Synaptic Proteome Divergence in the Prefrontal Cortex of Tame and Aggressive Red Foxes (Vulpes vulpes)

The biological mechanisms behind aggressive and affiliative behaviors are difficult to pinpoint. In the Farm-Fox Experiment, conventional foxes were selectively bred since 1959 in two different directions, one for tame and another for aggressive response to humans. The distinct differences in social behavior of tame, aggressive, and conventional populations are genetically based and the three populations live in conditions that control for factors that could impact social reactions, such as environment and social experiences. Genomic and transcriptomic studies of genetic differences among the fox populations have highlighted genes involved in synaptic processes in the prefrontal cortex. To investigate how the synaptic mechanisms differ between the three fox populations, synaptosomes were isolated from prefrontal and premotor cortex extracts of sixteen female foxes. Tandem mass tags with liquid chromatography tandem mass spectrometry (LC-MS) were used to identify and quantify the relative abundance of the proteins. The results were sorted into protein groups and compared between populations using a limma analysis to determine proteins with differential expression (DE). In the tame versus aggressive comparison, 174 protein groups were found to be DE, while only five were found in the conventional versus aggressive comparison. Most DE protein groups had lower fold expression in the aggressive population compared to tame and aggressive populations. ADGRB2 was found to be the most DE protein group, with 11-fold higher expression in aggressive foxes than in tame foxes. ADGRB2 was previously shown to affect depression-like behavior in mice and is involved in the vascular endothelial growth factor signaling pathway, that is known to influence neurogenesis. Enrichment analyses on the DE protein groups found gene ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways that were enriched in the tame versus aggressive comparison, including multiple, highly enriched terms involving ribosome and translation. Local translation at synapses plays an important role in synaptic plasticity and, as a result, can profoundly influence behavior. This study highlighted potential mechanisms that could underly the behavioral differences between tame and aggressive foxes.