Mitochondrial protein import clogging as a mechanism of disease.

Mitochondrial biogenesis requires the import of >1,000 mitochondrial preproteins from the cytosol. Most studies on mitochondrial protein import are focused on the core import machinery. Whether and how the biophysical properties of substrate preproteins affect overall import efficiency is underexplored. Here, we show that protein traffic into mitochondria can be disrupted by amino acid substitutions in a single substrate preprotein. Pathogenic missense mutations in ADP/ATP translocase 1 (ANT1), and its yeast homolog ADP/ATP carrier 2 (Aac2), cause the protein to accumulate along the protein import pathway, thereby obstructing general protein translocation into mitochondria. This impairs mitochondrial respiration, cytosolic proteostasis, and cell viability independent of ANT1's nucleotide transport activity. The mutations act synergistically, as double mutant Aac2/ANT1 causes severe clogging primarily at the translocase of the outer membrane (TOM) complex. This confers extreme toxicity in yeast. In mice, expression of a super-clogger ANT1 variant led to neurodegeneration and an age-dependent dominant myopathy that phenocopy ANT1-induced human disease, suggesting clogging as a mechanism of disease. More broadly, this work implies the existence of uncharacterized amino acid requirements for mitochondrial carrier proteins to avoid clogging and subsequent disease.

Inside our cells, compartments known as mitochondria generate the chemical energy required for life processes to unfold. Most of the proteins found within mitochondria are manufactured in another part of the cell (known as the cytosol) and then imported with the help of specialist machinery. For example, the TOM and TIM22 channels provide a route for the proteins to cross the two membrane barriers that separate the cytosol from the inside of a mitochondrion. ANT1 is a protein that is found inside mitochondria in humans, where it acts as a transport system for the cell's energy currency. Specific mutations in the gene encoding ANT1 have been linked to degenerative conditions that affect the muscles and the brain. However, it remains unclear how these mutations cause disease. To address this question, Coyne et al. recreated some of the mutations in the gene encoding the yeast equivalent of ANT1 (known as Aac2). Experiments in yeast cells carrying these mutations showed that the Aac2 protein accumulated in the TOM and TIM22 channels, creating a 'clog' that prevented other essential proteins from reaching the mitochondria. As a result, the yeast cells died. Mutant forms of the human ANT1 protein also clogged up the TOM and TIM22 channels of human cells in a similar way. Further experiments focused on mice genetically engineered to produce a "super-clogger" version of the mouse equivalent of ANT1. The animals soon developed muscle and neurological conditions similar to those observed in human diseases associated with ANT1. The findings of Coyne et al. suggest that certain genetic mutations in the gene encoding the ANT1 protein cause disease by blocking the transport of other proteins to the mitochondria, rather than by directly affecting ANT1's nucleotide trnsport role in the cell. This redefines our understanding of diseases associated with mitochondrial proteins, potentially altering how treatments for these conditions are designed.

First Report of Botryosphaeria dothidea Causing Stem Canker and Dieback of Apple Trees in Ontario, Canada.

