhibitors of geranylgeranylation.     

Fecundity in Drosophila following desiccation is dependent on nutrition and selection regime

Life-history trade-offs of populations of Drosophila melanogaster selected for enhanced desiccation resistance (D populations) include increased pupal mortality, retarded development, increased longevity, and decreased fecundity. We tested the effects of acute desiccation on fecundity and the effects of various nutritional regimes on fecundity following a bout of desiccation in the D populations and their control populations (C populations). Female flies were desiccated for 8 h (C populations) or 24 h (D populations) and then recovered on one of four treatments: distilled water, a saline solution, a saline and sucrose solution, or food. Each treatment was tested in the presence and absence of a yeast supplement. Fecundity was then measured on an oviposition medium over a 12-h period. Fecundity was also measured in flies that did not undergo a desiccation stress. Yeast increased fecundity under all conditions examined in the C populations but not in the D populations. There was an overall effect of recovery treatment on fecundity but no effect of desiccation stress.     

Direct visualization of sperm competition and sperm storage in Drosophila.

Drosophila females engage in multiple matings [1] [2] [3] [4] even though they can store sperm in specialized organs for most of their life [5]. The existence of sperm competition in Drosophila has been inferred from the proportion of progeny sired by the second male in double-mating experiments [6] [7] [8]. Investigators have used this approach to quantify genetic variation underlying sperm competition [8] [9] [10], to elucidate its genetic basis [11], to identify the dependence of different male competitive ability on the genotype of the females with which they mate [12] and to discern the potential role of sperm competition in species isolation [13] [14]. This approach assumes that the sperm from two males stored in a female compete to fertilize the eggs. The mechanism by which sperm competition is accomplished is still unknown, however. Here, fluorescence microscopy, cytometry, and differently labeled sperm were used to analyze the fate of sperm inside the female's sperm storage organs, to quantify sperm competition, and to assess how closely paternity success corresponds to the appearance and location of the sperm. The results show that the first male's sperm is retained for a shortened period if the female remates, and that the second males that sire more progeny either induce females to store and use more of their sperm or strongly displace resident sperm.     

The effect of hormone therapy on olfactory sensitivity is dependent on apolipoprotein E genotype

Patients with Alzheimer's disease (AD) show a deficit in olfactory threshold sensitivity. The Apolipoprotein E (ApoE) 4 allele is associated with increased risk of AD and earlier symptom onset. Hormone therapy (HT) may exert neuroprotective effects on brain areas affected by AD. The current study investigated the effect of HT on performance on an olfactory threshold test in 4 positive and 4 negative non-hysterectomized, non-demented, elderly females and AD patients. Among the non-demented participants, 4 positive females who had received HT performed 1) significantly better than those without HT, and 2) at levels similar to those of 4 negative females. In contrast, those without HT who were 4 positive performed significantly worse than those who were 4 negative. HT had no effect on performance in AD patients regardless of 4 status. These results suggest that HT may offer protection against loss of olfactory function in 4 positive individuals in preclinical stages of AD. Future research is warranted in order to investigate further the neuroprotective role of HT on sensory and cognitive functions in non-demented aging individuals.     

The association between leukocytes and sperm quality is concentration dependent

Background  

To evaluate the association between leukocytes (polymorphonuclear granulocytes -PMNL) and semen parameters at different leukocyte concentrations.     

Hemiclonal analysis reveals significant genetic, environmental and genotype x environment effects on sperm size in Drosophila melanogaster

Spermatozoa are the most diverse of all animal cells. Variation in size alone is enormous and yet there are still no clear evolutionary explanations that can account for such diversity. The basic genetics of sperm form is also poorly understood, although sperm size is known to have a strong genetic component. Here, using hemiclonal analysis of Drosophila melanogaster, we demonstrate that there is not only a significant additive genetic component contributing to phenotypic variation in sperm length but also a significant environmental effect. Furthermore, the plasticity of sperm size has a significant genetic component to it (a genotype x environment interaction). A genotype x environment interaction could contribute to the maintenance of the substantial genetic variation in this trait and thereby explain the persistent inter-male differences in sperm size seen in numerous taxa. We suggest that the low conditional dependence and high heritability but low evolvability (the coefficient of additive genetic variation) of sperm length is more consistent with a history of stabilizing selection rather than either sexual selection or strong directional selection.     

Female genotypes affect sperm displacement in Drosophila.

