A comprehensive phylogeny helps clarify the evolutionary history of host breadth and lure response in the Australian Dacini fruit flies (Diptera: Tephritidae)

The tribe Dacini (Diptera: Tephritidae) contains over 930 recognised species and has been widely studied due to the economic importance of some taxa, such as the Oriental fruit fly Bactrocera dorsalis. Despite the attention this group has received, very few phylogenetic reconstructions have comprehensively sampled taxa from a single biogeographic region, thereby limiting our capacity to address more targeted evolutionary questions. To study the evolution of diet breadth and male lure response, two key traits fundamental to understanding dacine diversity and the biology of pest taxa, we analysed 273 individuals representing 144 described species from Australia (80% continental coverage), the Pacific, and select close relatives from South-east Asia to estimate a dated molecular phylogenetic reconstruction of the Dacini. We utilised seven loci with a combined total of 4,332 nucleotides, to estimate both Bayesian and Maximum Likelihood phylogenies of the tribe. Consistent with other molecular phylogenies of the tribe, there was a high level of disagreement between the placement of species in the phylogeny and their current subgeneric and species-complex level taxonomies. The Australian fauna exhibit high levels of endemism, with radiations of both exclusively Australian clades, and clades that originate elsewhere (e.g. the Bactrocera dorsalis species group). Bidirectional movement of species has occurred between Papua New Guinea and Australia, with evidence for multiple incursions over evolutionary time. The Bactrocera aglaiae species group emerged sister to all other Bactrocera species examined. Divergence time estimates were ∼ 30 my younger than previously reported for this group, with the tribe diverging from its most recent common ancestor ∼ 43 mya. Ancestral trait reconstruction and tests for trait phylogenetic signal revealed a strong signal for the evolution of male lure response across the tree, with cue-lure/raspberry ketone lure response the ancestral trait. Methyl eugenol response has arisen on multiple, independent occasions. The evolution of host breadth exhibited a weaker signal; yet, basal groups were more likely to be host specialists. Both the evolution of lure response and host fruit use provide predictive information for the outbreak management of understudied pest fruit flies for which direct inference of these features may be lacking. Our results, which parallel those of earlier research into the closely-related African Dacus spp., demonstrate how geographically focussed taxon coverage allows Dacini phylogenetics to more explicitly test evolutionary hypotheses, thereby progressing our understanding of the evolution of this highly diverse and recently-radiated group of flies.

Functional redundancy between Apc and Apc2 regulates tissue homeostasis and prevents tumorigenesis in murine mammary epithelium

Aberrant Wnt signaling within breast cancer is associated with poor prognosis, but regulation of this pathway in breast tissue remains poorly understood and the consequences of immediate or long-term dysregulation remain elusive. The exact contribution of the Wnt-regulating proteins adenomatous polyposis coli (APC) and APC2 in the pathogenesis of human breast cancer are ill-defined, but our analysis of publically available array data sets indicates that tumors with concomitant low expression of both proteins occurs more frequently in the 'triple negative' phenotype, which is a subtype of breast cancer with particularly poor prognosis. We have used mouse transgenics to delete Apc and/or Apc2 from mouse mammary epithelium to elucidate the significance of these proteins in mammary homeostasis and delineate their influences on Wnt signaling and tumorigenesis. Loss of either protein alone failed to affect Wnt signaling levels or tissue homeostasis. Strikingly, concomitant loss led to local disruption of β-catenin status, disruption in epithelial integrity, cohesion and polarity, increased cell division and a distinctive form of ductal hyperplasia with 'squamoid' ghost cell nodules in young animals. Upon aging, the development of Wnt activated mammary carcinomas with squamous differentiation was accompanied by a significantly reduced survival. This novel Wnt-driven mammary tumor model highlights the importance of functional redundancies existing between the Apc proteins both in normal homeostasis and in tumorigenesis.

Apc and p53 interaction in DNA damage and genomic instability in hepatocytes

Disruption of Apc within hepatocytes activates Wnt signaling, perturb differentiation and ultimately lead to neoplasia. Apc negatively regulates Wnt signaling but is also involved in organizing the cytoskeleton and may play a role in chromosome segregation. In vitro studies have implicated Apc in the control of genomic stability. However, the relevance of this data has been questioned in vivo as Apc is lost earlier than the onset of genomic instability. Here, we analyse the relationship between immediate loss of Apc and the acquisition of genomic instability in hepatocytes. We used Cre-lox technology to inactivate Apc and in combination with p53 in vivo, to define the consequences of gene loss upon cell-cycle regulation, proliferation, death and aneuploidy. We show that whilst Apc loss leads to increased proliferation, it also leads to increased apoptosis, the accumulation of p53, p21 and markers of DSBs and DNA repair. Flow cytometry revealed an increased 4N DNA content, consistent with a G2 arrest. Levels of anaphase bridges were also elevated, implicating failed chromosome segregation. This was accompanied by an increase in centrosome number which demonstrates a role for Apc in maintaining euploidy.

To address the role of p53 in these processes, we analyzed combined loss of Apc and p53, which led to a further increase in proliferation, cell death, DNA damages and repair and a bypass of G2 arrest than was observed with Apc loss. However we observed only a marginal effect on anaphase bridges and centrosome number which could be due to increased cell death. Our data therefore establishes, in an in vivo setting, that APC loss leads to a DNA damage signature and genomic instability in the liver and that additional loss of p53 leads to an increase in the DNA damage signal but not to an immediate increase in the genomic instability phenotype.

Wnt-driven intestinal tumourigenesis is suppressed by Chk1 deficiency but enhanced by conditional haploinsufficiency

Chk1 is essential in maintaining genomic stability due to its role in cell cycle regulation. Several recent studies have indicated that the abrogation of checkpoints in tumourigenesis through the inhibition of Chk1 may be of therapeutic value. To further investigate the role of Chk1 in the mouse small intestine and its potential role as a therapy for colorectal cancer, we simultaneously deleted Chk1 and Apc in the mouse small intestine. We found that homozygous loss of Chk1 is not compatible with Wnt-driven proliferation and resulted in the suppression of Wnt-driven tumourigenesis in the mouse small intestine. In contrast, heterozygous loss of Chk1 in a Wnt-driven background resulted in an increase in DNA damage and apoptosis and accelerated both tumour development and progression.

