Talking the talk, but not walking the walk: RT-qPCR as a paradigm for the lack of reproducibility in molecular research

Tissue Specific Reference Genes for MicroRNA Expression Analysis in a Mouse Model of Peripheral Nerve Injury

MicroRNAs (miRNAs) have emerged as master switch regulators in many biological processes in health and disease, including neuropathy. miRNAs are commonly quantified by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR), usually estimated as relative expression through reference genes normalization. Different non-coding RNAs (ncRNAs) are used for miRNA normalization; however, there is no study identifying the optimal reference genes in animal models for peripheral nerve injury. We evaluated the stability of eleven ncRNAs, commonly used for miRNA normalization, in dorsal root ganglia (DRG), dorsal horn of the spinal cord (dhSC), and medial prefrontal cortex (mPFC) in the mouse spared nerve injury (SNI) model. After RT-qPCR, the stability of each ncRNA was determined by using four different methods: BestKeeper, the comparative delta-Cq method, geNorm, and NormFinder. The candidates were rated according to their performance in each method and an overall ranking list was compiled. The most stable ncRNAs were: sno420, sno429, and sno202 in DRG; sno429, sno202, and U6 in dhSC; sno202, sno420, and sno142 in mPFC. We provide the first reference genes' evaluation for miRNA normalization in different neuronal tissues in an animal model of peripheral nerve injury. Our results underline the need for careful selection of reference genes for miRNA normalization in different tissues and experimental conditions. We further anticipate that our findings can be used in a broad range of nerve injury related studies, to ensure validity and promote reproducibility in miRNA quantification.

The effect of reverse transcription enzymes and conditions on high throughput amplicon sequencing of the 16S rRNA

It is assumed that the sequencing of ribosomes better reflects the active microbial community than the sequencing of the ribosomal RNA encoding genes. Yet, many studies exploring microbial communities in various environments, ranging from the human gut to deep oceans, questioned the validity of this paradigm due to the discrepancies between the DNA and RNA based communities. Here, we focus on an often neglected key step in the analysis, the reverse transcription (RT) reaction. Previous studies showed that RT may introduce biases when expressed genes and ribosmal rRNA are quantified, yet its effect on microbial diversity and community composition was never tested. High throughput sequencing of ribosomal RNA is a valuable tool to understand microbial communities as it better describes the active population than DNA analysis. However, the necessary step of RT may introduce biases that have so far been poorly described. In this manuscript, we compare three RT enzymes, commonly used in soil microbiology, in two temperature modes to determine a potential source of bias due to non-standardized RT conditions. In our comparisons, we have observed up to six fold differences in bacterial class abundance. A temperature induced bias can be partially explained by G-C content of the affected bacterial groups, thus pointing toward a need for higher reaction temperatures. However, another source of bias was due to enzyme processivity differences. This bias is potentially hard to overcome and thus mitigating it might require the use of one enzyme for the sake of cross-study comparison.

The Selection and Validation of Reference Genes for mRNA and microRNA Expression Studies in Human Liver Slices Using RT-qPCR

The selection of a suitable combination of reference genes (RGs) for data normalization is a crucial step for obtaining reliable and reproducible results from transcriptional response analysis using a reverse transcription-quantitative polymerase chain reaction. This is especially so if a three-dimensional multicellular model prepared from liver tissues originating from biologically diverse human individuals is used. The mRNA and miRNA RGs stability were studied in thirty-five human liver tissue samples and twelve precision-cut human liver slices (PCLS) treated for 24 h with dimethyl sulfoxide (controls) and PCLS treated with β-naphthoflavone (10 µM) or rifampicin (10 µM) as cytochrome P450 (CYP) inducers. Validation of RGs was performed by an expression analysis of CYP3A4 and CYP1A2 on rifampicin and β-naphthoflavone induction, respectively. Regarding mRNA, the best combination of RGs for the controls was YWHAZ and B2M, while YWHAZ and ACTB were selected for the liver samples and treated PCLS. Stability of all candidate miRNA RGs was comparable or better than that of generally used short non-coding RNA U6. The best combination for the control PCLS was miR-16-5p and miR-152-3p, in contrast to the miR-16-5b and miR-23b-3p selected for the treated PCLS. Our results showed that the candidate RGs were rather stable, especially for miRNA in human PCLS.