Apple trees (Malus domestica L. Borkh.) exhibiting extensive and unknown tree fruit decline symptoms were observed in commercial orchards over the past 5 years in Ontario, Canada. The trees exhibited shoot dieback, attached wilted leaves and cankers on the main trunk. Trees with rapid development of cankers upward from the graft union developed extensive vascular discoloration that resulted in sudden collapse of the entire tree. In 2018-19, up to 42% mortality was observed on 2- to 8-year old apple trees. Nine symptomatic trees were collected from two orchards located in southwestern and one in southcentral Ontario. Samples (1 cm length) were collected from symptomatic trunk and shoot tissue, surface sterilized with 70% ethanol for 30 sec, followed by 1% NaClO for 20 min and three rinses in sterile water. The samples were air-dried and placed on a 2% potato dextrose agar (PDA, Difco) culture media supplemented with kanamycin (50 mg L-1). The PDA plates were incubated at 22°C for 5 days in the dark. All fungal colony-forming units that developed were hyphal-tip transferred to individual PDA plates and incubated at 22°C for 7 days in the dark. Purified mycelial isolates were classified into morphotypes prior to molecular identification. One morphotype showed white to olive-green colonies that developed on a moderately dense mycelial mat with aerial hyphae. Several solitary and globose black pycnidia that contained a single ostiole were produced on pine needles on PDA after incubation at 22°C for 14 days in the dark. Conidia were hyaline, fusiform, aseptate with an average size of 3.9 - 5.2 x 21.4 - 26.6 µm (N=50). Genomic DNA was extracted from 5-day old culture of a representative isolate, #M68-17, grown on PDA using the Plant/Fungi DNA Isolation Kit (Norgen Biotech Corp., Thorold, ON, Canada). The rDNA internal transcribed spacer (ITS), translation elongation factor 1- alpha gene (TEF-1α), and ß-tubulin gene (TUB2) were amplified using the primer pairs ITS1/ITS4 (White et al. 1990), EF1-728F/EF1-986R (Carbone and Kohn 1999), and Bt2a/Bt2b (O'Donnell et al. 1998), respectively, and sequenced. The nucleotide sequences obtained (GenBank # MZ926850, MZ934654, MZ934655) were 100.00% similar to those of Botyrosphaeria dothidea (Moug. ex Fr.) Ces. & De Not. isolates from other hosts in several countries in the NCBI database (MT111097, MT309401, MN515421, respectively). Randomized Accelerated Maximum Likelihood (RAxML) analysis using the three gene sequence data was completed (Stamatakis et al. 2008). The isolate #M68-17 was clustered with high bootstrap support values with the B. dothidea isolates from the fungal biodiversity centre (CBS) collection, including the ex-epitype (CBS 115476, CBS 110302) (Fig. 1). A living culture of the representative isolate, #M68-17, was deposited in the Canadian Collection of Fungal Cultures (DAOMC 252246). Pathogenicity tests were conducted in the lab on wood cuttings and in planta. Ten 20 cm apple cuttings and five potted one year old apple seedlings were surface sterilized, wounded and inoculated with 4 mm mycelium agar plug from a 5-day old culture of isolate #M68-17 and wrapped with Parafilm. Three control apple cuttings and seedlings were inoculated with PDA plugs and incubated in the same environment. Cuttings were placed inside a clear plastic container with moist paper towels and incubated at room temperature in the dark. Seedlings were placed in an open-air area between two greenhouses and watered as needed. Twelve days post-inoculation, the average length of the developed necrotic lesions on cuttings was 8.8 ± 0.4 cm. Necrotic and sunken canker symptoms appeared at 10 days, spread upward from the inoculation point and by 6 weeks the upper portion of the seedling was dead (Fig. 2). B. dothidea was isolated from all the inoculated cuttings and seedlings, thus fulfilling Koch's postulates. Control cuttings and seedlings showed no symptoms, and the fungus was not isolated from the wood. B. dothidea was reported as a pathogen causing cankers on a wide range of woody crop plants including apples, almonds, pistachios, hazelnut, walnut, olive and grapes in the United States, China, Uruguay, Spain, Tunisia and Turkey (Chebil et al. 2014; Delgado-Cerrone et al. 2016; Moral et al. 2019; Tang et al. 2012; Türkölmez et al. 2016). However, this is the first report of B. dothidea causing stem canker and death of young apple seedlings in Ontario, Canada. The findings suggest that B. dothidea has the potential to severely affect apple production in Ontario. Accurate identification of pathogen(s) associated with apple decline will support management of the disease.

The mRNA repressor TRIM71 cooperates with Nonsense-Mediated Decay factors to destabilize the mRNA of CDKN1A/p21.

Nonsense-mediated decay (NMD) plays a fundamental role in the degradation of premature termination codon (PTC)-containing transcripts, but also regulates the expression of functional transcripts lacking PTCs, although such 'non-canonical' functions remain ill-defined and require the identification of factors targeting specific mRNAs to the NMD machinery. Our work identifies the stem cell-specific mRNA repressor protein TRIM71 as one of these factors. TRIM71 plays an essential role in embryonic development and is linked to carcinogenesis. For instance, TRIM71 has been correlated with advanced stages and poor prognosis in hepatocellular carcinoma. Our data shows that TRIM71 represses the mRNA of the cell cycle inhibitor and tumor suppressor CDKN1A/p21 and promotes the proliferation of HepG2 tumor cells. CDKN1A specific recognition involves the direct interaction of TRIM71 NHL domain with a structural RNA stem-loop motif within the CDKN1A 3'UTR. Importantly, CDKN1A repression occurs independently of miRNA-mediated silencing. Instead, the NMD factors SMG1, UPF1 and SMG7 assist TRIM71-mediated degradation of CDKN1A mRNA, among other targets. Our data sheds light on TRIM71-mediated target recognition and repression mechanisms and uncovers a role for this stem cell-specific factor and oncogene in non-canonical NMD, revealing the existence of a novel mRNA surveillance mechanism which we have termed the TRIM71/NMD axis.

