The genetic abnormality called microsatellite instability, or MSI, has been linked to cancer since its discovery in 1993 (1). MSI is the accumulation of insertion or deletion errors at microsatellite repeat sequences in cancer cells and results from a functional deficiency within one or more major DNA mismatch repair proteins (dMMR). This deficiency, and the resulting genetic instability, is closely related to the carcinogenicity of tumors (2).
Historically MSI has been used to screen for Lynch Syndrome, a dominant hereditary cancer propensity. More recently, tumors with deficient MMR function have been identified as being more likely to respond to immune checkpoint inhibitor (ICI) therapies (3.). Because MSI can be the first evidence of an MMR deficiency, MSI-High status is predictive of a positive response to immunotherapies such as ICI therapies. (3).
Ah, the wonders and frustrations of cloning. We’ve all been there. After careful planning, you have created the cloned plasmid containing your DNA sequence of interest, transformed it into bacterial cells and carefully spread those cells on a plate to grow. Now you stand at your bench gazing down at your master piece: a plate full of tiny bacterial colonies. Somewhere inside those cells is your DNA sequence, happily replicating with its plasmid host. But wait – logic tells you that not ALL of those colonies can contain your plasmid. There must be hundreds of colonies. Which ones have your plasmid? You begin to panic. Visions of yourself old and grey and still screening colonies flash through your mind. At the next bench, your lab-mate is cheerfully selecting colonies to screen. Although there are hundreds of colonies on her plate as well, some are white and some are blue. She is only picking the white colonies. What does she know that you don’t? 
