Honeybee Castes Set by Maternal and Paternal Genes

By Blake Jackson

Researchers at Penn State have uncovered how genetic conflicts between mother-and father-inherited genes determine whether female honey bee larvae develop into reproductive queens or sterile worker bees.

Though genetically identical, queen larvae live longer and reproduce, while worker larvae support the colony without laying eggs.

“Imagine if your mother's genes and your father's genes were in constant disagreement about how you should develop that is essentially what genomic imprinting is, and we see that it happens across the tree of life: from honey bees to humans," said Sean Bresnahan, lead author and former Penn State doctoral candidate.

The team discovered this genetic “argument” occurs during a key developmental window-192 hours after the egg is laid-when the larva’s fate becomes irreversible.

To distinguish paternal and maternal genes, researchers used instrumental insemination to create specific crosses between queens and drones. By analyzing RNA from larvae, they tracked which genes were expressed from the mother or father. “We found patrigenes were expressed at higher levels in queen-destined larvae, and matrigenes were expressed at higher levels in worker-destined larvae,” Bresnahan said.

Further investigation showed that patrigenes and matrigenes often operate in the same cellular pathways but act in opposition, balancing gene expression. Previous studies ruled out DNA methylation-a common gene regulation method in mammals and plants-as the mechanism in bees.

Instead, the researchers found that histone modifications-chemical tags on proteins around which DNA is wrapped-regulate gene expression based on parent origin.

Using a method involving antibodies to isolate tagged histones, they revealed these histone changes control whether patrigenes or matrigenes are active. “We found that, in honey bees, parent-of-origin expression is regulated by histone modifications,” Bresnahan said.

This chromatin-based imprinting is common across many species and may represent an ancestral genetic toolkit. Understanding these mechanisms could improve selective breeding of bees for desirable traits, such as colony productivity and resilience.

Bresnahan now applies these insights to human health, studying how parent-of-origin gene expression in the placenta influences maternal-child outcomes. “The skills I developed studying parent-of-origin effects translate directly to my current studies of maternal-child health mediated through the placenta,” he said.

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