In ASU's School of Life Sciences, Nasonia species have been utilized to conduct studies in genetics, epigenetics, male courtship behavior, evolution of speciation and social insect societies by consortium members Juergen Gadau, associate professor and associate dean for graduate studies; Stephen Pratt, assistant professor; Florian Wolschin, assistant research professor; and Joshua Gibson, doctoral student, who are also members of the Social Insect Research Group in ASU's College of Liberal Arts and Sciences. Gadau was one of eight researchers, including Werren and Richards, who developed the original Nasonia Whitepaper sent to the National Institutes of Health to encourage funding for the sequencing project in 2004.
Like the fruit fly Drosophila, a standard model for genetic studies for decades, Nasonia are small, can be easily grown in a laboratory, and reproduce quickly. However, Nasonia wasps offer an additional feature of interest: the males have only one set of chromosomes, instead of two sets like fruit flies and people.
"A single set of chromosomes, which is more commonly found in lower single-celled organisms such as yeast, is a handy genetic tool, particularly for studying how genes interact with each other," says Werren.
Unlike fruit flies, these wasps also modify their DNA in ways similar to humans and other vertebrates – a process called "methylation," which plays an important role in regulating how genes are turned on and off during development.
"In human genetics we are trying to understand the genetic basis for quantitative differences between people such as height, drug interactions and susceptibility to disease," says Richards. "These genome sequences combined with haploid-diploid genetics of Nasonia allow us to cheaply and easily answer these important questions in an insect system, and then follow up any insights in humans."
The wasps have an additional advantage in that closely related species of Nasonia can be cross-bred, facilitating the identification of genes involved in species' differences.
"Nasonia is currently the best genomic model system for understanding the genetic architecture of early speciation and complex phenotypes like behavior," says Gadau.
A Nasonia female drills into the host with her stinger (thin yellow tube emerging from her abdomen and going into the host). She will inject venom into in, lay her eggs, and feed upon the host.
(Photo Credit: Video by J. Adam Fenster (University of Rochester) and courtesy of the Werren Laboratory)
Mitochondrial messaging
"Because we have sequenced the genomes of three closely related species, we are able to study what changes have occurred during the divergence of these species from one another," says Werren. "One of the interesting findings is that DNA of mitochondria, a small organelle that 'powers' the cell in organisms as diverse as yeast and people, evolves very fast in Nasonia. Because of this, the genes of the cell's nucleus that encode proteins for the mitochondria must also evolve quickly to 'keep up."
It is these co-adapting gene sets that appear to cause problems in hybrids when the species mate with each other. Gadau's ASU team is among the research groups delving into these mitochondrial-nuclear gene interactions. Since mitochondria are involved in a number of human diseases, as well as fertility and aging, the rapidly evolving mitochondria of Nasonia and coadapting nuclear genes could be useful research tools to investigate these processes.
"Mitochondrial diseases in humans which have their origin in the malfunction of this interaction are the most frequent genetic disorders in humans," Gadau notes. "What we learn in Nasonia might help us to understand how these diseases work and may lead to cures."
Another startling discovery is that Nasonia has been picking up and using genes from bacteria and Pox viruses (relatives of the human smallpox virus). "We don't yet know what these genes are doing in Nasonia," says Werren, "but the acquisition of genes from bacteria and viruses could be an important mechanism for evolutionary innovation in animals, and this is a striking potential example."
Study springboard
A series of companion papers are set to be released, in addition to the Science study. One, published today in Public Library of Science (PLoS) Genetics, reports the first identification of the DNA responsible for a quantitative trait gene in Nasonia, and heralds Nasonia joining the ranks of model genetic systems. Eight more publications, authored by the ASU investigators and their colleagues, will soon follow, to be published in Heredity, Insect Molecular Biology and PLoS.
"Emerging from these genome studies are a lot of opportunities for exploiting Nasonia in topics ranging from pest control to medicine, genetics, and evolution," says Werren.
Here are the Nasonia Genome Working Group members from Arizona State University team (left to right): Florian Wolschin, Juergen Gadau, Stephen Pratt and Josh Gibson from the Social Insect Research Group in the School of Life Sciences.
(Photo Credit: Zachary Shaffer)
Werren and colleague Christopher Desjardins hold vials containing the Nasonia parasitoid wasps and the Sarcophaga flesh flies that they sting and kill. The wasps are very small (about the size of the tip of a pen).
(Photo Credit: Photo by Adam Fenster (University of Rochester) and provided courtesy of the Werren Laboratory.)
Source: Arizona State University