library_construction_protocol: For young, 3-day-old zebrafish heart samples, we sequenced N=2 with about n=500 hearts pooled. For the adult heart samples, we sequenced N=2 hearts at UI, 3 and 7 dpi with each n=4-6 pooled hearts. A negative binomial test was performed to determine significantly changed genes. Around 20,000 genes were found. RNA was isolated from young (3 days old), adult (~6 months old), and regenerating (3 and 7 dpi) zebrafish hearts as per manufacturers' protocol (TRIzol, ThermoFisher). The libraries were sequenced together on an Illumina HiSeq 4000 (Illumina Inc., San Diego, CA).