Cross-species Single-cell Transcriptomics Reveals Neuronal Similarities and Heterogeneity in Amniote Pallium

The amniote pallium, a vital component of the forebrain, has undergone considerable evolutionary divergence across species and is critical for a variety of functions including sensation, memory and learning. The relationship between pallial subregions in different species remain elusive, particularly regarding the identification of homologous neurons and their similar or distinct signatures. Here, we utilized single-nucleus RNA sequencing to examine over 130,000 nuclei from macaque (Macaca fascicularis) neocortex, alongside datasets from human (Homo sapiens), mouse (Mus musculus), zebra finch(Taeniopygia guttata), turtle (Chrysemys picta bellii), and lizard (Pogona vitticeps), for a cross-species comparison. Our research revealed the transcriptomic conservation and species-specific distinctions within the amniote pallium, such as significant similarities among cell subtypes and species-preferred PVALB+ inhibitory neuron subtypes. Furthermore, we elucidated the correlations between pallial subregions and identified several transcription factor candidates, emphasizing their potential roles in regulating gene expression in mammalian pallial neurons as compared to their avian and reptilian counterparts, including RARB, DLX2, STAT6, NR3C1, and THRB. This investigation highlights conserved nature of inhibitory neurons, remarkable regional divergence of excitatory neurons, species-specific gene expression and regulation in amniote pallial neurons, providing valuable insights into the evolutionary trajectory of the amniote pallium.