Expression patterns of SP1 and SP3 during mouse spermatogenesis: SP1 down-regulation correlates with two successive promoter changes and translationally compromised transcripts

Regulatory Pathways in Growth Plate Chondrocytes that Are Impacted by Matrix Vesicle microRNA Identified by Targeted RISC Pulldown and Sequencing of the Resulting Transcriptome

During endochondral bone formation, growth plate chondrocytes are differentially regulated by various factors and hormones. As the cellular phenotype changes, the composition of the extracellular matrix is altered, including the production and composition of matrix vesicles (MV) and their cargo of microRNA. The regulatory functions of these MV microRNA in the growth plate are still largely unknown. To address this question, we undertook a targeted bioinformatics approach. A subset of five MV microRNA was selected for analysis based on their specific enrichment in these extracellular vesicles compared to the parent cells (miR-1-3p, miR-22-3p, miR-30c-5p, miR-122-5p, and miR-133a-3p). Synthetic biotinylated versions of the microRNA were produced using locked nucleic acid (LNA) and were transfected into rat growth plate chondrocytes. The resulting LNA to mRNA complexes were pulled down and sequenced, and the transcriptomic data were used to run pathway analysis pipelines. Bone and musculoskeletal pathways were discovered to be regulated by the specific microRNA, notably those associated with transforming growth factor beta (TGFβ) and Wnt pathways, cell differentiation and proliferation, and regulation of vesicles and calcium transport. These results can help with understanding the maturation of the growth plate and the regulatory role of microRNA in MV.

Transcriptional regulation of the alternative sex hormone-binding globulin promoter by KLF4

In most mammals the major site of sex hormone-binding globulin (SHBG) synthesis is the liver wherefrom it is secreted into the bloodstream and is the primary determinant of sex steroid access to target tissues. The minor site of SHBG synthesis is the testis and in lower mammals testicular SHBG has long been known to be synthesized and secreted by Sertoli cells. However, human testicular SHBG is expressed in developing germ cells from an upstream alternative promoter (altP-SHBG). Transcripts arising from this region comprise an alternative first exon (1A) with the resultant protein confined to the acrosomal compartment of the mature spermatozoa. I have dissected the regulatory components of the alternative SHBG promoter and identified motifs that are required for optimal transcriptional activity from this region. Transcriptional activity is driven by two CACCC elements that appear to be functionally redundant. The transcription factor KLF4 interacts with promoter the region spanning these elements in vivo. Knockdown of Klf4 results in decreased altP-SHBG activity, while Klf4 overexpression relieves the effects of knockdown. Based on their shared patterns of expression in vivo, I conclude that KLF4 is a transcriptional regulator of SHBG in male germ cells.

1α,25-Dihydroxyvitamin D3 Regulates microRNA Packaging in Extracellular Matrix Vesicles and Their Release in the Matrix

Growth plate chondrocytes are regulated by numerous factors and hormones as they mature during endochondral bone formation, including transforming growth factor beta-1 (TGFb1), bone morphogenetic protein 2 (BMP2), insulin-like growth factor-1 (IFG1), parathyroid hormone and parathyroid hormone related peptide (PTH, PTHrP), and Indian hedgehog (IHH). Chondrocytes in the growth plate's growth zone (GC) produce and export matrix vesicles (MVs) under the regulation of 1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃]. 1α,25(OH)₂D₃ regulates MV enzyme composition genomically and 1α,25(OH)₂D₃ secreted by the cells acts on the MV membrane nongenomically, destabilizing it and releasing MV enzymes. This study examined the regulatory role 1α,25(OH)₂D₃ has over production and packaging of microRNA (miRNA) into MVs by GC cells and the release of miRNA by direct action on MVs. Costochondral cartilage GC cells were treated with 1α,25(OH)₂D₃ and the miRNA in the cells and MVs sequenced. We also treated MVs with 1α,25(OH)₂D₃ and determined if the miRNA was released. To assess whether MVs can act directly with chondrocytes and if this is regulated by 1α,25(OH)₂D₃, we stained MVs with a membrane dye and treated GC cells with them. 1α,25(OH)₂D₃ regulated production and packaging of a unique population of miRNA into MVs compared to the vehicle control population. 1α,25(OH)₂D₃ treatment of MVs did not release miRNA. Stained MVs were endocytosed by GC cells and this was increased with 1α,25(OH)₂D₃ treatment. This study adds new regulatory roles for 1α,25(OH)₂D₃ with respect to packaging and transport of MV miRNAs.

