Increased frequency of the k-ras G12C mutation in MYH polyposis colorectal adenomas

Colorectal tumours from MYH polyposis patients display an excess of somatic G : C --> T : A transversions in the adenomatous polyposis coli gene. Here, we identify k-ras mutations in nine out of 54 (16.7%) MYH polyposis tumours. Their presence was associated with increased dysplasia and tubulovillous morphology (P=0.005). G : C --> T : A transversions in k-ras were significantly more frequent in MYH polyposis adenomas than in sporadic or familial adenomatous polyposis-associated tumours (P<or=0.002), and all resulted in a glycine-to-cysteine substitution at codon 12.

Differential effect of nitric oxide synthase inhibition on sigmoid colon longitudinal and circular muscle responses to nicotine and nerve stimulation in vitro

BACKGROUND

Nicotine has been shown to release nitric oxide from nerves in human sigmoid colon. This effect has been used to investigate the innervation and functional relationship of the longitudinal and circular muscle layers.

METHODS

Strips of longitudinal and circular muscle were obtained from 19 patients with colorectal cancer. The strips from ten patients were subjected to electrical field stimulation (EFS) in vitro using stimulus parameters for selective stimulation of nerves. The effect of nicotine 1-10 micromol/l on EFS responses was then measured in the presence and absence of a nitric oxide synthase inhibitor, nitro-L-arginine methyl ester (L-NAME) 200 micromol/l. The effect of nicotine on spontaneous activity was investigated in the muscle strips from the other nine patients.

RESULTS

Both longitudinal and circular strips responded to EFS with contraction. The time to achieve a peak contractile response (time to peak; TTP) was significantly longer (P<0.001) in circular strips. L-NAME reduced the mean(s.e.m.) TTP in circular muscle from 23.3(2.0) to 17.2(1.5) s (P=0.007) and altered its pattern of response to resemble that of longitudinal muscle. Nicotine 10 micromol/l reduced the contraction to EFS in circular (P<0.001) but not in longitudinal (P=0.347) muscle. The nicotine-induced reduction in circular muscle contraction was blocked by L-NAME 200 micromol/l (P=0.005).

CONCLUSION

These findings suggest that nitric oxide release on neural stimulation is greater in circular than in longitudinal muscle.

High-Resolution MRI of the Anatomy Important in Total Mesorectal Excision of the Rectum

OBJECTIVE

The surgical removal of a rectal carcinoma and the adjacent lymph nodes in an en bloc package lessens the risk of local recurrence due to residual tumor. Heightened awareness of good surgical techniques has created much interest in the anatomy involved in total mesorectal excision surgery, with particular focus on the fascial planes and nerve plexuses and their relationship to the surgical planes of excision. Clear preoperative depiction of these relationships is of value in determining tumor resectability. The aim of this study was to describe the radiologic appearance of these anatomic structures. SUBJECTS AND METHODS. High-spatial-resolution T2-weighted MRI was performed using a 1.5-T system in cadaveric sections and in patients before they underwent total mesorectal excision surgery. Anatomic dissections of sagitally sectioned hemipelves were compared with MRIs obtained in vivo to establish criteria for visualization of the structures relevant to anterior resection of the rectum.

RESULTS

High-spatial-resolution MRI depicted a number of structures of importance in total mesorectal excision surgery. The mesorectal fascia, which forms the boundary of the surgical excision plane in total mesorectal excision, was identified, and the presacral fascia, peritoneal reflection, and Denonvilliers' fascia were also shown. Structures 1-2 mm in diameter were visualized because the contrast resolution afforded by T2-weighted fast spin-echo imaging permitted depiction of the inferior hypogastric nerve plexus and the fascial planes within the posterior pelvis.

CONCLUSION

Anatomic landmarks important to the performance of rectal cancer surgery, in particular the mesorectal fascia, may be defined on MRI and are of potential importance in the staging of tumors, assessing resectability, planning surgery, and selecting patients for preoperative neoadjuvant therapy.

