DNA-binding protein which modulates activity of several transcription factors including RB1 (retinoblastoma-associated protein) and AR (androgen receptor) (PubMed:17043311, PubMed:23487765). May function as part of an mSin3A repressor complex (By similarity). Has no intrinsic transcriptional activity (PubMed:23487765). Plays a role in the regulation of epigenetic modifications at the PWS/AS imprinting center near the SNRPN promoter, where it might function as part of a complex with RB1 and ARID4B (PubMed:17043311). Involved in spermatogenesis, together with ARID4B, where it acts as a transcriptional coactivator for AR and enhances expression of genes required for sperm maturation (PubMed:23487765). Regulates expression of the tight junction protein CLDN3 in the testis, which is important for integrity of the blood-testis barrier (PubMed:23487765). Plays a role in myeloid homeostasis where it regulates the histone methylation state of bone marrow cells and expression of various genes involved in hematopoiesis (PubMed:18728284). May function as a leukemia suppressor (PubMed:18728284). Identified in mSin3A corepressor complexes together with SIN3A, SIN3B, RBBP4, RBBP7, SAP30, BRMS1, HDAC1 and HDAC2 (By similarity). Interacts with BRMS1 (By similarity). Interacts with RB1 (By similarity). Interacts with ARID4B (PubMed:17043311). Interacts with AR (PubMed:23487765). Expressed in Sertoli cells of the testis. The function of the Tudor-knot domain, also named chromodomain-like, is uncertain. One study suggests that it mediates binding to lysine-methylated histone tails, with strongest affinity for H4K20me3 and H3K36me3. However, another study failed to find any interaction between this domain and histone H4K20me3 peptide. Viable and fertile, although females have reduced fertility (PubMed:17043311, PubMed:18728284). At two months of age, animals show abnormal blood cell production accompanied by mild anemia, leukopenia and thrombocytopenia. Hematologic abnormalities become progressively more severe with age (PubMed:18728284). Monocytosis is observed at 5 months onwards, along with splenomegaly and hepatomegaly (PubMed:18728284). Approximately 12% of animals develop acute myeloid leukemia (AML) and/or myeloid sarcoma (PubMed:18728284). Mortality increases rapidly from age 6 months onwards, with no survival past 22 months (PubMed:18728284). Expansion of hematopoietic stem cell and common myeloid progenitor cell populations, and their downstream lineage, is observed in bone marrow and spleen; the effect is most significant in spleen (PubMed:18728284). Bone marrow cells show altered patterns of histone methylation and significantly increased levels of both H3K4me3 and H3K9me3 (PubMed:18728284). Expression of HOXB3, HOXB5, HOXB6, HOXB8 and PITX2 in bone marrow cells is reduced (PubMed:18728284). No effect on histone methylation at the PWS/AS imprinting center (PubMed:17043311). Double knockouts with ARID4B heterozygotes show a more severe hematologic phenotype with 83% of animals progressing to AML, and with earlier age of onset (PubMed:18728284). In bone marrow cells, expression of FOXP3 is significantly reduced (PubMed:18728284). Males show progressive reduction in fertility from 2 months of age onwards, with reduced testis size and variable defects in seminal vesicle formation (PubMed:23487765). Spermatogenesis is partially blocked from the meiois II stage onwards leading to reduced numbers of mature spermatozoa (PubMed:23487765). Expression in testis of CLDN3, an androgen receptor-regulated gene, is significantly reduced (PubMed:23487765). Expression of PTGDS is also reduced, whereas expression of INHA and EMB is moderately increased (PubMed:23487765). Maternal-specific trimethylation of H4K20 and H3K9 at the PWS/AS imprinting center is significantly reduced (PubMed:17043311).