Emerging patterns of plasmid-host coevolution that stabilize antibiotic resistance

Multidrug resistant bacterial pathogens have become a serious global human health threat, and conjugative plasmids are important drivers of the rapid spread of resistance to last-resort antibiotics. Whereas antibiotics have been shown to select for adaptation of resistance plasmids to their new bacterial hosts, or vice versa, a general evolutionary mechanism has not yet emerged. Here we conducted an experimental evolution study aimed at determining general patterns of plasmid-bacteria evolution. Specifically, we found that a large conjugative resistance plasmid follows the same evolutionary trajectories as its non-conjugative mini-replicon in the same and other species. Furthermore, within a single host-plasmid pair three distinct patterns of adaptive evolution led to increased plasmid persistence: i) mutations in the replication protein gene (trfA1); ii) the acquisition by the resistance plasmid of a transposon from a co-residing plasmid encoding a putative toxin-antitoxin system; iii) a mutation in the host's global transcriptional regulator gene fur. Since each of these evolutionary solutions individually have been shown to increase plasmid persistence in other plasmid-host pairs, our work points towards common mechanisms of plasmid stabilization. These could become the targets of future alternative drug therapies to slow down the spread of antibiotic resistance.

Evolved plasmid-host interactions reduce plasmid interference cost

Antibiotic selection drives adaptation of antibiotic resistance plasmids to new bacterial hosts, but the molecular mechanisms are still poorly understood. We previously showed that a broad-host-range plasmid was poorly maintained in Shewanella oneidensis, but rapidly adapted through mutations in the replication initiation gene trfA1. Here we examined if these mutations reduced the fitness cost of TrfA1, and whether this was due to changes in interaction with the host's DNA helicase DnaB. The strains expressing evolved TrfA1 variants showed a higher growth rate than those expressing ancestral TrfA1. The evolved TrfA1 variants showed a lower affinity to the helicase than ancestral TrfA1 and were no longer able to activate the helicase at the oriV without host DnaA. Moreover, persistence of the ancestral plasmid was increased upon overexpression of DnaB. Finally, the evolved TrfA1 variants generated higher plasmid copy numbers than ancestral TrfA1. The findings suggest that ancestral plasmid instability can at least partly be explained by titration of DnaB by TrfA1. Thus under antibiotic selection resistance plasmids can adapt to a novel bacterial host through partial loss of function mutations that simultaneously increase plasmid copy number and decrease unfavorably high affinity to one of the hosts' essential proteins.

Evolutionary Paths That Expand Plasmid Host-Range: Implications for Spread of Antibiotic Resistance

The World Health Organization has declared the emergence of antibiotic resistance to be a global threat to human health. Broad-host-range plasmids have a key role in causing this health crisis because they transfer multiple resistance genes to a wide range of bacteria. To limit the spread of antibiotic resistance, we need to gain insight into the mechanisms by which the host range of plasmids evolves. Although initially unstable plasmids have been shown to improve their persistence through evolution of the plasmid, the host, or both, the means by which this occurs are poorly understood. Here, we sought to identify the underlying genetic basis of expanded plasmid host-range and increased persistence of an antibiotic resistance plasmid using a combined experimental-modeling approach that included whole-genome resequencing, molecular genetics and a plasmid population dynamics model. In nine of the ten previously evolved clones, changes in host and plasmid each slightly improved plasmid persistence, but their combination resulted in a much larger improvement, which indicated positive epistasis. The only genetic change in the plasmid was the acquisition of a transposable element from a plasmid native to the Pseudomonas host used in these studies. The analysis of genetic deletions showed that the critical genes on this transposon encode a putative toxin-antitoxin (TA) and a cointegrate resolution system. As evolved plasmids were able to persist longer in multiple naïve hosts, acquisition of this transposon also expanded the plasmid's host range, which has important implications for the spread of antibiotic resistance.

Reciprocal inhibition becomes facilitation after spinal cord injury: clinical application of a system identification approach

Alteration in spinal inputs from descending pathways following spinal cord injury (SCI) affects different mechanisms including reciprocal Ia inhibition. However, whether there is a consistent pattern of change in reciprocal inhibition following SCI is uncertain. Typical attempts to evaluate reciprocal inhibition have been restricted to electrophysiological measurements, which may have limited translation to function. Our objective was to address the uncertainty regarding changes in reciprocal inhibition after SCI by quantitatively evaluating reciprocal inhibition of ankle extensors from ankle flexors using our novel, more functionally relevant system identification approach. To evaluate reciprocal inhibition using the system identification technique, a series of small-amplitude PseudoRandom Binary Sequence (PRBS) perturbations were applied to the ankle when subjects contracted their dorsiflexors. Depression of reflex stiffness with tibialis anterior (TA) activation was evaluated as reciprocal inhibition. Our results showed that reflex stiffness decreased continuously as dorsiflexor torque increased in the healthy control subjects whereas it remained almost unchanged in the SCI subjects, indicating the absence of reciprocal inhibition in patients. This pattern was consistent with the results obtained from electrophysiological measures in a exploratory control experiment revealing depression of the control H-reflex but no change to the SCI H-reflex. These findings suggest that our system identification mechanical technique is a reliable and valid approach for evaluating reciprocal inhibition. Furthermore, our results demonstrate that reciprocal inhibition can diminish or change to reciprocal facilitation after SCI, which in turn can result in reflex hyperexcitability and unwanted activity of ankle extensors triggered by TA activity. This suggests that reciprocal facilitation may play a major role in pathophysiology of spasticity and impaired function.

