This entry represents gametocyte-specific factor 1 (Gtsf1, Cue110), previously known as FAM112B, from vertebrates. Gtsf1 is expressed predominantly in male germ cells []where it is required for spermatogenesis and retrotransposon suppression []. It shares protein sequence similarity with Drosophila Gtsf1, not included in this entry. Gtsf1 is an essential component of the Piwi-mediated transcriptional silencing complex in Drosophila [], and there are indications suggesting its involvement in Piwi-mediated transcriptional repression in vertebrates too [].