Identification and characterization of a conservative W chromosome-linked circRNA in half-smooth tongue sole (Cynoglossus semilaevis) reveal its female-biased expression in immune organs

Circular RNAs (CircRNAs) represent an important class of noncoding RNAs to regulate biological and development processes. In the present study, the cDNA library was constructed and sequenced using Illumina Hiseq 2000 platform to identify circRNAs in half-smooth tongue sole. In the sequencing library, we validated a conservatively expressed circRNA with 363 nucleotides on W chromosome (termed as Wcirc5284614), which was spliced with the exon3, exon4, and exon5 of CNOT6L. Reverse transcription polymerase chain reaction indicated that Wcirc5284614 was mainly expressed in female's immune tissues, especially in the head kidney and spleen of the female. Comparative analysis showed that circRNA was highly conservative in vertebrate. These circRNA profiles provide new valuable resources for further study on the function and mechanism of circRNAs in half-smooth tongue sole, especially in immune organs.