Host range diversification within the IncP-1 plasmid group

Broad-host-range plasmids play a critical role in the spread of antibiotic resistance and other traits. In spite of increasing information about the genomic diversity of closely related plasmids, the relationship between sequence divergence and host range remains unclear. IncP-1 plasmids are currently classified into six subgroups based on the genetic distance of backbone genes. We investigated whether plasmids from two subgroups exhibit a different host range, using two IncP-1γ plasmids, an IncP-1β plasmid and their minireplicons. Efficiencies of plasmid establishment and maintenance were compared using five species that belong to the Alphaproteobacteria, Betaproteobacteria and Gammaproteobacteria. The IncP-1β plasmid replicated and persisted in all five hosts in the absence of selection. Of the two IncP-1γ plasmids, both were unable to replicate in alphaproteobacterial host Sphingobium japonicum, and one established itself in Agrobacterium tumefaciens but was very unstable. In contrast, both IncP-1γ minireplicons, which produced higher levels of replication initiation protein than the wild-type plasmids, replicated in all strains, suggesting that poor establishment of the native plasmids is in part due to suboptimal replication initiation gene regulation. The findings suggest that host ranges of distinct IncP-1 plasmids only partially overlap, which may limit plasmid recombination and thus result in further genome divergence.

Comparative genomics of IncP-1ε plasmids from water environments reveals diverse and unique accessory genetic elements

The goal of this study was to determine and compare the complete genome sequences of three new broad-host-range conjugative plasmids. Plasmids pMLUA1, pMLUA3 and pMLUA4 were previously recovered from estuarine water by exogenous plasmid isolation and ranged in size from ∼55 to 59 kb. Comparative genomics showed that their backbone region was identical to the prototype pKJK5 and other IncP1-ε plasmids captured from soils. The accessory region was inserted between the tra region and parA, and presented the typical IncP-1ε ISPa17 and Tn402-like transposon modules. Nevertheless, new class 1 integrons were identified (In794, carrying aadA5 and In795, carrying qacF5-aadA5), as well as a composite transposon IS26-msr(E)-mph(E)-IS26 carrying genes that confer resistance to macrolides. A new insertion sequence, termed ISUnCu17, was also identified on pMLUA3. The architecture of the accessory regions implies the occurrence of multiple insertions and deletions. These data support the notion that IncP-1 plasmids from the ε subgroup are proficient in the capture of diverse genetic elements, including antibiotic resistance genes, and thus may contribute to the co-selection of several resistance determinants. This study constitutes the first report of completely sequenced IncP-1ε plasmids from water environments, and enhances our understanding of the geographic distribution and genetic diversity of these replicons.

Invasion of E. coli biofilms by antibiotic resistance plasmids

In spite of the contribution of plasmids to the spread of antibiotic resistance in human pathogens, little is known about the transferability of various drug resistance plasmids in bacterial biofilms. The goal of this study was to compare the efficiency of transfer of 19 multidrug resistance plasmids into Escherichia coli recipient biofilms and determine the effects of biofilm age, biofilm-donor exposure time, and donor-to-biofilm attachment on this process. An E. coli recipient biofilm was exposed separately to 19 E. coli donors, each with a different plasmid, and transconjugants were determined by plate counting. With few exceptions, plasmids that transferred well in a liquid environment also showed the highest transferability in biofilms. The difference in transfer frequency between the most and least transferable plasmid was almost a million-fold. The 'invasibility' of the biofilm by plasmids, or the proportion of biofilm cells that acquired plasmids within a few hours, depended not only on the type of plasmid, but also on the time of biofilm exposure to the donor and on the ability of the plasmid donor to attach to the biofilm, yet not on biofilm age. The efficiency of donor strain attachment to the biofilm was not affected by the presence of plasmids. The most invasive plasmid was pHH2-227, which based on genome sequence analysis is a hybrid between IncU-like and IncW plasmids. The wide range in transferability in an E. coli biofilm among plasmids needs to be taken into account in our fight against the spread of drug resistance.

Transforming neurorehabilitation of walking following stroke: the promise of non-invasive brain stimulation--a review

PURPOSE

This narrative review discusses the neurophysiology of human motor cortex as it influences gait, and recent advances in the application of non-invasive brain stimulation to the lower limb motor cortex of stroke survivors. Although walking is a high priority following stroke, the efficacy of promising new therapies has yet to warrant their widespread clinical use. For the upper limb, numerous brain stimulation protocols have been described. These protocols, adapted for the leg, are now being used to examine the cortical control of gait. This research discounts the long-held notion that "we walk from our spinal cords".

METHODS

Our review describes this research as it relates to the lower limb, especially the use of non-invasive brain stimulation to enhance neuroplasticity. The review also discusses the possible development of a prognostic algorithm for walking recovery after stroke.

CONCLUSION

This review concludes with the expectation that novel brain stimulation protocols combined with therapy will eventually demonstrate a level of effectiveness sufficient to promote their wide acceptance in neurorehabilitation settings.

The complete genome sequences of four new IncN plasmids from wastewater treatment plant effluent provide new insights into IncN plasmid diversity and evolution

The dissemination of antibiotic resistance genes among bacteria often occurs by means of plasmids. Wastewater treatment plants (WWTP) were previously recognized as hot spots for the horizontal transfer of genetic material. One of the plasmid groups that is often associated with drug resistance is the incompatibility group IncN. The aim of this study was to gain insights into the diversity and evolutionary history of IncN plasmids by determining and comparing the complete genome sequences of the four novel multi-drug resistance plasmids pRSB201, pRSB203, pRSB205 and pRSB206 that were exogenously isolated from the final effluent of a municipal WWTP. Their sizes range between 42,875 bp and 56,488 bp and they share a common set of backbone modules that encode plasmid replication initiation, conjugative transfer, and plasmid maintenance and control. All plasmids are transferable at high rates between Escherichia coli strains, but did not show a broad host range. Different genes conferring resistances to ampicillin, streptomycin, spectinomycin, sulfonamides, tetracycline and trimethoprim were identified in accessory modules inserted in these plasmids. Comparative analysis of the four WWTP IncN plasmids and IncN plasmids deposited in the NCBI database enabled the definition of a core set of backbone genes for this group. Moreover, this approach revealed a close phylogenetic relationship between the IncN plasmids isolated from environmental and clinical samples. Phylogenetic analysis also suggests the existence of host-specific IncN plasmid subgroups. In conclusion, IncN plasmids likely contribute to the dissemination of resistance determinants between environmental bacteria and clinical strains. This is of particular importance since multi-drug resistance IncN plasmids have been previously identified in members of the Enterobacteriaceae that cause severe infections in humans.