Validation of a real-time PCR assay for detection of swinepox virus

Swine are the only known hosts of swinepox virus (SWPV), the sole member of the genus Suipoxvirus, family Poxviridae. Rapid diagnosis is recommended for appropriate interventions because of the high morbidity associated with this virus. This study describes a real-time quantitative PCR (qPCR) assay for rapid detection and quantification of SWPV. The detection limit, repeatability, reproducibility, and specificity of this assay were determined. The efficiency was 96%, and the R² value was 0.996. The detection limit was 1 fg or 10^-0.5 TCID₅₀/50 μL. Tests showed that the greatest source of error in the SWPV qPCR assay was variation between analysts rather than different qPCR kits or equipment. All nucleic acids from other viruses or samples collected from swine were negative in the specificity test. qPCR for SWPV is a new method with tested variables that allows main sources of error in laboratory diagnosis and viral quantification to be identified.

Inter-genus gene expression analysis in livestock fibroblasts using reference gene validation based upon a multi-species primer set

Quantitative reverse transcription PCR (RT-qPCR) remains as an accurate approach for gene expression analysis but requires labor-intensive validation of reference genes using species-specific primers. To ease such demand, the aim was to design and test a multi-species primer set to validate reference genes for inter-genus RT-qPCR gene expression analysis. Primers were designed for ten housekeeping genes using transcript sequences of various livestock species. All ten gene transcripts were detected by RT-PCR in Bos taurus (cattle), Bubalus bubalis (buffaloes), Capra hircus (goats), and Ovis aries (sheep) cDNA. Primer efficiency was attained for eight reference genes using B. taurus—O. aries fibroblast cDNA (95.54–98.39%). The RT-qPCR data normalization was carried out for B. taurus vs. O. aries relative gene expression using Bestkeeper, GeNorm, Norm-finder, Delta CT method, and RefFinder algorithms. Validation of inter-genus RT-qPCR showed up-regulation of TLR4 and ZFX gene transcripts in B. taurus fibroblasts, irrespectively of normalization conditions (two, three, or four reference genes). In silico search in mammalian transcriptomes showed that the multi-species primer set is expected to amplify transcripts of at least two distinct loci in 114 species, and 79 species would be covered by six or more primers. Hence, a multi-species primer set allows for inter-genus gene expression analysis between O. aries and B. taurus fibroblasts and further reveals species-specific gene transcript abundance of key transcription factors.

Decreased expression of apoptosis-inducing factor in renal cell carcinoma is associated with poor prognosis and reduced postoperative survival

Apoptosis-inducing factor (AIF) serves a crucial role in cell death and is involved in several types of cancer, including kidney cancer. The present study aimed to explore the association between AIF expression and patient survival based on tumor grades. AIF expression in 96 patients with renal cell carcinoma (RCC) was investigated using immunohistochemistry. Negative AIF expression was determined in 80 patients (83.3%). mRNA expression of AIF was analyzed in RCC and adjacent tissue samples from 15 patients. AIF mRNA expression in RCC tissues were significantly lower compared with that in adjacent tissues. Analysis of histopathological grades revealed that AIF expression was negatively associated with RCC grade, with AIF expression in Grade II tumors being lower than Grade I types, but higher than Grade III. Finally, 68 patients were followed up for 6-118 months, and it was revealed that the overall postoperative survival rate of patients with negative AIF expression was significantly lower compared with those those with positive AIF expression. These results suggest that decreased AIF expression could be associated with worsening RCC grade. Therefore, reduced AIF expression may potentially help diagnose RCC and distinguish tumor grades.

Robust reference gene design and validation for expression studies in the large milkweed bug, Oncopeltus fasciatus, upon cardiac glycoside stress

Despite its history as a developmental and evolutionary model organism, gene expression analysis in the large milkweed bug, Oncopeltus fasciatus, has rarely been explored using quantitative real-time PCR. The strength of this method depends greatly on the endogenous controls used for normalization, which are lacking for the milkweed bug system. Here, to fill in this gap in our knowledge, we validated the stability of a set of ten candidate reference genes identified from the O. fasciatus transcriptome, and did so upon exposure to a dietary toxin, a cardiac glycoside, and across four different exposure periods. To increase robustness against gDNA contaminants, genome resources were used to design intron-bridging primers. A comprehensive stability validation by the Bestkeeper, Normfinder, geNorm and comparative ΔCt methods identified ef1a and tubulin as the most stable genes across treatments and time points, whereas 18S rRNA was the most unstable. However, accounting for the temporal scale indicated that time point confined normalizers might enable higher quantification accuracy for treatment comparison. Overall this study demonstrates: (i) a robust RT-qPCR primer design approach is possible for non-model organisms where genome annotation is often incomplete, and (ii) the importance of detailed reference gene stability exploration in multifactorial experimental designs.

