Neuronal expression of Retinoid-Related Orphan Receptor Gamma (RORγ) and revisiting its role in the Central Nervous System
Retinoid-related orphan receptor gamma (ROR{gamma}) 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 ROR{gamma}-expressing immune populations in embryonic brain development and central nervous system (CNS) function. Notably, ROR{gamma}-Cre-mediated deletion of the tuberous sclerosis complex (TSC) has been reported to cause spontaneous seizures and premature lethality, leading to the conclusion that ROR{gamma}-expressing immune cells directly regulate CNS physiology. Using multiple ROR{gamma}-based reporter mouse lines, we identified unexpected and widespread neuronal labeling throughout the forebrain and cerebellum. ROR{gamma}-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 ROR{gamma} expression in embryonic neurons. In contrast, a ROR{gamma}-GFP reporter showed no detectable ROR{gamma} expression in the postnatal brain, either at baseline or following pilocarpine-induced status epilepticus. These findings demonstrate that ROR{gamma} expression is not restricted to the immune lineage and reveal previously unrecognized developmental expression in the embryonic brain. Consequently, seizures observed following ROR{gamma}-Cre-mediated deletion of TSC1 are unlikely to arise from ROR{gamma}-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 ROR{gamma}-expressing immune cells based on ROR{gamma}-Cre-driven genetic models. SignificanceThis work identifies transient neuronal ROR{gamma} expression as a critical confounder in immune-targeted genetic studies and reveals a previously unrecognized embryonic expression of ROR{gamma} in neurons that may contribute to neurodevelopment. Our findings further raise the possibility that embryonic neurons represent unintended off-targets when deploying therapeutic strategies involving ROR{gamma} ligands.