Sequencing and comparative analysis of IncP-1α antibiotic resistance plasmids reveal a highly conserved backbone and differences within accessory regions

Although IncP-1 plasmids are important for horizontal gene transfer among bacteria, in particular antibiotic resistance spread, so far only three plasmids from the subgroup IncP-1α have been completely sequenced. In this study we doubled this number. The three IncP-1α plasmids pB5, pB11 and pSP21 were isolated from bacteria of two different sewage treatment plants and sequenced by a combination of next-generation and capillary sequencing technologies. A comparative analysis including the previously analysed IncP-1α plasmids RK2, pTB11 and pBS228 revealed a highly conserved plasmid backbone (at least 99.9% DNA sequence identity) comprising 54 core genes. The accessory elements of the plasmid pB5 constitute a class 1 integron interrupting the parC gene and an IS6100 copy inserted into the integron. In addition, the tetracycline resistance genes tetAR and the ISTB11-like element are located between the klc operon and the trfA-ssb operon. Plasmid pB11 is loaded with a Tn5053-like mercury resistance transposon between the parCBA and parDE operons and contains tetAR that are identical to those identified in plasmid pB5 and the insertion sequence ISSP21. Plasmid pSP21 harbours an ISPa7 element in a Tn402 transposon including a class 1 integron between the partitioning genes parCBA and parDE. The IS-element ISSP21 (99.89% DNA sequence identity to ISSP21 from pB11), inserted downstream of the tetR gene and a copy of ISTB11 (identical to ISTB11 on pTB11) inserted between the genes pncA and pinR. On all three plasmids the accessory genes are almost always located between the backbone modules confirming the importance of the backbone functions for plasmid maintenance. The striking backbone conservation among the six completely sequenced IncP-1α plasmids is in contrast to the much higher diversity within the IncP-1β subgroup.

Dual reporter system for in situ detection of plasmid transfer under aerobic and anaerobic conditions

We designed a new genetic tool to detect plasmid transfer under anaerobic and aerobic conditions. The system is based on the T7 RNA polymerase gene and a T7 promoter-driven oxygen-independent green fluorescent protein, evoglow, alone or in combination with red fluorescent protein DsRed. Constructs are available as plasmids and mini-mariner transposons.

Cardioprotective effects of cerium oxide nanoparticles in a transgenic murine model of cardiomyopathy

OBJECTIVE

Cerium oxide (CeO2) nanoparticles have been shown to protect cells in culture from lethal stress, but no protection in vivo has been reported. Cardiac-specific expression of monocyte chemoattractant protein (MCP)-1 in mice causes ischemic cardiomyopathy associated with activation of endoplasmic reticulum (ER) stress. The aim of this study was to assess the effects of CeO2 nanoparticles on cardiac function and remodeling as well as ER stress response in this murine model of cardiomyopathy.

METHODS

MCP-1 transgenic mice (MCP mice) and wild-type controls were administered intravenously 15 nmol of CeO2 nanoparticles or vehicle only twice a week for 2 weeks. Cardiac function, myocardial histology, nitrotyrosine formation, expression of cytokines, and ER stress-associated genes were evaluated.

RESULTS

Treatment with CeO2 nanoparticles markedly inhibited progressive left ventricular dysfunction and dilatation in MCP mice and caused a significant decrease in serum levels of MCP-1, C-reactive protein, and total nitrated proteins. The infiltration of monocytes/macrophages, accumulation of 3-nitrotyrosine, apoptotic cell death, and expression of proinflammatory cytokines, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 in the myocardium were markedly inhibited by CeO2 nanoparticles. Expression of the key ER stress-associated genes, including glucose-regulated protein 78 (Grp78), protein disulfide isomerase (PDI), and heat shock proteins (HSP25, HSP40, HSP70), were also suppressed by CeO2 nanoparticles.

CONCLUSIONS

CeO2 nanoparticles protect against the progression of cardiac dysfunction and remodeling by attenuation of myocardial oxidative stress, ER stress, and inflammatory processes probably through their autoregenerative antioxidant properties.

Activation of endoplasmic reticulum stress response during the development of ischemic heart disease

Endoplasmic reticulum (ER) stress has been found to be associated with neurodegenerative diseases and diabetes mellitus. Whether ER stress is involved in the development of heart disease is not known. Cardiac-specific expression of monocyte chemoattractant protein-1 (MCP-1) in mice causes the development of ischemic heart disease. Here we report that microarray analysis of gene expression changes in the heart of these transgenic mice revealed that a cluster of ER stress-related genes was transcriptionally activated in the heart during the development of ischemic heart disease. The gene array results were verified by quantitative real-time PCR that showed highly elevated transcript levels of genes involved in unfolded protein response such as ER and cytoplasmic chaperones, oxidoreductases, protein disulfide isomerase (PDI) family, and ER-associated degradation system such as ubiquitin. Immunoblot analysis confirmed the expression of chaperones, PDI, and ubiquitin. Immunohistochemical analyses showed that ER stress proteins were associated mainly with the degenerating cardiomyocytes. A novel ubiquitin fold modifier (Ufm1) that has not been previously associated with ER stress and not found to be induced under any condition was also found to be upregulated in the hearts of MCP mice (transgenic mice that express MCP-1 specifically in the heart). The present results strongly suggest that activation of ER stress response is involved in the development of ischemic heart disease in this murine model.

