May be involved in the maintenance of active epigenetic status of target genes. May inhibit differentiation of embryonic stem (ES) cells into a primitive ectoderm lineage. Interacts with DPPA2 (PubMed:21896782). Interacts with PCGF1 (By similarity). Associated with transcriptionally active chromatin. Expressed in pluripotent embryonic cells, but not in differentiated somatic tissues. Expressed in 4-cell embryo, morula and blastocyst. At 7.5 dpc, detected in the epiblast. At 10.0 dpc, expressed in the primordial germ cells and at 12.0 dpc in the embryonic gonads. At 14.5 dpc, expression is restricted to testis. 6 days after birth, still detected in primitive type A spermatogonia. Expressed in undifferentiated embryonic stem cells, but expression decreases upon differentiation (at protein level). The mortality of mutant animals is increased at birth and most die within 3 days. The few surviving neonates show growth retardation, but they catch up with wild-type mice by 20 weeks of age.