On resolving ambiguities in microbial community analysis of partial nitritation anammox reactors

PCR-based methods have caused a surge for integration of eco-physiological approaches into research on partial nitritation anammox (PNA). However, a lack of rigorous standards for molecular analyses resulted in widespread data misinterpretation and consequently lack of consensus. Data consistency and accuracy strongly depend on the primer selection and data interpretation. An in-silico evaluation of 16S rRNA gene eubacterial primers used in PNA studies from the last ten years unraveled the difficulty of comparing ecological data from different studies due to a variation in the coverage of these primers. Our 16S amplicon sequencing approach, which includes parallel sequencing of six 16S rRNA hypervariable regions, showed that there is no perfect hypervariable region for PNA microbial communities. Using qPCR analysis, we emphasize the significance of primer choice for quantification and caution with data interpretation. We also provide a framework for PCR based analyses that will improve and assist to objectively interpret and compare such results.

Template-ready PCR method for detection of human telomerase reverse transcriptase mRNA in sputum

Human telomerase reverse transcriptase (hTERT) mRNA in tissue is a biomarker of lung cancer, but hTERT mRNA in sputum had not been successfully detected with conventional reverse transcription PCR methods. Here, we developed a novel PCR protocol: Template-Ready PCR (TRPCR), to detect sputum hTERT mRNA, in which probes serve as templates of amplification. While free probes and dsDNA were removed in template preparation through aspiration and restriction digestion, probes that formed into heterocomplex with target RNA remained intact for PCR amplification. By fishing out the heterocomplex and amplifying the probes, TRPCR achieved sensitivity higher than reverse transcription-quantitative PCR (RT-qPCR). ROC curve of sputum hTERT mRNA by TRPCR assay showed the discrimination in high sensitivity and specificity between patients with lung cancer and lung cancer-free donors at the PCR Ct cutoff of 33. We further validated this approach through TRPCR assay of sputum from 858 lung cancer patients and 480 non-malignant pulmonary disease patients. 722 (84.2%) cases from 858 with lung cancer patients were detected as positive, whereas 461 (96.0%) cases from 480 non-malignant pulmonary disease patients were detected as negative, suggesting that TRPCR assay of sputum hTERT mRNA can serve as a non-invasive molecular diagnosis of lung cancer.

Transcriptomic studies and assessment of Yersinia pestis reference genes in various conditions

Reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) is a very sensitive widespread technique considered as the gold standard to explore transcriptional variations. While a particular methodology has to be followed to provide accurate results many published studies are likely to misinterpret results due to lack of minimal quality requirements. Yersinia pestis is a highly pathogenic bacterium responsible for plague. It has been used to propose a ready-to-use and complete approach to mitigate the risk of technical biases in transcriptomic studies. The selection of suitable reference genes (RGs) among 29 candidates was performed using four different methods (GeNorm, NormFinder, BestKeeper and the Delta-Ct method). An overall comprehensive ranking revealed that 12 following candidate RGs are suitable for accurate normalization: gmk, proC, fabD, rpoD, nadB, rho, thrA, ribD, mutL, rpoB, adk and tmk. Some frequently used genes like 16S RNA had even been found as unsuitable to study Y. pestis. This methodology allowed us to demonstrate, under different temperatures and states of growth, significant transcriptional changes of six efflux pumps genes involved in physiological aspects as antimicrobial resistance or virulence. Previous transcriptomic studies done under comparable conditions had not been able to highlight these transcriptional modifications. These results highlight the importance of validating RGs prior to the normalization of transcriptional expression levels of targeted genes. This accurate methodology can be extended to any gene of interest in Y. pestis. More generally, the same workflow can be applied to identify and validate appropriate RGs in other bacteria to study transcriptional variations.

