library_construction_protocol: During necropsy a piece of fLX tissue was placed in 600 μL of RNAlater (MilliporeSigma: #R0901500ML) and stored at −80°C until analysis. For RNA extraction, 20–30 mg of tissue was weighed out, placed into a 2 mL tube with 600 μL of RLT buffer with 1% β–mercaptoethanol and a 5 mm stainless steel bead (Qiagen, Hilden, Germany: #69989), then dissociated using a Qiagen TissueLyser II (Qiagen) with the following cycle: two min dissociation at 1800 oscillations/min, one min rest, two min dissociation at 1800 oscillations/min. Dissociated tissues were centrifuged at 13,000 rpm for 10 min at room temperature and cleared supernatant was transferred to a new 1.5 mL eppendorf tube. RNA extractions were performed using a Qiagen RNeasy Plus Mini Kit (Qiagen: #74134), according to the manufacturer's instructions (Qiagen: #79256). RNA was eluted in 30 μL of RNase/DNase free water and quantified by Nanodrop. Total RNA was sent to BGI genomics (Hong Kong, China) for polyA-selected library preparation and sequencing (Pair-ends, 100 bp, 20M reads per sample).