Advances in the Comprehensive Tree Shrew Brain Atlas

The tree shrew is a small mammal characterized by a short gestation period, a relatively short lifespan, and low maintenance costs. It exhibits a close genetic relationship with primates and humans. The tree shrew possesses an eight-layered neocortex, limited cortical gyrification, an expanded subventricular zone, and sensory, visual, and motor cortices that resemble those of primates, along with comparable neurotransmitter systems, cognitive potential, and neural flexibility. These features render it a promising animal model for neurological disease research. A comprehensive understanding of its brain morphology, neural projections, neural circuits, and neuronal diversity is crucial both in terms of elucidating normal brain function and in order to establish this species as a reliable model in investigations of the mechanisms underlying neural injury and neurodegenerative diseases. Currently, studies on tree shrew brain development remain limited. This review presents a comprehensive summary of two-dimensional (2D) and three-dimensional (3D) comparative anatomical studies based on brain region localization, histological section staining, and MRI-derived brain imaging data in the tree shrew. It also analyzes the developmental characteristics of neural progenitor cells in this species. Furthermore, the review compares brain atlases of mice, non-human primates (NHPs), humans, and tree shrews generated using single-cell sequencing and spatial transcriptomic technologies. Finally, it outlines future research directions that emphasize the importance of integrating morphology and functional neuroimaging data with multi-omics data to construct a multimodal, four-dimensional (4D) brain development atlas of the tree shrew.