Table 1. . Circular RNAs classification and function.

Type	Derivation	Location	Function	Examples	Ref.
EcircRNA	Exons	Mainly cytoplasm	MiRNA sponge; cis-regulation at post-transcriptional level; protein binding; encode functional proteins	Cdr1as; circ-ITCH; hsa_circ_0031288; circ-FBXW7	[10,26–28]
EIcircRNA	Exons and introns	Mainly nucleus	Cis-regulation of parent gene	circEIF3J; circPAIP2	[5]
CircRNA	Introns	Mainly nucleus	Cis-regulation of parent gene	circ-ankrd52; circ-mcm5; circ-sirt7	[6]

CircRNA: Circular intronic RNA; EcircRNA: Exonic RNA; EIcircRNA: exon–intron RNA.