[Astrocyte research in complex brains]

During mammalian evolution, the cerebrum underwent remarkable changes: the brain surface expanded, and cortical folding increased. Neurons and astrocytes have increased in number and have acquired greater morphological complexity and functional diversity. Mice transplanted with human astrocytes show improved memory and learning abilities, suggesting that astrocyte functions were enhanced during evolution. Recently, human astrocytes have been shown to exhibit a larger cellular territory as well as morphological diversity. These findings suggest that evolutionary changes in astrocyte number, morphology, and function play an important role in the emergence of higher brain functions. However, research on astrocytes in enlarged, highly folded brains remains limited. To address this issue, we are investigating the molecular mechanisms that regulate astrocyte changes during evolution and their functional significance, using the ferret as a model system because of its well-developed brain structure. In this article, we provide an overview of our findings, focusing on the regulation of astrocyte number and its role in cortical folding.