Implementation of Physical Activity into routine Clinical pracTice in Rheumatic Musculoskeletal Disease: The IMPACT-RMD study protocol and rationale.

BACKGROUND: Physical activity is an important intervention for improving disease-related symptoms and systemic manifestations in rheumatic and musculoskeletal disease (RMDs). However, studies suggest that RMD patients report that the lack of individualized and consistent information about physical activity from managing doctors and healthcare professionals, acts as a barrier for engagement. On the other hand, managing doctors and healthcare professionals report lack of knowledge in this area and thus lack of confidence to educate and advise RMD patients about the beneficial effects of physical activity. The aim of the present study therefore, is to develop two e-Learning courses for RMD doctors and health professionals: a) the first one to provide consistent information about the collective benefits of physical activity in RMDs and b) the second on how to implement physical activity advice in routine clinical practice. METHODS: An international collaboration of seven countries, consisting of one academic institution and one patient organization from each country, will co-develop the two e-Learning courses. The final e-Learning courses will primarily target to improve - through physical activity advice - RMD symptoms which are important for patients. DISCUSSION: The main result of this study will be to co-develop two e-Learning courses that can be used by managing RMD doctors and healthcare professionals to be made aware of the overall benefits of physical activity in RMDs as well as how to implement physical activity advise within their practice.

The influence of macrophage growth factors on Theiler's Murine Encephalomyelitis Virus (TMEV) infection and activation of macrophages.

Macrophages are common targets for infection and innate immune activation by many pathogenic viruses including the neurotropic Theiler's Murine Encephalomyelitis Virus (TMEV). As both infection and innate activation of macrophages are key determinants of viral pathogenesis especially in the central nervous system (CNS), an analysis of macrophage growth factors on these events was performed. C3H mouse bone-marrow cells were differentiated in culture using either recombinant macrophage colony stimulating factor (M-CSF) or granulocyte-macrophage colony-stimulating factor (GM-CSF), inoculated with TMEV (BeAn) and analyzed at various times thereafter. Cytokine RNA and protein analysis, virus titers, and flow cytometry were performed to characterize virological parameters under these culture conditions. GM-CSF-differentiated macrophages showed higher levels of TMEV viral RNA and proinflammatory molecules compared to infected M-CSF-differentiated cells. Thus, GM-CSF increases both TMEV infection and TMEV-induced activation of macrophages compared to that seen with M-CSF. Moreover, while infectious viral particles decreased from a peak at 12h to undetectable levels at 48h post infection, TMEV viral RNA remained higher in GM-CSF- compared to M-CSF-differentiated macrophages in concert with increased proinflammatory gene expression. Analysis of a possible basis for these differences determined that glycolytic rates contributed to heightened virus replication and proinflammatory cytokine secretion in GM-CSF compared to M-CSF-differentiated macrophages. In conclusion, we provide evidence implicating a role for GM-CSF in promoting virus replication and proinflammatory cytokine expression in macrophages, indicating that GM-CSF may be a key factor for TMEV infection and the induction of chronic TMEV-induced immunopathogenesis in the CNS.

Co-existence of intact stemness and priming of neural differentiation programs in mES cells lacking Trim71.