Functional expression cloning reveals proapoptotic role for protein phosphatase 4

Functional expression cloning strategies are highly suitable for the analysis of the molecular control of apoptosis. This approach has two critical advantages. Firstly, it eliminates prior assumptions about the properties of the proteins involved, and, secondly, it selectively targets proteins that are causally involved in apoptosis control and which affect the crucial cellular decision between survival and death. The application of this strategy to the isolation of cDNAs conferring resistance to dexamethasone and gamma-irradiation resulted in the isolation of a partial cDNA for the catalytic subunit of protein phosphatase 4 (PP4). Cells transfected with this partial cDNA in an expression vector downregulated PP4 and were resistant to both dexamethasone and UV radiation, as demonstrated by both membrane integrity and colony-forming assays. These observations suggest that PP4 plays an important proapoptotic role in T lymphocytes.

Morphologic predictors of lymph node status in rectal cancer with use of high-spatial-resolution MR imaging with histopathologic comparison

PURPOSE

To evaluate signal intensity and border characteristics of lymph nodes at high-spatial-resolution magnetic resonance (MR) imaging in patients with rectal cancer and to compare these findings with size in prediction of nodal status.

MATERIALS AND METHODS

Forty-two patients who underwent total mesorectal excision of the rectum to determine if they had rectal carcinoma were studied with preoperative thin-section MR imaging. Lymph nodes were harvested from 42 transversely sectioned surgical specimens. The slice of each lymph node was carefully matched with its location on the corresponding MR images. Nodal size, border contour, and signal intensity on MR images were characterized and related to histologic involvement with metastases. Differences in sensitivity and specificity with border or signal intensity were calculated with CIs by using method 10 of Newcombe.

RESULTS

Of the 437 nodes harvested, 102 were too small (<3 mm) to be depicted on MR images, and only two of these contained metastases. In 15 (68%) of 22 patients with nodal metastases, the size of normal or reactive nodes was equal to or greater than that of positive nodes in the same specimen. Fifty-one nodes were above the area imaged, and seven of these contained metastases. The diameter of benign and malignant nodes was similar; therefore, size was a poor predictor of nodal status. If a node was defined as suspicious because of an irregular border or mixed signal intensity, a superior accuracy was obtained and resulted in a sensitivity of 51 (85%) of 60 (95% CI: 74%, 92%) and a specificity of 216 (97%) of 221 (95% CI: 95%, 99%).

CONCLUSION

Prediction of nodal involvement in rectal cancer with MR imaging is improved by using the border contour and signal intensity characteristics of lymph nodes instead of size criteria.

Peritoneal dialysis: changes to the structure of the peritoneal membrane and potential for biocompatible solutions

BACKGROUND

Peritoneal dialysis (PD) is now established as a viable and successful alternative to hemodialysis (HD) for patients starting on renal replacement therapy. A number of studies have confirmed that equivalent adequacy and fluid balance are provided at least for the first four to five years of renal replacement therapy (RRT). Loss of peritoneal membrane function remains a major factor leading to treatment failure in a significant number of patients on PD. Numerous studies have suggested a relationship between these changes in function and structural changes in the membrane. A careful analysis of peritoneal biopsies from PD patients would allow the clear identification of those changes unique to PD, in addition to indicating possible correlations with glucose exposure as well as other functional parameters.

METHODS

We systematically examined peritoneal biopsies from 13 normal individuals, 29 uremic predialysis patients, 55 HD patients, and 157 patients on long-term PD. Well-oriented specimens were stained with toluidine blue and examined by a blinded pathologist. Limited clinical data has allowed a preliminary analysis of structure-function relationships.