Dietary biotin supplementation increases proliferation pathways in mice testes without affecting serum follicle-stimulating hormone levels and stem cell factor expression

Supplements containing pharmacological concentrations of biotin are commercially available. The mechanisms by which biotin at pharmacological concentrations exerts its action have been the subject of multiple investigations, particularly for biotin's medicinal potential and wide use for cosmetic purposes. Several studies have reported that biotin supplementation increases cell proliferation; however, the mechanisms involved in this effect have not yet been characterized. In a previous study, we found that a biotin-supplemented diet increased spermatogonia proliferation. The present study was focused on investigating the molecular mechanisms involved in biotin-induced testis cell proliferation. Male BALB/cAnNHsd mice were fed a control or a biotin-supplemented diet (1.76 or 97.7 mg biotin/kg diet) for eight weeks. Compared with the control group, the biotin-supplemented mice presented augmented protein abundance of the c-kit-receptor and pERK1/2Tyr204 and pAKTSer473, the active forms of ERK/AKT proliferation signaling pathways. No changes were observed in the testis expression of the stem cell factor and in the serum levels of the follicle-stimulating hormone. Analysis of mRNA abundance found an increase in cyclins Ccnd3, Ccne1, Ccna2; Kinases Cdk4, Cdk2; and E2F; and Sp1 & Sp3 transcription factors. Decreased expression of cyclin-dependent kinase inhibitor 1a (p21) was observed but not of Cdkn2a inhibitor (p16). The results of the present study identifies, for the first time, the mechanisms associated with biotin supplementation-induced cell proliferation, which raises concerns about the effects of biotin on male reproductive health because of its capacity to cause hyperplasia, especially because this vitamin is available in large amounts without regulation.

Specific MicroRNAs Found in Extracellular Matrix Vesicles Regulate Proliferation and Differentiation in Growth Plate Chondrocytes

Matrix vesicles (MVs) are extracellular organelles produced by growth plate cartilage cells in a zone-specific manner. MVs are similar in size to exosomes, but they are tethered to the extracellular matrix (ECM) via integrins. Originally associated with matrix calcification, studies now show that they contain matrix processing enzymes and microRNA that are specific to their zone of maturation. MVs produced by costochondral cartilage resting zone (RC) chondrocytes are enriched in microRNA 503 whereas those produced by growth zone (GC) chondrocytes are enriched in microRNA 122. MVs are packaged by chondrocytes under hormonal and factor regulation and release of their contents into the ECM is also under hormonal control, suggesting that their microRNA might have a regulatory role in growth plate proliferation and maturation. To test this, we selected a subset of these enriched microRNAs and transfected synthetic mimics back into RC and GC cells. Transfecting growth plate chondrocytes with select microRNA produced a broad range of phenotypic responses indicating that MV-based microRNAs are involved in the regulation of these cells. Specifically, microRNA 122 drives both RC and GC cells toward a proliferative phenotype, stabilizes the matrix and inhibits differentiation whereas microRNA 22 exerts control over regulatory factor production. This study demonstrates the strong regulatory capability possessed by unique MV enriched microRNAs on growth plate chondrocytes and their potential for use as therapeutic agents.

Histone Post-Translational Modifications and CircRNAs in Mouse and Human Spermatozoa: Potential Epigenetic Marks to Assess Human Sperm Quality

Spermatozoa (SPZ) are motile cells, characterized by a cargo of epigenetic information including histone post-translational modifications (histone PTMs) and non-coding RNAs. Specific histone PTMs are present in developing germ cells, with a key role in spermatogenic events such as self-renewal and commitment of spermatogonia (SPG), meiotic recombination, nuclear condensation in spermatids (SPT). Nuclear condensation is related to chromatin remodeling events and requires a massive histone-to-protamine exchange. After this event a small percentage of chromatin is condensed by histones and SPZ contain nucleoprotamines and a small fraction of nucleohistone chromatin carrying a landascape of histone PTMs. Circular RNAs (circRNAs), a new class of non-coding RNAs, characterized by a nonlinear back-spliced junction, able to play as microRNA (miRNA) sponges, protein scaffolds and translation templates, have been recently characterized in both human and mouse SPZ. Since their abundance in eukaryote tissues, it is challenging to deepen their biological function, especially in the field of reproduction. Here we review the critical role of histone PTMs in male germ cells and the profile of circRNAs in mouse and human SPZ. Furthermore, we discuss their suggested role as novel epigenetic biomarkers to assess sperm quality and improve artificial insemination procedure.

