Cross-Species BAC Transgenesis Reveals Long-Range Regulation Drives Variation in Brain Oxytocin Receptor Expression and Social Behaviors

Although oxytocin (OXT) exhibits a highly conserved neuroanatomical pattern among vertebrates, the distribution of OXT receptor (OXTR) in brain varies considerably across species and is associated with species-typical social behavior. To investigate the genomic basis of the phylogenetic plasticity in brain Oxtr expression and its social behavioral consequences, we generated transgenic mice carrying a bacteria artificial chromosome (BAC) harboring the entire prairie vole Oxtr locus and flanking intergenic regulatory regions. We established eight independent “volized” mouse lines expressing prairie vole Oxtr (pv Oxtr ). Strikingly, despite conserved Oxtr expression in mammary gland of all transgenic mouse lines, each line displayed a unique pattern of brain expression distinct from both mice and prairie voles. Together with topologically associating domain (TAD) structure analysis with mouse genome, our findings suggest that unlike Oxt , Oxtr expression patterns in brain, involve contributions of distal regulatory elements beyond the BAC insert. In contrast, Oxtr expression in peripheral tissues appears resistant to such distal influences. Moreover, the “volized” mouse lines with different brain Oxtr expression patterns showed differences in partner preference and maternal behaviors, providing direct functional evidence that variation in brain Oxtr expression can drive differences in social behaviors. We propose that brain Oxtr expression is transcriptionally sensitive to long-range interactions with distal genomic elements, rendering it more susceptible to diverse regulatory influences. This supports a model in which regulatory flexibility facilitates the evolutionary diversification of social behavior, while maintaining essential peripheral Oxtr expression. Highlights Unlike essential physiological phenomenon including feeding, sex, parturition and lactation, which are conserved across mammalian species, there is extraordinary diversity of social behaviors between and within species. Comparative studies across species suggest that variation in brain oxytocin receptor expression may mediate diversity in social behavior. Subtle variations in human oxytocin receptor sequence have been related to psychiatric phenotypes. Our studies suggest that the oxytocin receptor gene is hypersensitive to long-distance sequence variation, as revealed by differential expression patterns when the BAC transgene was inserted at different genomic sites, leading to variability in brain expression and social behavior. This research provides new insights into the evolvability of genes producing diversity in social behaviors, which allows efficient adaptation of animals to variable environment. Furthermore, our cross-species study demonstrates that diversity in brain OXTR expression patterns leads to variation in mouse social behaviors. The “volized” Oxtr mouse lines generated here present a valuable resource for further exploring OXTR expression regulation and neural circuits/networks mediating social behavioral variability.