| Summary: | BACE1 is the sole secretase for generating β-amyloid (Aβ) in vivo and is being actively pursued as a drug target for the treatment of Alzheimer’s disease. Transmembrane BACE1 exerts its biological activity by cleaving its membrane-bound cellular substrates. Here, we reveal that BACE1 directly regulates the level of membrane-anchored full-length Jagged1 (Jag1), a signaling molecule important for the control of neurogenesis and astrogenesis, via interaction with its cognate Notch receptor. We show that shedding of Jag1 is reduced in BACE1 null mice and upregulated Jag1 enhances Notch signaling via cell-cell juxtacrine interactions. Additional biochemical assays confirmed that overexpression of BACE1 enhanced cleavage of Jag1. Consequently, BACE1 null mice exhibit a significant increase in astrogenesis with a corresponding decrease in neurogenesis in their hippocampi during early development. Hence, BACE1 appears to function as a signaling protease that controls the balance of neurogenesis and astrogenesis via the Jag1-Notch pathway.
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