Meeting Abstract

P2-46    Single neuron transcriptomics and in-situ hybridization chain reaction reveal molecular fingerprints for neurons in the brain of the nudibranch Berghia stephanieae Ramirez, MD*; Bui, TN; Katz, PS; University of Massachusetts Amherst; Massachusetts Institute of Technology; University of Massachusetts Amherst mdramirez@umass.edu

Knowing neuron types is key for understanding neural circuits and brain function. Single cell transcriptomics allows large-scale identification of neurons, even in "non-traditional" animals. We made single neuron transcriptomes for ~2000 cells from the brain and rhinophore ganglia of the nudibranch, Berghia stephanieae. We used standard clustering and differential gene expression analyses to find gene markers for clusters of neurons with similar expression profiles. CCWamide, only recently found in Platynereis, is a top marker in one cluster. Although CCWamide has not been described in any mollusc, using in-situ hybridization chain reaction (HCR), we labeled a large number of neurons throughout the cerebral-pleural ganglia of Berghia. Temptin, known only as a reproductive pheromone in Aplysia, was a top marker for a cluster composed of neurons from the rhinophore ganglia (RG). The enzyme nitric oxide (NO) synthase was another top marker for RG neurons and is thought to be important for olfaction. Many top markers lack sequence similarity with genes in public databases (e.g. NCBI), emphasizing that there is much to learn from “non-model” animals. Surprisingly, we found orthologs of these genes in other gastropods, suggesting they may be molluscan novelties with unknown functions. Finally, we also labeled genes important for neuron function. Numerous neuropeptides were often co-expressed in different subsets of peptidergic neurons. Other neurons instead expressed choline acetyltransferase, the synthetic enzyme for acetylcholine. Transcription factors like sox2 and brn3 labeled unique sets of spatially segregated neurons, in patterns unlike those seen for neurotransmitters. These molecular fingerprints for cell types in the Berghia brain will enable us to create a brain-wide neuronal atlas for this new reference species.