Gary A. Cobbs

The use of landmarks to define territorial boundaries.

Numerous anecdotal reports suggest that members of many territorial species use naturally occurring landmarks to define the boundaries of their territories. In the work reported here, we first tested whether artificial landmarks would be adopted as boundaries by territorial male cicada killer wasps, Sphecius speciosus. To perform this test, we set out wooden dowels on a flat, grassy lawn on which male wasps were defending mating territories. The dowels were situated so that they did not coincide with any existing territorial boundary. After we provided the dowels, the wasps established new territorial boundaries coinciding with the dowels. We hypothesized that using visual landmarks as territorial borders might lower defensive costs, and indeed, focal samples on territorial wasps revealed that borders that were defined by dowels cost less to defend than did borders that were not defined by any landmark. This result suggests that the use of natural landmarks as territorial boundaries may have evolved as a result of the reduced defensive costs that accrue to these boundaries. Furthermore, defensive costs may not depend directly on territory size: territory owners may be able to reduce defensive costs by selecting sites with high tactical defensibility. Copyright 1999 The Association for the Study of Animal Behaviour.

Characterization of N-acetyltransferase 1 and 2 polymorphisms and haplotype analysis for inflammatory bowel disease and sporadic colorectal carcinoma

BackgroundN-acetyltransferase 1 (NAT1) and 2 (NAT2) are polymorphic isoenzymes responsible for the metabolism of numerous drugs and carcinogens. Acetylation catalyzed by NAT1 and NAT2 are important in metabolic activation of arylamines to electrophilic intermediates that initiate carcinogenesis. Inflammatory bowel diseases (IBD) consist of Crohns disease (CD) and ulcerative colitis (UC), both are associated with increased colorectal cancer (CRC) risk. We hypothesized that NAT1 and/or NAT2 polymorphisms contribute to the increased cancer evident in IBD.MethodsA case control study was performed with 729 Caucasian participants, 123 CRC, 201 CD, 167 UC, 15 IBD dysplasia/cancer and 223 controls. NAT1 and NAT2 genotyping were performed using Taqman based techniques. Eight single nucleotide polymorphisms (SNPs) were characterized for NAT1 and 7 SNPs for NAT2. Haplotype frequencies were estimated using an Expectation-Maximization (EM) method. Disease groups were compared to a control group for the frequencies at each individual SNP separately. The same groups were compared for the frequencies of NAT1 and NAT2 haplotypes and deduced NAT2 phenotypes.ResultsNo statistically significant differences were found for any comparison. Strong linkage disequilibrium was present among both the NAT1 SNPs and the NAT2 SNPs.ConclusionThis study did not demonstrate an association between NAT1 and NAT2 polymorphisms and IBD or sporadic CRC, although power calculations indicate this study had sufficient sample size to detect differences in frequency as small as 0.05 to 0.15 depending on SNP or haplotype.

CARD15 Genotype-Phenotype Relationships in a Small Inflammatory Bowel Disease Population with Severe Disease Affection Status

Inflammatory bowel disease (IBD; MIM# 266600) is subdivided on the basis of clinical findings as either Crohn’s disease (CD), ulcerative colitis (UC), or indeterminate colitis (IC). Three previously described mutations within the IBD susceptibility gene CARD15 (R702W, G908R, 1007fs) increase susceptibility to CD with a terminal ileal and/or ileocolonic location and fibrostenosing behavior. We undertook an association study using 477 unrelated IBD patients (248 CD, 172 UC, 57 IC) and 104 population controls to determine whether these previously described associations could be replicated in a small, accurately phenotyped cohort. Case-control and family-based approaches were employed to analyze CARD15 mutant allele and haplotype data. Analyses were initially performed in unstratified IBD cohorts. The R702W mutant allele was associated with CD on case-control analysis (q=0.036, P=.004), and 1007fs with CD on pedigree disequilibrium testing (P=.020). All 3 CARD15 mutations increased susceptibility to a variety of CD subphenotypic manifestations, including early-onset CD in individuals with a family history of IBD, and CD complicated by extraintestinal disease. We also present evidence to suggest that R702W may predispose to a more generalized form of CD. Additionally, we confirm that CARD15 mutations are associated with terminal ileal/ileocolonic, and to a lesser extent, fibrostenosing CD.

