TY - JOUR T1 - Classifying <em>Drosophila</em> Olfactory Projection Neuron Subtypes by Single-cell RNA Sequencing JF - bioRxiv DO - 10.1101/145045 SP - 145045 AU - Hongjie Li AU - Felix Horns AU - Bing Wu AU - Qijing Xie AU - Jiefu Li AU - Tongchao Li AU - David Luginbuhl AU - Stephen R. Quake AU - Liqun Luo Y1 - 2017/01/01 UR - http://biorxiv.org/content/early/2017/06/03/145045.abstract N2 - How a neuronal cell type is defined and how this relates to its transcriptome are still open questions. The Drosophila olfactory projection neurons (PNs) are among the best-characterized neuronal types: Different PN classes target dendrites to distinct olfactory glomeruli and PNs of the same class exhibit indistinguishable anatomical and physiological properties. Using single-cell RNA-sequencing, we comprehensively characterized the transcriptomes of 40 PN classes and unequivocally identified transcriptomes for 6 classes. We found a new lineage-specific transcription factor that instructs PN dendrite targeting. Transcriptomes of closely-related PN classes exhibit the largest difference during circuit assembly, but become indistinguishable in adults, suggesting that neuronal subtype diversity peaks during development. Genes encoding transcription factors and cell-surface molecules are the most differentially expressed, indicating their central roles in specifying neuronal identity. Finally, we show that PNs use highly redundant combinatorial molecular codes to distinguish subtypes, enabling robust specification of cell identity and circuit assembly. ER -