library_construction_protocol: Chickens were euthanized by carbon dioxide inhalation followed by decapitation. The head was hemi-sectioned and the cochlea duct was isolated in cold DEPC-treated PBS. The basilar papilla was dissected from the cochlear duct and divided into three pieces: base, middle, and apex. Each piece was collected in a separate tubes containing Trizol reagent and quickly frozen to minimize RNA degradation. Total RNA from 12 chickens (24 cochleas) were used for 3 biological replicates for each region. RNA was isolated using Trizol reagent according to the manufacturere's instructions. 1μg of total RNA from each sample was reverse transcribed into cDNA and amplified using Illumina TruSeq RNA Sample Prep Kit v2. For library preparation, mRNA was enriched by oligo-dT to minimize DNA contamination. The PCR products for the cDNA library were purified and selected using the AMPure XP bead (Beckman Coulter). The DNA was quantified using Tapestation2100 – D1000 Screen Tape. The cDNA libraries were multiplexed and sequenced on the Illumina Hi-Seq 4000 platform, and 101-bp paired-end reads were generated.