Regulatory networks for differentiation and pluripotency in embryonic stem (ES) cells have long been suggested to be mutually exclusive. However, with the identification of many new components of these networks ranging from epigenetic, transcriptional, and translational to even post-translational mechanisms, the cellular states of pluripotency and early differentiation might not be strictly bi-modal, but differentiating stem cells appear to go through phases of simultaneous expression of stemness and differentiation genes. Translational regulators such as RNA binding proteins (RBPs) and micro RNAs (miRNAs) might be prime candidates for guiding a cell from pluripotency to differentiation. Using Trim71, one of two members of the Tripartite motif (Trim) protein family with RNA binding activity expressed in murine ES cells, we demonstrate that Trim71 is not involved in regulatory networks of pluripotency but regulates neural differentiation. Loss of Trim71 in mES cells leaves stemness and self-maintenance of these cells intact, but many genes required for neural development are up-regulated at the same time. Concordantly, Trim71(-/-) mES show increased neural marker expression following treatment with retinoic acid. Our findings strongly suggest that Trim71 keeps priming steps of differentiation in check, which do not pre-require a loss of the pluripotency network in ES cells.

SHP-1-dependent macrophage differentiation exacerbates virus-induced myositis.

Virus-induced myositis is an emerging global affliction that remains poorly characterized with few treatment options. Moreover, muscle-tropic viruses often spread to the CNS, causing dramatically increased morbidity. Therefore, there is an urgent need to explore genetic factors involved in this class of human disease. This report investigates critical innate immune pathways affecting murine virus-induced myositis. Of particular importance, the key immune regulator src homology region 2 domain-containing phosphatase 1 (SHP-1), which normally suppresses macrophage-mediated inflammation, is a major factor in promoting clinical disease in muscle. We show that Theiler's murine encephalomyelitis virus (TMEV) infection of skeletal myofibers induces inflammation and subsequent dystrophic calcification, with loss of ambulation in wild-type (WT) mice. Surprisingly, although similar extensive myofiber infection and inflammation are observed in SHP-1(-/-) mice, these mice neither accumulate dead calcified myofibers nor lose ambulation. Macrophages were the predominant effector cells infiltrating WT and SHP-1(-/-) muscle, and an increased infiltration of immature monocytes/macrophages correlated with an absence of clinical disease in SHP-1(-/-) mice, whereas mature M1-like macrophages corresponded with increased myofiber degeneration in WT mice. Furthermore, blocking SHP-1 activation in WT macrophages blocked virus-induced myofiber degeneration, and pharmacologic ablation of macrophages inhibited muscle calcification in TMEV-infected WT animals. These data suggest that, following TMEV infection of muscle, SHP-1 promotes M1 differentiation of infiltrating macrophages, and these inflammatory macrophages are likely involved in damaging muscle fibers. These findings reveal a pathological role for SHP-1 in promoting inflammatory macrophage differentiation and myofiber damage in virus-infected skeletal muscle, thus identifying SHP-1 and M1 macrophages as essential mediators of virus-induced myopathy.

Connexin43 is dispensable for phagocytosis.

Macrophages that lack connexin43 (Cx43), a gap junction protein, have been reported to exhibit dramatic deficiencies in phagocytosis. In this study, we revisit these findings using well-characterized macrophage populations. Cx43 knockout (Cx43(-/-)) mice die soon after birth, making the harvest of macrophages from adult Cx43(-/-) mice problematic. To overcome this obstacle, we used several strategies: mice heterozygous for the deletion of Cx43 were crossed to produce Cx43(+/+) (wild type [WT]) and Cx43(-/-) fetuses. Cells isolated from 12- to 14-d fetal livers were used to reconstitute irradiated recipient animals. After reconstitution, thioglycollate-elicited macrophages were collected by peritoneal lavage and bone marrow was harvested. Bone marrow cells and, alternatively, fetal liver cells were cultured in media containing M-CSF for 7-10 d, resulting in populations of cells that were >95% macrophages based on flow cytometry. Phagocytic uptake was detected using flow cytometric and microscopic techniques. Quantification of phagocytic uptake of IgG-opsonized sheep erythrocytes, zymosan particles, and Listeria monocytogenes failed to show any significant difference between WT and Cx43(-/-) macrophages. Furthermore, the use of particles labeled with pH-sensitive dyes showed equivalent acidification of phagosomes in both WT and Cx43(-/-) macrophages. Our findings suggest that modulation of Cx43 levels in cultured macrophages does not have a significant impact on phagocytosis.

Isolation, expansion and functional assessment of CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients awaiting kidney transplantation.

