We describe a novel zinc finger protein, ZID (zinc finger protein with interaction domain). At its amino terminus ZID contains a 120-amino-acid conserved motif present in a large family of proteins that includes both the otherwise unrelated zinc finger proteins, such as Ttk, GAGA, and ZFS, and a group of poxvirus proteins: We therefore refer to this domain as the POZ (poxvirus and zinc finger) domain. The POZ domains of ZID, Ttk, and GAGA act to inhibit the interaction of their associated finger regions with DNA. This inhibitory effect is not dependent on interactions with other proteins and does not appear dependent on specific interactions between the POZ domain and the finger region. The POZ domain acts as a specific protein-protein interaction domain: The POZ domains of ZID and Ttk can interact with themselves but not with each other, POZ domains from ZF5, or the viral protein SalF17R. However, the POZ domain of GAGA can interact efficiently with the POZ domain of Ttk. In transfection experiments, the ZID POZ domain inhibits DNA binding in NIH-3T3 cells and appears to localize the protein to discrete regions of the nucleus. We discuss the implications of multimerization for the function of POZ domain proteins.

Sex in mammals is determined in the foetal gonad by the presence or absence of the Y chromosome gene Sry, which controls whether bipotential precursor cells differentiate into testicular Sertoli cells or ovarian granulosa cells1. This pivotal decision in a single gonadal cell type ultimately controls sexual differentiation throughout the body. Sex determination can be viewed as a battle for primacy in the foetal gonad between a male regulatory gene network in which Sry activates Sox9 and a female network involving Wnt/β-catenin signaling (Supplemental Fig. 1)2. In females the primary sex-determining decision is not final: loss of the FOXL2 transcription factor in adult granulosa cells can reprogramme granulosa cells into Sertoli cells2. Here we show that sexual fate is also surprisingly labile in the testis: loss of the DMRT1 transcription factor3 in mouse Sertoli cells, even in adults, activates Foxl2 and reprogrammes Sertoli cells into granulosa cells. In this environment, theca cells form, oestrogen is produced, and germ cells appear feminized. Thus Dmrt1 is essential to maintain mammalian testis determination, and competing regulatory networks maintain gonadal sex long after the foetal choice between male and female. Dmrt1 and Foxl2 are conserved throughout vertebrates4,5 and Dmrt1-related sexual regulators are conserved throughout metazoans3. Antagonism between Dmrt1 and Foxl2 for control of gonadal sex may therefore extend beyond mammals. Reprogramming due to loss of Dmrt1 also may help explain the etiology of human syndromes linked to DMRT1, including disorders of sexual differentiation6 and testicular cancer7.

The only molecular similarity in sex determination found so far among phyla is between the Drosophila doublesex (dsx) and Caenorhabditis elegans mab-3 genes. dsx and mab-3 contain a zinc finger-like DNA-binding motif called the DM domain, perform several related regulatory functions, and are at least partially interchangeable in vivo. A DM domain gene called Dmrt1 has been implicated in male gonad development in a variety of vertebrates, on the basis of embryonic expression and chromosomal location. Such evidence is highly suggestive of a conserved role(s) for Dmrt1 in vertebrate sexual development, but there has been no functional analysis of this gene in any species. Here we show that murine Dmrt1 is essential for postnatal testis differentiation, with mutant phenotypes similar to those caused by human chromosome 9p deletions that remove the gene. As in the case of 9p deletions, Dmrt1 is dispensable for ovary development in the mouse. Thus, as in invertebrates, a DM domain gene regulates vertebrate male development.

The gene for acute myeloid leukemia-1 (AML-1) is one of the most frequently translocated genes in human cancer. It is targeted by t(8;21) and t(3;21) in AML and by t(12;21) in acute lymphocytic leukemia (39). AML-1 is also indirectly targeted by inv(16), which disrupts core binding factor beta, an AML-1-interacting protein. AML-1 binds the enhancer core motif (TGT/cGGT) and regulates a variety of viral and cellular genes in concert with other factors (31). t(8;21) is one of the most frequent translocations found in AML, comprising 10 to 15% of cases with discernible translocations (39). The t(8;21) fusion protein AML-1/ETO acts as a repressor of transcription in transient-transfection assays (10,31,32,43). When expressed during development, the t(8;21) fusion protein yielded the same phenotype as AML-1 deficiency (37, 45).Although eight-twenty-one (ETO; also known as MTG8 [myeloid tumor gene 8] [8,34]) was identified at the breakpoint of t(8;21), little is known about the normal function of the protein. ETO is the human homologue of the Drosophila Nervy protein (9), and it shares four homologous domains with the Nervy protein. These include a region with extensive homology to a Drosophila coactivator, transcription-activating factor 110 (TAF110), a predicted hydrophobic heptad repeat (HHR), a small domain with no other homology, termed the Nervy domain (27), and the MYND (myeloid-Nervy-DEAF-1 [12]) domain. The MYND domain is present in numerous human, murine, Caenorhabditis elegans, and Drosophila proteins and contains two putative zinc finger (ZF) motifs (9,12,31). ETO is expressed in hematopoietic cells and in the brain, but another closely related family member is ubiquitously expressed (19). A third closely related factor, MTG16, is fused to AML-1 by t(16;21) (20).AML-1 is a site-specific DNA binding protein that can both activate and repress transcription (2, 28, 36). The t(8;21) fusion protein AML-1/ETO contains the N-terminal 177 amino acids of AML-1, including the DNA binding domain, fused to nearly all of ETO (7,8,34). The fusion protein inhibits AML-1-dependent transactivation (10, 32). AML-1/ETO also repressed both basal transcription and Ets-1-dependent activation of the multidrug resistance 1 promoter (27). Similarly, AML-1/ETO inhibited both AML-1 and C/EBP␣-dependent transactivation of the neutrophil protein 3 (NP-3) promoter (44). AML-1/ETO-mediated repression is dependent on both the DNA binding domain of AML-1 and ETO sequences (24). AML-1/ETO acts at substoichiometric levels and thus does not compete with AML-1 for DNA binding sites within promoters, nor does it act to "squelch" transcription (24). Thus, we hypothesized that ETO recruits a corepressor or normally functions as a corepressor to inhibit transcription (30,31,33).Several corepressor proteins have been recently described that associate with histone deacetylases (HDACs) to repress transcription (3,5,13,17,38,40,42). The nuclear hormone corepressor N-CoR was identified through interactions with the thyroid hormone receptor and associa...