Testicular biopsies microarray analysis reveals circRNAs are involved in the pathogenesis of non-obstructive azoospermia

Circular RNAs (circRNAs) have been reported to be involved in many diseases. But there is no report on circRNAs in non-obstructive azoospermia (NOA). The purpose of this paper is to explore the circular RNA expression profile and potential functions of circRNAs in NOA patients. We first preformed circRNA expression profiling analysis using a circRNA microarray in testicular samples from NOA and obstructive azoospermia (OA) patients. CircRNAs were validated by qRT-PCR. Bioinformatics analysis were used to construct the ceRNA network. GO and KEGG enrichment analysis were performed by using DAVID. Microarray analysis identified 82 differentially expressed circRNAs in NOA specimens. The differential expression of hsa_circRNA_402130, hsa_circRNA_072697, hsa_circRNA_030050, hsa_circRNA_100812 and hsa_circRNA_406168 was confirmed by qRT-PCR. Enrichment analysis revealed the association of hsa_circRNA_402130 and hsa_circRNA_072697 with multiple signaling pathways. The data indicated that circRNAs were significantly dysregulated in NOA specimens and might involve in the pathogenesis of NOA.

A truncated form of a transcription factor Mamo activates vasa in Drosophila embryos

Expression of the vasa gene is associated with germline establishment. Therefore, identification of vasa activator(s) should provide insights into germline development. However, the genes sufficient for vasa activation remain unknown. Previously, we showed that the BTB/POZ-Zn-finger protein Mamo is necessary for vasa expression in Drosophila. Here, we show that the truncated Mamo lacking the BTB/POZ domain (MamoAF) is a potent vasa activator. Overexpression of MamoAF was sufficient to induce vasa expression in both primordial germ cells and brain. Indeed, Mamo mRNA encoding a truncated Mamo isoform, which is similar to MamoAF, was predominantly expressed in primordial germ cells. The results of our genetic and biochemical studies showed that MamoAF, together with CBP, epigenetically activates vasa expression. Furthermore, MamoAF and the germline transcriptional activator OvoB exhibited synergy in activating vasa transcription. We propose that a Mamo-mediated network of epigenetic and transcriptional regulators activates vasa expression.

Aryl hydrocarbon receptor gene transitions (c.-742C>T; c.1661G>A) and idiopathic male infertility: a case-control study with in silico and meta-analysis

Aryl hydrocarbon receptor (AHR) is responsible for crucial events in male reproductive biology. Here, the association of the AHR transitions c.-742C>T and c.1661G>A with idiopathic male infertility was investigated in a case-control study, which is followed by a meta-analysis and a bioinformatic investigation. Blood and semen samples were obtained from a total of 135 idiopathic infertile men and 130 healthy controls. Participants were genotyped for the transitions using a PCR-RFLP method. A meta-analysis of five sets of data evaluated the association of c.1661G>A with male infertility, and using an in silico analysis, the possible molecular effects of the transitions predicted. Genotypes and alleles of AHR-c.-742C>T and c.1661G>A polymorphisms were not associated with the risk of male infertility significantly. However, the frequency of C/A haplotype was significantly associated with the increased risk of male infertility, and T/A haplotype was higher among controls significantly. Also, the frequencies of combined genotypes CT/GG, CT/GA and TT/GG were significantly associated with decreased risk of infertility. And, the meta-analysis showed that the AA versus GA/GG recessive model is associated with decreased risk of male infertility among the Iranian population. In silico analysis predicted that c.-742C>T does not alter the binding sites of the proposed transcription factors, but c.1661G>A poses a tolerable structural disturbance in AHR protein. In conclusion, these results showed that AHR c.-742C>T and c.1661G>A transitions separately could not be nominated as a risk or protective factor for male infertility. However, some combined models could affect infertility risk, especially among Iranian men.

