Fruit-fly Sleep Linked to Immune Hemocytes Clearing Brain Lipids at the Blood-Brain Barrier

Overview

The Nature podcast presents two interconnected stories. The first investigates how sleep interacts with the immune system in fruit flies. Amita Sehgal explains that researchers asked whether immune cells influence daily sleep, not just under disease conditions. The second story surveys ancient DNA from the Low Countries, revealing regional deviations in Europe's peopling and the bell beaker contact that reshaped ancestry across the continent.

Drosophila sleep and hemocytes: a brain-cleaning role for immune cells

In fruit flies, circulating hemocytes (macrophage-like cells) migrate near the brain’s dorsal surface during sleep. They do not cross the blood-brain barrier but interact with the brain’s surface and nearby neurosecretory cells. The key discovery centers on the eater (ETE) protein on hemocytes, which drives phagocytosis and lipid uptake. Neurons and cortex glia generate lipids during sleep to protect against oxidative damage; these lipids are handed off to cortex glia and then to hemocytes for clearance. This “trash-clearing” function appears to support normal sleep, preserved memory, and longer lifespan. When the eater pathway is disrupted, lipid buildup increases oxidative stress, and flies exhibit impaired memory, reduced sleep, and shorter lifespans.

"We were interested in determining whether cells of the immune system are relevant for sleep." - Amita Sehgal, University of Pennsylvania and HHMI

Broader implications and future directions

The researchers propose that lipid transport and metabolism may be central to sleep-related brain maintenance, potentially conserved in other tissues and contexts, including neurodegeneration models where sleep loss could worsen pathology via lipid handling. Next steps include identifying the specific lipids involved and testing whether similar mechanisms operate beyond fruit flies, with implications for aging and brain health.

Ancient DNA in the Low Countries: a regional twist on Europe’s farmer expansion

The second half of the program surveys a genetic-time snapshot from 112 individuals dated between 10,000 and 3,700 years ago in the Netherlands, Belgium, and Luxembourg. The Low Countries show Western hunter-gatherer ancestry persisting longer than in many other parts of Europe, even as Anatolian farmer ancestry begins to spread. This regional pattern helps explain why this area later became influential in the broader European cultural and genetic landscape, including the bell beaker expansion that transformed Britain’s ancestry profile.

David Reich notes that the persistence of hunter-gatherer ancestry in this region lasted several millennia longer than in neighboring areas, a surprising and nuanced twist. Evelina Altener explains that the first farmers settled in landscapes that were less conducive to farming, suggesting a hybrid adoption of farming practices rather than a wholesale replacement. The mixing that did occur appears to have been primarily through women, with some male-driven transfer as well, indicating complex social dynamics behind genetic exchange.

"Anatolian farmer ancestry starts trickling in, but it really stays about 50% for several thousand years longer than elsewhere." - David Reich, Harvard University

"These first farmers, we see all over Europe, that they really settled on areas with a specific type of soil that is super fertile and really, really suitable for the type of agriculture that they performed." - Evelina Altener, Leiden University Medical Centre

Conclusions

The episode concludes that European prehistory was not a uniform story of farmers displacing hunter-gatherers. Instead, regional landscapes and social movements produced nuanced, region-specific genetic and cultural exchanges that shaped later European diversity and beaker ancestry. The interviewees emphasize that assumptions about historical trajectories should be tested against regional data to reveal the true complexity of human history.