The common shrew undergoes an extraordinary seasonal transformation: its brain shrinks by up to 30% each winter, only to fully regenerate when warmer weather returns. This remarkable ability, known as Dehnel’s phenomenon, isn’t unique to shrews – moles, weasels, and stoats share the trait – but understanding how they do it could offer insights into preventing or even reversing brain degeneration in humans.
Evolutionary Origins and Genetic Drivers
Researchers led by William Thomas at Stony Brook University have mapped the common shrew’s genome, comparing it to other mammals exhibiting this seasonal brain plasticity. The team built on previous work examining gene expression during brain shrinkage and regrowth, identifying key genetic mechanisms at play.
The study revealed that genes responsible for brain cell creation are significantly upregulated in species that shrink and regrow their brains. The shrew, in particular, shows increased expression of VEGFA, a gene linked to blood-brain barrier permeability (potentially enhancing nutrient sensing). Other upregulated genes relate to DNA repair and longevity, suggesting a highly coordinated system.
How Does Brain Shrinkage Work?
The process isn’t about losing brain cells permanently. Instead, shrews appear to reduce brain volume by shedding water, supported by the activity of water-regulation genes. This reversible loss avoids the detrimental effects typically seen in neurodegenerative conditions. The researchers describe a “finely tuned system” that preserves neural integrity during extreme physiological changes.
Implications for Human Health
While caution is necessary when extrapolating animal findings to humans, the study identifies potential biomarkers and therapeutic targets for neurodegenerative diseases. As cell biologist Aurora Ruiz-Herrera points out, the genes involved in energy homeostasis and the blood-brain barrier could offer new avenues for research.
“The shrew’s ability to reversibly regulate brain shrinkage without lasting damage is a fascinating model for understanding how we might protect or restore neural function in humans.”
The shrew’s extraordinary adaptation highlights nature’s capacity for resilience and regeneration, opening up exciting possibilities for future medical breakthroughs.
