The Tuberous Sclerosis gene, Tsc1, represses parvalbumin+/fast-spiking properties in somatostatin-lineage cortical interneurons

Medial ganglionic eminence (MGE)-derived somatostatin (SST)+ and parvalbumin (PV)+ cortical interneurons (CINs), have characteristic molecular, anatomical and physiological properties. However, mechanisms regulating their diversity remain poorly understood. Here, we show that conditional loss of the Tuberous Sclerosis (TS) gene, Tsc1, which inhibits mammalian target of rapamycin (MTOR), causes a subset of SST+ CINs, to express PV and adopt fast-spiking (FS) properties, characteristic of PV+ CINs. These changes also occur when only one allele of Tsc1 is deleted, making these findings relevant to individuals with TS. Notably, treatment with rapamycin, which inhibits MTOR, reverses these changes in adult mice. These data reveal novel functions of MTOR signaling in regulating PV expression and FS properties, which may contribute to some neuropsychiatric symptoms observed in TS. Moreover, they suggest that CINs can exhibit properties intermediate between those classically associated with PV+ or SST+ CINs, which may be dynamically regulated by the MTOR signaling.