Endogenous c-Myc is essential for p53-induced apoptosis in response to DNA damage in vivo

Recent studies have suggested that C-MYC may be an excellent therapeutic cancer target and a number of new agents targeting C-MYC are in preclinical development. Given most therapeutic regimes would combine C-MYC inhibition with genotoxic damage, it is important to assess the importance of C-MYC function for DNA damage signalling in vivo. In this study, we have conditionally deleted the c-Myc gene in the adult murine intestine and investigated the apoptotic response of intestinal enterocytes to DNA damage. Remarkably, c-Myc deletion completely abrogated the immediate wave of apoptosis following both ionizing irradiation and cisplatin treatment, recapitulating the phenotype of p53 deficiency in the intestine. Consistent with this, c-Myc-deficient intestinal enterocytes did not upregulate p53. Mechanistically, this was linked to an upregulation of the E3 Ubiquitin ligase Mdm2, which targets p53 for degradation in c-Myc-deficient intestinal enterocytes. Further, low level overexpression of c-Myc, which does not impact on basal levels of apoptosis, elicited sustained apoptosis in response to DNA damage, suggesting c-Myc activity acts as a crucial cell survival rheostat following DNA damage. We also identify the importance of MYC during DNA damage-induced apoptosis in several other tissues, including the thymus and spleen, using systemic deletion of c-Myc throughout the adult mouse. Together, we have elucidated for the first time in vivo an essential role for endogenous c-Myc in signalling DNA damage-induced apoptosis through the control of the p53 tumour suppressor protein.

Mating compatibility among four pest members of the Bactrocera dorsalis fruit fly species complex (Diptera: Tephritidae)

Bactrocera dorsalis (Hendel), Bactrocera papayae Drew & Hancock, Bactrocera philippinensis Drew & Hancock, and Bactrocera carambolae Drew & Hancock are pest members within the B. dorsalis species complex of tropical fruit flies. The species status of these taxa is unclear and this confounds quarantine, pest management, and general research. Mating studies carried out under uniform experimental conditions are required as part of resolving their species limits. These four taxa were collected from the wild and established as laboratory cultures for which we subsequently determined levels of prezygotic compatibility, assessed by field cage mating trials for all pair-wise combinations. We demonstrate random mating among all pair-wise combinations involving B. dorsalis, B. papayae, and B. philippinensis. B. carambolae was relatively incompatible with each of these species as evidenced by nonrandom mating for all crosses. Reasons for incompatibility involving B. carambolae remain unclear; however, we observed differences in the location of couples in the field cage for some comparisons. Alongside other factors such as pheromone composition or other courtship signals, this may lead to reduced interspecific mating compatibility with B. carambolae. These data add to evidence that B. dorsalis, B. papayae, and B. philippinensis represent the same biological species, while B. carambolae remains sufficiently different to maintain its current taxonomic identity. This poses significant implications for this group's systematics, impacting on pest management, and international trade.

In vivo and in vitro models for the therapeutic targeting of Wnt signaling using a Tet-OΔN89β-catenin system

Although significant progress has been made in understanding the importance of Wnt signaling in the initiation of colorectal cancer, less is known about responses that accompany the reversal of oncogenic Wnt signaling. The aim of this study was to analyze in vivo and in vitro responses to an 'ideal' Wnt pathway inhibitor as a model for the therapeutic targeting of the pathway. A tetracycline-inducible transgenic mouse model expressing truncated β-catenin (ΔN89β-catenin) that exhibited a strong intestinal hyperplasia was analyzed during the removal of oncogenic β-catenin expression both in 3D 'crypt culture' and in vivo. Oncogenic Wnt signaling was rapidly and completely reversed. The strongest inhibition of Wnt target gene expression occurred within 24 h of doxycycline removal at which time the target genes Ascl2, Axin2 and C-myc were downregulated to levels below that in the control intestine. In vitro, the small molecule Wnt inhibitor CCT036477 induced a response within 4 h of treatment. By 7 days following doxycycline withdrawal, gene expression, cell proliferation and tissue morphology were undistinguishable from control animals.In conclusion, these results demonstrate that the reversal of Wnt signaling by inhibitors should ideally be studied within hours of treatment. The reversible system described, involving medium throughput in vitro approaches and rapid in vivo responses, should allow the rapid advance of early stage compounds into efficacy models that are more usually considered later in the drug discovery pipeline.

Wing shape as a potential discriminator of morphologically similar pest taxa within the Bactrocera dorsalis species complex (Diptera: Tephritidae)

Four morphologically cryptic species of the Bactrocera dorsalis fruit fly complex (B. dorsalis s.s., B. papayae, B. carambolae and B. philippinensis) are serious agricultural pests. As they are difficult to diagnose using traditional taxonomic techniques, we examined the potential for geometric morphometric analysis of wing size and shape to discriminate between them. Fifteen wing landmarks generated size and shape data for 245 specimens for subsequent comparisons among three geographically distinct samples of each species. Intraspecific wing size was significantly different within samples of B. carambolae and B. dorsalis s.s. but not within samples of B. papayae or B. philippinensis. Although B. papayae had the smallest wings (average centroid size=6.002 mm±0.061 SE) and B. dorsalis s.s. the largest (6.349 mm±0.066 SE), interspecific wing size comparisons were generally non-informative and incapable of discriminating species. Contrary to the wing size data, canonical variate analysis based on wing shape data discriminated all species with a relatively high degree of accuracy; individuals were correctly reassigned to their respective species on average 93.27% of the time. A single sample group of B. carambolae from locality 'TN Malaysia' was the only sample to be considerably different from its conspecific groups with regards to both wing size and wing shape. This sample was subsequently deemed to have been originally misidentified and likely represents an undescribed species. We demonstrate that geometric morphometric techniques analysing wing shape represent a promising approach for discriminating between morphologically cryptic taxa of the B. dorsalis species complex.

Absolute requirement for STAT3 function in small-intestine crypt stem cell survival

The transcription factor signal transducer and activator of transcription 3 (STAT3) is frequently activated in human cancers. Interestingly, STAT3 also maintains the pluripotency and self-renewal of murine embryonic stem cells, and several tissue stem cell types. To investigate whether STAT3 also maintains the small-intestine crypt stem cell, we conditionally inactivated a Floxed Stat3 allele (Stat3(fl)) in murine small-intestine crypt stem cells. Following Cre recombinase expression, apoptosis increased in Stat3(fl/-) experimental crypts relative to Stat3(wt/-) controls before declining. Control Stat3(wt/-) mice carrying a Flox-STOP LacZ reporter transgene stably expressed LacZ after Cre induction. In contrast, Stat3(fl/-) intestine LacZ expression initially increased modestly, before declining to background levels. Quantitative PCRs revealed a similar transient in recombined Stat3(fl) allele levels. Long-term bromodeoxyuridine labelling directly demonstrated that functional STAT3 is required for +4 to +6 region label-retaining small-intestine stem cell survival. Rapid clearance of recombined Stat3(fl/-) cells involves apoptosis potentially induced by elevated c-Myc in non-recombined cells and involves elevated p53 expression and caspase 3 activation. Intriguingly, Stat3(fl/-) intestine recombination triggered dramatically upregulated polycomb transcriptional repressor Bmi1 - potentially accelerating recombined crypt repopulation. In summary, STAT3 activity is absolutely required for small-intestine crypt stem cell survival at both the +4 to +6 label-retaining and crypt base columnar cell locations.

