UC San Diego

Mesial temporal lobe epilepsy (mTLE) is the most common form of temporal lobe epilepsy in adults, and is characterized by seizure activities and pathological changes in the limbic region, including the hippocampal formation. The dentate gyrus (DG) is thought to be a critical node in the hippocampus, with its unique properties, to prevent hippocampus from overexcitation. DG is also one of the only two places in mammalian brain that has new neurons born during adulthood. In both human and animal mTLE models, dramatic changes in migration and wiring of immature new-born dentate granule cells cause them to form pathological excitatory connections with neighboring DGCs. This has been considered as a major contributor to hippocampal hyperexcitability and epileptogenisis in mTLE. Studies have shown that grafting GABAergic inhibitory interneurons into epileptic mTLE mouse model can significantly reduce seizure activity. However, isolating safe, effective and ethical source of inhibitory precursor cells could be challenging for human patients. Hence, we hypothesize that using retrovirus in vivo to overexpress complement inhibitory transcription factors in aberrant DGCs can reprogram them into GABAergic inhibitory interneurons. In order to reach that goal, we first identified Sox2 transcription factor as a way to maintain or reverse the development of adult-born immature DGCs into a multipotent state. However, in the process, we have noticed substantial fluorescent signals in the hilus region, which should not contain any dividing cells. With multiple staining, we have discovered that the extensive fluorescent signals largely mossy cells that appeared to be infected with retrovirus. With further experiments, we found that red fluorescent gene mScarlet was the root cause. We later replaced mScarlet with another red fluorescent reporter gene dTomato and did not see any red fluorescent signal in the hilus region. Future work would involve making a retrovirus construct that contains Sox2 and alternative red fluorescent proteins such as dTomato as well as an inducible Sox2 construct that will give us temporal control. Moreover, we will investigate the possible combination of inhibitory GABAergic and proneural transcription factors Lhx6, Dlx5, Ascl2 and Ngn2, and co-inject with Sox2 construct.