Microglia in early brain development: A window of opportunity.

Microglia, brain-resident macrophages, are increasingly recognized for their roles in early brain development, particularly during the prenatal and early postnatal periods. These cells enter the brain during embryogenesis, long before other glial populations fully emerge, and actively shape neural circuits while responding to environmental cues. During this critical window, microglia exhibit a remarkable diversity of states, some resembling those seen in neurodegeneration, suggesting that microglia use shared pathways across life stages. Here, we review emerging insights into how microglial states regulate early neurodevelopment and how their functional diversity influences brain physiology under both normal and immune-challenged conditions. Understanding these state-function relationships not only advances our knowledge of neurodevelopment but also informs potential therapeutic strategies for neurodevelopmental and neurodegenerative disorders.