BACKGROUND: The immunosuppressive properties of regulatory T cells have emerged as an attractive tool for the development of immunotherapies in various disease contexts, e.g. to treat transplantation induced immune reactions. This paper focuses on the process of obtaining and functionally characterizing CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients awaiting kidney transplantation. METHODS: From October 2010 to March 2011 uremic patients awaiting living donor kidney transplantation, and their corresponding kidney donors, were enrolled in the study. A total of seven pairs were included. Isolation of CD4+CD25+FoxP3+ regulatory T cells was performed by magnetic activated cell sorting of peripheral blood mononuclear cells obtained from the uremic patients. Donor specific Tr1 cells were differentiated by repetitive stimulation of immature CD4+ T cells with immature dendritic cells, with the T cells coming from the future kidney recipients and the dendritic cells from the corresponding kidney donors. Cells were then expanded and functionally characterized by the one-way mixed leukocyte reaction and assessment of IL-10 production. Phenotypic analysis was performed by flow cytometry. RESULTS: The fraction of CD4+CD25+FoxP3+ regulatory T cells after expansion varied from 39.1 to 50.4% and the cells retained their ability to substantially suppress the mixed leukocyte reaction in all but one patient (3.8-19.2% of the baseline stimulated leukocyte activity, p<0.05). Tr1 cells were successfully differentiated from all but one patient and produced high levels of IL-10 when stimulated with immature dendritic cells (1,275-11,038% of the baseline IL-10 secretion, p<0.05). CONCLUSION: It is practically feasible to obtain and subsequently expand CD4+CD25+FoxP3+ regulatory T cells and Tr1 cells from uremic patients without loss of function as assessed by in vitro analyses. This forms a base for adoptive regulatory T cell therapy in the setting of living donor kidney transplantation.

Practice environments of nurses in ambulatory oncology settings: a thematic analysis.

BACKGROUND: : The practice environments of nurses have been studied extensively in inpatient settings, but rarely in the ambulatory context. As the majority of cancer care is delivered in ambulatory settings, a better understanding of the nursing practice environment may contribute to quality improvement efforts. OBJECTIVE: : We sought to examine the features of nursing practice environments that contribute to quality patient care and nursing job satisfaction. METHODS: : In 2009-2010, we conducted focus groups with nurses who cared for adults with cancer outside inpatient units. A semistructured moderator guide explored practice environment features that promoted safe, high-quality care and high job satisfaction. We also asked nurses to identify practice environment features that hindered quality care and reduced job satisfaction. We conducted thematic analysis to report themes and to construct a conceptual framework. RESULTS: : From 2 focus groups, composed of 13 participants, nurses reported that variability in workloads, support from managers and medical assistants, and the practice's physical resources could facilitate or hinder high-quality care and job satisfaction. High-quality communication across team members improved patient safety and satisfaction. CONCLUSIONS: : Consistent with research findings from inpatient settings, nurses identified staffing and resource adequacy, management support, and collegiality as important inputs to high-quality care. IMPLICATIONS FOR PRACTICE: : These findings can inform quality improvement initiatives in ambulatory oncology practices. Strengthening nurse-medical assistant relationships, smoothing patient workload variability, and implementing strategies to strengthen communication may contribute to quality cancer care. Studies to test our proposed conceptual framework would bridge existing knowledge gaps in ambulatory settings.

Development of biocontrol agents from food microbial isolates for controlling post-harvest peach brown rot caused by Monilinia fructicola.