Homoserine and asparagine are host signals that trigger in planta expression of a pathogenesis gene in Nectria haematococca

Some pathogenesis-related genes are expressed in fungi only when the pathogen is in the host, but the host signals that trigger these gene expressions have not been identified. Virulent Nectria haematococca infects pea plants and requires either pelA, which is induced by pectin, or pelD, which is induced only in planta. However, the host signal(s) that trigger pelD expression was unknown. Here we report the isolation of the host signals and identify homoserine and asparagine, two free amino acids found in uniquely high levels in pea seedlings, as the pelD-inducing signals. N. haematococca has evolved a mechanism to sense the host tissue environment by using the high levels of two free amino acids in this plant, thereby triggering the expression of pelD to assist the pathogenic process.

Foot force direction control during leg pushes against fixed and moving pedals in persons post-stroke

The component of foot force generated by muscle action (F(m)) during pedaling in healthy humans has a nearly constant direction with increasing force magnitude. The present study investigated the effect of stroke on the control of foot force. Ten individuals with hemiparesis secondary to a cerebral vascular accident performed pushing efforts against translationally fixed and moving pedals on a custom stationary cycle ergometer. We found that while F(m) direction remained constant with increasing effort in both the fixed- and moving-crank conditions for both limbs, the orientation of that force component differed between limbs. The non-paretic limb produced the same F(m) orientation as seen previously in healthy humans. However, relative to the non-paretic limb, the paretic limb force line-of-action was shifted away from the hip and closer to the knee in the sagittal-plane for both pedal motion conditions. In the frontal plane, the paretic limb force line-of-action was shifted laterally, closer to parallel to the midline, for both pedal motion conditions. These shifts were consistent with previously reported lower limb muscle weakness and alterations in muscle activation observed during pedaling tasks following stroke. The finding of similar orientations for static and dynamic pushing efforts suggests that limb posture could be a trigger for relative muscle activation levels. The preservation of a constant direction in F(m) with increasing force magnitude post-stroke, despite an orientation shift, suggests that control of lower limb force may be organized by magnitude and direction and that these two aspects are differentially affected by stroke.

Foot force direction in an isometric pushing task: prediction by kinematic and musculoskeletal models

The abilities of a kinematic model and a muscle model of the human lower limb to predict the stereotyped direction of the muscular component of foot force produced by seated subjects in a static task were tested and compared. Human subjects ( n=11) performed a quasi-static, lower-limb pushing task against an instrumented bicycle pedal, free to rotate about its own axis, but with the crank fixed. Each pushing trial consisted of applying a force from the resting level to a force magnitude target with the right foot. Ten force target magnitudes were used (200, 250, ..., 650 N) along with 12 pedal positions. For each pushing effort, the muscular contribution to the measured foot force was determined from push onset to peak attained force. This segment was well characterized by a straight line across subjects, pedal positions, and force target magnitudes. The linear nature of the muscular component allowed a characteristic direction to be determined for each trial. A three-joint (hip, knee, and ankle) and a two-joint (hip and knee) net joint torque optimization was applied to a sagittal-plane kinematic model to predict the characteristic force direction. A musculoskeletal model was also used to create a feasible force space (FFS) for the lower limb. This FFS represents the range of possible forces the lower limb could theoretically produce. From this FFS, the direction of the maximum feasible foot force was determined and compared with the characteristic direction of subject performance. The muscle model proved to be the most effective in predicting subject force direction, followed by the three-joint and two-joint net joint torques optimizations. Similarities between the predictions of the kinematic and muscle model were also found.

Psychological sequelae and alopecia among women with cancer

PURPOSE

This article reviews the relevant literature on treatment-induced alopecia in women with cancer and describes the development of a computer-assisted intervention to reduce distress associated with this side effect.

DESCRIPTION OF PROGRAM

Alopecia has been cited as the most disturbing anticipated side effect by up to 58% of women preparing for chemotherapy, with 8% being at risk for avoiding treatment. Women with cancer who experience alopecia as a side effect, compared with women with cancer and no alopecia, report lower self-esteem, poorer body image, and lower quality of life. Although physicians' recommendations are the most influential factor on cancer treatment choice, body image and effects on sexuality are the next most influential factors. A study of a computer-imaging intervention, based on concepts related to guided imagery and anticipatory grief, has been launched in an effort to aid women in coping with anticipated treatment-related alopecia.

RESULTS

While we are still waiting for final data collection and analysis from the computer intervention study, the feedback thus far has been positive.

CLINICAL IMPLICATIONS

The intervention described here may prove to be effective in desensitizing women with cancer to hair loss and facilitating an adjustment to self-acceptance. As such, a higher quality of life during the difficult time of coping may be maintained. The development of a computer-imaging intervention offers an opportunity to integrate a standard psychosocial intervention, personalized for each patient, into the routine patient care in the oncology setting.

Requirement for either a host- or pectin-induced pectate lyase for infection of Pisum sativum by Nectria hematococca

Fungal pathogens usually have multiple genes that encode extracellular hydrolytic enzymes that may degrade the physical barriers in their hosts during the invasion process. Nectria hematococca, a plant pathogen, has two inducible pectate lyase (PL) genes (pel) encoding PL that can help degrade the carbohydrate barrier in the host. pelA is induced by pectin, whereas pelD is induced only in planta. We show that the disruption of either the pelA or pelD genes alone causes no detectable decrease in virulence. Disruption of both pelA and pelD drastically reduces virulence. Complementation of the double disruptant with pelD gene, or supplementation of the infection droplets of the double disruptant with either purified enzyme, PLA, or PLD, caused a recovery in virulence. These results show that PL is a virulence factor. Thus, we demonstrate that disruption of all functionally redundant genes is required to demonstrate the role of host barrier-degrading enzymes in pathogenesis and that dismissal of the role of such enzymes based on the effects of single-gene disruption may be premature.

