Designing a Reporter Construct for Analyzing Gene Regulation

Bioluminescent reporter assays are an excellent choice for analyzing gene regulation because they provide higher sensitivity, wider dynamic range and better signal-to-background ratios compared to colorimetric or fluorescent assays. In a typical genetic reporter assay, cells are transfected with a vector that contains the sequence of interest cloned upstream of a reporter gene, and the reporter activity is used to determine how the target sequence influences gene expression under experimental conditions. A second control reporter encoded on the same or a different plasmid is an essential internal control. The secondary reporter is used to normalize the data and compensate for variability caused by differences in cell number, lysis efficiency, cell viability, transfection efficiency, temperature, and measurement time. 

Basic Introduction to the Strategy of Reporter Gene Assays

For genetic reporter assays, using a secondary control vector with a weak promoter like PGK or TK to ensures that the control does not interfere with activation of your primary reporter vector. Transfection of high amounts of the control plasmid or putting the control reporter under control of a strong promoter like CMV or SV40 often leads to transcriptional squelching or other interference with the experimental promoter (i.e., trans effects). Reporter assays can also be used to quantitatively evaluate microRNA activity by inserting miRNA target sites downstream or 3´ of the reporter gene. For example, the pmirGLO Dual-Luciferase miRNA Target Expression Vector is based on dual-luciferase technology, with firefly luciferase as the primary reporter to monitor mRNA regulation and Renilla luciferase as a control reporter for normalization.

Here in Technical Services we often talk with researchers who are just starting their project and looking for advice on designing their genetic reporter vector. They have questions like:

  • How much of the upstream promoter region should be included in the vector?
  • How many copies of a response element will be needed to provide a good response?
  • Does the location of the element or surrounding sequence alter gene regulation?
Continue reading “Designing a Reporter Construct for Analyzing Gene Regulation”

Tips for Successful Dual-Reporter Assays

Previously, we described some of the advantages of using dual-reporter assays (such as the Dual-Luciferase®, Dual-Glo® Luciferase and the Nano-Glo® Dual-Luciferase® Systems). Another post describes how to choose the best dual-reporter assay for your experiments. For an overview of luciferase-based reporter gene assays, see this short video:

These assays are relatively easy to understand in principle. Use a primary and secondary reporter vector transiently transfected into your favorite mammalian cell line. The primary reporter is commonly used as a marker for a gene, promoter, or response element of interest. The secondary reporter drives a steady level of expression of a different marker. We can use that second marker to normalize the changes in expression of the primary under the assumption that the secondary marker is unaffected by what is being experimentally manipulated.

While there are many advantages to dual-reporter assays, they require careful planning to avoid common pitfalls. Here’s what you can do to avoid repeating some of the common mistakes we see with new users:

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Diabetes Research: Measuring the Activity of Insulin

We rely on insulin supplied by our pancreas at the right dose and at the right time to control our blood glucose levels and energy storage. Insulin works by regulating the energy usage of various cell types in the body. When this process goes awry, it can cause diabetes.

There are two types of diabetes, defined by how insulin is dysregulated. In Type 1 Diabetes (T1D), the pancreas produces too little insulin. Patients need to give themselves insulin in order to respond to glucose in the diet. In Type 2 Diabetes (T2D), patients do not respond well to the insulin produced in their body. Therefore, they need to give themselves more to avoid hyperglycemia (high blood glucose).

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NanoLuc: Tiny Tag with a Big Impact

Synthetic biology—genetically engineering an organism to do or make something useful—is the central goal of the iGEM competition each year. After teams conquer the challenge of cloning their gene, the next hurdle is demonstrating that the engineered gene is expressing the desired protein (and possibly quantifying the level of expression), which they may do using a reporter gene.

Reporters can also play a more significant role in iGEM projects when teams design their organism with reporter genes to detect and signal the presence of specific molecules, like environmental toxins or biomarkers. Three of the iGEM teams Promega sponsored this year opted to incorporate some version of NanoLuc® Luciferase into their projects.

NanoLuc® luciferase is a small monomeric enzyme (19.1kDa, 171 amino acids) based on the luciferase from the deep sea shrimp Oplophorus gracilirostris. This engineered enzyme uses a novel substrate, furimazine, to produce high-intensity, glow-type luminescence in an ATP-independent reaction. Unlike other molecules for tagging and detecting proteins, NanoLuc® luciferase is less likely to interfere with enzyme activity and affect protein production due to its small size.

NanoLuc® Luciferase has also been engineered into a structural complementation reporter system, NanoBiT® Luciferase, that contains a Large subunit (LgBiT) and two small subunit options: low affinity SmBiT and high affinity HiBiT. Together, these NanoLuc® technologies provide a bioluminescent toolbox that was used by the iGEM teams to address a diverse set of biological challenges.

Here is an overview of each team’s project and how they incorporated NanoLuc® technology.

Continue reading “NanoLuc: Tiny Tag with a Big Impact”

Out-FOXOing High-Stage Neuroblastoma

Fluorescence microscopy of neuroblastoma cells.

In recent years, scientists have been hot on the trail of transcription factor FOXO3, tracing its involvement in various tumor-centric activities comprising the many trademarks of cancer, from drug resistance to metastasis to tumor angiogenesis.

FOXO3 is a member of the O sub-class of the forkhead box family of transcription factors. The forkhead box (FOX) family is characterized by a fork head DNA-binding domain (DBD), comprised of around 100 amino acids. They have also proven themselves to be a family of many hats, functioning in diverse roles ranging from metabolism, immunology, cell-cycle control, development, as well as cancer (1). The forkhead box O (FOXO) sub-class alone has demonstrated involvement in a variety of cellular outcomes, from drug resistance and longevity to apoptosis induction.

