Tips and Tools

Dealing with PCR Inhibitors

Posted on by Terri Sundquist
Inhibition

The polymerase chain reaction (PCR) has revolutionized modern biology as a quick and easy way to generate amazing amounts of genomic data. However, when PCR doesn’t work, it can be frustrating. At these times, PCR and reverse transcription PCR (RT-PCR) inhibitors seem to be everywhere: They lie dormant in your starting material and can co-purify with the template of interest, and they can be introduced during sample handling or reaction setup. The effects of these inhibitors can range from partial inhibition and underestimation of the target nucleic acid amount to complete amplification failure. What is a scientist to do?

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Practical Tips for HEK293 Cell Culture When Using cAMP-Glo™ Assay

Posted on by Nives Kovacevic
HEK293 cells stably expressing HaloTag®-ECS (ExtraCellular Surface; comprised of a signal sequence and single transmembrane domain of β1-integrin) fusion protein labeled with HaloTag® Alexa Fluor® 488 Ligand and then imaged.
HEK293 cells stably expressing HaloTag®-ECS fusion protein labeled
with HaloTag® Alexa Fluor® 488 Ligand and then imaged.

G Protein Coupled Receptors represent one of the largest classes of cell surface receptors and one of the most important classes for drug targets. Fifty of the top 200 drugs target GPCRs. GPCRs respond to various stimuli like light, odors, hormones, neurotransmitters and others. They cover virtually all therapeutic areas. When a particular GPCR is implicated in a disease, researchers screen the GPCR and its signaling pathways, the hope being that promising therapeutic targets might be identified. Major G-protein families signal via secondary messengers like cAMP, which in turn activate a range of effector systems to change cell behavior and/or gene transcription. There are various approaches and methods to study GPCRs and measure the increase or decrease of intracellular cAMP. However, the fastest and the most sensitive among all methods is a plate based cAMP-Glo™ Assay.

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Piecing the Puzzle Together: Using Multiple Assays to Better Understand What Is Happening with Your Cells

Posted on by Michele Arduengo

You often need several pieces of information to really understand what is happening within a cell or population of cells. If your cells are not proliferating, are they dying? Or, are you seeing cytostasis? If they are dying, what is the mechanism? Is it apoptosis or necrosis? If you are seeing apoptosis, what is the pathway: intrinsic or extrinsic?

If you are measuring expression of a reporter gene and you see a decrease in expression, is that decrease due to transfection inefficiencies, cytotoxicity, or true down regulation of your reporter gene?

To investigate these multiple parameters, you can run assays in parallel, but that requires more sample, and sample isn’t always abundant.

Multiplexing assays allows you to obtain information about multiple parameters or events (e.g., reporter gene expression and cell viability; caspase-3 activity and cell viability) from a single sample. Multiplexing saves sample, saves time and gives you a more complete picture of the biology that is happening with your experimental sample.

What information do you need about your cells to complete the picture?
What information do you need about your cells to complete the picture?

Multiplexing assay reagents to measure biomarkers in the same sample has often been considered an application only accomplished with antibodies or dyes and sophisticated detection instrumentation. However, Promega has developed microwell plate based assays for cells in culture that allow multiplexed detection of biomarkers in the same sample well using standard multimode multiwell plate readers. Continue reading “Piecing the Puzzle Together: Using Multiple Assays to Better Understand What Is Happening with Your Cells”

Methods for Quantitating Your Nucleic Acid Sample

Posted on by Sara Klink
Nucleic acid quanitation webinar

For most molecular biology applications, knowing the amount of nucleic acid present in your purified sample is important. However, one quantitation method might serve better than another, depending on your situation, or you may need to weigh the benefits of a second method to assess the information from the first. Our webinar “To NanoDrop® or Not to NanoDrop®: Choosing the Most Appropriate Method for Nucleic Acid Quantitation” given by Doug Wieczorek, one of our Applications Scientists, discussed three methods for quantitating nucleic acid and outlined their strengths and weaknesses.

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Top Ten Tips for Successful PCR

Posted on by Kelly Grooms

We decided to revisit a popular blog from our Promega Connections past for those of you in the amplification world. Enjoy:

magnesium-31

    • Modify reaction buffer composition to adjust pH and salt concentration.
    • Titrate the amount of DNA polymerase.
    • Add PCR enhancers such as BSA, betaine, DMSO, nonionic detergents, formamide or (NH4)2SO4.
    • Switch to hot-start PCR.
    • Optimize cycle number and cycling parameters, including denaturation and extension times.
    • Choose PCR primer sequences wisely.
    • Determine optimal DNA template quantity.
    • Clean up your DNA template to remove PCR inhibitors.
    • Determine the optimal annealing temperature of your PCR primer pair.

[Drum roll please]…and the  most important thing you can do to improve your PCR results is:

  • Titrate the magnesium concentration.

Successful Ligation and Cloning of Your Insert

Posted on by Sara Klink
Ligation and cloning
Cloning PCR product.

You have PCR amplified your insert of interest, made sure the PCR product is A tailed and are ready to clone into a T vector (e.g., pGEM®-T Easy Vector). The next step is as simple as mixing a few microliters of your purified product with the cloning vector in the presence of DNA ligase, buffer and ATP, right? In fact, you may need to consider the molar ratio of T vector to insert.

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Don’t Let Ribonucleases Ruin Your Week(end): Establish a Ribonuclease-free Environment

Posted on by Kelly Grooms
buffers_image1_274x218

My very first job in science was in a lab that worked exclusively with RNA, and it was only after I moved on to a different job that I learned just how much different the world of DNA research is from that of RNA. When working with DNA, for example, you rarely if ever have the sample you have labored over reduced to a fuzzy blur at the bottom of a gel because it has been degraded beyond rescue. With RNA, unfortunately, this happens all too frequently. In fact, a labmate of mine once put up a poll on the door to our lab asking if it was better to discover that your RNA sample was degraded on a Monday or a Friday.