Development of adrenal zonation in fetal rats defined by expression of aldosterone synthase and 11beta-hydroxylase

The adult rat adrenal cortex is comprised of three concentric steroidogenic zones that are morphologically and functionally distinguishable: the zona glomerulosa, zona intermedia, and the zona fasciculata/reticularis. Expression of the zone-specific steroidogenic enzymes, cytochrome P450 aldosterone synthase (P450aldo), and P450 11beta hydroxylase (P45011beta), produced by the zona glomerulosa and zona fasciculata/reticularis, respectively, can be used to define the adrenal cortical cell phenotype of these two zones. In this study, immunohistochemistry and in situ hybridization were used to determine the ontogeny of expression of P450aldo and P45011beta to monitor the pattern of development of the rat adrenal cortex. RIA was used to measure adrenal content of aldosterone and corticosterone, the resulting products of the two enzymatic pathways. Double immunofluorescent staining for both enzymes at gestational day 16 (E16) showed P45011beta protein expressed in cells distributed throughout most of the adrenal intermixed with a separate, but smaller, population of cells expressing P450aldo protein. Whereas expression of P45011beta protein retained a similar pattern of distribution from E16 to adulthood (ignoring distribution of SA-1 positive, presumptive medullary cells), P450aldo protein changed its pattern of distribution by E19, becoming localized in a discontinuous ring of cells adjacent to the capsule. By postnatal day 1, P450aldo protein distribution was similar to that observed in adult glands; P450aldo-positive cells formed a continuous zone underlying the capsule. In situ hybridization showed that the pattern of P45011beta messenger RNA expression paralleled protein expression at all times, whereas P450aldo messenger RNA paralleled protein at E19 and after, but was undetectable before E19. However, adrenal aldosterone and corticosterone, as measured by RIA, were detected by E16, supporting the functional capacity of both phenotypes for all ages studied. These data suggest that the development of the adrenal zona glomerulosa occurs in two distinct phases; initial expression of the glomerulosa phenotype in scattered cells of the inner cortex before E17, followed by a change in distribution to the outer cortex between E17 and E19. It is hypothesized that this change in distribution occurs via cell differentiation, rather than cell migration, and that a possible regulator of these events is the fetal renin-angiotensin system.

Movement of badgers (Meles meles) in a high-density population: individual, population and disease effects

The movement of 1763 badgers trapped between 36 social groups in Woodchester Park, Gloucestershire, over 18 years was analysed to determine the frequency and duration of moves, the factors associated with a predisposition to move and the spatial pattern of movements. Of those badgers whose capture history could be categorized, nearly half had moved. Of these, 73.1% were classified as 'occasional movers', 22.1% as 'permanent movers' and 4.8% as 'frequent movers'. Most adult badgers that moved made occasional moves (78.8%, n = 67). Cubs made all types of move including permanent moves (29%, n = 10). Seventy per cent of females were non-movers compared with 37% of males. Badgers were significantly more likely to move to smaller groups, whereas male badgers were significantly more likely to move to groups with a greater proportion of females. The spatial pattern of movement differed from the distribution of groups with bovine tuberculosis in the study area. However, temporal changes in movement were significantly related to the incidence of Mycobacterium bovis infection in the following year, indicating that as the movement of badgers between groups varies so does the incidence of bovine tuberculosis in the population. This finding is of central importance in the formulation of badger control policy.

Absorption of folate from fortified cereal-grain products and of supplemental folate consumed with or without food determined by using a dual-label stable-isotope protocol

The absorption of folic acid in fortified white and whole-wheat bread, rice, or pasta or in solution was evaluated in human subjects with use of a single-dose, dual-label, stable-isotope protocol that did not involve prior loading of subjects with nonlabeled folate. In each of five sequential trials, 14 adults received a single oral dose of [13C5]folic acid in one of the four fortified cereal-grain products or in water concurrently with an intravenous injection of [2H2]folic acid. In two additional trials, subjects received oral [13C5]folic acid with or without a light breakfast meal. In all trials, urine was collected 24-36 h postdosing and the isotopic labeling of urinary folates determined. Isotope excretion ratios of urinary folates (% [13C5]folate dose/% [2H2]folate dose), which were used as criteria of absorption, indicated no significant differences among the various fortified foods and the control (P = 0.607). Because statistical power was sufficient to have detected a 50% difference from the control, these results suggest that [13C5]folic acid in these fortified cereal-grain foods was highly available. This study also suggests that fortification will contribute effectively to the folate status of the population. Consuming [13C5]folic acid after a light breakfast meal led to a small reduction in absorption relative to the control without food (P < 0.085). Between-subject variation in this protocol exceeded that observed in previous studies conducted using prior saturation of subjects with nonlabeled folic acid. We recommend that either prior saturation or multiple doses be used in future applications of this technique to improve precision.