RFX2 Is a Major Transcriptional Regulator of Spermiogenesis

Spermatogenesis consists broadly of three phases: proliferation of diploid germ cells, meiosis, and finally extensive differentiation of the haploid cells into effective delivery vehicles for the paternal genome. Despite detailed characterization of many haploid developmental steps leading to sperm, only fragmentary information exists on the control of gene expression underlying these processes. Here we report that the RFX2 transcription factor is a master regulator of genes required for the haploid phase. A targeted mutation of Rfx2 was created in mice. Rfx2^-/- mice are perfectly viable but show complete male sterility. Spermatogenesis appears to progress unperturbed through meiosis. However, haploid cells undergo a complete arrest in spermatid development just prior to spermatid elongation. Arrested cells show altered Golgi apparatus organization, leading to a deficit in the generation of a spreading acrosomal cap from proacrosomal vesicles. Arrested cells ultimately merge to form giant multinucleated cells released to the epididymis. Spermatids also completely fail to form the flagellar axoneme. RNA-Seq analysis and ChIP-Seq analysis identified 139 genes directly controlled by RFX2 during spermiogenesis. Gene ontology analysis revealed that genes required for cilium function are specifically enriched in down- and upregulated genes showing that RFX2 allows precise temporal expression of ciliary genes. Several genes required for cell adhesion and cytoskeleton remodeling are also downregulated. Comparison of RFX2-regulated genes with those controlled by other major transcriptional regulators of spermiogenesis showed that each controls independent gene sets. Altogether, these observations show that RFX2 plays a major and specific function in spermiogenesis.

Failure of spermatogenesis, which is presumed to often result from genetic defects, is a common cause of male sterility. Although numerous genes associated with defects in male spermatogenesis have been identified, numerous cases of genetic male infertility remain unelucidated. We report here that the transcription factor RFX2 is a master regulator of gene expression programs required for progression through the haploid phase of spermatogenesis. Male RFX2-deficient mice are completely sterile. Spermatogenesis progresses through meiosis, but haploid cells undergo a complete block in development just prior to spermatid elongation. Gene expression profiling and ChIP-Seq analysis revealed that RFX2 controls key pathways implicated in cilium/flagellum formation, as well as genes implicated in microtubule and vesicle associated transport. The set of genes activated by RFX2 in spermatids exhibits virtually no overlap with those controlled by other known transcriptional regulators of spermiogenesis, establishing RFX2 as an essential new player in this developmental process. RFX2-deficient mice should therefore represent a valuable new model for deciphering the regulatory networks that direct sperm formation, and thereby contribute to the identification of causes of human male infertility.

Sp1 and the 'hallmarks of cancer'

For many years, transcription factor Sp1 was viewed as a basal transcription factor and relegated to a role in the regulation of so-called housekeeping genes. Identification of Sp1's role in recruiting the general transcription machinery in the absence of a TATA box increased its importance in gene regulation, particularly in light of recent estimates that the majority of mammalian genes lack a TATA box. In this review, we briefly consider the history of Sp1, the founding member of the Sp family of transcription factors. We review the evidence suggesting that Sp1 is highly regulated by post-translational modifications that positively and negatively affect the activity of Sp1 on a wide array of genes. Sp1 is over-expressed in many cancers and is associated with poor prognosis. Targeting Sp1 in cancer treatment has been suggested; however, our review of the literature on the role of Sp1 in the regulation of genes that contribute to the 'hallmarks of cancer' illustrates the extreme complexity of Sp1 functions. Sp1 both activates and suppresses the expression of a number of essential oncogenes and tumor suppressors, as well as genes involved in essential cellular functions, including proliferation, differentiation, the DNA damage response, apoptosis, senescence and angiogenesis. Sp1 is also implicated in inflammation and genomic instability, as well as epigenetic silencing. Given the apparently opposing effects of Sp1, a more complete understanding of the function of Sp1 in cancer is required to validate its potential as a therapeutic target.

A conserved noncoding sequence can function as a spermatocyte-specific enhancer and a bidirectional promoter for a ubiquitously expressed gene and a testis-specific long noncoding RNA

