library_construction_protocol: RNA was extracted using the PureLinkTM RNA Mini Kit (Life Technologies, Cat. No. 12183025). The RNA concentration was measured using the Epoch microplate spectrophotometer (BioTek). Prior to library generation for RNA-sequencing, the quality of the RNA was determined using a 2200 TapeStation and RNA screen tapes (Agilent Technologies). The mRNA libraries were generated by the Biopolymers Facility at Harvard Medical School using the KAPA mRNA HyperPrep kit (Roche) and included poly-A enrichment. The quality of these libraries was assessed by a 2200 TapeStation analyzer using D1000 screen tapes (Agilent Technologies), and q-PCR. mRNA libraries were generated by the Biopolymers Facility at Harvard Medical School using the KAPA mRNA HyperPrep kit (Roche) and included poly-A enrichment. The quality of these libraries was assessed by a 2200 TapeStation analyzer using D1000 screen tapes (Agilent Technologies), and q-PCR. Libraries were multiplexed into two pools and subsequently sequenced (paired-end, 50 cycles) using two NextSeq Mid Output flow cells per library (Illumina).