Rapid cell-surface prion protein conversion revealed using a novel cell system

Prion diseases are fatal neurodegenerative disorders with unique transmissible properties. The infectious and pathological agent is thought to be a misfolded conformer of the prion protein. Little is known about the initial events in prion infection because the infecting prion source has been immunologically indistinguishable from normal cellular prion protein (PrP(C)). Here we develop a unique cell system in which epitope-tagged PrP(C) is expressed in a PrP knockdown (KD) neuroblastoma cell line. The tagged PrP(C), when expressed in our PrP-KD cells, supports prion replication with the production of bona fide epitope-tagged infectious misfolded PrP (PrP(Sc)). Using this epitope-tagged PrP(Sc), we study the earliest events in cellular prion infection and PrP misfolding. We show that prion infection of cells is extremely rapid occurring within 1 min of prion exposure, and we demonstrate that the plasma membrane is the primary site of prion conversion.

Host use and crop impacts of Oribius Marshall species (Coleoptera: Curculionidae) in Eastern Highlands Province, Papua New Guinea

Oribius species are small flightless weevils endemic to the island of New Guinea and far northern Cape York, Australia. The adults feed externally on leaves, developing fruit and green bark, but their impact as pests and general host use patterns are poorly known. Working in Eastern Highlands Province, Papua New Guinea, we carried out structured host use surveys, farmer surveys, shade-house growth trials and on-farm and on-station impact trials to: (i) estimate the host range of the local Oribius species; (ii) understand adult daily activity patterns; (iii) elucidate feeding habits of the soil dwelling larvae; and (iv) quantify the impacts of adult feeding damage. Oribius inimicus and O. destructor accounted for nearly all the Oribius species encountered locally, of these two O. inimicus was the most abundant. Weevils were collected from 31 of 33 plants surveyed in the Aiyura Valley, and a combination of farmer interviews and literature records provided evidence for the beetles being pestiferous on 43 crops currently or previously grown in the Highlands. Adult weevils had a distinct diurnal pattern of being in the upper plant canopy early in the morning and, to a lesser extent, again late in the afternoon. For the remainder of the day, beetles resided within the canopy, or possibly off the plant. Movement of adults between plants appeared frequent. Pot trials confirmed the larvae are root feeders. Quantified impact studies showed that the weevils are damaging to a range of vegetable and orchard crops (broccoli, capsicum, celery, French bean, Irish potato, lettuce, orange and strawberry), causing average yield losses of around 30-40%, but up to 100% on citrus. Oribius weevils pose a significant and, apparently, growing problem for Highland's agriculture.

Normal stem cells in cancer prone epithelial tissues

The concept of a cancer stem cell is not a new one, being first suggested over 100 years ago. Over recent years the concept has enjoyed renewed enthusiasm, partly because of our growing understanding of the nature of somatic stem cells, but also because of a growing realisation that the development of strategies that target cancer stem cells may offer considerable advantages over conventional approaches. However, despite this renewed enthusiasm the existence of cancer stem cells remains controversial in many tumour types and any potential relationship to the normal stem cell pool remains poorly defined. This review summarises key elements of our understanding of the normal stem cell populations within animal models of the predominant cancer prone epithelial tissues, and further investigates the potential links between these populations and putative cancer stem cells.

The intestinal stem cell niche studied through conditional transgenesis

Despite a wealth of experimental data, the precise mechanisms governing the maintenance and regeneration of the intestine remain relatively poorly elucidated. After physical or genetic injury, stem cells from the intestinal crypt are killed and the subsequent repopulation process recruits new stem cells from sources currently unknown. Understanding the genetic elements that determine stem cell fate and the basis by which repopulation occurs will greatly aid our understanding of both stem cell plasticity and the contribution made by the stem cell compartment to malignant disease. It would also provide a better platform to develop therapies to regenerate damaged intestinal epithelia as seen after radiation injuries or inflammatory bowel disease such as Crohn's disease. In this review we discuss some of the basic mechanisms that regulate intestinal stem cell viability and maintenance, and also summarise recent data from our laboratory on the requirement for the Wnt pathway in these processes.

53BP1 deficiency in intestinal enterocytes does not alter the immediate response to ionizing radiation, but leads to increased nuclear area consistent with polyploidy

The p53-binding protein 53BP1 has been implicated in the DNA damage response and genomic instability. Previous reports have highlighted these roles in vivo in haematopoietic lineages. To investigate the importance of 53BP1 to the DNA damage response in epithelial cells in vivo, we have investigated the role of 53BP1 in mediating apoptosis and proliferation within the murine small intestine following gamma-irradiation. 53BP1 deficiency does not affect the immediate response to gamma-irradiation with normal levels of apoptosis, proliferation and p53 and p21 accumulation. However, 48 h post-gamma-irradiation there was a significant accumulation of cells with much larger nuclei marked by p53 and p21 accumulation. These data reflect increases in polyploidy observed 53BP1-/- deficient fibroblasts following gamma-irradiation. At 72 h post-irradiation both the 4N and 8N populations were significantly increased in 53BP1-/- MEFS. Taken together, these results show that following in vivo exposure to gamma-irradiation, 53BP1 is dispensable for signalling apoptosis and cell-cycle arrest in the intestinal epithelium. However, it is important for prevention of genomic instability within this epithelial cell population.

Can hybridization cause local extinction: a case for demographic swamping of the Australian native Senecio pinnatifolius by the invasive Senecio madagascariensis?

Hybridization between native and invasive species can have several outcomes, including enhanced weediness in hybrid progeny, evolution of new hybrid lineages and decline of hybridizing species. Whether there is a decline of hybridizing species largely depends on the relative frequencies of parental taxa and the viability of hybrid progeny. Here, the individual- and population-level consequences of hybridization between the Australian native Senecio pinnatifolius and the exotic Senecio madagascariensis were investigated with amplified fragment length polymorphism (AFLP) markers, and this information was used to estimate the annual loss of viable seeds to hybridization. A high frequency (range 8.3-75.6%) of hybrids was detected in open pollinated seeds of both species, but mature hybrids were absent from sympatric populations. A hybridization advantage was observed for S. madagascariensis, where significantly more progeny than expected were sired based on proportional representation of the two species in sympatric populations. Calculations indicated that S. pinnatifolius would produce less viable seed than S. madagascariensis, if hybridization was frequency dependent and S. madagascariensis reached a frequency of between 10 and 60%. For this native-exotic species pair, prezygotic isolating barriers are weak, but low hybrid viability maintains a strong postzygotic barrier to introgression. As a result of asymmetric hybridization, S. pinnatifolius would appear to be under threat if S. madagascariensis increases numerically in areas of contact.