Tissue-specific gene expression is tightly regulated by various elements such as promoters, enhancers, and long noncoding RNAs (lncRNAs). In the present study, we identified a conserved noncoding sequence (CNS1) as a novel enhancer for the spermatocyte-specific mouse testicular cell adhesion molecule 1 (Tcam1) gene. CNS1 was located 3.4kb upstream of the Tcam1 gene and associated with histone H3K4 mono-methylation in testicular germ cells. By the in vitro reporter gene assay, CNS1 could enhance Tcam1 promoter activity only in GC-2spd(ts) cells, which were derived from mouse spermatocytes. When we integrated the 6.9-kb 5'-flanking sequence of Tcam1 with or without a deletion of CNS1 linked to the enhanced green fluorescent protein gene into the chromatin of GC-2spd(ts) cells, CNS1 significantly enhanced Tcam1 promoter activity. These results indicate that CNS1 could function as a spermatocyte-specific enhancer. Interestingly, CNS1 also showed high bidirectional promoter activity in the reporter assay, and consistent with this, the Smarcd2 gene and lncRNA, designated lncRNA-Tcam1, were transcribed from adjacent regions of CNS1. While Smarcd2 was ubiquitously expressed, lncRNA-Tcam1 expression was restricted to testicular germ cells, although this lncRNA did not participate in Tcam1 activation. Ubiquitous Smarcd2 expression was correlated to CpG hypo-methylation of CNS1 and partially controlled by Sp1. However, for lncRNA-Tcam1 transcription, the strong association with histone acetylation and histone H3K4 tri-methylation also appeared to be required. The present data suggest that CNS1 is a spermatocyte-specific enhancer for the Tcam1 gene and a bidirectional promoter of Smarcd2 and lncRNA-Tcam1.

Auto-regulation of the Sohlh1 gene by the SOHLH2/SOHLH1/SP1 complex: implications for early spermatogenesis and oogenesis

Tissue-specific basic helix-loop-helix (bHLH) transcription factor proteins often play essential roles in cellular differentiation. The bHLH proteins SOHLH2 and SOHLH1 are expressed specifically in spermatogonia and oocytes and are required for early spermatogonial and oocyte differentiation. We previously reported that knocking out Sohlh2 causes defects in spermatogenesis and oogenesis similar to those in Sohlh1-null mice, and that Sohlh1 is downregulated in the gonads of Sohlh2-null mice. We also demonstrated that SOHLH2 and SOHLH1 can form a heterodimer. These observations led us to hypothesize that the SOHLH2/SOHLH1 heterodimer regulates the Sohlh1 promoter. Here, we show that SOHLH2 and SOHLH1 synergistically upregulate the Sohlh1 gene through E-boxes upstream of the Sohlh1 promoter. Interestingly, we identified an SP1-binding sequence, called a GC-box, adjacent to these E-boxes, and found that SOHLH1 could bind to SP1. Furthermore, chromatin-immunoprecipitation analysis using testes from mice on postnatal day 8 showed that SOHLH1 and SP1 bind to the Sohlh1 promoter region in vivo. Our findings suggest that an SOHLH2/SOHLH1/SP1 ternary complex autonomously and cooperatively regulates Sohlh1 gene transcription through juxtaposed E- and GC-boxes during early spermatogenesis and oogenesis.

Overexpression of histone deacetylases in cancer cells is controlled by interplay of transcription factors and epigenetic modulators

Histone deacetylases (HDACs) that deacetylate histone and nonhistone proteins play crucial roles in a variety of cellular processes. The overexpression of HDACs is reported in many cancer types and is directly linked to accelerated cell proliferation and survival. However, little is known about how HDAC expression is regulated in cancer cells. In this study, we found that HDAC1 and HDAC2 promoters are regulated through collaborative binding of transcription factors Sp1/Sp3 and epigenetic modulators, including histone H3K4 methyltransferase SET1 and histone acetyltransferase p300, whose levels are also elevated in colon cancer cell lines and patient samples. Interestingly, Sp1 and Sp3 differentially regulate HDAC1 and HDAC2 promoter activity. In addition, Sp1/Sp3 recruits SET1 and p300 to the promoters. SET1 knockdown (KD) results in a loss of the H3K4 trimethylation mark at the promoters, as well as destabilizes p300 at the promoters. Conversely, p300 also influences SET1 recruitment and H3K4me3 level, indicating a crosstalk between p300 and SET1. Further, SET1 KD reduces Sp1 binding to the HDAC1 promoter through the increase of Sp1 acetylation. These results indicate that interactions among transcription factors and epigenetic modulators orchestrate the activation of HDAC1 and HDAC2 promoter activity in colon cancer cells.