Evaluation of SLC11A1 as an inflammatory bowel disease candidate gene

BackgroundSignificant evidence suggests that a promoter polymorphism withinthe gene SLC11A1 is involved in susceptibility to both autoimmune and infectious disorders. The aim of this study was to evaluate whether SLC11A1 has a role in the susceptibility to inflammatory bowel disease (IBD) by characterizing a promoter polymorphism within the gene and two short tandem repeat (STR) markers in genetic proximity to SLC11A1.MethodsThe studied population consisted of 484 Caucasians with IBD, 144 population controls, and 348 non-IBD-affected first-degree relatives of IBD patients. IBD subjects were re-categorized at the sub-disease phenotypic level to characterize possible SLC11A1 genotype-phenotype correlations. Polymorphic markers were amplified from germline DNA and typed using gel electrophoresis. Genotype-phenotype correlations were defined using case-control, haplotype, and family-based association studies.ResultsThis study did not provide compelling evidence for SLC11A1 disease association; most significantly, there was no apparent evidence of SLC11A1 promoter allele association in the studied Crohns disease population.ConclusionOur results therefore refute previous studies that have shown SLC11A1 promoter polymorphisms are involved in susceptibility to this form of IBD.

Stepwise kinetic equilibrium models of quantitative polymerase chain reaction.

BackgroundNumerous models for use in interpreting quantitative PCR (qPCR) data are present in recent literature. The most commonly used models assume the amplification in qPCR is exponential and fit an exponential model with a constant rate of increase to a select part of the curve. Kinetic theory may be used to model the annealing phase and does not assume constant efficiency of amplification. Mechanistic models describing the annealing phase with kinetic theory offer the most potential for accurate interpretation of qPCR data. Even so, they have not been thoroughly investigated and are rarely used for interpretation of qPCR data. New results for kinetic modeling of qPCR are presented.ResultsTwo models are presented in which the efficiency of amplification is based on equilibrium solutions for the annealing phase of the qPCR process. Model 1 assumes annealing of complementary targets strands and annealing of target and primers are both reversible reactions and reach a dynamic equilibrium. Model 2 assumes all annealing reactions are nonreversible and equilibrium is static. Both models include the effect of primer concentration during the annealing phase. Analytic formulae are given for the equilibrium values of all single and double stranded molecules at the end of the annealing step. The equilibrium values are then used in a stepwise method to describe the whole qPCR process. Rate constants of kinetic models are the same for solutions that are identical except for possibly having different initial target concentrations. Analysis of qPCR curves from such solutions are thus analyzed by simultaneous non-linear curve fitting with the same rate constant values applying to all curves and each curve having a unique value for initial target concentration. The models were fit to two data sets for which the true initial target concentrations are known. Both models give better fit to observed qPCR data than other kinetic models present in the literature. They also give better estimates of initial target concentration. Model 1 was found to be slightly more robust than model 2 giving better estimates of initial target concentration when estimation of parameters was done for qPCR curves with very different initial target concentration. Both models may be used to estimate the initial absolute concentration of target sequence when a standard curve is not available.ConclusionsIt is argued that the kinetic approach to modeling and interpreting quantitative PCR data has the potential to give more precise estimates of the true initial target concentrations than other methods currently used for analysis of qPCR data. The two models presented here give a unified model of the qPCR process in that they explain the shape of the qPCR curve for a wide variety of initial target concentrations.

An alternative cyclin-D1 splice site is not linked to inflammatory bowel disease-associated neoplasia.

