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 âˆ¼ 30 my younger than previously reported for this group, with the tribe diverging from its most recent common ancestor âˆ¼ 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.

Short communication: Effect of a citrus extract in lactating dairy cows.

Dry matter intake is a main driver of energy balance in lactating dairy cows, and some plant extracts have been commercially fed to dairy cows to stimulate feed intake. Citrus extracts contain several bioactive components and have been shown to modify metabolism in other animal models. Our hypothesis was that a citrus extract would increase dry matter intake. Two experiments were conducted to determine the effect of a citrus extract on intake and milk production in lactating dairy cows. In experiment one, 11 early-lactation dairy cows (experiment 1; 77 ± 15 d in milk, mean ± standard deviation) were used in a switchback design, and in experiment two, 15 mid-lactation Holstein cows (experiment 2; 157 ± 44 d in milk, mean ± standard deviation) were used in a crossover design. In both experiments, treatments were control (no supplement) or a citrus extract (4 g/d in experiment 1 and 4.5 g/d in experiment 2). Treatment periods were 21 and 14 d in experiment 1 and experiment 2, respectively, with the final 7 d used for sample and data collection. No effect was observed for treatment on dry matter intake, feeding behavior, milk yield, milk fat yield, milk protein yield, or milk composition in either experiment. Treatment also had no effect on milk trans fatty acid profile, but the extract increased total 16 carbon fatty acids 0.9 and 0.6 percentage points in experiment 1 and experiment 2, respectively. Plasma nonesterified fatty acids were decreased 6 h after feeding in both experiments (11.1 and 16.0 µEq/L in experiment 1 and experiment 2, respectively). Plasma insulin was increased 1 h before feeding compared with the control in experiment 1 (3.36 vs. 2.13 µIU/mL) and tended to increase 1.79 units 1 h before feeding in experiment 2. The citrus extract had no effect on feed intake or milk production at the dose investigated, but changed plasma insulin and nonesterified fatty acids, indicating some metabolic effects requiring further investigation.

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 ß-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 (adenomatous polyposis coli) within hepatocytes activates Wnt signalling, perturbs differentiation and ultimately leads to neoplasia. Apc negatively regulates Wnt signalling but is also involved in organizing the cytoskeleton and may have 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 on cell cycle regulation, proliferation, death and aneuploidy. We show that, although Apc loss leads to increased proliferation, it also leads to increased apoptosis, the accumulation of p53, p21 and markers of double-strand breaks 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 analysed 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.

The effect of rumen digesta inoculation on the time course of recovery from classical diet-induced milk fat depression in dairy cows.

Ten ruminally cannulated cows were used in a crossover design that investigated the effect of rumen digesta inoculation from non-milk fat-depressed cows on recovery from classical diet-induced milk fat depression (MFD) characterized by reduced fat yield, reduced de novo milk fat synthesis, and increased alternate trans isomers. Two additional cows fed a high-fiber and low-polyunsaturated fatty acid (FA) diet (31.8% neutral detergent fiber, 4.2% FA, and 1.2% C18:2) were used as rumen digesta donors. Milk fat depression was induced during the first 10d of each period by feeding a low-fiber and high-polyunsaturated FA diet (induction; 26.1% neutral detergent fiber, 5.8% FA, and 1.9% C18:2), resulting in a 30% decrease in milk fat yield. A recovery phase followed where all cows were switched to the high-forage, low-polyunsaturated FA diet and were allocated to (1) control (no inoculation) or (2) ruminal inoculation with donor cow digesta (8 kg/d for 6d). Milk yield and composition were measured every 3d. Milk yield progressively decreased during recovery. Milk fat concentration increased progressively during the recovery phase and no effect of treatment existed at any time point. Also, no treatment effect of milk fat yield was detected. The concentration of milk de novo FA increased progressively during recovery for both treatments and was higher for inoculated compared with control cows on d 6. In agreement, milk fat concentration of trans-10,cis-12 conjugated linoleic acid decreased progressively in both treatments and was lower in inoculated cows on d 3 and 6. Ruminal inoculation from non-milk fat-depressed cows did not change milk fat yield, but slightly accelerated the rate of recovery of de novo FA synthesis and normal ruminal FA biohydrogenation, demonstrating a possible opportunity for other interventions that improve the ruminal environment to accelerate recovery from this condition.

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.

EEG and electrodermal activity in girls with Attention-Deficit/Hyperactivity Disorder.

OBJECTIVE: This study investigated the Hypoarousal Model of Attention-Deficit/Hyperactivity Disorder (AD/HD) in girls. METHODS: 40 girls with AD/HD and 40 girl controls (aged 7-12 years) had an eyes-closed resting EEG recorded from 19 electrodes and Fourier transformed. Estimates for total power, absolute and relative power in the delta, theta, alpha, beta and gamma frequency bands, and theta/beta ratio were analysed in nine cortical regions. Skin conductance level (SCL) was simultaneously recorded. Regression analyses explored relationships between symptoms and physiology. RESULTS: Compared with controls, girls with AD/HD had globally elevated relative delta, globally reduced absolute beta, and globally reduced absolute and relative gamma activity. Girls with AD/HD also had lower mean SCL. Inattentive symptoms were predicted by elevated frontal relative delta, reduced SCL, and reduced temporal relative gamma activity, while elevated hyperactive-impulsive symptoms correlated with elevated frontal relative delta activity in both the patient and control groups. CONCLUSIONS: These EEG results are comparable with the limited female AD/HD literature. Girls with AD/HD are hypoaroused, indicated by reduced SCL, and appear to have an anomalous arousal mechanism. Absolute and relative gamma results are similar to previous findings in AD/HD children. Symptom correlations with physiology offer intriguing insights for future research. SIGNIFICANCE: This is the first study to examine CNS arousal exclusively in girls with AD/HD.

