Last modified: Thursday, January 14, 2010
Wasp genomes are sequenced, revealing surprises
FOR IMMEDIATE RELEASE
Jan. 14, 2010
BLOOMINGTON, Ind. -- A consortium of more than 100 scientists has completed an analysis of the DNA sequence of three parasitic wasp species, and the project has turned up a few surprises in the process. The genome project, described in this week's issue of Science, was led by University of Rochester and Baylor College of Medicine scientists, with Indiana University Bloomington biologists providing key genetic findings.
Photo by Michael Clark, courtesy of the Werren Laboratory
A Nasonia female is stinging a fly pupal host, injecting venom and laying her eggs within it. The offspring will emerge approximately two weeks later.
"We've gained a better appreciation for the diversity of genes that are found among the insects," said evolutionary biologist John Colbourne, who led IU's contribution. "There are likely 5 to 10 million species of insects and crustaceans on the globe that altogether show a staggering variety of methods to survive and reproduce. This project completes the initial description of the ninth distinct group of insects, and we find yet more novel features of the genome. Some can be matched to unique biological attributes."
Colbourne is the genomics director for IU's Center for Genomics and Bioinformatics.
The three wasp species are all members of the genus Nasonia -- vitripennis, giraulti, longicornis. And all three wasps sting and lay eggs within the larvae of agricultural pests as a food source for the wasps' young.
While digesting the vast information produced by the project (about 250 million base pairs per species, and tens of thousands of gene variants and proteins), consortium scientists found that the majority of Nasonia's genes are shared with humans and other animals, while one of every five genes belong to insects alone, and roughly two of every 100 genes are singularly shared between wasps and their close cousins, the honeybee. Evidence is found for many instances of "lateral gene transfer," in which the wasps' genomes absorbed genetic material from viruses, bacteria, and other Nasonia species. The scientists also identified a variety of important genes for the animal's way of life -- genes involved in the production of venoms, genes likely responsible for the origin of each species, and genes that regulate the action of other genes in modifying DNA by adding (or removing) methyl groups.
By investigating the gene and gene transcripts that ultimately code for proteins that define a wide variety of wasp cell types, the scientists have named 79 genes that could be involved in the production and organization of wasp venoms. The scientists recognized some of these genes as similar to those found in other venom-producing insects, but about half of the 79 candidate venom genes seemed unique to the wasps. The venoms of Nasonia wasps are known to have diverse effects on their targets -- from ataxia to paralysis to death.
The scientists examined the many subtle genetic differences between the three wasp species. They found distinct, correlated changes in nuclear and mitochondrial genes that seem to have occurred around the time of each species lineage's evolution, suggesting the coevolution of these nuclear and mitochondrial genes could have played a role in the origins of each species.
The wasps possess a full complement of methylation/de-methylation genes, which are used to modify nuclear chromosomes so that target genes are turned on or off. DNA methylation was once thought to be the exclusive property of mammals, but discoveries of methylation systems in wasps, honeybees, and other non-mammalian animals seem to suggest DNA methylation is likely to be far more common -- and older -- than once thought. Not all organisms possess the system. Fruit flies, for example, don't have it.
Nasonia wasps are used in agriculture to control insect pests. An understanding of the wasps' genetics could lead to tweaks in the wasps' DNA that improves their efficacy or specificity for particular pests (leaving other, beneficial insects alone). Nasonia giraulti and longicornis are native to North America, and vitripennis is found around the world.
Nasonia is the second hymenopteran insect genus to have its genome sequenced. Apis (mellifera, or honeybee), was the first. Like Apis, Nasonia females have two sets of chromosomes, while the males have only one. This split character in the insects' genetic identities can actually make studying them easier. By isolating active genes in males, scientists can more easily determine the purpose and qualities of those genes, in part because there is only one copy of those genes present -- no second copy can interfere with the expression of the first, nor mask its effects. Just as importantly, the genetic systems of Nasonia and Apis simplify the breeding of genetically pure or near-pure lines.
Nasonia differs from Apis in important ways. For one, DNA methylation in Apis is known to help determine bees' caste status. Bees are true social insects, whereas Nasonia wasps live largely solitary lives.
"This project's quality in the assembly of the data and in its interpretation really adds value to the larger pursuit of decoding the genetic basis for an insect's way of life," Colbourne said. "For every endeavor to understand why one species is special in any regard, the answer is found by comparing its traits and genome composition to those of other species. We have some ways still to go for knowing how social insects evolved from the solitary ancestors of bees and wasps, or how species like Nasonia developed a parasitic lifestyle. But by continuing to assemble leading biologists from many disciplines to cooperate at analyzing and comparing these huge sets of genome data, we get a better handle on the evolution of these species -- what makes them different and why."
Scientists from dozens of academic institutions and industry contributed to the genome project. It was funded primarily with grants from the National Human Genome Research Institute. Indiana University Bloomington scientists received support from the Indiana Center for Insect Genomics (Indiana 21st Century Research and Technology Fund), the National Institutes of Health, and the Indiana METACyt Initiative, funded in part through a major grant from the Lilly Endowment, Inc.
To speak with Colbourne, please contact David Bricker, University Communications, at 812-856-9035 or brickerd@indiana.edu.
