Single cell RNA-sequencing of Drosophila melanogaster developing Wg region

The Drosophila visual system is a powerful model to study the development of neural circuits. Projection neurons that relay visual information from the lobula part of the optic lobe to the central brain (the lobula columnar neurons-LCNs), are thought to integrate different visual cues controlling specific behavioral outputs in response to these stimuli. There are ~20 classes of LCNs whose projections form highly specific, non-overlapping synaptic domains in the brain called optic glomeruli. Although functional investigations of several LCN circuits have been carried out, very little is known about their developmental origin and the neural stem cell lineages that generate the LCN subtypes.We performed single cell RNA-seq of FACS-sorted neurons labeled by a wg-Gal4 driver that is expressed in the tips of the outer proliferation center (tOPC) and ventral tips of the inner proliferation center (vtIPC), as well as in some neurons in the central brain. We dissociated brains at the late larval stage (wandering L3), when there is an active production of neurons, and obtained 65,851 single cell transcriptomes using the Chromium system (10X Genomics). We found that the tOPC and vtIPC is the putative origin of many LCNs. We show that LCNs originate from neural stem cells in four distinct regions in the fly brain that exhibit different modes of neurogenesis, including the ventral and dorsal tOPC, the vtIPC and the central brain. This convergence of similar neurons illustrates the complexity of generating neuronal diversity in the brain and likely reflects the evolutionary origin of each LCN subtype that detects a highly specific visual feature and mediates a behavior that might be specific to each species.