RESULTS

The median thickness of the submesothelial compact collagenous zone was 40 microm in normal individuals, 150 microm in uremic patients, 150 microm in patients on HD, and 2550 microm in patients on PD (P < 0.001 for all vs. normal individuals). Compact zone thickness increased significantly with duration of PD therapy (0 to 24 months, 180 microm;>97 months, 600 microm). Vascular changes comprised progressive subendothelial hyalinization of postcapillary venules, with luminal narrowing or obliteration. These changes were present in uremic patients and increased significantly with PD duration (P = 0.0001).

CONCLUSIONS

These data indicate that morphologic changes in the postcapillary venules and the submesothelial compact zone of PD patients begin during the uremic phase of their illness. This is then worsened by time spent on PD. The relationships with glucose exposure or glucose degradation products have yet to be established.

Morphologic predictors of lymph node status in rectal cancer with use of high-spatial-resolution MR imaging with histopathologic comparison

PURPOSE

To evaluate signal intensity and border characteristics of lymph nodes at high-spatial-resolution magnetic resonance (MR) imaging in patients with rectal cancer and to compare these findings with size in prediction of nodal status.

MATERIALS AND METHODS

Forty-two patients who underwent total mesorectal excision of the rectum to determine if they had rectal carcinoma were studied with preoperative thin-section MR imaging. Lymph nodes were harvested from 42 transversely sectioned surgical specimens. The slice of each lymph node was carefully matched with its location on the corresponding MR images. Nodal size, border contour, and signal intensity on MR images were characterized and related to histologic involvement with metastases. Differences in sensitivity and specificity with border or signal intensity were calculated with CIs by using method 10 of Newcombe.

RESULTS

Of the 437 nodes harvested, 102 were too small (<3 mm) to be depicted on MR images, and only two of these contained metastases. In 15 (68%) of 22 patients with nodal metastases, the size of normal or reactive nodes was equal to or greater than that of positive nodes in the same specimen. Fifty-one nodes were above the area imaged, and seven of these contained metastases. The diameter of benign and malignant nodes was similar; therefore, size was a poor predictor of nodal status. If a node was defined as suspicious because of an irregular border or mixed signal intensity, a superior accuracy was obtained and resulted in a sensitivity of 51 (85%) of 60 (95% CI: 74%, 92%) and a specificity of 216 (97%) of 221 (95% CI: 95%, 99%).

CONCLUSION

Prediction of nodal involvement in rectal cancer with MR imaging is improved by using the border contour and signal intensity characteristics of lymph nodes instead of size criteria.

Preoperative assessment of prognostic factors in rectal cancer using high-resolution magnetic resonance imaging

BACKGROUND

The aim was to determine the accuracy of preoperative magnetic resonance imaging (MRI) in the evaluation of pathological prognostic factors that influence local recurrence and survival in rectal cancer.

METHODS

Ninety-eight patients undergoing total mesorectal excision for biopsy-proven rectal cancer were assessed prospectively using high-resolution MRI for tumour (T) and nodal (N) staging using the tumour node metastasis classification, depth of extramural tumour spread, the presence or absence of extramural venous invasion, a threatened circumferential resection margin and serosal involvement at or above the peritoneal reflection. Preoperative magnetic resonance assessment of these prognostic factors was compared with histopathological findings in carefully matched whole-mount sections of the resection specimen.

RESULTS

There was 94 per cent weighted agreement (weighted kappa = 0.67) between MRI and pathology assessment of T stage. Agreement between MRI and histological assessment of nodal status was 85 per cent (kappa = 0.68). Although involvement of small veins by tumour was not discernible using MRI, large (calibre greater than 3 mm) extramural venous invasion was identified correctly in 15 of 18 patients (kappa = 0.64). MRI predicted circumferential resection margin involvement with 92 per cent agreement (kappa = 0.81). Seven of nine patients with peritoneal perforation by tumour (stage T4) were identified correctly using MRI.

CONCLUSION

High-resolution MRI of the rectum allows preoperative identification of important surgical and pathological prognostic risk factors. This may allow both better selection and assessment of patients undergoing preoperative therapy.

