Cross species single-nucleus characterization of mammillary body.

As distinct nuclei within the posterior hypothalamus, the mammillary body (MB) is an essential component of the central nervous system and plays a critical role in memory processing in mammals. To date, however, its cellular heterogeneity across different species has yet to be systematically characterized. Here, leveraging single-nucleus transcriptomics of MB in mice, humans, and pigs, we delineated the cellular composition, transcriptional regulation and neuronal functional potentials in the MB. In mice, we identified five glutamatergic neuronal subtypes marked by Tachykinin 2 (Tac2) in lateral mammillary nucleus (LM), parvalbumin (PV), dopamine receptor D2 (Drd2), and neurotensin (Nts) in medial part of the medial mammillary nucleus, and nitric oxide synthase 1 (Nos1) in lateral part of the medial mammillary nucleus, and the spatial distribution of these markers was validated at RNA level. Additionally, we showed that Tac2 neurons possess functional potentials related to ionotropic signaling, synaptic transmission, and plasticity, and Nos1 neurons were inferred to the most cell interactions in the MB. Marker genes that showed partial discriminative power in human and pig data, together with heterogeneity comparisons within cell types between human and pig, revealed both potential cross-species heterogeneity and convergence in the MB. To sum up, our cross-species single-nucleus transcriptomics presents a cell-specific gene expression portrait of the mammalian MB across different species, which may have implications for neural signaling and disease vulnerability.