A new article published in Genome Biology investigates why, despite its apparent simplicity, it needs 20,000 genes when animals as complex as humans make do with only 30,000 or so.

Jonathan Hodgkin from the University of Oxford proposes that there are both genetic and ecological reasons that might explain why the worm has so many genes (or why the human has so few).

The genetic reasons behind the large gene number in C. elegans include: the presence of genes that no longer have any function, the need for genes to code individually for large proteins (rather than combining protein modules from smaller genes, as occurs in the human), the fact that much of the worm's development and morphology are "hard-wired" in its genes, and the rarity of "alternative splicing" (a process whereby different forms of a protein are assembled using the information from a single gene).

The ecological reasons behind the large number of genes found in C. elegans require an understanding of the worm's natural environment.

C. elegans lives in soil, feeding on bacteria associated with rotting vegetable matter. Soil is a complex environment containing a wide variety of bacteria, fungi and viruses that may try and infect the worm as it wriggles through the soil.

C. elegans has had to evolve through geological time to cope with the challenges it faces from other soil-dwelling organisms. Its ability to fend off a bacterial toxin, for example, has recently been shown to be affected by mutation in five different genes.

Hodgkin suggests that this battle between the microbes in the soil and the worm may have contributed to the worm needing a vast number of genes to survive.

Hodgkin concludes by suggesting that to understand the function of the genome of an organism we must also study the environment in which the organism lives -- and that for many endangered species, we may already be too late.

(Editor's Note: Full text of the article is available at this URL.)

[Contact: Gordon Fletcher]

23-Oct-2001