As winter approaches, the common shrew (Sorex araneus) undergoes a remarkable transformation, shrinking its brain by about 30 percent to save energy. Come spring, it’s pretty fascinating—this little creature manages to regenerate its brain, neurons and all.
Researchers have traced the evolutionary roots of this intriguing adaptation, identifying the genes that likely make it possible. This discovery not only sheds light on the shrew’s abilities but might also open new avenues for understanding and potentially treating human brain degeneration.
The adaptation is termed Dehnel’s phenomenon, named after the Polish zoologist August Dehnel. He was the first to document this fascinating ability of shrews, which helps them cope with seasonal energy scarcity.
While this phenomenon is rare, shrews aren’t alone in it; European moles (Talpa europaea), common weasels (Mustela nivalis), and stoats (Mustela erminea) also experience seasonal brain shrinkage. These small mammals have fast metabolisms and don’t hibernate, which probably explains why they resort to such drastic measures when food becomes scarce.
William Thomas, an ecologist at Stony Brook University, led a study aiming to map the entire genome of the common shrew and compared it to other species displaying Dehnel’s phenomenon to identify any genetic adaptations. This study builds on prior work that examined seasonal gene expression changes in two areas of the shrew’s brain, focusing on which DNA segments were more active during these significant physical changes.
By analyzing the data, researchers found that genes involved in creating brain cells were more active in various species demonstrating Dehnel’s phenomenon. Specifically, in shrews, they observed increased expression of VEGFA, a gene linked to keeping the blood-brain barrier permeable, possibly enhancing nutrient detection in the brain. Notably, the shrew’s genome also contained genes tied to DNA repair and longevity.
Genes related to water regulation were also found to be active, supporting the idea that shrews achieve this impressive brain volume reduction by losing water rather than brain cells.
The researchers suggest this adaptation points to “a finely tuned system” that allows common shrews to manage brain shrinkage without incurring the usual negative effects typically seen in neurodegeneration. It’s quite the balancing act, isn’t it?
Cell biologist Aurora Ruiz-Herrera from the Autonomous University of Barcelona notes that the involvement of genes related to energy balance and the blood-brain barrier may provide clues for identifying biomarkers and therapeutic targets concerning neurodegenerative diseases, although she emphasizes caution when applying these findings to humans.
This study appears in Molecular Biology and Evolution.
