The minor caste, on the other hand, is smaller and more numerous. "They do most of the nursing within a colony, take care of the young, and they will also go out and collect most of the food," says Simola. "On average, 75 to 80 percent of the foraging activity is done by the minors." The minor also has a considerably shorter lifespan than the major caste, making the ant castes a good model for longevity studies as well as behavioral studies.
But how do such marked differences arise when both the major and the minor castes share the same genome? "For all intents and purposes, those two castes are identical when it comes to their gene sequences," notes senior author Berger, professor of Cell and Developmental Biology. "The two castes are a perfect situation to understand how epigenetics, how regulation 'above' genes, plays a role in establishing these dramatic differences in a whole organism."
To understand how caste differences arise, the team examined the role of modifications of histones (protein complexes around which DNA strands are wrapped in a cell's nucleus) throughout the Camponotus floridanus genome, producing the first genome-wide epigenetic maps of genome structure in a social insect. Histones can be altered by the addition of small chemical groups, which affect the expression of genes. Therefore, specific histone modifications can create dramatic differences between genetically similar individuals, such as the physical and behavioral differences between ant castes.
"These chemical modifications of histones alter how compact the genome is in a certain region," Simola explains. "Certain modifications allow DNA to open up more, and some of them to close DNA more. This, in turn, affects how genes get expressed, or turned on, to make proteins. These modifications establish specific features of different tissues within an indivi
|Contact: Karen Kreeger|
University of Pennsylvania School of Medicine