An extracellular vesicle targeting ligand that binds to Arc proteins and facilitates Arc transport in vivo

Communication between distant cells can be mediated by extracellular vesicles (EVs) that deliver proteins and RNAs to recipient cells. Little is known about how EVs are targeted to specific cell types. Here we identify the Drosophila cell-surface protein Stranded at second (Sas) as a targeting ligand for EVs. Full-length Sas is present in EV preparations from transfected Drosophila Schneider 2 (S2 cells). Sas is a binding partner for the Ptp10D receptor tyrosine phosphatase, and Sas-bearing EVs preferentially target to cells expressing Ptp10D. We used co-immunoprecipitation and peptide binding to show that the cytoplasmic domain (ICD) of Sas binds to dArc1. dArc1 and mammalian Arc are related to retrotransposon Gag proteins. They form virus-like capsids which encapsulate Arc and other mRNAs and are transported between cells via EVs. The Sas ICD contains a motif required for dArc1 binding that is shared by the mammalian and Drosophila amyloid precursor protein (APP) orthologs, and the Sas and APP ICDs also bind to mammalian Arc. Sas facilitates delivery of dArc1 capsids bearing dArc1 mRNA into distant Ptp10D-expressing recipient cells in vivo . ### Competing Interest Statement Justin M. Reitsma is affiliated with AbbVie. The author has no other competing interests to declare. * aa : amino acid AD : Alzheimer’s disease Ap : apterous APP : amyloid precursor protein Co-IP : coimmunoprecipitation CSP : cell surface protein ECD : extracellular domain EM : electron microscopy EV : extracellular vesicle EVT : 345 aa region absent from Sas PA/PC isoform FISH : fluorescence in situ hybridization FN-III : Fibronectin Type III GOF : gain of function (overexpression) ICD : cytoplasmic domain immuno-EM : immuno-electron microscopy MVB : multivesicular body NMJ : neuromuscular junction NTA : nanoparticle tracking analysis ORF : open reading frame PTB : phosphotyrosine binding Ptp10D : Drosophila receptor tyrosine phosphatase gene located at 10D on the chromosome map RPTP : receptor tyrosine phosphatase Sas : Stranded at second SasFL : full-length Sas (PB/PD isoform) Sasshort : Sas isoform lacking EVT region (PA/PC isoform) SG : salivary gland TM : transmembrane UAS : upstream activation sequence UTR : untranslated region VFWC : von Willebrand factor C VNC : ventral nerve cord