Histological changes in the oesophageal squamous mucosa: correlation with ambulatory 24 hour pH monitoring

AIMS

To determine the value of squamous mucosal histology in the assessment of patients with gastro-oesophageal reflux symptoms.

METHODS

Sixty six patients with reflux symptoms underwent endoscopy with oesophageal biopsy, manometry, and 24 hour oesophageal pH testing. The following histological features were assessed in squamous mucosa: the degree of basal cell hyperplasia, the degree of papillary zone elongation, and the density of neutrophil and eosinophil infiltration. Comparisons were made between the histological findings and the oesophageal function tests.

RESULTS

The correlation between the traditionally accepted histological markers of gastro-oesophageal reflux disease in squamous mucosa and 24 hour pH testing was predominantly negative, with the exception of neutrophil inflammation in the squamous mucosa of patients with complicated reflux disease.

CONCLUSIONS

This study was unable to confirm the value of the Ismail-Beigi criteria as histological markers of acid reflux. By inference, biopsy of the oesophageal squamous mucosa is of limited value in the assessment of patients with reflux symptoms.

Inflammation at the cardio-oesophageal junction: relationship to acid and bile exposure

BACKGROUND

The aetiology of inflammation in cardiac mucosa at the gastro-oesophageal junction (carditis) is unclear, although gastro-oesophageal reflux has been suggested.

OBJECTIVES

To correlate histological features of carditis with oesophageal acid exposure (gastro-oesophageal reflux) and proximal gastric bile exposure (duodenogastric reflux) in patients with symptoms of gastro-oesophageal reflux disease (GORD).

METHODS

Sixty-six patients with reflux symptoms underwent endoscopy with biopsy, oesophageal manometry, 24-h oesophageal pH testing and 24-h proximal gastric Bilitec 2000 testing. Inflammation in glandular mucosa was assessed using the updated Sydney System. Fifteen healthy volunteers underwent pH and Bilitec 2000 testing and served as controls.

RESULTS

There was no correlation between either the presence or histological grade of carditis and oesophageal acid exposure or proximal gastric bilirubin exposure. Patients with reflux symptoms had as much duodenogastric reflux into the proximal stomach as did control subjects.

CONCLUSIONS

We were unable to establish either gastro-oesophageal or duodenogastric reflux as the predominant cause of inflammation in cardiac mucosa.

Effect of smoking and transdermal nicotine on colonic nicotinic acetylcholine receptors in ulcerative colitis

BACKGROUND

Ulcerative colitis (UC) is a disease largely of non-smokers, in which nicotine is of therapeutic value. The mode of action is unknown, but may involve nicotinic acetylcholine receptors (nAChRs) in the bowel wall.

AIM

To investigate the presence of nAChRs in rectal mucosa, and the effect of smoking and nicotine on their expression.

DESIGN

Prospective case-control study.

METHODS

In situ hybridization (ISH) and immunocytochemistry (ICC) were used to show alpha3 nAChRs in colonic mucosa. Rectal mucosa was examined from controls (n=55) and patients with inactive UC (n=62), both smokers and non-smokers, by ICC, using two antibodies to show the density and distribution of receptors in the mucosa. Non-smokers with UC (n=43) were given transdermal nicotine or placebo patches for 6 months, and rectal biopsies, taken before and after treatment, were examined by ICC to show nAChRs.

RESULTS

In normal colon, ISH and ICC showed alpha3 subunit in a wide variety of cells, including mucosal epithelium. In rectal biopsies, neither smoking nor nicotine influenced the expression of alpha3 immunoreactivity in epithelium, either in controls or UC. However, controls had a significantly greater density of immunodetectable mucosal epithelium alpha3 subunit, compared with UC patients.

DISCUSSION

The presence of nAChRs in colonic epithelium may be pertinent to the beneficial effect of nicotine in UC, but since neither smoking nor nicotine treatment is associated with any change in the expression of epithelial alpha3 nAChRs, the effect may be due to functional changes in the receptor. The decreased number of alpha3 nAChRs in UC compared with controls may be related to an increased cell turnover in UC.

