Tuberous Sclerosis 2 Gene Is Expressed at High Levels in Specific Types of Neurons in the Mouse Brain

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by mental retardation, epilepsy and hamartomatous growth in many tissues. The gene (TSC2) encoding a tumor suppressor protein whose mutations cause TSC, has been demonstrated to be expressed at high levels in the adult and developing brain, raising the question of whether or not the TSC2 gene product has unique roles in differentiation related to cytoskeletal interactions within the central nervous system, in addition to a tumor suppressor function. To determine the expression of TSC2 in functionally distinct neuron types of the mouse brain, we carried out in situ hybridization with digoxigeninlabeled riboprobes for the detection of TSC2 mRNA. High levels of the TSC2 gene were in neurons of the pyramidal and dentate granular layer in the hippocampus, cerebellar Purkinje cells, neurons of the piriform cortex, motor neurons in the medulla and interneurons in the striatum, while intermediate levels were in cortical neurons, striatal neurons, septal neurons, thalamic neurons and neurons in the substantia nigra compacta. Thus, the high expression of the TSC2 gene has restricted distribution in specific neuronal types which are characterized by well-developed dendrites and rich in usedependent long-term changes in synaptic efficacy. These results suggest that the function of the TSC2 gene product may be involved on a cellular basis in neuronal plasticity and relevant to mental retardation observed in TSC patients.