Wnt signalling in the mouse intestine

The Apc(Min/+) mouse has emerged as a powerful model of human intestinal tumour predisposition. As such, it has provided a platform for studying genetic and epigenetic modifiers of adenoma predisposition, and for assessing the chemotherapeutic potential of a plethora of different agents. The development of new conditional and hypomorphic Apc alleles, together with models carrying mutations in other Wnt pathway components, has greatly extended the scope of experimentation. Together these approaches are being used to identify and validate key critical targets of the Wnt pathway, such as Mash2, Tiam1 and the Eph/Ephrins. They have also established a fundamental role for Wnt in the development and maintenance of normal intestinal physiology, and in particular control of the stem cell niche. These activities are now being dissected at the level of individual Wnt components, with some surprising dependencies revealed. In terms of adenoma development, these models also support a 'just right' notion for tightly controlled beta-catenin activity both in normal physiology and neoplastic development. They also indicate a two-stage dependency for some Wnt pathway targets, with an initial requirement that is subsequently overcome to permit progression. Finally, these models establish that the Wnt pathway does not operate in isolation, and that both normal and diseased physiology develops in a dynamic interplay with other pathways such as the Notch, Hedgehog and BMP pathways. The comprehensive understanding arising from these studies should lead the identification of novel prognostic markers and therapeutic targets, and also open the possibility of tissue engineering in the intestine.

Seasonal phenology of Bactrocera minax (Diptera: Tephritidae) in western Bhutan

The Chinese citrus fruit fly, Bactrocera (Tetradacus) minax (Enderlein), is one of the major citrus pests in Bhutan and can cause >50% mandarin (Citrus reticulata Blanco) fruit drop. As part of the development of a management strategy for the fly in mandarin orchards, population monitoring and experimental manipulations were carried out to determine: (i) adult emergence period; (ii) adult phenology patterns; (iii) period of crop susceptibility; and (iv) period from fruit drop to pupation. In western Bhutan, adult flies emerge from the overwintering pupal stage in late April/early May. Most flies are mature by the end of May and it is inferred that mating occurs at this time: from the beginning of June males rapidly disappear from the population and by mid- to late June are rare or absent from traps. Mature females are present in the mandarin crop at the beginning of June, but very little oviposition occurs until mid-June, while most damage has occurred by mid-July. Initiation of oviposition into mandarins is almost certainly linked to crop phenology. Adult flies disappear from the orchard system during August. After fruit drop, larvae were recorded leaving the fruit to pupate within 13 days. The use of early to mid-season protein bait sprays and/or targeted use of systemic insecticides during the one month oviposition period, plus the removal of fallen fruit once every 10 days, are recommended as control strategies.

DNA damage hypersensitivity in cells lacking BRCA2: a review of in vitro and in vivo data

Since the discovery of the tumour suppressor BRCA2 (encoded by breast-cancer susceptibility gene 2), cells lacking the fully functional protein have consistently been found to show increased sensitivity to a variety of DNA-damaging agents, particularly those that cross-link DNA. In this short review, we will bring together these findings and discuss them in the light of our recent in vivo data in the mouse small intestine, which suggests that deletion of cells lacking Brca2 is necessary to avoid the development of potentially tumorigenic clones in this tissue, a system that may be less effective in the mammary glands of humans with germline mutations in BRCA2.

Opiine parasitoids (Hymenoptera: Braconidae) of tropical fruit flies (Diptera: Tephritidae) of the Australian and South Pacific region

Opiine wasps are parasitoids of dacine fruit flies, the primary horticultural pests of Australia and the South Pacific. A taxonomic synopsis and distribution and host records (44% of which are new) for each of the 15 species of dacine-parasitizing opiine braconids found in the South Pacific is presented. Species dealt with are Diachasmimorpha hageni (Fullaway), D. kraussii (Fullaway), D. longicaudata (Ashmead), D. tryoni (Cameron), Fopius arisanus (Sonan), F. deeralensis (Fullaway), F. ferrari Carmichael & Wharton sp. n., F. illusorius (Fischer) comb. n., F. schlingeri Wharton, Opius froggatti Fullaway, Psyttalia fijiensis (Fullaway), P. muesebecki (Fischer), P. novaguineensis (Szépligeti) and Utetes perkinsi (Fullaway). A potentially undescribed species, which may be a colour morph of F. vandenboschi (Fullaway), is diagnosed but not formally described. Fopius vandenboschi sensu stricto, Diachasmimorpha fullawayi Silvestri, Psyttalia concolor Szépligeti and P. incisi Silvestri have been liberated into the region but are not considered to have established: a brief diagnosis of each is included. Biosteres illusorius Fischer is formally transferred to the genus Fopius. A single opiine specimen reared from a species of Bactrocera (Bulladacus) appears to be Utetes albimanus (Szépligeti), but damage to this specimen and to the holotype (the only previously known specimen) means that this species remains unconfirmed as a fruit fly parasite: a diagnosis of U. cf. albimanus is provided. Psyttalia novaguineensis could not be adequately separated from P. fijiensis using previously published characterizations and further work to resolve this complex is recommended. A key is provided to all taxa.

Studying the consequences of immediate loss of gene function in the intestine: APC

The use of mouse models to study neoplasia is proving particularly powerful in dissecting the mechanisms underlying disease initiation and progression. However, the majority of these models have been somewhat limited in studying the very early effects of loss of gene function, as tumour initiation relies upon either constitutive loss of gene function or spontaneous somatic loss of function. We have therefore adopted a strategy of using an inducible Cre-lox-based system to analyse the effects of loss of gene function, the use of which is reviewed here for the intestinal tumour suppressor APC (adenomatous polyposis coli). Using this approach, we have conditionally and synchronously inactivated APC in virtually all the epithelial cells of the adult murine small intestine. After 5 days following induction of Cre-mediated recombination, mice show grossly altered crypt/villus architecture. Deficiency in APC perturbs migration, alters the normal programme of differentiation and results in increased proliferation and apoptosis. Microarray analysis reveals the transcriptome to be significantly altered; reflecting both gross phenotypic changes and changes in transcriptional activation. These findings demonstrate that APC is indeed the critical determinant of cell fate in the intestinal epithelium, explaining its role as the cellular ‘gatekeeper’ in preventing neoplasia.

