View Program - 63rd Annual Drosophila Research Conference

To respond to the world around them, adult flies rely on the input of a network of diverse sensory organs that are distributed across the body. The developmental genetic processes that drive divergence between different classes of sensory organs remain poorly resolved. Yet resolving these processes is critical to understanding how sensory systems function and evolve. Progress in this area has been limited by the difficulty of characterizing transcriptomic differences between sensory organs using bulk and single-cell RNA-seq (scRNA-seq): many sensory organs are rare, patchily distributed, difficult to dissociate into constituent cell-types, and embedded in undigestible cuticle. To overcome these difficulties, we developed a fine-scale dissection technique and dissociation protocol to target the pupal first tarsal segment of D. melanogaster males for scRNA-seq at multiple time points. This region is uncommonly enriched for sensory organs, containing large numbers of mechanosensory and chemosensory bristles, campaniform sensilla, the distal tibial chordotonal organ, and the sex comb, a male-specific evolutionary innovation present in a subset of Drosophilid species. Our datasets have allowed us to resolve distinct expression profiles for constituent bristle cells (sockets, shafts, sheaths, and neurons) separately for mechanosensory and chemosensory bristles and sex comb teeth. Furthermore, by subclustering neuronal populations, our data point to a combinatorial transcription factor code that specifies each of the four different chemosensory neuron classes (including male- and female-pheromone sensing neurons) and mechanosensory neurons. We verify this code using a combination of transgenic reporters and antibody staining. Finally, we recover a small population of neurons, enriched for the Pax family transcription factors eyg and toe, that mark campaniform sensilla. Using overexpression and RNAi experiments, we show that the expression of eyg and toe in campaniform sensilla suppresses bristle growth, giving rise to the characteristic dome morphology of these strain-detecting organs. Collectively, our work describes an array of developmental genetic differences that define the diverse sensory capabilities of the adult leg.

Charting the development of leg sensory organs at the single-cell level