Sex-determining mechanisms are highly variable between phyla. Only one example has been found in which structurally and functionally related genes control sex determination in different phyla: the sexual regulators mab-3 of Caenorhabditis elegans and doublesex of Drosophila both encode proteins containing the DM domain, a novel DNA-binding motif. These two genes control similar aspects of sexual development, and the male isoform of DSX can substitute for MAB-3 in vivo, suggesting that the two proteins are functionally related. DM domain proteins may also play a role in sexual development of vertebrates. A human gene encoding a DM domain protein, DMRT1, is expressed only in the testis in adults and maps to distal 9p24.3, a short interval that is required for testis development. Earlier in development we find that murine Dmrt1 mRNA is expressed exclusively in the genital ridge of early XX and XY embryos. Thus Dmrt1 and Sry are the only regulatory genes known to be expressed exclusively in the mammalian genital ridge prior to sexual differentiation. Expression becomes XY-specific and restricted to the seminiferous tubules of the testis as gonadogenesis proceeds, and both Sertoli cells and germ cells express Dmrt1. Dmrt1 may also play a role in avian sexual development. In birds the heterogametic sex is female (ZW), and the homogametic sex is male (ZZ). Dmrt1 is Z-linked in the chicken. We find that chicken Dmrt1 is expressed in the genital ridge and Wolffian duct prior to sexual differentiation and is expressed at higher levels in ZZ than in ZW embryos. Based on sequence, map position, and expression patterns, we suggest that Dmrt1 is likely to play a role in vertebrate sexual development and therefore that DM domain genes may play a role in sexual development in a wide range of phyla.

The corepressor BCOR potentiates transcriptional repression by the proto-oncoprotein BCL6 and suppresses the transcriptional activity of a common mixed-lineage leukemia fusion partner, AF9. Mutations in human BCOR cause male lethal, X-linked oculofaciocardiodental syndrome. We identified a BCOR complex containing Polycomb group (PcG) and Skp-Cullin-F-box subcomplexes. The PcG proteins include RING1, RYBP, NSPC1, a Posterior Sex Combs homolog, and RNF2, an E3 ligase for the mono-ubiquitylation of H2A. BCOR complex components and mono-ubiquitylated H2A localize to BCL6 targets, indicating that the BCOR complex employs PcG proteins to expand the repertoire of enzymatic activities that can be recruited by BCL6. This also suggests that BCL6 can target PcG proteins to DNA. In addition, the BCOR complex contains components of a second ubiquitin E3 ligase, namely, SKP1 and FBXL10 (JHDM1B). We show that BCOR coimmunoprecipitates isoforms of FBXL10 which contain a JmjC domain that recently has been determined to have histone H3K36 demethylase activity. The recruitment of two distinct classes of E3 ubiquitin ligases and a histone demethylase by BCOR suggests that BCOR uses a unique combination of epigenetic modifications to direct gene silencing.The BCL6 gene encodes a sequence-specific transcriptional repressor (17, 23, 65) that is highly expressed in germinal center B cells. Germinal centers are maturation sites within lymphoid tissues where antigen-stimulated B cells proliferate, hypermutate their immunoglobulin (Ig) genes, undergo Ig class switch recombination, and give rise to progeny plasma cells that produce antibodies with high affinity for antigen (63). BCL6 plays a central role in this process, modulating the transcription of genes involved in lymphocyte activation, cell cycle arrest, apoptosis, and differentiation (5, 22, 49, 54, 59-61, 66, 75, 76). Deregulated expression of BCL6 in germinal center B cells plays an oncogenic role in non-Hodgkin's lymphomas (4, 16), presumably by inhibiting apoptosis and enhancing proliferation.BCL6 belongs to a subclass of zinc finger proteins with a POZ/BTB domain at the N terminus and Cys 2 -His 2 zinc fingers at the C terminus (3,70,87). BCL6 can interact with a variety of corepressors via several domains, including the POZ domain, a central repression domain, and the zinc fingers (19,24,25,29,36,45,82). The central domain of BCL6 recruits the corepressor MTA3 and its associated HDAC-containing chromatin remodeling complex (Mi-2/NuRD) (29). Importantly, MTA3 knockdown in B cells derepresses BCL6 targets that are upregulated upon differentiation into plasma cells (29). The POZ domain of BCL6 interacts with NCOR, SMRT, and BCOR in a mutually exclusive fashion (37). In BCL6-positive lymphoma cells, peptides that bind to the POZ domain of BCL6 and block interactions with NCOR, SMRT, and BCOR cause apoptosis and cell cycle arrest. The peptides do not, however, cause plasma cell differentiation (61). This suggests that the functions of BCL6 may be segregated among different corepr...

