Microglial maturation across human and mouse as a reference for interpreting large-animal models of perinatal brain injury.

Microglia play dynamic roles in the developing brain and are central mediators of injury responses in perinatal brain injury. In mice, microglial gene regulatory and transcriptional programes reveal progression through early, pre-mature and mature stages. In contrast, microglial maturation has not been systematically characterised in the large-brained species most widely used to model human perinatal brain injury, particularly sheep and pigs. These large-animal models are indispensable as they share gyrencephaly, an expanded subplate, and clinically relevant physiology with the human infant brain. Here, we integrate established mouse and human frameworks of microglial maturation with a critical re-analysis of available sheep and pig datasets to assess whether rodent-derived insights into microglial development extend to large-animal models. Current sheep datasets lack sufficient resolution to infer maturation states, whereas pig data, although limited, reveal stage-dependent patterns consistent with late-gestation human development. This review also briefly considers emerging data on microglial development in non-human primates and the extent to which microglial gene expression programes appear conserved across species. Overall, microglial transitions are most dynamic during fetal and early postnatal life, underscoring the importance of developmentally aligned benchmarks for interpreting injury responses and informing microglia-targeted neuroprotective strategies. IMPACT: This article provides the first structured comparison of microglial maturation across human and mouse and uses these frameworks to benchmark large-brain animal models of perinatal brain injury, addressing a key translational gap. It shows that while existing sheep datasets lack sufficient resolution to define microglial maturation states, available pig data align closely with human late-gestation microglial development, supporting their use for developmental benchmarking. The work highlights that failure to account for microglial developmental stage risks misinterpretation of injury responses and underscores the need for developmentally aligned microglial markers in large-animal and non-human primate models to guide microglia-targeted neuroprotective strategies.