Leucine-Rich Repeat Transmembrane Proteins Instruct Discrete Dendrite Targeting in an Olfactory Map

Olfactory systems utilize discrete neural pathways to process and integrate odorant information. In Drosophila, axons of first-order olfactory receptor neurons (ORNs) and dendrites of second-order projection neurons (PNs) form class-specific synaptic connections at ∼50 glomeruli. The mechanisms underlying PN dendrite targeting to distinct glomeruli in a 3-dimensional discrete neural map are unclear. Here we show that the leucine-rich repeat (LRR) transmembrane protein Capricious (Caps) is differentially expressed in different classes of PNs. Loss- and gain-of-function studies indicate that Caps instructs the segregation of Caps-positive and negative PN dendrites to discrete glomerular targets. Moreover, Caps does not mediate homophilic interactions and regulates PN dendrite targeting independent of pre-synaptic ORNs. The closely related protein Tartan plays a partially redundant function with Capricious. These LRR proteins are likely part of a combinatorial cell-surface code that instructs discrete olfactory map formation.