Age-related difference in susceptibility of Apc(Min/+) mice towards the chemopreventive efficacy of dietary aspirin and curcumin

The nonsteroidal anti-inflammatory drug aspirin and the spice curcumin retard adenoma formation when administered long-term to Apc(Min/+) mice, a model of human familial adenomatous polyposis coli. Both agents interfere with cyclooxygenase activity. When aspirin is administered to Apc(Min/+) mice only postweaning, but not before, it is inefficacious, while curcumin given postweaning is active. Here the hypothesis was tested that dietary aspirin (0.05%) or curcumin (0.2%) prevent or delay adenoma formation in offsprings when administered to Apc(Min/+) mothers and up to the end of weaning, but not afterwards. Whereas curcumin was without effect when administered in this way, aspirin reduced numbers of intestinal adenomas by 21%. When aspirin given up to the end of weaning was combined with curcumin administered from the end of weaning for the rest of the animals' lifetime, intestinal adenoma numbers were reduced by 38%. The combination was not superior to intervention postweaning with curcumin alone. These results show that aspirin exerts chemopreventive activity in the Apc(Min/+) mouse during tumour initiation/early promotion, while curcumin is efficacious when given at a later stage of carcinogenic progression. Thus, the results suggest that in this mouse model aspirin and curcumin act during different 'windows' of neoplastic development.

Hyperkinetic disorder in the ICD-10: EEG evidence for a definitional widening?

This study investigated EEG differences between children with Hyperkinetic Disorder (HKD), HKD sub-threshold attention deficit (HKDsub), and control children, in order to determine from an EEG perspective whether children with HKDsub represent a valid clinical disorder. Twenty-four boys were included in each of the three age-matched groups. The HKD group had greater total power and absolute delta and theta, more relative theta, and less relative alpha and beta than the control group. The HKDsub group had EEG profiles which were different from both control children and children with HKD, with the HKDsub group having EEG results generally between the HKD and control group. Additionally, a number of topographic differences were found in the frontal regions which suggest that the two HKD groups have independent EEG components. These results support the inclusion of a diagnostic category of attention deficit in future editions of the ICD.

Mouse models with modified p53 sequences to study cancer and ageing

Experiments with p53 transgenic and p53 gene-targeted mouse strains have substantiated, and in some cases challenged, a number of hypotheses on the biology of the p53 protein. New questions have emerged regarding similarities and differences between murine and human genetic networks in various tissues. Mouse models with targeted p53 alleles are now applied not only to investigate tumour susceptibility, but also to address questions pertinent to molecular epidemiology, chemoprevention, development of anticancer p53-specific pharmaceuticals, and ageing.

Assessment of change with the Developmental Behaviour Checklist

BACKGROUND

The Developmental Behaviour Checklist (DBC) is a 96-item instrument designed for assessing behavioural and emotional problems among young people with intellectual disability.

METHODS

The present study investigated the validity of the DBC as a measure of change. Changes in individual's DBC scores were correlated with changes in expert clinicians' ratings of the same subjects.

RESULTS

A high correlation was found between expert clinician ratings of change in behaviour and change in the total behaviour problem score of the DBC.

CONCLUSIONS

The DBC is able to measure changes in behaviour and emotions which are recognized by an experienced clinician who is following the progress of a child with ID.

Low frequency ultrasonic propagation through fibre reinforced, polymer composites

This paper concentrates upon mesoscale variations observed in the time-of-flight (TOF) area scans of shear wave propagation through 'identically processed', injection moulded, glass fibre reinforced, polypropylene plaques. The effect of these structural variations on the derived 3D stiffness constants is discussed. Hence the random measurement errors associated with the stiffness constant measurements are differentiated from the intrinsic process-induced spatial variations. Interesting correlations between TOF and received amplitudes of shear wave propagation have been found and our tentative interpretation of these data in terms of mesostructural variations in the reinforcing fibre locations and fibre orientations is presented.

Automated reconstruction of curvilinear fibres from 3D datasets acquired by X-ray microtomography

The characterization of fibrous structures is important in both composites and textiles research for relating to the bulk properties of the material. However, the microscopic nature of the fibres and their high densities make them very difficult to characterize. Many techniques have been developed for the measurement and characterization of fibrous structures but they tend to be restricted to measurements on the sample surface or within physical cross-sections. X-ray microtomography can be used to non-destructively probe the internal structure of a range of fibrous materials, providing large amounts of 3D data. A technique has been developed for tracing fibres within 3D datasets acquired by X-ray microtomography and this has been applied to a glass fibre reinforced composite and also a non-woven textile sample. The 3D fibrous structures of both samples were successfully reconstructed and their fibre orientation distributions calculated. This technique enables novel characterizations, such as the through-thickness variation of fibre orientation in non-wovens.

EEG-defined subtypes of children with attention-deficit/hyperactivity disorder

OBJECTIVES

This study investigated the presence of EEG clusters within a sample of children with the combined type of attention-deficit/hyperactivity disorder (ADHD).

METHODS

Subjects consisted of 184 boys with ADHD and 40 age-matched controls. EEG was recorded from 21 sites during an eyes-closed resting condition and Fourier transformed to provide estimates for total power, and relative power in the delta, theta, alpha and beta bands, and for the theta/beta ratio. Factor analysis was used to group sites into 3 regions, covering frontal, central and posterior regions. These data were subjected to cluster analysis.

RESULTS

Three distinct EEG clusters of children with ADHD were found. These were characterized by (a) increased slow wave activity and deficiencies of fast wave, (b) increased high amplitude theta with deficiencies of beta activity, and (c) an excess beta group.

CONCLUSIONS

These results indicate that children with ADHD do not constitute a homogenous group in EEG profile terms. This has important implications for studies of the utility of EEG in the diagnosis of ADHD. Efforts aimed at using EEG as a tool to discriminate ADHD children from normals must recognize the variability within the ADHD population if such a tool is to be valid and reliable in clinical practice.

Suppression of intestinal and mammary neoplasia by lifetime administration of aspirin in Apc(Min/+) and Apc(Min/+), Msh2(-/-) mice

Numerous studies have indicated that exposure to nonsteroidal anti-inflammatory drugs is associated with a lowered risk of colorectal cancer. However, analyses of the effect of aspirin upon tumorigenesis in Apc(Min/+) mice have yielded contrasting results. We show that adult dietary exposure to aspirin does not suppress intestinal tumorigenesis in Apc(Min/+) mice, but that continual exposure from the point of conception does. To test whether this regime could suppress the phenotype of murine models of hereditary nonpolyposis colorectal cancer, Msh2-deficient mice were exposed to aspirin. This did not modify the mutator phenotype of Msh2(-/-) mice, but weakly extended survival. Finally, we analyzed (Apc(Min/+), Msh2(-/-)) mice and found that lifetime aspirin exposure significantly delayed the onset of both intestinal and mammary neoplasia. Thus embryonic and perinatal exposure to aspirin suppresses neoplasia specifically associated with the loss of Apc function, opening a potential window of opportunity for nonsteroidal anti-inflammatory drug intervention.