The Ultimate qPCR Experiment: Producing Publication Quality, Reproducible Data the First Time

Quantitative PCR (qPCR) is one of the most common techniques for quantification of nucleic acid molecules in biological and environmental samples. Although the methodology is perceived to be relatively simple, there are a number of steps and reagents that require optimization and validation to ensure reproducible data that accurately reflect the biological question(s) being posed. This review article describes and illustrates the critical pitfalls and sources of error in qPCR experiments, along with a rigorous, stepwise process to minimize variability, time, and cost in generating reproducible, publication quality data every time. Finally, an approach to make an informed choice between qPCR and digital PCR technologies is described.

Evaluation of Reference Genes for Normalization of RT-qPCR Gene Expression Data for Trichoplusia ni Cells During Antheraea pernyi (Lepidoptera: Saturniidae) Multicapsid Nucleopolyhedrovirus (AnpeNPV) Infection

Baculovirus infection impacts global gene expression in the host cell, including the expression of housekeeping genes. Evaluation of candidate reference genes during a viral infection will inform the selection of appropriate reference gene(s) for the normalization of expression data generated by Reverse Transcription Quantitative Real-timePolymerase Chain Reaction (RT-qPCR). Antheraea pernyi multicapsid nucleopolyhedrovirus (AnpeNPV) is able to infect the High Five cells (Tn-Hi5). In the present study, 10 candidate reference genes were evaluated in AnpeNPV-infected Tn-Hi5 cells. Gene expression data were analyzed using geNorm, NormFinder, BestKeeper, and RefFinder. The candidate genes were further validated as reliable reference genes for RT-qPCR by analyzing the expression of three target genes. The results of data analysis using four statistical methods showed that RPS18 was the least stable among the candidate reference genes tested. 18S rRNA and 28S rRNA were not suitable as reference genes for RT-qPCR analysis in AnpeNPV-infected Tn-Hi5 cells. Comprehensive ranking of the 10 candidate reference genes by RefFinder analysis indicated that Ann B, c45128_g1, and ACT were the top three genes. Normalization of the expression of three target genes using the candidate reference genes indicated the same expression pattern when Ann B and c45128_g1 were used as reference genes, with slight differences in the relative expression at each infection time point. Overall, Ann B and c45128_g1 were recommended to be more suitable than the most commonly used reference genes, such as ACT, GAPDH, and TUB, for RT-qPCR data normalization in AnpeNPV-infected Tn-Hi5 cells up to 48 hpi.

High Fidelity of Mouse Models Mimicking Human Genetic Skeletal Disorders

The 2019 International Skeletal Dysplasia Society nosology update lists 441 genes for which mutations result in rare human skeletal disorders. These genes code for enzymes (33%), scaffolding proteins (18%), signal transduction proteins (16%), transcription factors (14%), cilia proteins (8%), extracellular matrix proteins (5%), and membrane transporters (4%). Skeletal disorders include aggrecanopathies, channelopathies, ciliopathies, cohesinopathies, laminopathies, linkeropathies, lysosomal storage diseases, protein-folding and RNA splicing defects, and ribosomopathies. With the goal of evaluating the ability of mouse models to mimic these human genetic skeletal disorders, a PubMed literature search identified 260 genes for which mutant mice were examined for skeletal phenotypes. These mouse models included spontaneous and ENU-induced mutants, global and conditional gene knockouts, and transgenic mice with gene over-expression or specific base-pair substitutions. The human X-linked gene ARSE and small nuclear RNA U4ATAC, a component of the minor spliceosome, do not have mouse homologs. Mouse skeletal phenotypes mimicking human skeletal disorders were observed in 249 of the 260 genes (96%) for which comparisons are possible. A supplemental table in spreadsheet format provides PubMed weblinks to representative publications of mutant mouse skeletal phenotypes. Mutations in 11 mouse genes (Ccn6, Cyp2r1, Flna, Galns, Gna13, Lemd3, Manba, Mnx1, Nsd1, Plod1, Smarcal1) do not result in similar skeletal phenotypes observed with mutations of the homologous human genes. These discrepancies can result from failure of mouse models to mimic the exact human gene mutations. There are no obvious commonalities among these 11 genes. Body BMD and/or radiologic dysmorphology phenotypes were successfully identified for 28 genes by the International Mouse Phenotyping Consortium (IMPC). Forward genetics using ENU mouse mutagenesis successfully identified 37 nosology gene phenotypes. Since many human genetic disorders involve hypomorphic, gain-of-function, dominant-negative and intronic mutations, future studies will undoubtedly utilize CRISPR/Cas9 technology to examine transgenic mice having genes modified to exactly mimic variant human sequences. Mutant mice will increasingly be employed for drug development studies designed to treat human genetic skeletal disorders.

