Single-cell RNA Sequencing Reveals Midbrain Dopamine Neuron Diversity Emerging During Mouse Brain Development

Midbrain dopamine (mDA) neurons constitute a heterogenous group of cells that have been intensely studied, not least because mDA neuron degeneration causes major symptoms in Parkinson’s disease. Diversity of mDA neurons has previously been well characterized anatomically but understanding diversity at a more complete molecular level has not previously been achieved. Here, we used single cell RNA sequencing of isolated mouse neurons expressing the transcription factor Pitx3, a marker for all types of mDA neurons. Analyses included cells isolated during development up until adulthood and was validated by histological characterization of newly identified markers. This characterization identified seven neuron subgroups divided in two major branches of developing Pitx3-expressing neurons. Five of these groups were dopaminergic, one glutamatergic and one GABAergic. Analyses also indicated evolutionary conservation of diversity in humans. This comprehensive molecular characterization will provide a molecular framework for further studies of the developing and mature mDA neuron subgroups in the mammalian brain. Sequencing libraries were prepared from FACS sorted individual neurons with the Smart-Seq2 protocol (Picelli et al. Nature Methods 2013)