Biallelic germline mutations in MYH predispose to multiple colorectal adenoma and somatic G:C-->T:A mutations

We have recently demonstrated that inherited defects of the base excision repair gene MYH predispose to multiple colorectal adenomas and carcinoma. Three affected siblings from a single British family were identified as Y165C/G382D compound heterozygotes and both missense mutations were shown to be functionally compromised. Here, we report the identification of seven further unrelated patients with >100 colorectal adenomas (six with colorectal cancer) and biallelic germline mutations in MYH: four were homozygous for truncating mutations, two were homozygous for Y165C and one was a Y165C/G382D compound heterozygote. As predicted from studies of the bacterial and yeast orthologues of MYH, colorectal tumours from affected individuals displayed a significant excess of somatic G:C-->T:A mutations in APC, as compared to sporadic ( chi(2)=242.96, P<10(-20)) or FAP-associated ( chi(2)=194.85, P<10(-20)) colorectal tumours. The sequence immediately downstream of the somatic G:C-->T:A mutations was predominantly AA, irrespective of the nature of the germline MYH mutations. These findings confirm the role of MYH in colorectal adenoma and carcinoma predisposition.

Candidate tumour suppressor LUCA-15 can regulate multiple apoptotic pathways

Functional screening of a human bone marrow cDNA library for suppressors of CD95-mediated apoptosis has led to the identification of a 326 bp fragment (Je2), which not only suppresses CD95-induced apoptosis in Jurkat T-cells, but maps to 3p21.3, to an intronic region of the candidate TSG LUCA-15 locus. Here we report that overexpression of Je2 in CEM-C7 T-cell line is able to suppress CD95-mediated apoptosis, and apoptosis induced by TNFalpha and the glucocorticoid analogue dexamethasone, but was not able to suppress death induced by the topoisomerase II inhibitor etoposide. Je2 inhibition of apoptosis is also associated with a change in the pattern of expression of LUCA-15-encoded proteins. Je2 might therefore function to inhibit apoptosis by destabilising message expression of LUCA-15 and promoting the degradation of its RNA and protein. This suppression of apoptosis by Je2 also appears to be associated with up-regulation of the apoptosis inhibitory protein Bcl-x(L). This study confirms that Je2 is a selective inhibitor of cell death and further implicates LUCA-15 gene locus in the control of apoptosis.

Production of antigen-specific human monoclonal antibodies: comparison of mice carrying IgH/kappa or IgH/kappa/lambda transloci

Here we compare human monoclonal antibody (MAb) production from mouse strains that carry disruptions of their endogenous mouse IgH/IgK loci and harbor human IgM + Igkappa(BABkappa) or human IgM + Igkappa + IgA transloci (BABkappa,lambda). We found that whereas both strains proved effective for the isolation of antigen-specific IgM antibodies, many of the IgM MAbs elicited from BABkappa comprise human mu chains that are associated with mouse lambda chains. In contrast, BABkappa,lambda mice gave rise to fully functional, polymeric human IgM antibodies comprising both human IgH and human IgL chains. Therefore, the inclusion of a human Iglambda translocus (in addition to the human IgH + Igkappa transloci) not only diminishes problems of endogenous mouse Iglambda expression but also provides a strain of mice that yields fully human MAbs to a wide range of antigens, as witnessed by the isolation of MAbs to human blood cells, tumor cell lines, and an immunoglobulin idiotype.

