Here’s a challenge: grab a handful of brightly coloured jelly beans, put them all in your mouth and chew. Then try and figure out all the individual flavours. Although you might be able to spot distinctive cherry or tangy lemon, you would probably struggle to identify every single taste. But pop them into your mouth one at a time and each flavour is easy to distinguish.
This scenario is very similar to the problem experienced by researchers investigating the changes in gene activity that happen in individual cells during the development of diseases such as Alzheimer’s and cancer. Previously, scientists had to mash up tissue samples containing many thousands or millions of cells and look at the average overall result – just like eating a whole handful of jelly beans at once.
Thanks to improvements in technology, researchers can now look at gene activity patterns in single cells taken from healthy or abnormal tissue and get a true readout of its individual ‘flavour’. But getting the right kind of samples for single cell analysis isn’t easy.
“We need to start with living cells extracted from fresh material,” explains Holger Heyn, leader of the Single Cell Genomics team at the CNAG-CRG. “Here in Barcelona we are right next to the hospital and have all the machines we need to separate the cells. But this simply isn’t possible for many medical or research facilities.”
Instead, tissue samples taken from a patient are often preserved with formaldehyde so they can be sent off for analysis elsewhere. But this preservative effectively glues all the cells together so they can’t be separated. Alternatively, samples can be snap-frozen with dry ice or liquid nitrogen, although this damages the cells so much that they disintegrate upon thawing. And without single cells, researchers can’t do single cell analysis.
So Heyn decided to develop an alternative method that could be used to preserve samples gathered from anywhere in the world while still allowing single cells to be separated out at a later date.