A dual-label stable-isotopic protocol is suitable for determination of folate bioavailability in humans: evaluation of urinary excretion and plasma folate kinetics of intravenous and oral doses of [13C5] and [2H2]folic acid

Stable isotopic protocols for the study of folate absorption were conducted to determine the following: (1) the equivalence of the [13C5] and [2H2] forms of folic acid, and (2) the merits of short-term plasma kinetics from injected and oral doses vs. urinary excretion of [13C5] and [2H2]folates. Another objective was to evaluate the merits of protocols not involving "saturation" of subjects with nonlabeled folate. Oral administration of [13C5] and [2H2]folic acid ( approximately 500 nmol each) to adult subjects (n = 4) yielded an equivalent 24-h urinary excretion of approximately 2% of each dose (molar ratio of urinary [13C5]/[2H2]folates = 0.96 +/- 0.055; mean +/- SEM). Expression of urinary excretion as a ratio of [13C5]/[2H2]folates yielded less within-group variability than seen for absolute excretion of each form of labeled folate. In the second study, subjects received 226 nmol of [2H2]folic acid intravenously and 1010 nmol of [13C5]folic acid orally. Isotopic enrichment of plasma [2H2]folates rose rapidly and returned to near basal values by approximately 2 h postdose. In contrast, enrichment of plasma [13C5]folates was detected until 4 h after dose, whereas enrichment values were far lower than seen with [2H2]folate. Adjusting for the difference in dose, the molar response of plasma area under the curve for isotopic enrichment was 15- to 20-fold greater for injected folates. In view of this very limited short-term plasma response even with a relatively large oral dose, presumably due to hepatic first-pass uptake, these findings suggest that plasma kinetics would be of limited usefulness in assessing the relative bioavailability of nutritionally relevant oral doses of labeled folate.

Differential gene expression of cytochrome P450 11beta-hydroxylase in rat adrenal cortex after in vivo activation

In situ hybridization histochemistry was used to monitor the expression of 3beta-hydroxysteroid dehydrogenase, delta4-isomerase (3betaHSD) and cytochrome P450 11beta-hydroxylase (P45011beta) messenger RNA (mRNA) in adult rat adrenals after stimulation in vivo. In Exp 1, adrenals were collected from rats injected with saline or ACTH for 1, 2, 3, or 4 days. Adrenal sections from saline-treated rats showed uniform expression of 3betaHSD mRNA that extended from the adrenal capsule to the medullary border. In contrast, P45011beta mRNA showed high levels in the outer fasciculata and low levels in the inner fasciculata/reticularis. In response to ACTH, the integrated density of 3betaHSD hybridization did not increase until 4 days. The integrated density of P45011beta hybridization increased in ACTH-treated rats between 1-4 days due to increased hybridization in the inner fasciculata/reticularis. In Exp 2, rats were treated with ACTH or saline, and adrenals were harvested at 4, 8, or 24 h. The hybridization density of 3betaHSD did not change after ACTH or saline injection. Increased expression of P45011beta mRNA was observed at 4 and 8 h, but not 24 h post-ACTH. In Exp 3, to determine the response to acute stress, adrenals were collected from rats 24 h after surgical laparotomy. The integrated density of 3betaHSD labeling did not change, whereas both hybridization area and mean density of P45011beta increased. Increased expression of P45011beta mRNA was observed in the inner fasciculata similar to that observed after ACTH injection. In addition, adrenal cells were more responsive to ACTH in vitro after surgical stress. These results suggest that the rat adrenal cortex can respond to acute stress by up-regulation of the expression of steroidogenic enzyme genes and that this occurs in part by increasing the number of cells actively expressing P45011beta mRNA. The adrenal response after stress most likely results at least in part from stimulation by ACTH. These findings suggest that changes in adrenal steroidogenesis in response to ACTH may result from recruitment of steroidogenic cells to synthesize and secrete corticosteroids.

Phenotypic changes and proliferation of adrenocortical cells during adrenal regeneration in rats

Adrenal regeneration after enucleation includes both cell proliferation and differentiation, but the phenotype of the proliferating cell remains controversial. Immunoperoxidase localization of cytochrome P450 aldosterone synthase (P450aldo) and cytochrome P450 11 beta-hydroxylase (P45011 beta) and of Ki-67 was used to identify adrenocortical cell phenotypes and proliferating cells, respectively. Comparisons were made between regenerating and intact adrenals collected from rats on low or normal Na+ diets. During the first week after enucleation, P45011 beta was expressed reflecting the presence of fasciculata cells; however, P450aldo was detected only in adrenals from low Na+ rats. On normal and low Na+, glomerulosa cells were replaced by intermedia cells, whereas on low Na+, glomerulosa cells were replaced by fasciculata cells. Proliferation was observed only in glomerulosa and fasciculata, but not intermedia cells. These findings suggest that the expression of the glomerulosa cell phenotype is decreased in the early stages of adrenal regeneration, that differentiation from a glomerulosa to an intermediate or fasciculata cell phenotype is influenced by low Na+ and that glomerulosa and fasciculata cells proliferate in response to enucleation.

Targeted replacement of the mycocerosic acid synthase gene in Mycobacterium bovis BCG produces a mutant that lacks mycosides

A single gene (mas) encodes the multifunctional enzyme that catalyzes the synthesis of very long chain multiple methyl branched fatty acids called mycocerosic acids that are present only in slow-growing pathogenic mycobacteria and are thought to be important for pathogenesis. To achieve a targeted disruption of mas, an internal 2-kb segment of this gene was replaced with approximately the same size hygromycin-resistance gene (hyg), such that hyg was flanked by 4.7- and 1.4-kb segments of mas. Transformation of Mycobacterium bovis BCG with this construct in a plasmid that cannot replicate in mycobacteria yielded hygromycin-resistant transformants. Screening of 38 such transformants by PCR revealed several transformants representing homologous recombination with single crossover and one with double crossover. With primers representing the hyg termini and those representing the mycobacterial genome segments outside that used to make the transformation construct, the double-crossover mutant yielded PCR products expected from either side of hyg. Gene replacement was further confirmed by the absence of the vector and the 2-kb segment of mas replaced by hyg from the genome of the mutant. Thin-layer and radio-gas chromatographic analyses of the lipids derived from [1-14C]propionate showed that the mutant was incapable of synthesizing mycocerosic acids and mycosides. Thus, homologous recombination with double crossover was achieved in a slow-growing mycobacterium with an intron-containing RecA. The resulting mas-disrupted mutant should allow testing of the postulated roles of mycosides in pathogenesis.