SIGNIFICANCE

Great progress is being made identifying mutant genes responsible for human rare genetic skeletal disorders and mouse models for genes affecting bone mass, architecture, mineralization and strength. This review organizes data for 441 human genetic bone disorders with regard to heredity, gene function, molecular pathways, and fidelity of relevant mouse models to mimic the human skeletal disorders. PubMed weblinks to citations of 249 successful mouse models are provided.

Validation of reference genes for quantitative real-time PCR in tiger beetles across sexes, body parts, sexual maturity and immune challenge

Reference genes are frequently used as normalizers for expression studies despite not being previously verified to present suitable stabilities. Considering the interest that tiger beetles have generated in the past years, resulting in a variety of studies, it is crucial to dispose of a validated reference gene panel for expression studies. Nine candidate genes were tested in Cicindela campestris and Calomera littoralis across several conditions and their transcription levels were assessed with geNorm, NormFinder, BestKeeper and ΔC_Tmethod algorithms. Results showed high stabilities across sexes, immune challenge and gonad developmental stages for all genes tested, while body parts comparison presented less constant expression values. Only two genes are sufficient to perform a proper normalization for most of the conditions tested, except for the body parts comparison in C. littoralis, which requires the use of at least three reference genes. On the whole, no universal gene is found to be suitable for all situations, but according to the acceptable range of values, NADH, B-t, Vatpase and ArgKin seem to present the most constant expression stability, indicating their suitability as reference genes in most of the conditions. This is the first report evaluating the stability of housekeeping genes in adephagan beetles.

Critical Evaluation of Gene Expression Changes in Human Tissues in Response to Supplementation with Dietary Bioactive Compounds: Moving Towards Better-Quality Studies

Pre-clinical cell and animal nutrigenomic studies have long suggested the modulation of the transcription of multiple gene targets in cells and tissues as a potential molecular mechanism of action underlying the beneficial effects attributed to plant-derived bioactive compounds. To try to demonstrate these molecular effects in humans, a considerable number of clinical trials have now explored the changes in the expression levels of selected genes in various human cell and tissue samples following intervention with different dietary sources of bioactive compounds. In this review, we have compiled a total of 75 human studies exploring gene expression changes using quantitative reverse transcription PCR (RT-qPCR). We have critically appraised the study design and methodology used as well as the gene expression results reported. We herein pinpoint some of the main drawbacks and gaps in the experimental strategies applied, as well as the high interindividual variability of the results and the limited evidence supporting some of the investigated genes as potential responsive targets. We reinforce the need to apply normalized procedures and follow well-established methodological guidelines in future studies in order to achieve improved and reliable results that would allow for more relevant and biologically meaningful results.

The price of progress: Funding and financing Alzheimer's disease drug development

INTRODUCTION

Advancing research and treatment for Alzheimer's disease (AD) and the search for effective treatments depend on a complex financial ecosystem involving federal, state, industry, advocacy, venture capital, and philanthropy funding approaches.

METHODS

We conducted an expert review of the literature pertaining to funding and financing of translational research and drug development for AD.

RESULTS

The federal government is the largest public funder of research in AD. The National Institute on Aging, National Institute of Mental Health, National Institute of General Medical Sciences, and National Center for Advancing Translational Science all fund aspects of research in AD drug development. Non-National Institutes of Health federal funding comes from the National Science Foundation, Veterans Administration, Food and Drug Administration, and the Center for Medicare and Medicaid Services. Academic Medical Centers host much of the federally funded basic science research and are increasingly involved in drug development. Funding of the "Valley of Death" involves philanthropy and federal funding through small business programs and private equity from seed capital, angel investors, and venture capital companies. Advocacy groups fund both basic science and clinical trials. The Alzheimer Association is the advocacy organization with the largest research support portfolio relevant to AD drug development. Pharmaceutical companies are the largest supporters of biomedical research worldwide; companies are most interested in late stage de-risked drugs. Drugs progressing into phase II and III are candidates for pharmaceutical industry support through licensing, mergers and acquisitions, and co-development collaborations.