The culprits in this scenario are Ribonucleases (RNases). They are everywhere. They are incredibly stable and difficult to inactivate. And, if you work with RNA, they are your enemy. Take heart though, they can be defeated if you follow some pretty simple steps.

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Cell Line Misidentification Rears Its Ugly Head

Posted on by Michele Arduengo
Cancer cell illustration

Back in 2009, we reported on the problem of cell line contamination (1). In that article we reported the statistics that an estimated 15–20% of the time, the cell lines used by researchers are misidentified or cross-contaminated with another cell line (1). This presents a huge problem for the interpretation of data and the reproducibility of experiments, a key pillar in the process of science. We have revisited this topic several times, highlighting the issues cell and tissue repositories have discovered with cell lines submitted to them (2) and discussing the new guidelines issued by ANSI (3,4) for researchers regarding when during experimental processes cell lines should be authenticated and what methods are acceptable for identifying cell lines.

Just recently two papers were voluntarily retracted by their authors because of cross contamination among cell lines used in the laboratories. The first that came to my attention represented the first retraction from Nature Methods in its nine years of publication. In this paper, cross contamination of a primary gliomasphere cell lines with HEK cells expressing GFP resulted in “unexplained autofluorescence” associated with tumorigenicity (5). The second paper, retracted from Cancer Research by the original authors, was also another cross contamination story involving HEK cells (6). In this story a gene was incorrectly described as a tumor suppressor, that when silenced led to the formation of tumors in nude mice. It turns out that the contaminating HEK cells also failed to express this same gene.

So because of cross contamination of cell lines, two groups have voluntarily retracted papers. Being open and honest about what had happened with the cell lines and reaching the decision to retract the papers could not have been an easy thing, but these decisions benefit the scientific community in many ways. Obviously they benefit the researchers doing work on the specific research questions addressed by the papers by preventing researchers from pursuing paths that lead to dead ends. But in the bigger picture these retractions reinforce the argument that cell line authentication needs to become a routine and accepted part of any experimental process that depends on cell culture if we are to have confidence in the experimental results.

References

  1. Dunham, J.H. and Guthmiller, P.  (2009) Doing good science: Authenticating cell line identity. Promega Notes 101, 15–18.
  2. Duham, J.H. and Guthmiller, P. (2012) Doing good science: Authenticating cell line identity. Promega PubHub. [Internet: Accessed September 2013]
  3. Gopal, A. (2013) Fingerprinting  your cell lines. Promega Connections blog [Internet: Accessed September 2013]
  4. Sundquist, T. (2013) Preventing the heartache of cell line contamination. Promega Connections blog [Internet: Accessed September 2013]
  5. Evanko, D. (2013) A retraction resulting from cell line contamination.  Methagora blog. [Internet Accessed September 2013]
  6. Negorev, D. (2013) Retraction: Sp100 as a potent tumor suppressor: Accelerated senescence and rapid malignant transformation of human fibroblasts through modulation of an embryonic stem cell program. Can. Res. 73, 4960.

Preventing the Heartache of Cell Line Misidentification

Posted on by Terri Sundquist
Golden mask

It’s a scientist’s nightmare: Spending time and resources to investigate a biological phenomenon only to learn later that your cells are not what you think they are—their true identities hidden. As a result, all of the data that you’ve generated with those cells, published and unpublished, are cast into doubt. You thought that you knew your cells, that you could trust them, but your trust was misplaced. At some point, perhaps even before the traitorous cell line entered your laboratory, the cells were mislabeled, misidentified or contaminated with another cell line. It didn’t have to be this way. There are easy steps you can take to prevent the headache and heartache of cell line misidentification and contamination.

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Safety First (and Sensitivity too!): Diamond™ Nucleic Acid Dye

Posted on by admin
product photo for diamond™ nucleic acid dye

Gel electrophoresis and gel staining are common lab tasks that you may not think too much about.  It’s a fairly routine part of your day…purify DNA or RNA, check it on a gel.  As you probably know, interchelating agents like ethidium bromide can be used to visualize your nucleic acids on a gel for relatively low cost. The problem with ethidium bromide is that it’s highly mutagenic, making it less than ideal to work with and disposal of ethidium bromide can be quite costly. There are other commercially available alternatives to ethidium bromide that use fluorescent-based dyes to detect nucleic acids in gels. Some of these are touted to be safer than ethidium bromide; others are marketed as more sensitive.  If you are going to switch from an interchelating agent to something safer, you certainly don’t want to lose out on sensitivity.

To make your gel staining safer, more convenient, and more cost-effective, we’ve developed the Diamond™ Nucleic Acid Dye. This dye is not detectably genotoxic or cytotoxic at the 1:10,000 dilution recommended for gel staining, as determined by the Ames MPF™ Assay, is more sensitive than competing fluorescent-type “safe” dyes, and, in its concentrated form, is room-temperature stable for 90 days (1, 2).   If you are looking to switch to a safer, more sensitive way to stain your polyacrylamide or agarose gels to visualize your DNA or RNA, you may want to give the Diamond™ Nucleic Acid Dye a try.

  1.  Schagat, T. and Hendricksen, A. Diamond™ Nucleic Acid Dye is a Safe and Economical Alternative to Ethidium Bromide. [Internet] July 2013; tpub 125. [cited: 2013, July, 29].
  2. Truman, A., Hook, B. and Hendricksen, A. Diamond™ Nucleic Acid Dye: A Sensitive Alternative to SYBR® Dyes. [Internet] June 2013; tpub 121. [cited: 2013, July, 29].