The genome in a microchip

This is an article that appeared in the 4th edition of El·lipse, the PRBB monthly newspaper.

In the genomics world, the microarray is the king. Microarrays are 5 cm long and 2 cm wide slides in which up to one million microscopic drops can be placed next to each other. Each of these drops, which are chemically attached to the glass, forms a dot that contains a single probe – a piece of DNA that corresponds to a fragment of the genome. This way one can have a big collection of genes, even the whole genome, represented in a few slides. Microarrays allow scientists to do analyses in thousands of genes at once, analyses that would normally have to be done one gene at a time.

The most common of these analyses is the study of gene expression. Genes are “expressed” when they are activated in order to give rise to a protein, which will carry out the function specified by the gene. In this path from DNA to protein there are some intermediaries, the messenger RNAs (mRNAs). Each gene produces an mRNA, and the mRNAs are what scientists usually detect to know that a gene is being expressed. For this, mRNAs are isolated from cells, labelled with fluorescent molecules, and placed on the top of microarrays, where each mRNA will recognise its probe – the dot that contains its related DNA – and will bind it specifically. This way one can look at the microarray and see which dots are fluorescent; these will represent the genes that are being expressed.

With this system, scientists can find out which genes are expressed in a specific condition and at what level – according to the fluorescent intensity. They can also compare two conditions, by labelling the mRNAs from the different conditions with different colours. For instance, the gene expression of a healthy and a diseased person can be compared, or that of the same person before and after treatment with a drug. Knowing which genes are expressed in one condition or another gives hints as to which genes may be implied in the disease or what effect the drug has.

At the PRBB there is a core microarray service since 2001, directed by Dr. Lauro Sumoy (CRG). This service is used by several groups from the centres of the PRBB who work in very diverse fields, from molecular biology to evolution.