WNTs are lipid-modified proteins that control multiple functions in development and disease via short- and long-range signaling. However, it is unclear how these hydrophobic molecules spread over long distances in the mammalian brain. Here we show that WNT5A is produced by the choroid plexus (ChP) of the developing hindbrain, but not the telencephalon, in both mouse and human. Since the ChP produces and secretes the cerebrospinal fluid (CSF), we examine the presence of WNT5A in the CSF and find that it is associated with lipoprotein particles rather than exosomes. Moreover, since the CSF flows along the apical surface of hindbrain progenitors not expressing Wnt5a, we examined whether deletion of Wnt5a in the ChP controls their function and find that cerebellar morphogenesis is impaired. Our study thus identifies the CSF as a route and lipoprotein particles as a vehicle for long-range transport of biologically active WNT in the central nervous system.We thank Nadia Wänn for maintenance of mice colonies; the members of Bryja and Arenas lab for their help and suggestions; Martin Häring for help with in situ analysis; Johnny Söderlund and Alessandra Nanni for their technical and secretarial assistance; and the CLICK imaging facility at Karolinska Institutet for technical support. We thank MEYS CR for support to the following core facilities: Proteomics (CIISB research infrastructure project LM2015043), cellular imaging at CEITEC institution at Masaryk University (LM2015062 Czech-BioImaging) Czech Centre for Phenogenomics (LM2015040), Higher quality and capacity of transgenic model breeding (by MEYS and ERDF, OP RDI CZ.1.05/2.1.00/19.0395), Czech Centre for Phenogenomics: developing towards translation research (by MEYS and ESIF, OP RDE CZ.02.1.01/0.0/0.0/16_013/0001789). The collaboration between Masaryk University and Karolinska Institutet (KI-MU program), was co-financed by the European Social Fund and the state budget of the Czech Republic (CZ.1.07/2.3.00/20.0180). Funding to the VB lab was obtained from Neuron Fund for Support of Science (23/2016), and Czech Science Foundation (GA17-16680S). Work in the EA lab was supported by the Swedish Research Council (VR projects: DBRM, 2011-3116, 2011-3318 and 2016-01526), Swedish Foundation for Strategic Research (SRL program and SLA SB16-0065), European Commission (NeuroStemcellRepair), Karolinska Institutet (SFO Strat Regen, Senior grant 2018), Hjärnfonden (FO2015:0202 and FO2017-0059) and Cancerfonden (CAN 2016/572). Research in the JCV lab was supported by Karolinska Institutet Foundations. KK was supported by Masaryk University (MUNI/E/0965/2016). DP and ZZ were supported by the CEITEC 2020 (LQ1601) project from MEYS CR
