Neural stem cells (NSCs) proliferate and generate new neurons in the adult brain. A carbohydrate-binding protein (lectin), Galectin-1, is expressed in the NSCs in the subependymal zone (SEZ) of the adult mouse brain. The infusion and knockout of Galectin-1 in the SEZ results in an increase and decrease, respectively, of NSCs and subsequently born progenitor cells. The molecular mechanism of this effect, however, has been unknown. Previous studies outside the brain suggest that Galectin-1 binds to a carbohydrate structure of β1 Integrin and modulates cell adhesion. Here, we studied the functional interaction between Galectin-1 and β1 Integrin in the adult mouse SEZ. β1 Integrin was purified from adult SEZ tissue by binding to a Galectin-1 affinity column, and this binding depended on Galectin-1's carbohydrate-binding activity. In adult brain sections, Galectin-1-binding activity was detected on β1 Integrin-expressing cells in the SEZ. Furthermore, in the adult SEZ, the simultaneous infusion of a β1 Integrin-neutralizing antibody with Galectin-1 protein reversed the increasing effect of Galectin-1 on the number of adult neural progenitor cells (NPCs). Finally, intact β1 Integrin was required for Galectin-1's function in NPC adhesion in vitro. These results suggest that the interaction between β1 Integrin and Galectin-1 plays an important role in regulating the number of adult NPCs through mechanisms including cell adhesion.
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