Parasitoid wasp DNA code cracked

Researchers of the Evolutionary Genetics Research Group of Groningen University, together with a group of international colleagues, have unravelled the DNA sequence of three closely related species of Nasonia parasitoid wasps. The parasitoid wasp genome is published in the scientific journal Science on 15 January 2010.

Parasitoid wasps are used as biological control agents against harmful pest insects. Now that more is known about their genetic characteristics, they can be used more effectively for this purpose. However, they have a much larger scientific significance; the parasitoid wasp may well replace the fruit fly as the model system for genetic research.

Model organism

Nasonia parasitoid wasps lay their eggs in fly pupae. These pupae can be found in birds’ nests and dead animals, but they are also easy to cultivate in a laboratory. This last fact is the reason why the parasitoid wasp has developed into a model organism for genetic and evolutionary research in the last decennia.

Research has shown that Nasonia wasps have genes that determine which species of insects they attack. This knowledge can be applied to make the wasps more effective as biological agents against insect pests. The genes involved in producing the wasps’ venom have also been decoded. Because the wasp’s venom acts directly on the physiology of the animal it stings, the discovery and analysis of the venom genes will likely prove a rich source of knowledge for the development of new medicines, for example for neurological disorders.

Advantages

As genetic model systems, parasitoid wasps have a number of important advantages. They could even supplant the fruit fly, that for years has been the model organism for genetic research. Fruit flies are easy to cultivate in the laboratory and have a generation time of two weeks. This makes culturing easy, which is extremely important for successful genetic research.

Haplodiploid

Nasonia wasps have all these characteristics, but there is another characteristic that makes Nasonia particularly attractive for research. Because male Nasonia wasps hatch from unfertilized eggs (just as honeybee drones), Nasonia males have only one set of chromosomes instead of two, as do fruit flies and humans. Fertilized eggs produce Nasonia females with two sets of chromosomes. This is called haplodiploid reproduction and it is extremely useful for tracing genes and analysing interactions between them.

Cell differentiation

Another difference with fruit flies is that parasitoid wasps, just as humans and other vertebrates, can change the chemical structure of their DNA through a process known as DNA methylation. This process plays an important role in the activation and deactivation of genes during an organism’s development, however it can also cause congenital disorders if the process goes amiss. This is why the Nasonia wasp is also likely to be important in research on cell differentiation, a process that  is determinative for the development of an egg into a complete organism with various organs.

Hybrid offspring

An advantage of these three closely related species of Nasonia is that they can be cross-bred. In contrast to crossing horses and donkeys, which produces infertile mules, Nasonia hybrid offspring are fertile. This makes it easier to trace the genes that play a role in the materialization of the differences between species. Now that the DNA code of three closely related species has been unravelled it will be possible to study the changes that take place during and after speciation. This is a major step forward in research on one of the most important questions raised after the publication of Darwin’s Origin of Species.

A striking discovery in relation to this research is that the DNA of mitochondria – a cell’s power plants which have their own, relatively tiny, genome – evolve extremely rapidly in Nasonia. Genes in the cell nucleus must also evolve rapidly to keep up with the mitochondrial DNA. It is precisely mutually adapted gene complexes like these that become unbalanced in the hybrid offspring of cross-bred species. A number of research groups, including the University of Groningen’s Evolutionary Genetics team, are trying to discover precisely which interactions are less well tuned in hybrid offspring.

Mitochondria

Because mitochondria play an important role in a number of human diseases, as well as in ageing and fertility, research on Nasonia’s rapidly evolving mitochondria could provide more insight into these processes.

Biologist Dr Bart Pannebakker is one of the researchers on this project in Groningen. ‘I am utterly convinced,’ he says, ‘that the publication of this DNA sequence will lead to a better understanding of the fundamental processes in biology. This is certainly the case for evolutionary and developmental biology, where Nasonia has become such an important model system.’

The research was made possible thanks to the support of the Netherlands Organisation for Scientific Research (NWO).

Press info

More Information:
- Dr Bart Pannebakker, tel.: +31(0)50 363 8099, e-mail: b.a.pannebakker rug.nl
- Dr Louis van de Zande, tel.: +31 (0)50 363 2126, e-mail: louis.van.de.zande rug.nl
- Prof. Leo Beukeboom, +31 (0)50 363 8448, e-mail: l.w.beukeboom rug.nl