Age, but Not Sex, Modulates Foxp3 Expression in the Rat Brain across Development

The interconnectivity between brain development and the immune system has become an area of interest for many neuroscientists. However, to date, a limited number of known immune mediators of the peripheral nervous system (PNS) have been found to influence the development of the central nervous system (CNS). FOXP3 is a well-established mediator of regulatory T-cells in the PNS. However, the expression pattern of FOXP3 in the CNS and the PNS throughout development is unknown. To fill this void, we have characterized, in several brain regions, the developmental profile of Foxp3 for both sexes using rats. We found different patterns of Foxp3 in the CNS and PNS. In the CNS, we found Foxp3 was ubiquitously expressed, with the levels of Foxp3 varying by brain region. We also found both Foxp3 mRNA and protein levels peak during embryonic development and then steadily decrease with a peak increase during adulthood. In adulthood, the protein but not mRNA increases to the equivalent levels found at the embryonic stage of life. In the PNS, Foxp3 protein levels were low embryonically and increased steadily over the life of the animal with maximal levels reached in adulthood. Patterns observed for both the PNS and CNS were similar in males and females across all developmental timepoints. Our novel findings have implications for understanding how the neural immune system impacts neurodevelopmental disorders such as autism and schizophrenia.