Small RNA Sequencing and Annotation
To annotate microRNA genes in the bowhead genome, we conducted deep
sequencing of two small RNA libraries prepared from muscle and kidney tissues
(Greenland samples). Total RNA was isolated using mirVana miRNA
Isolation Kit (Ambion). Small RNA in the 15-40 nucleotides range was gel purified
and small RNA libraries were prepared for next-generation sequencing
using the ScriptMiner Small RNA-Seq Library Preparation Kit (Epicenter). The
two libraries were sequenced on an Illumina Hi-Seq 2000 instrument to
generate single end sequences of 50 nucleotides. Primary data analysis
was done using the Illumina CASAVA Pipeline software v.1.8.2, and the
sequence reads were further processed by trimming for adapters and
filtering for low quality using Trimmomatic (Lohse et al., 2012). Identification
of conserved and novel candidate microRNA genes in the bowhead genome
was accomplished by applying the miRDeep2 algorithm (Friedla¨ nder et al.,
2008, 2012).