Suprising new information on the HOX genes

Researchers at the University of Bergen are now able to present new information on the HOX genes – the “software” to design animals. The findings are published in today’s issue of Nature.

Some years ago researchers at the Sars Centre for Marine Molecular Biology at the UoB discovered the smallest genome among vertebrates in a tiny urochordate called Oikopleura dioica. The organism is five millimetres long and the genome consists of only 70 million megabases (Mb). Although the human genome is forty times bigger in comparison, this organism makes an excellent model. Studies of the compact oikopleura-genome may contribute to shedding new light on the human genome, and the researchers have made several surprising discoveries so far.

In the research that serves as the basis for a new article in Nature researchers at the Sars have examined the so-called HOX genes. These are important genes that are common for all animals. They play a role in controlling the development from the fertilised egg to the formation of the general body structure. In humans these genes ensure that the fingers and the ribs take the right shape and length.

From insects to human beings HOX genes are lined up tightly together in the chromosomes like pearls on a string. It is also believed that this grouping and sequence have had great significance for the genes to function in a proper and coordinated way. In other words, the HOX gene sitting first in line on the chromosome controls for example the development of the back part of the brain, the second gene is responsible for the upper part of the neck and so on along the body axis. However, when the researchers at the Sars Centre found these genes in Oikopleura dioica, it turned out that this was not the case here. These genes are not lined up tightly at all, but it still seems that their function is about the same as in animals where the genes are closer together.

“This discovery is interesting because it indicates that the generally accepted theory about the position and function of HOX genes is too simple. This work also has relevance for understanding the development of body shapes in the animal world in general” says Rolf Brudvik Edvardsen, research fellow, who – together with three Master’s students – is a co-author of the article “Hox cluster disintegration with persistent anteroposterior order of expression in Oikopleura dioica” in Nature.

The research is led by Professor Daniel Chourrout, director of the Sars Centre. The Centre has also cooperated with two genome centres in Paris and Berlin.