Excess beta activity in children with attention-deficit/hyperactivity disorder: an atypical electrophysiological group

Studies of children with attention deficit/hyperactivity disorder (ADHD) have typically found elevated levels of slow wave activity in their EEGs, but in two of our previous studies, a small subset of ADHD children with excess beta activity in the EEG was identified. The aim of this study was to determine whether children with excess beta activity represent a distinct electrophysiological subtype of ADHD, to quantify the differences in their EEGs, and to determine if this group of children with ADHD have behavioural profiles different from other children with ADHD. Results indicated that children with excess beta represent a small independent subset of children diagnosed with ADHD, which primarily consists of children with a diagnosis of ADHD combined type. Behaviourally, this group was similar to other children with ADHD, although the excess-beta group were more prone to temper tantrums and to be moody. The excess in beta activity was found primarily in the frontal regions and may be associated with frontal lobe self-regulation and inhibition control.

From efficacy to effectiveness: managing organisational change to improve health services for young people with deliberate self harm behaviour

Repeat Deliberate Self Harm is a recognised risk factor for completed suicide and therefore reduction by effective health service response represents a valid contribution to suicide prevention. However, only a small fraction of people with deliberate self harm presentations to general health settings actually reach specialist mental health follow-up appointments. Therefore, even if responses at that point are known to be effective they do not make a significant contribution to reducing repeat self-harm overall. We describe health system organisational change strategies to improve health service engagement for the target group, and present data demonstrating the effectiveness of these strategies.

Novel mechanism of hydrolysis of therapeutic beta-lactams by Stenotrophomonas maltophilia L1 metallo-beta-lactamase

Stopped-flow tryptophan fluorescence under single turnover and pseudo-first-order conditions has been used to investigate the kinetic mechanism of beta-lactam hydrolysis by the Stenotrophomonas maltophilia L1 metallo-beta-lactamase. For the cephalosporin substrates nitrocefin and cefaclor and the carbapenem meropenem, a substantial quench of fluorescence is observed on association of substrate with enzyme. We have assigned this to a rearrangement event subsequent to formation of an initial collision complex. For the colorimetric compound nitrocefin, decay of this dark inter- mediate represents the overall rate-determining step for the reaction and is equivalent to decay of a previously observed state in which the beta-lactam amide bond has already been cleaved. For both cefaclor and meropenem, the rate-determining step for hydrolysis is loss of a second, less quenched state, in which, however, the beta-lactam amide bond remains intact. We suggest, therefore, that the mechanism of hydrolysis of nitrocefin by binuclear metallo-beta-lactamases may be atypical and that cleavage of the beta-lactam amide bond is the rate-determining step for breakdown of the majority of beta-lactam substrates by the L1 enzyme.

Stability and folding rates of domains spanning the large A-band super-repeat of titin

Titin is a very large (>3 MDa) protein found in striated muscle where it is believed to participate in myogenesis and passive tension. A prominent feature in the A-band portion of titin is the presence of an 11-domain super-repeat of immunoglobulin superfamily and fibronectin-type-III-like domains. Seven overlapping constructs from human cardiac titin, each consisting of two or three domains and together spanning the entire 11-domain super-repeat, have been expressed in Escherichia coli. Fluorescence unfolding experiments and circular dichroism spectroscopy have been used to measure folding stabilities for each of the constructs and to assign unfolding rates for each super-repeat domain. Immunoglobulin superfamily domains were found to fold correctly only in the presence of their C-terminal fibronectin type II domain, suggesting close and possibly rigid association between these units. The domain stabilities, which range from 8.6 to 42 kJ mol(-1) under physiological conditions, correlate with previously reported mechanical forces required to unfold titin domains. Individual domains vary greatly in their rates of unfolding, with a range of unfolding rate constants between 2.6 x 10(-6) and 1.2 s(-1). This variation in folding behavior is likely to be an important determinant in ensuring independent folding of domains in multi-domain proteins such as titin.

XAFS study of the high-affinity copper-binding site of human PrP(91-231) and its low-resolution structure in solution

Here, we describe the structure of a C-terminal high-affinity copper-binding site within a truncated recombinant human PrP containing residues 91-231, which lacks the octapeptide repeat region. We show that at least two extra co-ordinating groups are involved in binding this copper(II) ion in conjunction with histidine residues 96 and 111 in a region of the molecule known to be critical in conferring strain type. In addition, using X-ray solution scattering, a low-resolution shape of PrP(91-231) is provided. The restored molecular envelope is consistent with the picture where the N-terminal segment, residues 91-120, extends out from the previously known globular domain containing residues 121-231.

Protochlorophyllide oxidoreductase: a homology model examined by site-directed mutagenesis

An homology model of protochlorophyllide reductase (POR) from Synechocystis sp. was constructed on a template from the tyrosine-dependent oxidoreductase family. The model showed characteristics appropriate to a globular, soluble protein and was used to generate a structure of the ternary complex of POR, nicotinamide adenine dinucleotide phosphate (NADPH), and protochlorophyllide. The POR ternary model was validated by mutagenesis experiments involving predicted coenzyme-binding residues and by chemical modification experiments. A core tryptophan residue was shown to be responsible for much of the protein's fluorescence. Both quenching of this residue by coenzyme and fluorescence resonance energy transfer (FRET) from the protein to the coenzyme allowed the binding constant of NADPH to be determined. Replacement of this residue by Tyr gave an active mutant with approximately halved fluorescence and a negligible FRET signal, consistent with the role of this residue in energy transfer to the NADPH at the active site and with the model. The mechanism of the enzyme is discussed in the context of the model and semiempirical molecular orbital calculations.

Location and properties of metal-binding sites on the human prion protein

Although a functional role in copper binding has been suggested for the prion protein, evidence for binding at affinities characteristic of authentic metal-binding proteins has been lacking. By presentation of copper(II) ions in the presence of the weak chelator glycine, we have now characterized two high-affinity binding sites for divalent transition metals within the human prion protein. One is in the N-terminal octapeptide-repeat segment and has a K(d) for copper(II) of 10(-14) M, with other metals (Ni(2+), Zn(2+), and Mn(2+)) binding three or more orders of magnitude more weakly. However, NMR and fluorescence data reveal a previously unreported second site around histidines 96 and 111, a region of the molecule known to be crucial for prion propagation. The K(d) for copper(II) at this site is 4 x 10(-14) M, whereas nickel(II), zinc(II), and manganese(II) bind 6, 7, and 10 orders of magnitude more weakly, respectively, regardless of whether the protein is in its oxidized alpha-helical (alpha-PrP) or reduced beta-sheet (beta-PrP) conformation. A role for prion protein (PrP) in copper metabolism or transport seems likely and disturbance of this function may be involved in prion-related neurotoxicity.

