Subdomain-Mediated Axon-Axon Signaling and Chemoattraction Cooperate to Regulate Afferent Innervation of the Lateral Habenula

• Proteomics studies identify subdomain-specific molecular codes in the habenula and FR
• Pretarget reciprocal axon-axon signaling regulates subdomain-specific axon targeting
• LAMP mediates interactions between reciprocal habenular and dopaminergic axons
• Subnucleus-specific Netrin-1 regulates axon target entry into the lateral habenula

SummaryA dominant feature of neural circuitry is the organization of neuronal projections and synapses into specific brain nuclei or laminae. Lamina-specific connectivity is controlled by the selective expression of extracellular guidance and adhesion molecules in the target field. However, how (sub)nucleus-specific connections are established and whether axon-derived cues contribute to subdomain targeting are largely unknown. Here, we demonstrate that the lateral subnucleus of the habenula (lHb) determines its own afferent innervation by sending out efferent projections that express the cell adhesion molecule LAMP to reciprocally collect and guide dopaminergic afferents to the lHb—a phenomenon we term subdomain-mediated axon-axon signaling. This process of reciprocal axon-axon interactions cooperates with lHb-specific chemoattraction mediated by Netrin-1, which controls axon target entry, to ensure specific innervation of the lHb. We propose that cooperation between pretarget reciprocal axon-axon signaling and subdomain-restricted instructive cues provides a highly precise and general mechanism to establish subdomain-specific neural circuitry.Video Abstract To view the video inline, enable JavaScript on your browser. However, you can download and view the video by clicking on the icon belowHelp with MP4 filesOptionsDownload video (67437 K)