HNRNPD and hepatocellular carcinoma: CircRNAs are pervasively expressed and can be conserved across species,[13, 14, 15, 33, 75] and several conserved circRNAs such as CDR1as in mammals and circBoule in metazoans have been investigated with animal models.[19, 20, 24] As for HCC or even cancers, almost all reported circRNAs are either not conserved or not subjected to examinations with genetically manipulated animal models.[5, 13] A previous report has revealed that the p21 mRNA stability is enhanced by circPCNX, which inhibits HNRNPD's binding to p21 mRNA in human HeLa cells,[50] although circPCNX is not conserved in mice.