An unconventional strategy of screening food microbes for biocontrol activity was used to develop biocontrol agents for controlling post-harvest peach brown rot caused by Monilinia fructicola. Forty-four microbial isolates were first screened for their biocontrol activity on apple fruit. Compared with the pathogen-only check, seven of the 44 isolates reduced brown rot incidence by >50%, including four bacteria: Bacillus sp. C06, Lactobacillus sp. C03-b and Bacillus sp. T03-c, Lactobacillus sp. P02 and three yeasts: Saccharomyces delbrueckii A50, S. cerevisiae YE-5 and S. cerevisiae A41. Eight microbial isolates were selected for testing on peaches by wound co-inoculation with mixtures of individual microbial cultures and conidial suspension of M. fructicola. Only two of them showed significant biocontrol activity after five days of incubation at 22 degrees C. Bacillus sp. C06 suppressed brown rot incidence by 92% and reduced lesion diameter by 88% compared to the pathogen-only check. Bacillus sp.T03-c reduced incidence and lesion diameter by 40% and 62%, respectively. The two isolates were compared with Pseudomonas syringae MA-4, a biocontrol agent for post-harvest peach diseases, by immersing peaches in an aliquot containing individual microbial isolates and the pathogen conidia. Treatments with isolates MA-4, C06 and T03-c significantly controlled brown rot by 91, 100, and 100% respectively. However, only isolates MA-4 and C06 significantly reduced brown rot by 80% and 15%, respectively when bacterial cells alone were applied. On naturally infected peaches, both the bacterial culture and its cell-free filtrate of the isolate C06 significantly controlled peach decay resulting in 77 and 90% reduction, respectively, whereas the treatment using only the bacterial cells generally had no effect. Isolate C06 is a single colony isolate obtained from a mesophilic cheese starter, and has been identified belonging to Bacillus amyloliquefaciens. The results have clearly demonstrated that isolate C06 has a great potential for being developed into a biocontrol agent.

Capillary electrophoresis for monitoring the effects of plasmapheresis: a feasibility study.

Plasmapheresis is an established method to treat patients with large monoclonal gammopathies (M-components) that increases the blood viscosity. During plasmapheresis the patient plasma is substituted with a mixture of saline, albumin and normal plasma. The treatment results in a reduction of the M-component in the circulation. Plasmapheresis causes changes in several proteins, which makes monitoring by nephelometric or turbidimetric analysis of specific proteins less suitable. Quantification of paraproteins by nephelometric assays are also known to be associated with technical problems. An alternative could be agarose gel electrophoresis but this method is too slow to permit monitoring during the plasmapheresis. Capillary electrophoresis of plasma proteins can be performed in less than 10 min. We have used the CAPILLARYS capillary electrophoresis system (Sebia, Paris, France) to monitor the effect of plasmapheresis treatment on 22 occasions. The mean reduction in M-component size was 51%, range 33-61%. Capillary electrophoresis is a rapid and inexpensive method that could be used to monitor the effect of plasmapheresis during the actual treatment.

Genetic basis of the K(0) phenotype in the Swedish population.

BACKGROUND: The absence of all Kell blood group antigens (K(0) phenotype) is very rare. K(0) persons, however, can produce clinically significant anti-Ku (K5) after transfusion and/or pregnancy and require K(0) blood for transfusion. Ten alleles giving rise to the K(0) phenotype have been reported: different populations were studied although none from Scandinavia. STUDY DESIGN AND METHODS: Three K(0) samples were identified by blood banks in Sweden (Uppsala, Umeå, and Linköping) during a 20-year period. Kell antigen typing was performed with standard serologic techniques by the respective blood banks and K(0) status was confirmed by the International Blood Group Reference Laboratory in Bristol, England. Polymerase chain reaction and DNA sequencing of the KEL coding region (exons 1-19) was performed on genomic DNA. RESULTS: The Uppsala K(0) was homozygous for a 1540C>T substitution in exon 13, leading to an immediate stop codon. The Umeå K(0) was homozygous for 1023delG in exon 8 that results in a frameshift and a premature stop codon in exon 9. In the Linköping K(0), a previously reported mutation g>a at +1 of intron 3 was found. CONCLUSION: Two novel and one previously reported null alleles at the KEL locus are described. The identified nonsense mutations abolish expression of the Kell glycoprotein and are thus responsible for the K(0) phenotype in these Swedish families.

No evidence that polyandry benefits females in Drosophila melanogaster.

Understanding the evolution of polyandry (mating with multiple males) is a major issue in the study of animal breeding systems. We examined the adaptive significance of polyandry in Drosophila melanogaster, a species with well-documented costs of mating in which males generally cannot force copulations. We found no direct fitness advantages of polyandry. Females that mated with multiple males had no greater mean fitness and no different variance in fitness than females that mated repeatedly with the same male. Subcomponents of reproductive success, including fecundity, egg hatch rate, larval viability, and larval development time, also did not differ between polyandrous and monogamous females. Polyandry had no affect on progeny sex ratios, suggesting that polyandry does not function against costly sex-ratio distorters. We also found no evidence that polyandry functions to favor the paternity of males successful in precopulatory sexual selection. Experimentally controlled opportunities for precopulatory sexual selection had no effect on postcopulatory sperm precedence. Although these results were generally negative, they are supported with substantial statistical power and they help narrow the list of evolutionary explanations for polyandry in an important model species.