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.

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-OΔN89ß-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 ß-catenin (ΔN89ß-catenin) that exhibited a strong intestinal hyperplasia was analyzed during the removal of oncogenic ß-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.

Dual inhibition of epidermal growth factor and insulin-like 1 growth factor receptors reduce intestinal adenoma burden in the Apc(min/+) mouse.

BACKGROUND: Identification of early molecular pathway changes may be useful as biomarkers for tumour response/resistance prediction, and here we provide direct in vivo proof of this concept. The type 1 insulin-like growth factor receptor (IGF1R) has been implicated in various aspects of adenoma development and metastasis. We show here that, in murine intestinal adenomas acutely exposed to a small molecular inhibitor of EGFR (gefitinib), there is concurrent suppression of EGFR downstream signalling and induction of IGF signalling. We therefore tested the hypothesis that blockade of EGFR signalling was being tempered by compensatory activation of the IGF pathway by examining the effect of chronic suppression of IGF1R using AZ12253801, a small molecular tyrosine kinase inhibitor of IGF1R. METHODS: Male Apc(min/+) mice with an intestinal tumour burden were exposed to a single dose of an inhibitor against EGFR (gefitinib), IGF1R (AZ12253801), 0.5% Tween 80 or combined EGFR/IGF1R inhibitor and culled 4 h post dosing. Tumour tissue was analysed to detect the early molecular pathways induced and anti-tumour phenotypic changes. Cohorts of male Apc(min/+) mice (n=15-17) were subsequently treated with gefitinib for a period of 8 weeks and subsequently exposed to single (either gefitinib or AZ12253801) or combined (gefitinib and AZ12253801) therapy. We also included a vehicle-treated cohort, which was never exposed to gefitinib and became symptomatic of the disease by day 150. RESULTS: Both single treatments delayed the onset of disease symptoms. Combined dosing with gefitinib and AZ12253801 similarly delayed the onset of symptoms, and at 200 days suppressed small intestinal tumourigenesis more effectively than either treatment alone (median small intestinal adenoma volume (47 mm(3) (comb) vs 248 mm(3) (AZ12253801), P=0.0003 and 47 mm(3) (comb) vs 123 mm(3) (gefitinib), P=0.0042, Mann-Whitney (two-sided) test). CONCLUSION: Our data provide evidence in support of the use of combinatorial therapy, and establishes the need to further define the precise benefit in vivo.

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.

Challenges encountered in the diagnosis of tuberculous otitis media: case report and literature review.

OBJECTIVE: To report a rare case of tuberculous otitis media, and to highlight barriers to clinical and microbiological diagnosis. METHOD: Case report and literature review. RESULTS: Tuberculous otitis media is a rare cause of chronic ear infection in the UK. Its symptoms may mimic a range of other otological conditions, including otitis media, chronic suppurative otitis media, cholesteatoma and necrotising otitis media. CONCLUSION: This case report highlights the challenges of obtaining a clinical diagnosis of tuberculous otitis media, and emphasises the fact that screening for acid-fast bacilli is not sufficient, in isolation, to rule out mycobacterial infection.

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.

Crystal structure of human prion protein bound to a therapeutic antibody.

Prion infection is characterized by the conversion of host cellular prion protein (PrP(C)) into disease-related conformers (PrP(Sc)) and can be arrested in vivo by passive immunization with anti-PrP monoclonal antibodies. Here, we show that the ability of an antibody to cure prion-infected cells correlates with its binding affinity for PrP(C) rather than PrP(Sc). We have visualized this interaction at the molecular level by determining the crystal structure of human PrP bound to the Fab fragment of monoclonal antibody ICSM 18, which has the highest affinity for PrP(C) and the highest therapeutic potency in vitro and in vivo. In this crystal structure, human PrP is observed in its native PrP(C) conformation. Interactions between neighboring PrP molecules in the crystal structure are mediated by close homotypic contacts between residues at position 129 that lead to the formation of a 4-strand intermolecular beta-sheet. The importance of this residue in mediating protein-protein contact could explain the genetic susceptibility and prion strain selection determined by polymorphic residue 129 in human prion disease, one of the strongest common susceptibility polymorphisms known in any human disease.

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.

Chk1 deficiency in the mouse small intestine results in p53-independent crypt death and subsequent intestinal compensation.

Chk1 is a serine/threonine protein kinase that is activated by a wide range of DNA-damaging agents to slow the cell cycle during S phase and G2/M. Abrogation of these cell-cycle checkpoints using Chk1 inhibitors results in hypersensitivity to DNA-damaging agents in vitro and may provide a potential therapeutic tool to sensitize tumour cells in vivo. We have generated a Cre-Lox-based mouse model in which Chkl can be inducibly deleted from somatic epithelial cells in the adult mouse small intestine and liver. Loss of Chk1 in the liver is tolerated with no apparent phenotype. In contrast, the loss of Chk1 within the small intestine results in immediate DNA damage and high levels of p53-independent apoptosis leading to crypt death. However, the intestine is able to compensate for this death by undergoing complete re-population with Chk1-proficient cells. These data therefore show that Chk1 deficiency is cell lethal, but the intestine can tolerate such lethality at the organ level.