Double-stranded RNA interference shows that Engrailed controls the synaptic specificity of identified sensory neurons

The transcription factor Engrailed (En) controls the topography of axonal p rojections by regulating the expression of cell-adhesion molecules [1-4] bu t it is not known whether it also controls the choice of individual synapti c target cells. In the cereal sensory system of the larval cockroach (Perip laneta americana), small numbers of identified wind-sensitive sensory neuro ns form highly specific synaptic connections with 14 identified giant inter neurons [5,6], and target-cell choice is independent of the pattern of axon al projections [6] En is a putative positional determinant in the array of cereal sensory neurons [7]. In the present study, double-stranded RNA (dsRN A) interference [8] was used to abolish En expression. This treatment chang ed the axonal arborisation and synaptic outputs of an identified En-positiv e sensory neuron so that it came to resemble a nearby En-negative cell, whi ch was itself unaffected. We thus demonstrate directly that En controls syn aptic choice, as well as axon projections.