2 protocols
nucleic acid sequencing protocol
Illumina HiSeq 1500
nucleic acid library construction protocol
10^4-10^5 cells from each macrophage subpopulation were sorted in 100-200 ul of Lysis/Binding Buffer (Life technologies), lysed for 5 min and frozen at -80°C. Cell lysates were thawed and mRNA was captured with 12 ul of Dynabeads oligo(dT) (Life technologies), and washed according to manufacture guidelines. Purified messenger RNA was eluted at 70°C with 10 ul of 10 mM Tris-Cl pH 7.5 and stored at -80°C cDNA was generated from 1ul of mRNA of each sample. cDNA quantity in each sample was evaluated by qPCR for Actin B gene, and then equivalent amounts of mRNA of each sample were taken for RNAseq library construction. Library construction was performed in a 96-well plate format. First, to open secondary RNA structures and allow annealing of the RT primer, the samples were incubated at 72˚C for 3 min and immediately transferred to 4˚C. Then, RT reaction mix (10 mM DTT, 4 mM dNTP, 2.5 U/µl Superscript III RT enzyme in 50 mM Tris-HCl (pH 8.3), 75 mM KCl, 3 mM MgCl2) was added into each well of the 96-well plate and the reaction was mixed. The 96-well plate was then spun down and moved into a cycler (Eppendorf) for the following incubation: 2 min at 42˚C, 50 min at 50˚C, 5 min at 85˚C. Indexed samples with equivalent amount of cDNA were pooled.  The pooled cDNA was converted to double-stranded DNA with a second strand synthesis kit (NEB) in a 20µl reaction, incubating for 2.5 h at 16˚C. The product was purified with 1.4x volumes of SPRI beads, eluted in 8 µl and in-vitro transcribed (with the beads) at 37˚C overnight for linear amplification using the T7 High Yield RNA polymerase IVT kit (NEB). Following IVT, the DNA template was removed with Turbo DNase I (Ambion) 15 min at 37˚C and the amplified RNA (aRNA) purified with 1.2x volumes of SPRI beads. Library preparation for high-throughput sequencing: The aRNA was chemically fragmented into short molecules (median size ~200 nucleotides) by incubating 3 min at 70˚C in Zn2+ RNA fragmentation solution (Ambion) and purified with two volumes of SPRI beads. The aRNA (5 µl) was preincubated 3 min at 70˚C with 1 µl of 100 µM ligation adapter; then, 14 µl of a mix containing 9.5% DMSO, 1 mM ATP, 20% PEG8000 and 1 U/µl T4 ligase in 50 mM Tris HCl pH7.5, 10 mM MgCl2 and 1mM DTT was added. The reaction was incubated at 22˚C for 2 h. The ligated product was reverse transcribed using Affinity Script RT enzyme (Agilent; reaction mix contains Affinity Script RT buffer, 10 mM DTT, 4 mM dNTP, 2.5 U/µl RT enzyme) and a primer complementary to the ligated adapter. The reaction was incubated for 2 min at 42˚C, 45 min at 50˚C and 5 min at 85˚C.  The cDNA was purified with 1.5x volumes of SPRI beads. The library was completed and amplified through a nested PCR reaction with 0.5 µM of P5_Rd1 and P7_Rd2 primers and PCR ready mix (Kapa Biosystems). The forward primer contains the Illumina P5-Read1 sequences and the reverse primer contains the P7-Read2 sequences. The amplified pooled library was purified with 0.7x volumes of SPRI beads to remove primer leftovers. Library concentration was measured with a Qubit fluorometer (Life Technologies) and mean molecule size was determined with a 2200 TapeStation instrument (Agilent). MARS-Seq libraries were sequenced using an Illumina HiSeq 1500. 3' RNA-seq for digital gene expression quantitation