The A245K mutation exposes another stage of the bacterial L-lactate dehydrogenase reaction mechanism

The A245K mutant of Bacillus stearothermophilus L-lactate dehydrogenase has been expressed in Escherichia coli and purified. A qualitative change in the reaction mechanism prior to the hydride transfer step in the reverse direction in the mutant is revealed. Both transient and steady state characteristics of the mutant are presented and show in contrast to the wild-type enzyme where a rearrangement of an enzyme-NADH-pyruvate complex is rate-limiting that in the mutant the rearrangement is much faster and hydride transfer is the first slow step. The steady state is limited by a new second slower conformation change involving an NAD+ complex. The mutation may provide a valuable framework for inhibitor and drug design research.

Msh-2 suppresses in vivo mutation in a gene dose and lesion dependent manner

Mice deficient for the mismatch repair (MMR) gene Msh2 show accelerated tumourigenesis and a reduced apoptotic response to DNA damage of methylation type. Here we examine the effect of mutation for Msh2 on in vivo mutation frequencies in the intestine as determined by loss of function at the Dolichos biflorus (Dlb-1) locus. Spontaneous mutation frequencies were scored in cohorts of ageing mice either wild type or mutant for Msh2. In mice less than 1 year old, mutation frequencies were only elevated in Msh2 null mice. However, beyond this age heterozygous Msh2 mice showed significantly higher mutation frequencies than controls. These findings implicate a gene dose dependent requirement for Msh2 in mutation suppression and prompted an analysis of young Msh2 mutants following exposure to DNA damage. Following exposure to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), Msh2 deficient mice show a reduced apoptotic response and an increase in mutation frequency. Heterozygotes did not differ from controls. Following exposure to cisplatin, no significant elevation was seen in mutation frequencies, even within homozygotes. This is particularly surprising given the association between cisplatin resistance and MMR deficiency. These findings therefore demonstrate a complex reliance upon functional Msh2 in mutation surveillance. We have identified three separate scenarios. First, where retention of both Msh2 alleles over an extended period of time appears critical to the suppression of spontaneous mutation; second, 3 weeks following exposure to MNNG, where only complete loss of Msh2 results in elevated mutation; and finally following cisplatin exposure, where induced levels of mutation are independent of Msh2 status.

Age and sex effects in the EEG: differences in two subtypes of attention-deficit/hyperactivity disorder

OBJECTIVES

This study investigated age-related changes and sex differences in the EEGs of two groups of children with attention-deficit/hyperactivity disorder (ADHD) combined type and ADHD predominantly inattentive type, in comparison with a control group of normal children.

METHODS

Forty boys and forty girls were included in each group. The EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide estimates for total power, absolute and relative power in the delta, theta, alpha and beta bands, and for theta/alpha and theta/beta ratios.

RESULTS

Total power, relative alpha, and the theta/alpha and theta/beta ratios were differentiated between all 3 groups. Sex differences between the ADHD subjects and the control group were greater in males than females and matured faster in males. With increasing age, the EEG of the ADHD inattentive group was found to change at a similar rate to the changes found in the normal group, with the differences in power levels remaining constant. In the ADHD combined group, the power was found to change at a greater rate than in the ADHD inattentive group, with power levels of the two ADHD groups becoming similar with age.

CONCLUSIONS

These results are supportive of a two-component model of ADHD, with the hyperactive/impulsive component maturing with age and the inattentive component remaining more stable.

Age and sex effects in the EEG: development of the normal child

OBJECTIVES

This study investigated age-related changes and sex differences in the EEGs of normal children.

METHODS

Forty boys and 40 girls, between the ages of 8 and 12 years, participated in this study. The EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide estimates for total power, absolute and relative power in the delta, theta, alpha and beta bands, and for theta/alpha and theta/beta ratios.

RESULTS

Absolute delta activity decreased with age. Relative delta and theta decreased and alpha and beta increased with increasing age. The theta/alpha and theta/beta ratios decreased with increasing age. All of these indicated a developmental reduction in slow wave activity. Maturational differences were found in the rates of change between the midline and the two hemispheres. In the absolute delta and the theta/beta ratio, the midline and the two hemispheres became more equipotential with age. In the beta band, power increased at a greater rate than in the two hemispheres. Sex differences were found, with males having less theta and more alpha than females.

CONCLUSIONS

These results indicated that maturation occurs earlier at the midline than in the two hemispheres. Females were also found to have a developmental lag in the EEG compared with males.

Ab initio protein structure prediction using physicochemical potentials and a simplified off-lattice model

This study describes a computational method for ab inito protein structure prediction. Protein conformation has been modeled by using six optimized backbone torsion angles and fixed side chains approximating rotationally averaged real side chains. The approximations aim to keep complexity of the structure description to a minimum without seriously compromising the accuracy of the structural representation. An evolutionary Monte Carlo algorithm has been developed to search through this restricted conformational space to locate low-energy protein structures. A simple physicochemical force field has been developed to assess the energies of different conformations within this structural description. The corresponding residue interaction energies are based on hydrophobic, hydrophilic, steric, and hydrogen-bonding potentials. The search procedure has been used to locate native energy minima from primary sequence alone. The 3-D structures of polypeptides up to 38 residues with both beta and alpha secondary structural elements have been accurately predicted. The search procedure has been found to be highly efficient and follows an energetically and structurally plausible pathway to locate native populations. The simple force field described in the study has been compared with a more complex all-atom model and been found to be similarly effective in predicting the structures of proposed independent folding units. Proteins 2001;43:186-202.

A role for mismatch repair in control of DNA ploidy following DNA damage

Many reports have shown a link between mismatch repair (MMR) deficiency and loss of normal cell cycle control, particularly loss of G2 arrest. However almost all of these studies utilized transformed cell lines, and thus the involvement of other genes in this phenotype cannot be excluded. We have examined the effects of cisplatin treatment on primary embryo fibroblasts (MEFs) derived from mice in which the MMR gene Msh2 had been inactivated (Msh2(-/-)). This analysis determined that both primary Msh2(-/-) and wild type (WT) fibroblasts exhibited an essentially identical G2 arrest following cisplatin treatment. Similarly, we observed a cisplatin-induced G2 arrest in immortalized MMR deficient (Mlh1(-/-) and Pms2(-/-)) and WT MEFs. p53 deficient primary MEFs (p53(-/-)) exhibited both a clear G2 arrest and an increase in cells with a DNA content of 8N in response to cisplatin. When the Msh2 and p53 defects were combined (p53(-/-)/Msh2(-/-)) the G2 arrest was essentially identical to the p53(-/-) fibroblasts. However, the p53(-/-)/Msh2(-/-) fibroblasts demonstrated a further increase in cells with an 8N DNA content, above that seen in the p53(-/-) fibroblasts. These results suggest that loss of MMR on its own is not enough to overcome G2 arrest following exposure to cisplatin but does play a role in preventing polyploidization, or aberrant DNA reduplication, in the absence of functional p53.

