title: Microbes & neurodevelopment--Absence of microbiota during early life increases activity-related transcriptional pathways in the amygdala.
abstract: The mammalian amygdala is a key emotional brain region for eliciting social behaviour, critically involved in anxiety and fear-related behaviours, and hence a focus of research on neurodevelopmental and stress-related disorders such as autism and anxiety. Recently, increasing evidence implicates host-microbe interactions in the aetiology of these conditions. Germ-free (GF) mice, devoid of any microbiota throughout organismal maturation, are a well-established tool to study the effects of absence of the microbiota on host physiology. A growing body of independently replicated findings confirm that GF animals demonstrate altered anxiety-related behaviour and impaired social behaviour. However, the underlying mechanisms of this interaction and the nature of the pathways involved are only insufficiently understood. To further elucidate the molecular underpinnings of microbe-brain interaction, we therefore exploited unbiased genome-wide transcriptional profiling to determine gene expression in the amygdala of GF and GF mice that have been colonised after weaning. Using RNA-sequencing and a comprehensive downstream analysis pipeline we studied the amygdala transcriptome and found significant differences at the levels of differential gene expression, exon usage and RNA-editing. Most surprisingly, we noticed upregulation of several immediate early response genes such as Fos, Fosb, Egr2 or Nr4a1 in association with increased CREB signalling in GF mice. In addition, we found differential expression and recoding of several genes implicated in brain physiology processes such as neurotransmission, neuronal plasticity, metabolism and morphology. In conclusion, our data suggest altered baseline neuronal activity in the amygdala of germ-free animals, which is established during early life and may have implications for understanding development and treatment of neurodevelopmental disorders.
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland; Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland.
authors.forename: Roman M
authors.initials: RM
authors.lastname: Stilling
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland; Department of Microbiology, University College Cork, Cork, Ireland.
authors.forename: Feargal J
authors.initials: FJ
authors.lastname: Ryan
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland; Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland.
authors.forename: Alan E
authors.initials: AE
authors.lastname: Hoban
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland.
authors.forename: Fergus
authors.initials: F
authors.lastname: Shanahan
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland; Department of Psychiatry and Neurobehavioural Sciences, University College Cork, Ireland.
authors.forename: Gerard
authors.initials: G
authors.lastname: Clarke
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland; Department of Microbiology, University College Cork, Cork, Ireland.
authors.forename: Marcus J
authors.initials: MJ
authors.lastname: Claesson
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland; Department of Psychiatry and Neurobehavioural Sciences, University College Cork, Ireland.
authors.forename: Timothy G
authors.initials: TG
authors.lastname: Dinan
authors.affiliation: APC Microbiome Institute, University College Cork, Cork, Ireland; Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland. Electronic address: j.cryan@ucc.ie.
authors.forename: John F
authors.initials: JF
authors.lastname: Cryan
mesh_terms: D000679:Amygdala / Q000254:growth & development / Q000378:metabolism* / Q000382:microbiology*; D000818:Animals; D020869:Gene Expression Profiling; D017781:Genes, Immediate-Early; D007398:Interpersonal Relations; D008297:Male; D051379:Mice; D064307:Microbiota / Q000502:physiology*; D009474:Neurons / Q000378:metabolism; D015398:Signal Transduction
keywords: Activity-induced; Differential gene expression; Gene regulation; Gut–brain axis; Hyper-excitability; Immediate early gene; MAP-kinase pathway; Microbiome; RNA editing; RNA-seq