Interaction between astrocytes and adult subventricular zone precursors stimulates neurogenesis

Neurogenesis continues in the mammalian subventricular zone (SVZ) throughou t life. However, the signaling and cell-cell interactions required for adul t SVZ neurogenesis are not known. In vivo, migratory neuroblasts (type A ce lls) and putative precursors (type C cells) are in intimate contact with as trocytes (type B cells). Type B cells also contact each other. We reconstit uted SVZ cell-cell interactions in a culture system free of serum or exogen ous growth factors, Culturing dissociated postnatal or adult SVZ cells on a strocyte monolayers-but not other substrates-supported extensive neurogenes is similar to that observed in vivo. SVZ precursors proliferated rapidly on astrocytes to form colonies containing up to 100 type A neuroblasts. By fr actionating the SVZ cell dissociates with differential adhesion to immobili zed polylysine, we show that neuronal colony-forming precursors were concen trated in a fraction enriched for type B and C cells. Pure type A cells cou ld migrate in chains but did not give rise to neuronal colonies. Because as trocyte-conditioned medium alone was not sufficient to support SVZ neurogen esis, direct cell-cell contact between astrocytes and SVZ neuronal precurso rs may be necessary for the production of type A cells.