"Classic" Reads--Edge Effects

What I am reading today:  

A Simple Technique for Reducing Edge Effect in Cell-Based Assays. (2003) Lundholt, Scudder & Pagliaro, Journal of Biomolecular Screening 8(5).  

(Thanks to Amy G. at LiCor for the heads up on the paper.)

Why am I reading it?

Edge effects can be a bane of any plate-based assay. What are they? Let's say you look at your plate-based results and see a pattern that relates not to the biology you want to study but instead, to the position of the wells on the plate. That might be an edge effect. Commonly, the outer wells of the plate will give skewed values and/or contain unhappy cells.

Edge effects have not been a big problem at the DRSC (info on how we accomplish that below). Nonetheless, it's worth thinking about. And exploring ways to keep edge effects at a minimum.

In the paper cited above, the authors describe placing a plate at room temperature prior to incubation at 37 degrees C (their study is on mammalian cells). As fly cells grow at 25 and ambient air is usually about 22, the method might not do much for Drosophila cell-based assays. But if you're visiting us from the mammalian screening world--or interested to do follow-up assays in that system after a fly cell screen--then the quick fix Lundholt et al. propose is probably worth keeping in mind.

How does the DRSC reduce edge effects?  We use a very low-tech tool--wet paper towels--to keep humidity (which appears to be a contributing factor) even and high.  Our incubator is humidified. But nonetheless, our screeners are encouraged to take the extra precaution of putting the plates on top of a layer of damp paper towels and close them up in plastic containers.

This simple solution seems to do the trick.  In general, we see little or no edge effects, and thus our users typically can include the outermost wells in data analysis.