Positive selection of growth-inhibitory genes

We have isolated a limited set of cDNAs that limit cell proliferation using a unique assay based on the dilution of a lipophilic fluorescent dye as transfected cells divide. The identification of growth-inhibitory factors has been limited by the lack of a strong assay for growth inhibitors. A growth-inhibited cell does not grow and so is at a selective disadvantage in vitro when compared with any growing cell. Several assays have been used to screen for growth-inhibitory genes; however, these approaches are either very difficult to implement, leaky, or not comprehensive. We have developed an assay that selects for cDNAs capable of inhibiting proliferation in which cells are nonspecifically labeled with a lipophilic fluorescent dye, PKH-2, and subsequently transfected with a cDNA library made from growth-inhibited cells. With each cell division, the amount of dye per cell is reduced by one-half. Over time, growth-inhibited cells will retain more dye per cell relative to actively growing cells. The population is then analyzed by fluorescence-activated cell sorting, and the brightest cells in the population are isolated. This assay has allowed us to select pools of cDNAs enriched for growth-inhibitory activities and may provide a general method for identifying growth-inhibitory genes active in varying biological contexts. We report here the successful application of the dye retention assay to the selection of cDNAs that inhibit epithelial cell proliferation.

Surface signaling in pathogenesis

Surface signaling plays a major role in fungal infection. Topographical features of the plant surface and chemicals on the surface can trigger germination of fungal spores and differentiation of the germ tubes into appressoria. Ethylene, the fruit-ripening hormone, triggers germination of conidia, branching of hyphae, and multiple appressoria formation in Colletotrichum, thus allowing fungi to time their infection to coincide with ripening of the host. Genes uniquely expressed during appressoria formation induced by topography and surface chemicals have been isolated. Disruption of some of them has been shown to decrease virulence on the hosts. Penetration of the cuticle by the fungus is assisted by fungal cutinase secreted at the penetration structure of the fungus. Disruption of cutinase gene in Fusarium solani pisi drastically decreased its virulence. Small amounts of cutinase carried by spores of virulent pathogens, upon contact with plant surface, release small amounts of cutin monomers that trigger cutinase gene expression. The promoter elements involved in this process in F. solani pisi were identified, and transcription factors that bind these elements were cloned. One of them, cutinase transcription factor 1, expressed in Escherichia coli, is phosphorylated. Several protein kinases from F. solani pisi were cloned. The kinase involved in phosphorylation of specific transcription factors and the precise role of phosphorylation in regulating cutinase gene transcription remain to be elucidated.

Cutinase gene disruption in Fusarium solani f sp pisi decreases its virulence on pea

Fusarium solani f sp pisi (Nectria haematococca) isolate 77-2-3 with one cutinase gene produced 10 to 20% of the cutinase produced by isolate T-8 that has multiple cutinase genes, whereas cutinase gene-disrupted mutant 77-102 of isolate 77-2-3 did not produce cutinase. On the surface of pea stem segments, lesion formation was most frequent and most severe with T-8, less frequent and less severe with 77-2-3, and much less frequent and much milder with the gene-disrupted mutant. Microscopic examination of the lesions caused by the mutant strongly suggest that it penetrated the host mostly via the stomata. In seedling assays, 77-2-3 caused severe lesions on every seedling and stunted growth, whereas the mutant showed very mild lesions on one-third of the seedlings with no stunting. Thus, cutinase gene disruption resulted in a significant decrease in the pathogenicity of F. s. pisi on pea.

Identification of regulatory elements in the cutinase promoter from Fusarium solani f. sp. pisi (Nectria haematococca)

The cutinase gene from Fusarium solani f. sp. pisi (Nectria haematococca) is induced upon contact with the plant cuticular polymer, cutin, by the unique hydroxy fatty acid monomers released by cutinase carried by virulent strains of the fungus, and this gene is also catabolite-repressed by glucose. Functional elements of the cutinase promoter were studied in vivo by transforming F. solani pisi with fusions of 5'-flanking regions of the cutinase gene and the gene encoding chloramphenicol acetyltransferase (cat). DNA-binding proteins from F. solani pisi were analyzed in vitro by gel shift experiments, methylation interference analysis, and UV-cross-linking experiments. Thus, we identified four promotor elements involved in cutinase gene regulation: a silencer, positive-acting G-rich element, an element that binds a basal transcription factor, and a palindrome necessary for induction by cutin monomer. A silencer between -287 and -249 keeps basal gene expression low but also influences the inducibility of the gene. To restore high levels of induction, a G-rich positive-acting element with sequence similarities to other fungal elements acts as an antagonist to the silencer. Basal transcription is mediated by the first 141 base pairs of the cutinase promoter. The binding site of transcription factor CTF2 was identified between the TATA box and the transcription initiation sites. Gene induction by cutin monomers is regulated by CTF1, most probably a dimeric DNA-binding protein of 49 kDa with a palindromic recognition site at -170.

Evidence for possible involvement of an elastolytic serine protease in aspergillosis

A number of isolates of Aspergillus fumigatus obtained from the hospital environment produced extracellular elastolytic activity. This activity was found to be catalyzed by a single 33-kDa protein which was purified and characterized to be a serine protease. A. fumigatus, when grown on the insoluble structural material obtained from murine and bovine lung, produced the same extracellular 33-kDa elastolytic protease, indicating that this enzyme is likely to be produced when the organism infects the lung. Polymerase chain reaction with an oligonucleotide primer based on the N-terminal amino acid sequence of the elastolytic enzyme yielded a cDNA which was cloned and sequenced. The active serine motif showed more similarity to subtilisin than to mammalian elastase. The amino acid sequence showed 80% identity to the alkaline protease from Aspergillus oryzae. Screening of hospital isolates of Aspergillus flavus showed great variation in the production of elastolytic activity and a much lower level of activity than that produced by A. fumigatus. The elastolytic protease from A. flavus was shown to be a serine protease susceptible to modification and inactivation by active serine and histidine-directed reagents. This protease cross-reacted with the antibodies prepared against the elastolytic protease from A. fumigatus. Immunogold localization of the elastolytic enzyme showed that A. fumigatus germinating and penetrating into the lungs of neutropenic mice secreted the elastolytic protease. An elastase-deficient mutant generated from a highly virulent isolate of A. fumigatus caused drastically reduced mortality when nasally introduced into the lung of neutropenic mice. All of the evidence suggests that extracellular elastolytic protease is a significant virulence factor in invasive aspergillosis.

