A corset of adhesions during development establishes individual neural stem cell niches and controls adult behaviour

Neural stem cells (NSCs) reside in a defined cellular microenvironment, the niche, which supports the generation and integration of neuronal lineages. The mechanisms building a sophisticated niche structure around NSCs, and their functional relevance for neurogenesis are yet to be understood. In the Drosophila larval brain, the cortex glia (CG) encase individual NSC lineages, organizing the stem cell population and newborn neurons into a stereotypic structure. We first found that lineage information is dominant over stem cell fate. We then discovered that, in addition to timing, the balance between multiple adhesion complexes supports the individual encasing of NSC lineages. An intra-lineage adhesion through homophilic Neuroglian interactions provides strong binding between cells of a same lineage, while a weaker interaction through Neurexin-IV exists between CG to NSC lineages. Their loss leads to random, aberrant grouping of several NSC lineages together, and to altered axonal projection of newborn neurons. Further, we link the loss of these two adhesion complexes during development to locomotor hyperactivity in the resulting adults. Altogether, our findings identify a corset of adhesions building a neurogenic niche at the scale of individual stem cell and provide the proof-of-principle that mechanisms supporting niche formation during development define adult behaviour.