Genetic basis of sex determination in the haplodiploid wasp Nasonia vitripennis

PhD ceremony: Ms. E.C. Verhulst, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: Genetic basis of sex determination in the haplodiploid wasp Nasonia vitripennis

Promotor(s): prof. L.W. Beukeboom

Faculty: Mathematics and Natural Sciences

In the research of Eveline Verhulst the involvement of epigenetic modification in sex determination is shown for the first time. Both humans and the fruitfly Drosophila reproduce sexually, so their offspring has genes from both father and mother. The parasitic wasp Nasonia also reproduces sexually but females can produce offspring without mating. This offspring receives genes from the mother only and will develop as male. When a Nasonia female does mate, she can choose whether to fertilize her eggs or not. The fertilized eggs receive genes from father and mother, and will develop as females. In this way, mated females can regulate the amount of sons and daughters.

The most important gene in insect sex determination is transformer. When an insect embryo contains the transformer protein, a female will develop. When the transformer protein is absent, a male will develop. In Drosophila a male indirectly prevents the production of transformer protein. In Nasonia this is impossible, since males have no father! A Nasonia female puts an amount of transformer messengerRNA (mRNA) into her eggs which the embryo can use to produce transformer protein, but only when the embryo can also make transformer mRNA itself. An unfertilized embryo is unable to do this because the mother has locked the transformer gene in her eggs, resulting in male development. The father has put an accessible transformer gene in his sperm, so a fertilized egg can make transformer mRNA and develops as a female. The underlying mechanism is called ‘epigenetic modification’.