The olfactory system is crucial for animals in tasks such as foraging, mate selection, and predator avoidance due to its ability to detect and distinguish a vast array of environmental chemicals. Mice detect these chemicals via olfactory receptor (OR) proteins, which are uniquely expressed by olfactory sensory neurons (OSNs); each OSN expresses only one OR type. OSNs with the same OR converge their axons to a specific location in the olfactory bulb (OB), forming a structure known as a glomerulus. This precise organization ensures a consistent, spatially invariant pattern of glomerular activation for each odorant, playing a likely role in the brain's decoding of odor identities. Nevertheless, the exact locations of most glomeruli are unknown, and the mechanisms that create consistent glomerular maps across different animals are not fully understood. In this study, we leveraged spatial transcriptomics and machine learning to map the majority of glomerular positions within the mouse OB. Furthermore, single-cell RNA sequencing revealed distinct transcriptional profiles for each OSN type, characterized not only by their OR gene but also by a unique set of axon guidance genes. These profiles can predict the eventual location of each OSN's glomerulus within the olfactory bulb. We also identified a correlation between the spatial distribution of glomeruli and the characteristics of their corresponding ORs, suggesting a chemotopic arrangement in the mouse olfactory system.

Additionally, we probed the complexity of the OB by creating a spatially resolved cell atlas through spatial single-cell transcriptomics, revealing the identity and distribution of neuron subtypes that contribute to odor perception.