Insights into honey bee sex gene could bring sweet success in breeding

October 26, 2006

ANN ARBOR, Mich.---What makes a bee a he or a she?

Three years ago, scientists pinpointed a gene called csd that determines gender in honey bees, and now a research team led by University of Michigan evolutionary biologist Jianzhi "George" Zhang has unraveled details of how the gene evolved. The new insights could prove useful in designing strategies for breeding honey bees, which are major pollinators of economically important crops---and notoriously tricky to breed.

The findings of Zhang and collaborators appear in a special issue of Genome Research devoted to the biology of the honey bee. The issue will be published online and in print Oct. 26, coinciding with the publication of the honey bee genome sequence in the journal Nature.

Scientists have long known that in bees---as well as wasps, ants, ticks, mites and some 20 percent of all animals---unfertilized eggs develop into males, while females typically result from fertilized eggs. But that's not the whole story, and the discovery in 2003 of csd (the complementary sex determination gene) helped fill in the blanks. The gene has many versions, or alleles. Males inherit a single copy of the gene; bees that inherit two copies, each a different version, become female. Bees that have the misfortune of inheriting two identical copies of csd develop into sterile males but are quickly eaten at the larval stage by female worker bees.

The system works fine in nature, where it prevents the colony from wasting precious energy and resources on abnormal males incapable of carrying out the all-important role of mating. But in bees raised for honey or for pollinating crops, the sex-determination system can cause problems. Beekeepers inbreed bees to select desirable traits, but inbreeding raises the odds of producing fertilized eggs with two copies of the same csd allele. If too many sterile males result, the colony may die out.

"If we know more details about how many alleles there are and what their frequencies are, bee breeders can design better strategies to avoid producing sterile males," Zhang said. "Our work aids in this effort by providing a direct tool to examine alleles from different populations."

In the research, Zhang and coworkers from U-M, Michigan State University and the University of Kansas sequenced csd genes from individuals in three closely related species of honey bee: the familiar backyard denizen Apis mellifera and the Asian honey bees Apis dorsata and Apis cerana. The group also sequenced six so-called neutral regions of the genome which, unlike genes, do not carry codes telling cells how to make proteins. Then, the researchers constructed gene genealogies---family trees for both the csd gene and the neutral regions.

Their results showed that csd is about seven times more variable than neutral regions of the honey bee genome. In addition, many csd variants are shared among the three species, evidence that the many different alleles have been preserved in these lineages for a very long time.

Such a pattern supports the idea that an evolutionary mechanism known as balancing selection has been at work. Evolution works through the process of natural selection, in which genetic mutations that offer some advantage are favored, and those that have harmful effects are weeded out. Typically, this results in one version of a gene becoming very common and other versions becoming rare or disappearing altogether. When balancing selection operates, however, natural selection favors a diverse mix of alleles, as seen with csd in honey bees.

The research also showed just how long the csd alleles have been around.

"We estimated the age of the alleles at about 14 million years," said Zhang. "We don't know for sure when the species formed, but it's thought to be about six to eight million years ago, so the alleles are even older than the species."
-end-
Zhang collaborated on the research with postdoctoral fellow Soochin Cho and undergraduate student Daniel Green of the University of Michigan, Zachary Huang of Michigan State University and Deborah Smith of the University of Kansas. The researchers received financial support from the U-M Office of the Vice President for Research, the National Institutes of Health and the University of Kansas General Research Fund.

For more information:

Jianzhi Zhang---http://www.lsa.umich.edu/eeb/people/jianzhi/

Genome Research---http://www.genome.org/

University of Michigan

Related Genome Articles from Brightsurf:

Genome evolution goes digital
Dr. Alan Herbert from InsideOutBio describes ground-breaking research in a paper published online by Royal Society Open Science.

Breakthrough in genome visualization
Kadir Dede and Dr. Enno Ohlebusch at Ulm University in Germany have devised a method for constructing pan-genome subgraphs at different granularities without having to wait hours and days on end for the software to process the entire genome.

Sturgeon genome sequenced
Sturgeons lived on earth already 300 million years ago and yet their external appearance seems to have undergone very little change.

A sea monster's genome
The giant squid is an elusive giant, but its secrets are about to be revealed.

Deciphering the walnut genome
New research could provide a major boost to the state's growing $1.6 billion walnut industry by making it easier to breed walnut trees better equipped to combat the soil-borne pathogens that now plague many of California's 4,800 growers.

Illuminating the genome
Development of a new molecular visualisation method, RNA-guided endonuclease -- in situ labelling (RGEN-ISL) for the CRISPR/Cas9-mediated labelling of genomic sequences in nuclei and chromosomes.

A genome under influence
References form the basis of our comprehension of the world: they enable us to measure the height of our children or the efficiency of a drug.

How a virus destabilizes the genome
New insights into how Kaposi's sarcoma-associated herpesvirus (KSHV) induces genome instability and promotes cell proliferation could lead to the development of novel antiviral therapies for KSHV-associated cancers, according to a study published Sept.

Better genome editing
Reich Group researchers develop a more efficient and precise method of in-cell genome editing.

Unlocking the genome
A team led by Prof. Stein Aerts (VIB-KU Leuven) uncovers how access to relevant DNA regions is orchestrated in epithelial cells.

Read More: Genome News and Genome Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.