Neuronal expression of Retinoid-Related Orphan Receptor Gamma (RORγ) and revisiting its role in the Central Nervous System.

Retinoid-related orphan receptor gamma (RORγ) is a lineage-defining transcription factor for T helper 17 (Th17) cells and has long been considered selectively expressed within the immune system. However, accumulating evidence has implicated Th17 cells and other RORγ-expressing immune populations in embryonic brain development and central nervous system (CNS) function. Notably, RORγ-Cre-mediated deletion of the tuberous sclerosis complex (TSC) has been reported to cause spontaneous seizures and premature lethality, leading to the conclusion that RORγ-expressing immune cells directly regulate CNS physiology. Using multiple RORγ-based reporter mouse lines, we identified unexpected and widespread neuronal labeling throughout the forebrain and cerebellum. RORγ-Cre:GFPf/- mice exhibited robust GFP expression in neurons despite the absence of detectable T cells in the brain. Neuronal recombination was evident prenatally and independently validated using the mT/mG reporter line, indicating transient RORγ expression in embryonic neurons. In contrast, a RORγ-GFP reporter showed no detectable RORγ expression in the postnatal brain, either at baseline or following pilocarpine-induced status epilepticus. These findings demonstrate that RORγ expression is not restricted to the immune lineage and reveal previously unrecognized developmental expression in the embryonic brain. Consequently, seizures observed following RORγ-Cre-mediated deletion of TSC1 are unlikely to arise from RORγ-expressing immune cell-dependent mechanisms but instead reflect direct neuronal loss of TSC1. Our results call for careful reinterpretation of prior studies attributing CNS phenotypes to RORγ-expressing immune cells based on RORγ-Cre-driven genetic models.