DISCUSSION

Together, the funding and financing entities involved in supporting AD drug development comprise a complex, interactive, dynamic financial ecosystem. Funding source interaction is largely unstructured and available funding is insufficient to meet all demands for new therapies. Novel approaches to funding such as mega-funds have been proposed and more integration of component parts would assist in accelerating drug development.

Improving the standardization of mRNA measurement by RT-qPCR

Human health and safety depend on reliable measurements in medical diagnosis and on tests that support the selection and evaluation of therapeutic intervention and newly discovered molecular biomarkers must pass a rigorous evaluation process if they are to be of benefit to patients. Measurement standardization helps to maximize data quality and confidence and ultimately improves the reproducibility of published research. Failure to consider how a given experiment may be standardized can be costly, both financially as well as in time and failure to perform and report pre-clinical research in an appropriately rigorous manner will hinder the development of diagnostic methods. Hence standardization is a crucial step in maintaining the integrity of scientific studies and is a key feature of robust investigation.

Transcriptional-Readthrough RNAs Reflect the Phenomenon of "A Gene Contains Gene(s)" or "Gene(s) within a Gene" in the Human Genome, and Thus Are Not Chimeric RNAs

Tens of thousands of chimeric RNAs, i.e., RNAs with sequences of two genes, have been identified in human cells. Most of them are formed by two neighboring genes on the same chromosome and are considered to be derived via transcriptional readthrough, but a true readthrough event still awaits more evidence and trans-splicing that joins two transcripts together remains as a possible mechanism. We regard those genomic loci that are transcriptionally read through as unannotated genes, because their transcriptional and posttranscriptional regulations are the same as those of already-annotated genes, including fusion genes formed due to genetic alterations. Therefore, readthrough RNAs and fusion-gene-derived RNAs are not chimeras. Only those two-gene RNAs formed at the RNA level, likely via trans-splicing, without corresponding genes as genomic parents, should be regarded as authentic chimeric RNAs. However, since in human cells, procedural and mechanistic details of trans-splicing have never been disclosed, we doubt the existence of trans-splicing. Therefore, there are probably no authentic chimeras in humans, after readthrough and fusion-gene derived RNAs are all put back into the group of ordinary RNAs. Therefore, it should be further determined whether in human cells all two-neighboring-gene RNAs are derived from transcriptional readthrough and whether trans-splicing truly exists.

While it is not deliberate, much of today's biomedical research contains logical and technical flaws, showing a need for corrective action

Biomedical research has advanced swiftly in recent decades, largely due to progress in biotechnology. However, this rapid spread of new, and not always-fully understood, technology has also created a lot of false or irreproducible data and artifacts, which sometimes have led to erroneous conclusions. When describing various scientific issues, scientists have developed a habit of saying "on one hand… but on the other hand…", because discrepant data and conclusions have become omnipresent. One reason for this problematic situation is that we are not always thoughtful enough in study design, and sometimes lack enough philosophical contemplation. Another major reason is that we are too rushed in introducing new technology into our research without assimilating technical details. In this essay, we provide examples in different research realms to justify our points. To help readers test their own weaknesses, we raise questions on technical details of RNA reverse transcription, polymerase chain reactions, western blotting and immunohistochemical staining, as these methods are basic and are the base for other modern biotechnologies. Hopefully, after contemplation and reflection on these questions, readers will agree that we indeed know too little about these basic techniques, especially about the artifacts they may create, and thus many conclusions drawn from the studies using those ever-more-sophisticated techniques may be even more problematic.

qPCR primer design revisited

Primers are arguably the single most critical components of any PCR assay, as their properties control the exquisite specificity and sensitivity that make this method uniquely powerful. Consequently, poor design combined with failure to optimise reaction conditions is likely to result in reduced technical precision and false positive or negative detection of amplification targets. Despite the framework provided by the MIQE guidelines and the accessibility of wide-ranging support from peer-reviewed publications, books and online sources as well as commercial companies, the design of many published assays continues to be less than optimal: primers often lack intended specificity, can form dimers, compete with template secondary structures at the primer binding sites or hybridise only within a narrow temperature range. We present an overview of the main steps in the primer design workflow, with data that illustrate some of the unexpected variability that often occurs when theory is translated into practice. We also strongly urge researchers to report as much information about their assays as possible in their publications.