Developmental pattern of the expression of malonyl-CoA decarboxylase gene and the production of unique lipids in the goose uropygial glands

The abundant fatty acid synthase in the uropygial gland of goose generates multimethyl-branched fatty acids as the major product because of the unique presence of the cytoplasmic malonyl-CoA decarboxylase which assures that only methylmalonyl-CoA is available to the synthase. If this conclusion is valid, the developmental pattern of expression of the gene for this tissue-specific decarboxylase should correlate with the appearance of other lipogenic enzymes and the production of the unique lipids. To test this possibility the levels of the decarboxylase, acetyl-CoA carboxylase, and fatty acid synthase in the gland of the embryonic and neonatal goose were measured by immunodiffusion and immunoblot assays for the proteins as well as the enzyme assays for the catalytic activities. Malonyl-CoA decarboxylase appeared several days before hatching as did the other two lipogenic enzymes and reached half-maximal levels by hatching. The levels of expression of the malonyl-CoA decarboxylase gene and cytoplasmic actin gene, which is not expected to be developmentally regulated, were measured by dot-blot analysis using cloned cDNA for the two proteins. The decarboxylase transcripts appeared 4 days prior to hatching and reached maximal levels by hatching, whereas the levels of cytoplasmic actin gene transcripts showed very little change. The appearance of oil droplets in the glands was clearly seen soon after hatching. These results show that malonyl-CoA decarboxylase gene expression is developmentally regulated in a manner consistent with its proposed role in the synthesis of the unique lipids of the uropygial gland.

Synthesis of methyl-branched fatty acids from methylmalonyl-CoA by fatty acid synthase from both the liver and the harderian gland of the guinea pig

Partially purified fatty acid synthase preparations from both the liver and the harderian gland of guinea pig showed the same relative rates of utilization of methylmalonyl-CoA when compared to malonyl-CoA. Radio gas-liquid chromatographic analysis of the products generated from [methyl-14C]methylmalonyl-CoA and from [2-14C]malonyl-CoA in the presence of unlabeled methylmalonyl-CoA showed that the enzyme from both tissues generated identical mixtures of branched fatty acids. Therefore, it is concluded that the production of methyl-branched acids only by the harderian gland is not due to any unique specificity of the fatty acid synthase of this gland, in contrast to the conclusion reached from results obtained from mass spectrometry of the products generated by crude extracts (Y. Seyama, H. Otsuka, A. Kawaguchi, and T. Yamakawa J. Biochem. 90, 789-797, 1981).

Biosynthesis of lipids by bovine meibomian glands

Isolated bovine meibomian glands incorporated exogenous [1-14C]acetate into lipids. Thin layer chromatographic analysis of the lipids showed that wax esters and sterol esters contained 61% of the total label. Radio gas liquid chromatographic analysis of the acid and alcohol moieties of both ester fractions showed the label was distributed equally between the two portions of the ester in both cases. Cholesterol and 5-alpha-cholest-7-en-3 beta-ol were the major labeled sterols, and anteiso-C25, anteiso-C27 and anteiso-C23 were the most highly labeled alcohols. The major labeled fatty acids in the wax esters were anteiso-C15, n-C16, anteiso-C17 and n-C18:1, whereas anteiso-C25 and anteiso-C27 were the major labeled acids in the sterol esters. The diester region with 6% of the total label contained labeled fatty acids and fatty alcohols each with anteiso-C25 as the major component and omega-hydroxy acids in which n-C32:1 was the major labeled component. The triglyceride fraction which contained 8% of the total lipids was composed of labeled fatty acids similar to those found in both sterol and wax ester fractions. Chromatographic analyses of the labeled lipids derived from exogenous labeled isoleucine showed that anteiso-branched products were preferentially labeled. The labeled triglyceride fraction derived from [U-14C] isoleucine also contained esterified C15, C13, C11, C9, C7 and possibly shorter anteiso-branched acids.

Gigantism associated with a pituitary tumour secreting growth hormone and prolactin and cured by transsphenoidal hypophysectomy

An 18-year old male is reported who presented with a history of a growtn spurt over the year preceding his admission. His height was above the 97th percentile, and he had incompletely developed secondary sexual characters. Pituitary evaluation demonstrated a moderately elevated level of growth hormone (hGH) not suppressible by a glucose load and not stimulable by TRH or by L-DOPA. Serum prolactin (PRL) concentration was also increased while gonadotrophin, thyroid and adrenal function were all subnormal. There was clear radiological evidence of a large pituitary tumour with suprasellar extension and transsphenoidal total hypophysectomy was performed. A mixed chromophobe and acidophilic adenoma was found and both growth hormone and prolactin were demonstrable in different cells of the tumour by the immunoperoxidase technique. Post-operatively the patient has hypopituitarism and levels of growth hormone and prolactin have remained low or undetectable after 6 months. Thus early diagnosis and surgical treatment of gigantism of this mixed hGH-PRL secreting pituitary tumour was associated with a cure, which contrasts with the unfavourable outcome of many of the patients previously reported.