Background Inflammatory bowel diseases (IBD) encompass inflammatory disorders affecting the gastrointestinal tract, primarily ulcerative colitis (UC) and Crohns disease (CD). The risk of developing colorectal cancer (CRC) is increased in patients with IBD. The CCND1 protein is the regulatory subunit of an enzyme that inactivates the retinoblastoma protein, a tumor suppressor protein, and promotes progression through the G1-S phase of the cell cycle. The CCND1 870G-A gene polymorphism influences susceptibility to colorectal cancer. The mutant allele of CCND1 in IBD-associated neoplasia leads to a greater frequency of alternate splicing during transcription, resulting in a more stable CCND1 protein. This creates a higher concentration of CCND1, facilitating easier passage through the G1/S checkpoint, abnormal cell cycle progression, and possibly carcinogenesis. Methods We conducted a case-control study involving 396 individuals with IBD. IBD subgroups included CD, UC, and indeterminate colitis (IC). We studied patients with sporadic colorectal cancer (n=75) and patients without gastrointestinal disease as a control group (n=93). We extracted DNA from blood and performed polymerase chain reaction followed by high-performance liquid chromatography to screen for mutations. We confirmed the polymorphism at nucleotide A870G in exon 4. For statistical analysis, we used exact analyses of two-way contingency tables. Power calculations were done and correction for multiple testing was performed by computing the false discovery rate (FDR). Results and discussion Our study had a power of 75% at a 0.05 significance level. A870G SNP allele frequency in the IBD group was 44.8%, compared to 51.6% in the control population. Only the IC group showed a significant association with CCND1 splice site after correction for multiple testing (FDR=0.042). There were no differences between the other IBD groups and controls. Conclusion We found an association between CCND1 A870G SNP and IC group only (p=0.014, FDR=0.042). However, our data do not show an association between CCND1 A870G SNP and CD-associated or UC-associated neoplasia.

SMAD2 and the relationship of colorectal cancer to inflammatory bowel disease

Inflammatory bowel diseases (IBDs) affecting the colon [Crohns disease (CD) and ulcerative colitis (UC)] are associated with an increased risk of colorectal cancer (CRC). Our previous work using oligonucleotide array data indicated that SMAD2 was significantly underexpressed in UC dysplastic tissue compared to benign UC. The aim of this current study was to determine whether single nucleotide polymorphisms (SNPs) within the SMAD2 gene are associated with IBD dysplasia/cancer. We performed an SNP haplotype-based case-control association study. Leukocyte DNA was obtained from 489 unrelated Caucasians (158 UC, 175 CD, 71 CRC, 85 controls). Eleven SNPs were genotyped. All 11 SNPs were in Hardy-Weinberg equilibrium in the control population. Strong linkage disequilibrium was observed among nearly all SMAD2 SNPs. There were no significant associations between SMAD2 allele or haplotype frequencies. Power calculations indicated good power for single-marker analysis (>0.8) and reasonably good power against effects of 0.1-0.15 for haplotype analysis. SMAD2 SNPs were not associated with the development of IBD dysplasia/cancer. This incongruity between our previous microarray data and the findings from this genotype study may be attributed to mechanisms such as alternative splicing of pre-mRNA SMAD2 and/or cross talk with other cellular pathways.

T-cell receptor γ: A microsatellite marker for colorectal cancer

Background: T-cell receptor γ (TCR-γ) is involved in maintaining host cell integrity and homeostasis of the human immune system. We hypothesize that polymorphism of the TCR-γ complex may be involved in the pathogenesis of colorectal cancer.Methods: The microsatellite markers D7S1818 and D7S2206 located within the TCR-γ antigen locus on chromosome 7p were amplified by polymerase chain reaction, and genotypes were determined for 22 patients with early onset of colorectal cancer (<60 years old) and for 38 population-based control subjects.Results: Genotype BC of D7S1818 (P=.049) and haplotype AC of D7S1818/D7S2206 (P ≤ .003) were associated with colorectal cancer as compared with the control population (extended Fisher’s exact test).Conclusions: This study identifies a novel genetic and clinical association between TCR-γ and early-onset colorectal cancer. Many young patients do not fulfill the criteria for hereditary colorectal cancer syndromes and are therefore not identified by established screening programs. Markers such as D7S1818 and D7S2206 may become useful in the identification of patients at risk of developing colorectal cancer and permit earlier therapeutic intervention.