Differential success of sperm is likely to be an important component of fitness. Extensive variation among male genotypes in competitive success of sperm in multiply mated females has been documented for Drosophila melanogaster. However, virtually all previous studies considered the female to be a passive vessel. Nevertheless, under certain conditions female fitness could be determined by her role in mediating use of sperm from multiple males. Here we ask whether females differ among genotypes in their tendency to exhibit last-male precedence. Competition of sperm from two tester male genotypes (bwD and B3-09, a third-chromosome isogenic line from Beltsville, MD) was quantified by doubly mating female lines that had been rendered homozygous for X, second, or third chromosomes isolated from natural populations. The composite sperm displacement parameter, P2'', was highly heterogeneous among lines, whether or not viability effects were compensated, implying the presence of polymorphic genes affecting access of sperm to eggs. Genetic variation of this type is completely neutral in the absence of pleiotropy or interaction between variation in the two sexes.     

Inhibitory activity of the Drosophila melanogaster serpin Necrotic is dependent on lysine residues in the D-helix

Necrotic is a member of the serine protease inhibitor or serpin superfamily. It is a potent inhibitor of elastase and chymotrypsin type proteases and is responsible for regulating the anti-fungal response in Drosophila melanogaster. Necrotic contains three basic lysine residues within the D-helix that are homologous to those found in the heparin-binding domain of antithrombin and heparin co-factor II. We show here that substitution of all three lysine residues for glutamines caused cellular necrosis and premature death in Drosophila in keeping with a loss of function phenotype. The lysine to glutamine substitutions had no effect on the overall structure of recombinant Necrotic protein but abolished the formation of stable complexes with target proteases. Individual substitutions with either glutamine or alanine demonstrated that lysine 68 was the most critical residue for inhibitory activity. Despite the homology to other serpins, Necrotic did not bind, nor was it activated by sulfated glycans. These data demonstrate a critical role for basic residues within the D-helix (and lysine 68 in particular) in the inhibitory mechanism of the serpin Necrotic.     

The function of the frizzled pathway in the Drosophila wing is dependent on inturned and fuzzy

The Drosophila epidermis is characterized by a dramatic planar or tissue polarity. The frizzled pathway has been shown to be a key regulator of planar polarity for hairs on the wing, ommatidia in the eye, and sensory bristles on the notum. We have investigated the genetic relationships between putative frizzled pathway downstream genes inturned, fuzzy, and multiple wing hairs (inturned-like genes) and upstream genes such as frizzled, prickle, and starry night (frizzled-like genes). Previous data showed that the inturned-like genes were epistatic to the frizzled-like genes when the entire wing was mutant. We extended those experiments and examined the behavior of frizzled clones in mutant wings. We found the domineering nonautonomy of frizzled clones was not altered when the clone cells were simultaneously mutant for inturned, multiple wing hairs, or dishevelled but it was blocked when the entire wing was mutant for inturned, fuzzy, multiple wing hairs, or dishevelled. Thus, for the domineering nonautonomy phenotype of frizzled, inturned and multiple wing hairs are needed in the responding cells but not in the clone itself. Expressing a number of frizzled pathway genes in a gradient across part of the wing repolarizes wing cells in that region. We found inturned, fuzzy, and multiple wing hairs were required for a gradient of frizzled, starry night, prickle, or spiny-legs expression to repolarize wing cells. These data argue that inturned, fuzzy, and multiple wing hairs are downstream components of the frizzled pathway. To further probe the relationship between the frizzled-like and inturned-like genes we determined the consequences of altering the activity of frizzled-like genes in wings that carried weak alleles of inturned or fuzzy. Interestingly, both increasing and decreasing the activity of frizzled and other upstream genes enhanced the phenotypes of hypomorphic inturned and fuzzy mutants. We also examined the relationship between the frizzled-like and inturned-like genes in other regions of the fly. For some body regions and cell types (e.g., abdomen) the inturned-like genes were epistatic to the frizzled-like genes, but in other body regions (e.g., eye) that was not the case. Thus, the genetic control of tissue polarity is body region specific.     

The effect of parasitism on host fecundity is dependent on temperature in a cockroach-acanthocephalan system

The fitness of infected organisms can vary greatly depending on the temperature at which they find themselves. Understanding the role of temperature in the fitness of infected organisms can be crucial to population studies, epidemiological studies, and when screening for biological control agents. We measured the effect of parasitism on host survival and reproduction at 4 constant temperatures using the acanthocephalan parasite Moniliformis moniliformis and its intermediate host, the cockroach Supella longipalpa. Infection did not affect cockroach survival at any temperature. Infection had a negative impact on cockroach fecundity but only at higher temperatures (28 and 31 C) and only later in infection (>20 days postinfection). At lower temperatures, infected and uninfected cockroaches had similar fecundities throughout the duration of the experiment (120 days). This study, along with previous studies, suggests that researchers would do well to consider environmental variables when exploring the effects of parasitism.