Researchers have made the first ever systematic attempt to analyse the function of all the genes in a multi-cellular organism. Two groups have worked out what a significant proportion of the genes of the roundworm Caenorhabditis elegans do, increasing by five times the number of this creature's genes of known function.

The teams used a technique called 'RNA interference' or 'RNAi', which stops the protein encoded by a given gene being made. They then assessed what happens to a cell and to a whole animal when those genes don't function.

Julie Ahringer and colleagues at the University of Cambridge, UK, and Anthony Hyman and colleagues at the European Molecular Biology Laboratory in Heidelberg, Germany, targeted all the genes on two of the six chromosomes of C. elegans.

A high percentage of the genes to which the teams have ascribed a role are conserved in evolution. The information gained from animal model studies like these should improve our understanding of the function and possible malfunctions of all our genes -- especially now that the human genome is virtually fully sequenced. The genome sequence of C. elegans was completed in 1998.

One gene at a time, the groups produced double-stranded RNA versions of the genes on chromosomes I and III, based on the sequence information available. They then injected worms with this double-stranded RNA or fed them on genetically modified bacteria containing it.

These procedures blocked the expression of the corresponding genes. The researchers then examined the roundworms for abnormalities in embryonic life, or at the larval or the adult stage.

Ahringer's work pinpoints which genes are essential for survival, and at which stage of life their function is first required. But further work is needed to understand the genes' exact roles.

Mariann Bienz who uses RNAi in fruitflies at Cambridge University, UK, comments that, "systematic approaches using RNAi could be more useful if they focus on a given biological process."

For instance, Hyman's team analysed in more detail the genes required for cell division, thus giving a better idea of what the gene products actually do and why they are indispensable.

Bienz also feels that such systematic approaches can be misleading. A systematic screen and an individual analysis can yield different results for the same gene. "When looking at so many genes, some results are more likely to be overlooked," she explains.

She also warns that, "extrapolating the results obtained in C. elegans to other species might often not be possible". In one species several genes might do the job done by just one gene in another species. So targeting one gene by RNAi might lead to embryonic death in one species but not in another.