library_construction_protocol: Following euthanasia by intraperitoneal injection of pentobarbital (70 mg/kg), brains were collected and briefly rinsed in phosphate-buffered saline (PBS). Choroid plexuses (CPs) were extracted and conserved at -80C until RNA extraction. Total RNAs were extracted from CP tissue using a hybrid technique combining the TRIzol reagent protocol (Invitrogen, Thermo Fisher Scientific) and the Quick-RNA™ Miniprep Kit (Zymo Research) was used. CP tissues were first homogenized in 500µL of cold TRIzol with ceramic beads using a high-speed tissue homogenizer and then 500µL of chloroform:isoamyl alcohol 24:1 (Sigma Aldrich) were added. Samples were vortexed for 20 seconds and incubated for 2 min at room temperature. The samples were then centrifuged at 10,000g for 18 min at 4°C. The aqueous phase, that contains RNAs, was transferred in a new Eppendorf tube. An equal volume of 100% ethanol was added and the mixture was then loaded into a Zymo-Spin™ IIICG Column from the Quick-RNA™ Miniprep Kit. Further steps were conducted according to the manufacturer's protocol. RNA-seq libraries were prepared using NEBNext® single cell/low input RNA library preparation Kit (New England Biolabs). Library preparation was initiated with 50ng of total RNA.