Characterization of dendritic spines in the Drosophila central nervous system

Dendritic spines are a characteristic feature of a number of neurons in the vertebrate nervous system and have been implicated in processes that include learning and memory. In spite of this, there has been no comprehensive analysis of the presence of spines in a classical genetic system, such as Drosophila, so far. Here, we demonstrate that a subset of processes along the dendrites of visual system interneurons in the adult fly central nervous system, called LPTCs, closely resemble vertebrate spines, based on a number of criteria. First, the morphology, size, and density of these processes are very similar to those of vertebrate spines. Second, they are enriched in actin and devoid of tubulin. Third, they are sites of synaptic connections based on confocal and electron microscopy. Importantly, they represent a preferential site of localization of an acetylcholine receptor subunit, suggesting that they are sites of excitatory synaptic input. Finally, their number is modulated by the level of the small GTPase dRac1. Our results provide a basis to dissect the genetics of dendritic spine formation and maintenance and the functional role of spines.