Ejaculate-female coevolution in Drosophila mojavensis.

Interspecific studies indicate that sperm morphology and other ejaculatory traits diverge more rapidly than other types of character in Drosophila and other taxa. This pattern has largely been attributed to postcopulatory sexual selection involving interaction between the sexes. Such divergence has been suggested to lead rapidly to reproductive isolation among populations and thus to be an 'engine of speciation.' Here, we test two critical predictions of this hypothesis: (i) there is significant variation in reproductive traits among incipient species; and (ii) divergence in interacting sex-specific traits exhibits a coevolutionary pattern among populations within a species, by examining geographical variation in Drosophila mojavensis, a species in the early stages of speciation. Significant among-population variation was identified in sperm length and female sperm-storage organ length, and a strong pattern of correlated evolution between these interacting traits was observed. In addition, crosses among populations revealed coevolution of male and female contributions to egg size. Support for these two important predictions confirms that coevolving internal characters that mediate successful reproduction may play an important part in speciation. The next step is to determine exactly what that role is.

Characterization of the citrate/acetate antiporter CitW of Klebsiella pneumoniae.

The genome of Klebsiella pneumoniae contains at least three different genes encoding citrate transporters. Recently, a third and hitherto unknown gene encoding a citrate transport system ( citW) was identified. Escherichia coli transformed with a plasmid expressing citW was able to grow on citrate as sole carbon and energy source, identifying CitW as a citrate carrier. In this report, we provide evidence that further specifies CitW as a Na(+)-independent citrate/citrate and citrate/acetate exchanger. Kinetic analysis of citrate uptake at different pH values identified Hcitrate(2-) as the transported citrate species, with a K(m) of 25 microM. Since citW is expressed under anoxic conditions and acetate is the main end-product of citrate fermentation in K. pneumoniae, citrate/acetate exchange might be its in vivo function. Sequence similarity searches identified CitW (454 amino acids, 48.15 kDa) as a member of the 2-hydroxycarboxylate transporter family (TC 2.A.24). The substrate specificity seems to partially contradict this phylogenetic classification, but appears logical with respect to the putative functional role of CitW in the citrate fermentation pathway of K. pneumoniae.

Identification of a gene cluster in Klebsiella pneumoniae which includes citX, a gene required for biosynthesis of the citrate lyase prosthetic group.

The biosynthesis of the 2'-(5"-phosphoribosyl)-3'-dephospho-coenzyme A (CoA) prosthetic group of citrate lyase (EC 4.1.3.6), a key enzyme of citrate fermentation, proceeds via the initial formation of the precursor 2'-(5"-triphosphoribosyl)-3'-dephospho-CoA and subsequent transfer to apo-citrate lyase with removal of pyrophosphate. In Escherichia coli, the two steps are catalyzed by CitG and CitX, respectively, and the corresponding genes are part of the citrate lyase gene cluster, citCDEFXG. In the homologous citCDEFG operon of Klebsiella pneumoniae, citX is missing. A search for K. pneumoniae citX led to the identification of a second genome region involved in citrate fermentation which comprised the citWX genes and the divergent citYZ genes. The citX gene was confirmed to encode holo-citrate lyase synthase, whereas citW was shown to encode a citrate carrier, the third one identified in this species. The citYZ genes were found to encode a two-component system consisting of the sensor kinase CitY and the response regulator CitZ. Remarkably, both proteins showed >or=40% sequence identity to the citrate-sensing CitA-CitB two-component system, which is essential for the induction of the citrate fermentation genes in K. pneumoniae. A citZ insertion mutant was able to grow anaerobically with citrate, indicating that CitZ is not essential for expression of citrate fermentation genes. CitX synthesis was induced to a basal level under anaerobic conditions, independent of citrate, CitB, and CitZ, and to maximal levels during anaerobic growth with citrate as the sole carbon source. Similar to the other citrate fermentation enzymes, CitX synthesis was apparently subject to catabolite repression.