PIWIL1 and seminoma: However, both in seminomas and non-seminomas tumors, the LINE-1 DNA hypomethylation may be also due to epigenetic inactivation of PIWI-interacting RNAs (piRNAs), a class of small non-coding RNAs, predominantly expressed in the germ cell lineage and transcribed from genome regions containing transcribed transposable and other repetitive elements, and different Argonaute protein family members (PIWIL1, PIWIL2, PIWIL4) [81, 82].