Distinct Transcriptomes Define Rostral and Caudal Serotonin Neurons

Abstract

The molecular architecture of developing serotonin (5HT) neurons is poorly understood yet its determination is likely to be essential for elucidating functional heterogeneity of these cells and the contribution of serotonergic dysfunction to disease pathogenesis. Here, we describe the purification of postmitotic embryonic 5HT neurons by flow cytometry for whole genome microarray expression profiling of this unitary monoaminergic neuron type. Our studies identified significantly enriched expression of hundreds of unique genes in 5HT neurons thus providing an abundance of new serotonergic markers. Furthermore, we identified several hundred transcripts encoding homeodomain, axon guidance, cell adhesion, intracellular signaling, ion transport, and imprinted genes associated with various neurodevelopmental disorders that were differentially enriched in developing rostral and caudal 5HT neurons. These findings suggested a homeodomain code that distinguishes rostral and caudal 5HT neurons. Indeed, verification studies demonstrated that Hmx homeodomain and Hox gene expression defined an Hmx+ rostral subtype and Hox+ caudal subtype. Expression of engrailed genes in a subset of 5HT neurons in the rostral domain further distinguished two subtypes defined as Hmx+En+ and Hmx+En-. The differential enrichment of gene sets for different canonical pathways and gene ontology categories provided additional evidence for heterogeneity between rostral and caudal 5HT neurons. These findings demonstrate a deep transcriptome and biological pathway duality for neurons that give rise to the ascending and descending serotonergic subsystems. Our databases provide a rich, clinically relevant, resource for definition of 5HT neuron subtypes and elucidation of the genetic networks required for serotonergic function.

A Genetically Defined Morphologically and Functionally Unique Subset of 5-HT Neurons in the Mouse Raphe Nuclei

“…However, the link between a neurochemical identity and a unique projection pattern remains an unresolved question in mice: in a recent study exploring neuropeptide expression in the raphe, none of the 12 peptides explored, including CRF, was found to be colocalized with 5-HT (Fu et al, 2010). In the future, more systematic analyses of the neurochemical/genomic identity of 5-HT neurons (Wylie et al, 2010) will be needed to extract precise neurochemical taxonomy of the dorsal and median raphe 5-HT neurons.…”

Gata2 and Gata3 regulate the differentiation of serotonergic and glutamatergic neuron subtypes of the dorsal raphe

“…Transcriptome analyses have mapped the differences in gene expression between and within the rostral and caudal clusters (Wylie et al, 2010;Okaty et al, 2015). In addition, the dorsal and median raphe serotonergic neurons display heterogeneity in their serotonin autoreceptor (Htr1a) and serotonin transporter (Sert; also known as Slc6a4) expression, electrophysiological properties, axonal morphology and susceptibility to neurotoxins (Mamounas et al, 1991;Crawford et al, 2010;Calizo et al, 2011;Kiyasova et al, 2013).…”

Functional Impact of An ADHD-Associated DIRAS2 Promoter Polymorphism

“…Boston naming test in a GWAS of the ageing brain and Wylie et al (Wylie et al, 2010) found a 13-fold increase in Diras2 expression in serotonergic neurons from the caudal hindbrain of mouse embryos, which could be indicative of a role of Di-ras2 in the regulation of the caudal serotonergic system. The latter is intriguing, as serotonin has been found to be critically involved in brain development and to impact on ADHD-related traits such as aggression and impulsivity (Azmitia, 2001;Halperin et al, 1994;Lucki, 1998).…”