The implementation of guidelines and computerised forms improves the completeness of cancer pathology reporting. The CROPS project: a randomised controlled trial in pathology

The aim of this study was to determine whether reporting guidelines and computerised form-based reports improve the completeness of histopathological cancer data available for patient management and population cancer registration and to evaluate the acceptability of the intervention. The study was a randomised controlled trial with a split unit design and stratified cluster randomisation. All 16 hospital pathology laboratories in Wales were randomly allocated to report either breast or colorectal resection specimens by computerised form or conventional free text. 1044 reports were analysed in the study arm, 998 in the control arm. Use of pre-defined forms led to a 28.4% (95% confidence interval (CI): 15.7-41.2%) increase in complete reporting of a minimum dataset required for cancer registration and a 24.5% (95% CI: 11.0-38.0%) increase in complete reporting of minimum data required for patient management. Form-based reporting was acceptable to pathologists and preferred by clinicians. In conclusion, guidelines and computerised forms significantly improve the quality of histopathology reporting.

Commitment to apoptosis induced by tumour necrosis factor-alpha is dependent on caspase activity

Tumour Necrosis Factor alpha binding at the cell surface induces a complex series of signaling events culminating in the caspase cascade, which is central to apoptosis. However, recent work from several laboratories has questioned caspase involvement in commitment to cell death. We have therefore investigated the involvement of caspases in the crucial commitment stage of tumour necrosis factor-induced apoptosis in human T-leukaemic CEM-C7 cells and breast carcinoma MCF-7 cells, using both peptide-based and viral caspase inhibitors. Our observations converge on the conclusion that commitment to death in these systems is dependent on caspase activity, e.g. baculovirus p35 produces over 50-fold protection of colony-forming ability, the most stringent criterion of cell survival. These observations strongly support the view that the caspase family is of great biological and medical significance, since caspase dysfunction resulting in failure to commit to cell death after treatment with tumour necrosis factor or other stimuli may contribute to cancer development.

An insight into the genetic pathway of adenocarcinoma of the small intestine

BACKGROUND

Although the adenoma to carcinoma pathway in colorectal cancer is well described, the mechanisms of carcinogenesis in the small intestine remain unclear.

AIMS

The aim of this study was to investigate candidate genes in the genetic pathway of adenocarcinoma of the small intestine.

SUBJECTS AND METHODS

A total of 21 non-familial, non-ampullary adenocarcinomas of the small intestine were analysed. DNA was extracted from formalin fixed paraffin wax embedded tissue using standard techniques. The replication error (RER) status was determined by amplification of BAT26. The mutation cluster region (MCR) of the adenomatous polyposis coli (APC) gene was screened using polymerase chain reaction single strand conformational polymorphism and direct sequencing. Immunohistochemistry was performed on formalin fixed paraffin wax embedded tissue using monoclonal antibodies for hMLH1, hMSH2, beta-catenin, E-cadherin, and p53.

RESULTS

Fourteen male and seven female patients with a median age of 64 years (range 21-85) presented with adenocarcinoma of the duodenum (10), jejunum (7), and ileum (4). One cancer (5%) was found to be RER+, and all tumours stained positive for hMLH1 and hMSH2. No mutations were detected in the MCR of the APC gene. beta-Catenin showed increased nuclear expression with loss of membranous staining in 10 cancers (48%). Absent or decreased membrane expression of E-cadherin was found in eight cancers (38%). Strong staining of p53 was found in the nucleus of five cancers (24%).

CONCLUSION

We did not detect mutations in the MCR of the APC gene, and this suggests that adenocarcinoma of the small intestine may follow a different genetic pathway to colorectal cancer. Abnormal expression of E-cadherin and beta-catenin was common and reflects an early alternative to APC in this pathway in which mutations may be found in adenocarcinoma of the small intestine.

