The Drosophila Homologue of the Amyloid Precursor Protein Is a Conserved Modulator of Wnt PCP Signaling

Abstract

Author SummaryWnt Planar Cell Polarity (PCP) signaling is a universal regulator of polarity in epithelial cells, but in neurons it regulates axon outgrowth, suggesting the existence of axonal modulators of Wnt-PCP activity. The Amyloid Precursor Proteins (APPs) are intensely investigated because of their link to Alzheimer's disease (AD). APP's in vivo function in the brain and the mechanisms underlying it remain unclear and controversial. In the present work we investigate the role of the Drosophila neuron-specific APP homologue, called APPL, during brain development. We find that APPL is required for the development of αβ neurons in the mushroom body, a structure critical for learning and memory. We find that APPL is a modulator of the Wnt-PCP pathway required for axonal outgrowth, but not for cell polarity. Molecularly, both human APP and fly APPL are found in membrane complexes with PCP receptors. Moreover, we show that APPL regulates PCP pathway activation through its downstream effector Abelson kinase (Abl), which modulates the phosphorylation of the Wnt adaptor protein Dishevelled (Dsh) and the subsequent activation of Wnt-PCP signaling. Taken together our data suggest that APPL is the first example of a neuron-specific modulator of the Wnt-PCP pathway.