Identification and structure of the nerve growth factor binding site on TrkA

Nerve growth factor (NGF) is involved in the development and maintenance of the nervous system and has been implicated as a possible therapeutic target molecule in a number of neurodegenerative diseases, especially Alzheimer's disease. NGF binds with high affinity to the extracellular region of a tyrosine kinase receptor, TrkA, which comprises three leucine-rich motifs (LRMs), flanked by two cysteine-rich clusters, followed by two immunoglobulin-like (Ig-like) domains. We have expressed the second Ig-like domain as a recombinant protein in E. coli and demonstrate that NGF binds to this domain with similar affinity to the native receptor. This domain (TrkAIg(2)) has the ability to sequester NGF in vitro, preventing NGF-induced neurite outgrowth, and in vivo, inhibiting NGF-induced plasma extravasation. We also present the three-dimensional structure of the TrkAIg(2) domain in a new crystal form, refined to 2.0 A resolution.

Electroencephalogram differences in two subtypes of attention-deficit/hyperactivity disorder

This study investigated EEG differences between children with two subtypes of Attention-Deficit/Hyperactivity Disorder (ADHD) and normal control subjects. EEG was recorded during an eyes-closed resting condition and Fourier transformed to provide absolute and relative power estimates for the delta, theta, alpha, and beta bands, and the mean frequency for each band was calculated. Ratio coefficients were also calculated between frequency bands. Mean group differences were found in the theta, alpha, and beta bands between all three groups. Similarly, differences were found between all three groups for the theta/alpha and theta/beta ratios and for the mean frequency of the total EEG. These results support a model of ADHD resulting from a developmental deviation rather than a maturational lag in the central nervous system. Differences between the clinical groups in frontal activity suggest that different neuroanatomical systems are involved in the different subtypes of ADHD.

The role of Stat3 in apoptosis and mammary gland involution. Conditional deletion of Stat3

STATs (signal transducer and activator of transcription) are a family of latent transcription factors which are activated in response to a variety of cytokines and growth factors. This family of signalling molecules have been implicated in growth, differentiation, survival and apoptosis. In this article, we will review work which highlights the role of individual STAT factors in mammary gland and demonstrate the value of genetically modified mice in defining the function of STAT3. Involution of the mouse mammary gland is characterised by extensive apoptosis of the epithelial cells and the activation of STAT3. STATs 3 and 5 have reciprocal patterns of activation throughout a mammary developmental cycle suggesting that STAT5 may be a survival factor and STAT3 a death factor for differentiated mammary epithelium. To clarify the role of STAT3 in mammary epithelial apoptosis, we have generated a conditional knockout using the lox/Cre recombination system. Mammary glands from crosses of transgenic mice expressing Cre recombinase under the control of the beta-lactoglobulin milk protein gene promoter with mice harbouring one floxed STAT3 allele and one null STAT3 allele, showed a decrease in epithelial apoptosis and a dramatic delay of the involution process upon forced weaning. This was accompanied by precocious activation of STAT1 and increases in p53 and p21 levels--these may act as a compensatory mechanism for initiating the eventual involution which occurs in STAT3 null mammary glands. This demonstrates for the first time the importance of STAT factors in signalling the initiation of physiological apoptosis in vivo and highlights the utility of the lox/Cre system for addressing the function of genes, which have an embryonic lethal phenotype, specifically in mammary gland.

The molecular biology of prion propagation

Prion diseases such as Creutzfeldt-Jakob disease (CJD) in humans and scrapie and bovine spongiform encephalopathy (BSE) in animals are associated with the accumulation in affected brains of a conformational isomer (PrP(Sc)) of host-derived prion protein (PrP(C)). According to the protein-only hypothesis, PrP(Sc) is the principal or sole component of transmissible prions. The conformational change known to be central to prion propagation, from a predominantly alpha-helical fold to one predominantly comprising beta structure, can now be reproduced in vitro, and the ability of beta-PrP to form fibrillar aggregates provides a plausible molecular mechanism for prion propagation. The existence of multiple prion strains has been difficult to explain in terms of a protein-only infectious agent but recent studies of human prion diseases suggest that strain-specific phenotypes can be encoded by different PrP conformations and glycosylation patterns. The experimental confirmation that a novel form of human prion disease, variant CJD, is caused by the same prion strain as cattle BSE, has highlighted the pressing need to understand the molecular basis of prion propagation and the transmission barriers that limit their passage between mammalian species. These and other advances in the fundamental biology of prion propagation are leading to strategies for the development of rational therapeutics.

A novel role for IRF-1 as a suppressor of apoptosis

The tumour suppressor IRF-1 is a transcription factor involved in the induction of apoptosis in several in vitro systems. Post-lactational involution of the mammary gland is characterized by extensive apoptosis of the epithelial cells. We have previously shown that signal transducer and activator of transcription (Stat) 3 drives apoptosis and involution in the mouse mammary gland. Since one of the downstream targets of the Stat signalling pathway is IRF-1, we have used IRF-1 knockout mice to address the potential role of this transcription factor in involution. Surprisingly, in the absence of IRF-1 significantly higher numbers of apoptotic cells were found in involuting glands at 48 h compared to control glands. In addition, the alveolar structure in IRF-1 null mammary glands had collapsed whereas in control glands the alveoli remained intact and distended. However, by 72 h control and null glands were morphologically similar suggesting that IRF-1 suppresses apoptosis only during the early, reversible, stage of involution. This suggests a survival role for IRF-1 in mammary epithelia and demonstrates a novel role for IRF-1 in vivo--suppression of premature epithelial apoptosis during mammary gland involution.

Progressive stabilization of intermediate and transition states in protein folding reactions by introducing surface hydrophobic residues

It can be argued from the principle of solvent exclusion that the introduction of hydrophobic residues onto the surface of a protein will not destabilize the folded state because the nonpolar side chain will be at least as exposed in the unfolded state as it is when the protein chain is folded. A comparison of the folding pathway of wild type and 11 site-directed mutants of CD2.d1 shows this to be true. In fact, owing to partial burial of nonpolar groups as folding proceeds, we find that the rapidly formed intermediate state and, to a greater extent, the transition state are generally stabilized by hydrophobic surface mutations. This effect is slightly moderated in the folded state presumably by the perturbation of van der Waals' contacts and/or local electrostatic interactions that have a greater influence in this fully compact structure. The fact that in all but one case we find that stabilization of the rapidly collapsed intermediate is accompanied by a faster acquisition of the folded state refutes the argument that I states are generally "off pathway" conformations or ensembles that lead to the inhibition of otherwise more rapid folding trajectories.