Morphologic changes in the peritoneal membrane of patients with renal disease

This study examined the morphologic features of the parietal peritoneal membranes of 130 patients undergoing peritoneal dialysis (PD) and compared them with the features of the peritoneal membranes of normal individuals, uremic predialysis patients, and patients undergoing hemodialysis. The median thickness of the submesothelial compact collagenous zone was 50 microm for normal subjects, 140 microm for uremic patients, 150 microm for patients undergoing hemodialysis, and 270 microm for patients undergoing PD (P < 0.001 for all versus normal subjects). Compact zone thickness increased significantly with the duration of PD therapy [0 to 24 mo, 180 microm (n = 58); 25 to 48 mo, 240 microm (n = 24); 49 to 72 mo, 300 microm (n = 13); 73 to 96 mo, 750 microm (n = 16); >97 mo, 700 microm (n = 19)]. Vascular changes included progressive subendothelial hyalinization, with luminal narrowing or obliteration. These changes were absent in samples from normal subjects but were present in 28% of samples from uremic patients and 56% of biopsies from patients undergoing PD. In the PD group, the prevalence of vasculopathy increased significantly with therapy duration (P = 0.0001). The density of blood vessels per unit length of peritoneum was significantly higher for patients with membrane failure and was correlated with the degree of fibrosis (P = 0.01). For the first time, a comprehensive cross-sectional analysis of the morphologic changes in the peritoneal membranes of patients undergoing PD is provided. The infrequency of fibrosis in the absence of vasculopathy suggests that vasculopathy may predispose patients to the development of fibrosis. This study provides a sufficiently large cohort of samples to allow structure-function relationships to be established, as well as providing a repository of tissue for further studies.

Inherited variants of MYH associated with somatic G:C-->T:A mutations in colorectal tumors

Inherited defects of base excision repair have not been associated with any human genetic disorder, although mutations of the genes mutM and mutY, which function in Escherichia coli base excision repair, lead to increased transversions of G:C to T:A. We have studied family N, which is affected with multiple colorectal adenomas and carcinoma but lacks an inherited mutation of the adenomatous polyposis coli gene (APC) that is associated with familial adenomatous polyposis. Here we show that 11 tumors from 3 affected siblings contain 18 somatic inactivating mutations of APC and that 15 of these mutations are G:C-->A transversions--a significantly greater proportion than is found in sporadic tumors or in tumors associated with familial adenomatous polyposis. Analysis of the human homolog of mutY, MYH, showed that the siblings were compound heterozygotes for the nonconservative missense variants Tyr165Cys and Gly382Asp. These mutations affect residues that are conserved in mutY of E. coli (Tyr82 and Gly253). Tyrosine 82 is located in the pseudo-helix-hairpin-helix (HhH) motif and is predicted to function in mismatch specificity. Assays of adenine glycosylase activity of the Tyr82Cys and Gly253Asp mutant proteins with 8-oxoG:A and G:A substrates show that their activity is reduced significantly. Our findings link the inherited variants in MYH to the pattern of somatic APC mutation in family N and implicate defective base excision repair in predisposition to tumors in humans.

MALARIA-INDUCED APOPTOSIS IN MOSQUITO OVARIES

Many insects are able to adjust their egg production according to physiological conditions such as nutrient supply and mating success. One way in which this is achieved is by resorption of some, or all, of the ovarian follicles at some stage during oogenesis. We have shown that the mosquito Anopheles stephensi responds in this manner when ookinetes of the malaria parasite Plasmodium yoelii nigeriensis first begin to invade the midgut. Little is known about the initiation and regulation of follicle resorption in any insect. Here, we demonstrate that there is a significant positive correlation between follicle resorption and the presence of follicular epithelial cells that are undergoing apoptosis. The parasite causes significantly more follicles to contain apoptotic cells from 16 h post-infection onwards. Injection of a caspase inhibitor immediately after feeding on an infective blood meal prevents parasite-induced resorption of follicles and thus demonstrates that apoptosis precedes resorption. Ultrastructural studies show that patches of follicular epithelial cells contain condensed nuclear chromatin, a characteristic of apoptosis, and that no patency develops in these cells. Our work suggests that apoptosis plays a role in malaria-initiated inhibition of mosquito oogenesis and that caspase is central to this process. Follicle resorption is one of the main factors contributing to malaria-induced fecundity reduction in mosquitoes.