The retrotransposon long interspersed element 1 (LINE-1 or L1) is the only mobile DNA element capable of autonomous mobilisation in the human genome. Surprisingly, the brain has been identified as a hotspot for somatic L1 activity, with neurons and their precursor cells showing higher L1 activity than other lineages. However, the contributions of L1 to neuronal physiology and neurological disease are poorly understood. In this project, we are investigating L1 activity in substantia nigra (SN) dopaminergic (DA) neurons, a midbrain DA neuronal subset whose selective degeneration constitutes the main hallmark of Parkinson's disease (PD). To determine if L1 has a role in the vulnerability of DA neurons to neurodegeneration, we are investigating L1 expression and activity in DA neurons under normal and stress-induced conditions in vivo. We have found that L1 mRNA expression levels are higher in SN DA neurons when compared to ventral tegmental area (VTA) DA neurons in the adult mouse midbrain. These differences in L1 expression between SN and VTA neurons are already apparent in the embryonic brain, suggesting that higher L1 activity is a signature of SN DA neurons determined during neurodevelopment. In a neurotoxin-induced mouse model of PD, preliminary data show increased L1 mRNA levels in SN DA neurons from the neurotoxin-treated hemisphere when compared with the untreated contralateral hemisphere. To clarify if this increment in L1 expression is due to specific L1 genomic loci being released from repression associated with DNA methylation, ongoing experiments aim to specifically isolate and sequence DNA and RNA from physiological and stress-induced DA neurons, and identify specific unmethylated and transcriptionally active L1 loci in this neuronal population using long-read sequencing. Further work will be conducted to manipulate L1 activity in DA neurons and understand the significance of L1 expression in DA neurons and its involvement in DA neurodegeneration.