Molecular characterization of projection neuron subtypes in the mouse olfactory bulb.

Sara Zeppilli,Andreas T Schaefer,Alexander Fleischmann,Tobias Ackels,Stefan Boeing,Nell Klimpert,Anton Crombach,Kimberly D Ritola,Robin Attey

doi:10.7554/elife.65445

Abstract

Projection neurons (PNs) in the mammalian olfactory bulb (OB) receive input from the nose and project to diverse cortical and subcortical areas. Morphological and physiological studies have highlighted functional heterogeneity, yet no molecular markers have been described that delineate PN subtypes. Here, we used viral injections into olfactory cortex and fluorescent nucleus sorting to enrich PNs for high-throughput single nucleus and bulk RNA deep sequencing. Transcriptome analysis and RNA in situ hybridization identified distinct mitral and tufted cell populations with characteristic transcription factor network topology, cell adhesion, and excitability-related gene expression. Finally, we describe a new computational approach for integrating bulk and snRNA-seq data and provide evidence that different mitral cell populations preferentially project to different target regions. Together, we have identified potential molecular and gene regulatory mechanisms underlying PN diversity and provide new molecular entry points into studying the diverse functional roles of mitral and tufted cell subtypes.

Highlights

The mammalian olfactory system is unique among sensory systems in that it bypasses the thalamus: olfactory receptor neurons (ORNs) in the nose project to the olfactory bulb (OB), a forebrain structure containing – in the mouse – approximately 500,000 neurons per hemisphere (Parrish-Aungst et al, 2007)
Single-nucleus RNA sequencing of olfactory bulb projection neurons distinguishes mitral and tufted cell types
Morphological differences between OB mitral and tufted cells have been described since the time of Cajal (The croonian lecture, 1894)

Summary

Introduction

The mammalian olfactory system is unique among sensory systems in that it bypasses the thalamus: olfactory receptor neurons (ORNs) in the nose project to the olfactory bulb (OB), a forebrain structure containing – in the mouse – approximately 500,000 neurons per hemisphere (Parrish-Aungst et al, 2007). Projection patterns might differ based on soma position along the dorsomedial–ventrolateral axis of the OB (Inokuchi et al, 2017; Chen et al, 2021) In parallel to this morphological diversity, numerous studies have described physiological heterogeneity both as a result of differential inputs from granule cells onto TCs and MCs (Christie et al, 2001; Ezeh et al, 1993; Geramita et al, 2016; Phillips et al, 2012) as well as intrinsic excitability and glomerular wiring (Burton and Urban, 2014; Gire et al, 2019). This work will provide a molecular entry point into disentangling the diversity of OB projection neurons and defining the functional roles of different MC/TC types

Results

C Module

Selection of TFs from each bulk RNA-Seq dataset

Discussion

Materials and methods