Summary The switch from mitosis to meiosis is a unique feature of germ cell development. In mammals, meiotic initiation requires retinoic acid (RA), which activates meiotic inducers including Stra8, but how the switch to meiosis is controlled in male germ cells (spermatogonia) remains poorly understood. Here we examine the role of the Doublesex-related transcription factor DMRT1 in adult spermatogenesis using conditional gene targeting in the mouse. Loss of Dmrt1 causes spermatogonia to precociously exit the spermatogonial program and enter meiosis. Dmrt1 therefore determines whether male germ cells undergo mitosis and spermatogonial differentiation or meiosis. Loss of Dmrt1 in spermatogonia also disrupts cyclical gene expression in Sertoli cells. DMRT1 acts in spermatogonia to restrict RA responsiveness, directly repress Stra8 transcription, and activate transcription of the spermatogonial differentiation factor Sohlh1, thereby preventing meiosis and promoting spermatogonial development. By coordinating spermatogonial development and mitotic amplification with meiosis, DMRT1 allows abundant, continuous production of sperm.

Lenz microphthalmia is inherited in an X-linked recessive pattern and comprises microphthalmia, mental retardation, and skeletal and other anomalies. Two loci associated with this syndrome, MAA (microphthalmia with associated anomalies) and MAA2, are situated respectively at Xq27-q28 (refs. 1,2) and Xp11.4-p21.2 (ref. 3). We identified a substitution, nt 254C→T; P85L, in BCOR (encoding BCL-6-interacting corepressor, BCOR 4 ) in affected males from the family with Lenz syndrome previously used to identify the MAA2 locus 3 . Oculofaciocardiodental syndrome (OFCD; OMIM 300166) is inherited in an X-linked dominant pattern with presumed male lethality and comprises microphthalmia, congenital cataracts, radiculomegaly, and cardiac and digital abnormalities. Given their phenotypic overlap, we proposed that OFCD and MAA2-associated Lenz microphthalmia were allelic, and we found different frameshift, deletion and nonsense mutations in BCOR in seven families affected with OFCD. Like wild-type BCOR, BCOR P85L and an OFCDmutant form of BCOR can interact with BCL-6 and efficiently repress transcription. This indicates that these syndromes are likely to result from defects in alternative functions of BCOR, such as interactions with transcriptional partners other than BCL-6. We cloned the zebrafish (Danio rerio) ortholog of BCOR and found that knock-down of this ortholog caused developmental perturbations of the eye, skeleton and central nervous system consistent with the human syndromes, confirming that BCOR is a key transcriptional regulator during early embryogenesis.We had previously localized MAA2 to a 10-Mb candidate region of Xp 3 . To identify the gene, we narrowed this region by excluding regions deleted in males with Xp deletions but without microphthalmia. Coriell cell line GM07947 is from a male with Duchenne muscular dystrophy, chronic granulomatous disease, McLeod phenotype and retinitis pigmentosa without microphthalmia 5 . Sequence-tagged site (STS) mapping confirmed previous data and oriented it to current genome maps. The deletion extended from DMD (telomeric) to between RPGR and OTC (centromeric; Fig. 1). The Coriell cell line GM10283 excluded two genes telomeric to DMD. This narrowed the critical region to ∼5 Mb, including 12 identified genes not known to be mutated in humans. One of these, DDX3, has an active Y homolog, and we therefore considered it unlikely to underlie a disorder with X-linked recessive inheritance. We sequenced the remaining 11 genes in members of the family in which MAA2 was originally identified. Ten of these genes showed no alterations, but we identified a missense change (nt 254C→T) in BCOR 4 that co-segregated with the disease phenotype (lod score of 2.46, above the threshold of 2.0 for X linkage 3 ). The corresponding residue of human BCOR, Pro85, is conserved in mouse, rat, chicken and pufferfish (Fig. 2), and we did not detect the nt 254C→T mutation among >450 control chromosomes. X-inactivation studies of peripheral blood leukocytes in two carriers of the mutation showed no ske...