Transcriptomic underpinnings of high and low mirror aggression zebrafish behaviours

Abstract

Background Aggression is an adaptive behaviour that animals use to protect offspring, defend themselves and obtain resources. Zebrafish, like many other animals, are not able to recognize themselves in the mirror and typically respond to their own reflection with aggression. However, mirror aggression is not an all-or-nothing phenomenon, with some individuals displaying high levels of aggression against their mirror image, while others show none at all. In the current work, we have investigated the genetic basis of mirror aggression by using a classic forward genetics approach - selective breeding for high and low mirror aggression zebrafish (HAZ and LAZ). Results We characterized AB wild-type zebrafish for their response to the mirror image. Both aggressive and non-aggressive fish were inbred over several generations. We found that HAZ were on average more aggressive than the corresponding LAZ across generations and that the most aggressive adult HAZ were less anxious than the least aggressive adult LAZ after prolonged selective breeding. RNAseq analysis of these fish revealed that hundreds of protein-encoding genes with important diverse biological functions such as arsenic metabolism (as3mt), cell migration (arl4ab), immune system activity (ptgr1), actin cytoskeletal remodelling (wdr1), corticogenesis (dgcr2), protein dephosphorylation (ublcp1), sialic acid metabolism (st6galnac3) and ketone body metabolism (aacs) were differentially expressed between HAZ and LAZ, suggesting a strong genetic contribution to this phenotype. DAVID pathway analysis showed that a number of diverse pathways are enriched in HAZ over LAZ including pathways related to immune function, oxidation-reduction processes and cell signalling. In addition, weighted gene co-expression network analysis (WGCNA) identified 12 modules of highly correlated genes that were significantly associated with aggression duration and/or experimental group. Conclusions The current study shows that selective breeding based of the mirror aggression phenotype induces strong, heritable changes in behaviour and gene expression within the brain of zebrafish suggesting a strong genetic basis for this behaviour. Our transcriptomic analysis of fish selectively bred for high and low levels of mirror aggression revealed specific transcriptomic signatures induced by selective breeding and mirror aggression and thus provides a large and novel resource of candidate genes for future study.

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“…Inflammation and immune functions were the most important pathways unveiled by the sPLS or sPLSDA analyses. Other transcriptomic studies conducted in mouse models of aggressiveness [ 60 ] or in zebrafish [ 61 ] but on brain tissues, led to the same conclusions. In mice prefrontal cortex of aggressive versus non-aggressive mice, the transcriptomic analysis uncovered NFKB and MAPK pathways which are known to be both involved in inflammation [ 60 ].…”

“…In mice prefrontal cortex of aggressive versus non-aggressive mice, the transcriptomic analysis uncovered NFKB and MAPK pathways which are known to be both involved in inflammation [ 60 ]. In brains of aggressive vs non-aggressive zebrafishes, RNAseq analysis also unveiled an important role of the inflammatory pathway such as MAPK, involving the expression of several pro-inflammatory cytokines, chemokine receptors and other genes related to immune system activation [ 61 ]. Changes in pro-inflammatory cytokine levels have been linked to aggressiveness in animals and humans [ 62 ].…”