Cell Behaviors and Genetic Lineages of the Mesencephalon and Rhombomere 1

Brain structures derived from the mesencephalon (mes) and rhombomere 1 (r1) modulate distinct motor and sensory modalities. The precise origin and cellular behaviors underpinning the cytoarchitectural organization of the mes and r1, however, are unknown. Using a novel inducible genetic fate mapping approach in mouse, we determined the fate and lineage relationships of mes/r1 cells with fine temporal and spatial resolution. We demonstrate that the mes and r1 are neuromeres that along with the isthmic organizer are partitioned along the anterior-posterior axis by lineage restriction boundaries established sequentially between E8.5 and E9.5. Furthermore, a small group of cells originating from the most posterior mes exhibit anterior intracompartmental expansion and contribute throughout the inferior colliculus. Finally, we also uncovered transient and differential genetic lineages of ventral midbrain dopaminergic and ventral hindbrain serotonergic neuronal precursors with respect to Wnt1 and Gli1 expression.