Munich

Biologists who make their own DNA microarrays, rather than relying on expensive commercial chips, should now be able to do a better do-it-yourself job, thanks to a set of human DNA clones made available by the German Genome Resource Centre (RZPD) in Berlin.

Microarrays are increasingly being used by researchers interested in gene expression, allowing them to compare the activity of thousands of genes in, for example, cancerous and non-cancerous tissues. Most commercial systems consist of arrays of thousands of short nucleotide synthetic sequences, called oligonucleotides, designed to bind to specific messenger RNAs (mRNAs), which are transcribed from active genes.

But many researchers opt instead to make their own cheaper microarrays from complementary DNAs (cDNAs), which are made from mRNAs directly, using a reverse transcriptase enzyme. Each cDNA binds to the same mRNA from which it was created. Once a researcher has obtained a library of cDNAs, they can make copies of the cDNAs to create many microarrays.

The non-profit RZPD says that its human cDNA clone set is of much higher quality than those produced by other labs, and is also better catalogued. The RZPD's first customers say that they can use the cDNA clones to create their own microarrays at a fraction of the cost of commercial oligonucleotide arrays.

The RZPD set has several advantages over other libraries. Each clone has been resequenced and verified as corresponding to its database sequence. About 10–20% of samples in most other cDNA libraries are incorrectly labelled. The RZPD has also gone to great lengths to be as sure as possible that each cDNA represents a unique gene, whereas most cDNA libraries contain multiple copies of mRNAs of particularly active genes.

“The availability of a sequence-verified, non-redundant cDNA library is fantastic — global approaches to biological research hinge on the availability of high-quality reagents,” says Steven Gullans, co-director of the Gene Array Center at the Brigham and Women's Hospital in Boston.

The RZPD clone set contains 32,000 genes, and a further 10,000 will be added over the next few months — giving it more genes than other libraries. “Spotting 40,000 or so cDNAs onto a microarray means that we can cover a large part of the human genome,” says Jobst Landgrebe, a biochemist at the University of Göttingen. He adds that it will cost him no more than 75 euros (US$75) to make a microarray from the cDNA set.

→ http://www.rzpd.de