Due to its pro-apoptotic and anti-proliferative proclivity, FOXO3 has been previously identified as a tumor suppressor gene. However, more and more studies have begun to flip the narrative on FOXO3, portraying it more as a devoted henchman, due to its roles in drug and radiotherapy resistance, cell-cycle arrest and long-term maintenance of leukemia-initiating stem cells in a variety of cancer types, including breast cancer, pancreatic cancer, glioblastoma, and both acute and chronic myeloid leukemia.

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MSI Testing of Tumor Cells for Better Tailored Treatment

There are as many different cancers as there are people with cancer. Unlike infectious diseases, which are caused by pathogens that are foreign to our bodies (bacteria, viruses, parasites), cancer cells arise from our body—our own cells gone rogue. Because cancer is a dysfunction of a person’s normal cells, every cancer reflects the genetic differences that mark us as individuals. Add to that environmental influences like diet, tobacco use, the microbiome and even occupation, and the likelihood of finding a “single” pharmaceutical cure for cancer becomes virtually impossible.

But, while looking for a single cure for all cancers may not be a fruitful activity, defining a best practice for understanding the genetic and protein biomarkers of individual tumors is proving worthwhile.

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Discussing the Future of Gene Editing at CRISPRcon Midwest

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Walking in to the first session at CRISPRcon Midwest.

Last week, a diverse group of stakeholders attended CRISPRcon Midwest, hosted by the Keystone Policy Center and the University of Wisconsin–Madison. The goal of the day-long conference was to emphasize the importance and value of gene editing technology, and how it must be communicated deliberately between scientists, the public, policymakers, and other stakeholders.

Julie Shapiro, Senior Policy Director of Keystone Policy Center, acted as Emcee for the event. Given the diverse group of attendees, she mentioned in her opening remarks that the event organizers were “seeking conversation, not consensus” and emphasized the “power of respectful dialogue.” A slide overhead showcased the ground rules for the day, which included statements such as “dare to listen, dare to share, and dare to disagree.”

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Word cloud generated from live polling results at CRISPRcon Midwest.

CRISPRcon aimed to included voices beyond those represented by keynote speakers and panelists, so they incorporated live polling through an online app to keep the audience engaged and an active participant in the conversations throughout the day. From the opening remarks, it was clear that this conference would not just deliver on its promise of thoughtful conversation about the science, but build further understanding about the societal impacts of a rapidly advancing technology.

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All You Need is a Tether: Improving Repair Efficiency for CRISPR-Cas9 Gene Editing

Ribonucleoprotein complex with Cas9, guide RNA and donor ssDNA. Copyright Promega Corporation.

With the advent of genome editing using CRISPR-Cas9, researchers have been excited by the possibilities of precisely placed edits in cellular DNA. Any double-stranded break in DNA, like that induced by CRISPR-Cas9, is repaired by one of two pathways: Non-homologous end joining (NHEJ) or homology-directed repair (HDR). Using the NHEJ pathway results in short insertions or deletions (indels) at the break site, so the HDR pathway is preferred. However, the low efficiency of HDR recombination to insert exogenous sequences into the genome hampers its use. There have been many attempts at boosting HDR frequency, but the methods compromise cell growth and behave differently when used with various cell types and gene targets. The strategy employed by the authors of an article in Communications Biology tethered the DNA donor template to Cas9 complexed with the ribonucleoprotein and guide RNA, increasing the local concentration of the donor template at the break site and enhancing homology-directed repair. Continue reading “All You Need is a Tether: Improving Repair Efficiency for CRISPR-Cas9 Gene Editing”

NLRP3: The New Hope for Treating Chronic Inflammatory Diseases

Our innate immune system was meant to do good. Up until a century ago, most humans died from infectious diseases like diarrhea, tuberculosis and meningitis. Over millions of years, our immune system has evolved to fight these life-threatening infections from pathogens. As a result, we have developed a highly efficient response to these tiny invaders. But it seems that our immune system may be turning against us.

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Striking Fear into the Heart of Cardiovascular Disease Using Zebrafish and NanoLuc® Luciferase

Representative images of ApoB-LP localization in zebrafish across developmental, genetic, pharmacological and dietary manipulations.
Credit: Figure 5.D of The LipoGlo reporter system for sensitive and specific monitoring of atherogenic lipoproteins by James Thierer, Stephen C. Ekker and Steven A. Farber.
Article licensed under Creative Commons Attribution 4.0 International License.

Cardiovascular diseases, or CVDs, are collectively the most notorious gang of cold-blooded killers threatening human lives today. These unforgiving villains, including the likes of coronary heart disease, cerebrovascular disease and pulmonary embolisms, are jointly responsible for more deaths per year than any other source, securing their seat as the number one cause of human mortality on a global scale.

One of the trademarks of most CVDs is the thickening and stiffening of the arteries, a condition known as atherosclerosis. Atherosclerosis is characterized by the accumulation of cholesterol, fats and other substances, which together form plaques in and on the artery walls. These plaques clog or narrow your arteries until they completely block the flow of blood, and can no longer supply sufficient blood to your tissues and organs. Or the plaques can burst, setting off a disastrous chain reaction that begins with a blood clot, and often ends with a heart attack or stroke.

Given the global prevalence and magnitude of this problem, there is a significant and urgent demand for better ways to treat CVDs. In a recent study published in Nature Communications, researchers at the Carnegie Institution for Science, Johns Hopkins University and Mayo Clinic are taking the fight to CVDs through the study of low-density lipoproteins (LDLs), the particles responsible for shuttling bad cholesterol throughout the bloodstream.

Continue reading “Striking Fear into the Heart of Cardiovascular Disease Using Zebrafish and NanoLuc® Luciferase”