GSM7253597: Pool112_RS2_Plate1-1-H22-D1; Mus musculus; OTHER
Approximately two weeks after the AAVretro injection, brains were extracted from the 56-63 day old INTACT mice, immediately submerged in ice-cold slicing buffer (2.5mM KCl, 0.5mM CaCl2, 7mM MgCl2, 1.25mM NaH2PO4, 110mM sucrose, 10mM glucose and 25mM NaHCO3) that was bubbled with carbogen, and sliced into 0.6 mm coronal sections starting from the frontal pole. From each AAVretro-injected brain, the slices were kept in the ice-cold dissection buffer from which selected brain regions (Supplementary Table 1) were manually dissected under a fluorescent dissecting microscope (Olympus SZX16), following the Allen Mouse Common Coordinate Framework (CCF), Reference Atlas, Version 3 (2015) (Extended Data Fig. 1). The dissected brain tissues were transferred to prelabeled microcentrifuge tubes, immediately frozen in dry ice, and subsequently stored at -80oC.   For each dissected brain region, samples from 2 males and 2 females were pooled separately as biological replicates for nuclei preparation. The 2-mL glass tissue dounce homogenizer and pestles (Sigma-Aldrich D8938-1SET) were pre-chilled on ice. Nuclei were prepared using a modified protocol as reported by Lacar et al., 201622. In summary, the frozen brain tissues were transferred to the dounce homogenizer with 1 mL ice-cold NIM buffer (0.25M sucrose, 25mM KCl, 5mM MgCl2, 10mM Tris-HCl (pH7.4), 1mM DTT (Sigma 646563), 10μl of protease inhibitor (Sigma P8340)), with 0.1% Triton X-100 and 5μM Hoechst 33342 (Invitrogen H3570), and gently homogenized on ice with the pestle 10-15 times. The homogenate was transferred to pre-chilled microcentrifuge tubes and centrifuged at 1000 rcf for 8 min at 4oC to pellet the nuclei. The pellet was resuspended in 1 mL ice-cold NIM buffer, and again centrifuged at 1000 rcf for 8 min at 4oC. The pellet was then resuspended in 450 μL of ice-cold NSB buffer (0.25M sucrose, 5mM MgCl2, 10mM Tris-HCl (pH7.4), 1mM DTT, 9ul of Protease inhibitor), and filtered through 40μM cell strainer. The filtered nuclei suspension was incubated on ice for at least 30 minutes with 50μl of nuclease-free BSA for at least 10 minutes, then incubated with GFP antibody, Alexa Fluor 488 (Invitrogen, A-21311) and anti-NeuN antibody (EMD Millipore MAB377) conjugated with Alexa Fluor 647 (Invitrogen A20173). GFP+/NeuN+ single nuclei were isolated using fluorescence-activated nuclei sorting (FANS) on a BD Influx sorter with 100μm nozzle, and sorted into 384-well plates preloaded with 2μl of digestion buffer for snmC-seq (20 mL digestion buffer consists of 10 mL M-digestion buffer (2×, Zymo D5021-9), 1 ml Proteinase K (20 mg, Zymo D3001-2-20), 9 mL water, and 10 µL unmethylated lambda DNA (100 pg/µL, Promega, D1521)). The collected plates were incubated at 50oC for 20 minutes then stored at -20 oC. The bisulfite conversion and library preparation were performed following the detailed snmC-seq2 protocol as previously described (Luo, C. et al., Nat. Commun. 2018, 9(1):3824.) or snmC-seq3 protocol described in (Liu, H. et al., Biorxiv. 2023:2023-04.). The libraries were sequenced on Illumina Novaseq 6000 using the S4 flow cell 2 x 150 bp mode.