Dysregulated microRNA clusters in response to retinoic acid and CYP26B1 inhibitor induced testicular function in dogs

Spermatogenesis is a multistep synchronized process. Diploid spermatogonia differentiate into haploid spermatozoa following mitosis, meiosis and spermiogenesis. Division and differentiation of male germ cells is achieved through the sequential expression of several genes. Numerous mRNAs in the differentiating germ cells undergo post-transcriptional and translational regulation. MiRNAs are powerful negative regulators of mRNA transcription, stability, and translation and recognize their mRNA targets through base-pairing. Retinoic acid (RA) signaling is essential for spermatogenesis and testicular function. Testicular RA level is critical for RA signal transduction. This study investigated the miRNAs modulation in an RA- induced testicular environment following the administration of all-trans RA (2 µM) and CYP26B1- inhibitor (1 µM) compared to control. Eighty four canine mature miRNAs were analyzed and their expression signatures were distinguished using real-time PCR based array technology. Of the miRNAs analyzed, miRNA families such as miR-200 (cfa-miR-200a, cfa-miR-200b and cfa-miR-200c), Mirlet-7 (cfa-let-7a, cfa-let-7b, cfa-let-7c, cfa-let-7g and cfa-let-7f), miR-125 (cfa-miR-125a and cfa-miR-125b), miR-146 (cfa-miR-146a and cfa-miR-146b), miR-34 (cfa-miR-34a, cfa-miR-34b and cfa-miR-34c), miR-23 (cfa-miR-23a and cfa-miR-23b), cfa-miR-184, cfa-miR-214 and cfa-miR-141 were significantly up-regulated with testicular RA intervention via administration of CYP26B1 inhibitor and all-trans-RA and species of miRNA such as cfa-miR-19a, cfa-miR-29b, cfa-miR-29c, cfa-miR-101 and cfa-miR-137 were significantly down-regulated. This study explored information regarding chromosome distribution, human orthologous sequences and the interaction of target genes of miRNA families significantly distinguished in this study using prediction algorithms. This study importantly identified dysregulated miRNA species resulting from RA-induced spermatogenesis. The present contribution serves as a useful resource for further elucidation of the regulatory role of individual miRNA in RA synchronized canine spermatogenesis.

Sp1 transcription factor and GATA1 cis-acting elements modulate testis-specific expression of mouse cyclin A1

Cyclin A1 is a male germ cell-specific cell cycle regulator that is essential for spermatogenesis. It is unique among the cyclins by virtue of its highly restricted expression in vivo, being present in pachytene and diplotene spermatocytes and not in earlier or later stages of spermatogenesis. To begin to understand the molecular mechanisms responsible for this narrow window of expression of the mouse cyclin A1 (Ccna1) gene, we carried out a detailed analysis of its promoter. We defined a 170-bp region within the promoter and showed that it is involved in repression of Ccna1 in cultured cells. Within this region we identified known cis-acting transcription factor binding sequences, including an Sp1-binding site and two GATA1-binding sites. Neither Sp1 nor GATA1 is expressed in pachytene spermatocytes and later stages of germ cell differentiation. Sp1 is readily detected at earlier stages of spermatogenesis. Site-directed mutagenesis demonstrated that neither factor alone was sufficient to significantly repress expression driven by the Ccna1 promoter, while concurrent binding of Sp1, and most likely GATA1 and possibly additional factors was inhibitory. Occupancy of Sp1 on the Ccna1 promoter and influence of GATA1-dependent cis-acting elements was confirmed by ChIP analysis in cell lines and most importantly, in spermatogonia. In contrast with many other testis-specific genes, the CpG island methylation status of the Ccna1 promoter was similar among various tissues examined, irrespective of whether Ccna1 was transcriptionally active, suggesting that this regulatory mechanism is not involved in the restricted expression of Ccna1.

Epigenetic silencing of spermatocyte-specific and neuronal genes by SUMO modification of the transcription factor Sp3

SUMO modification of transcription factors is linked to repression of transcription. The physiological significance of SUMO attachment to a particular transcriptional regulator, however, is largely unknown. We have employed the ubiquitously expressed murine transcription factor Sp3 to analyze the role of SUMOylation in vivo. We generated mice and mouse embryonic fibroblasts (MEFs) carrying a subtle point mutation in the SUMO attachment sequence of Sp3 (IKEE₅₅₃D mutation). The E₅₅₃D mutation impedes SUMOylation of Sp3 at K₅₅₁in vivo, without affecting Sp3 protein levels. Expression profiling revealed that spermatocyte-specific genes, such as Dmc1 and Dnahc8, and neuronal genes, including Paqr6, Rims3, and Robo3, are de-repressed in non-testicular and extra-neuronal mouse tissues and in mouse embryonic fibroblasts expressing the SUMOylation-deficient Sp3E₅₅₃D mutant protein. Chromatin immunoprecipitation experiments show that transcriptional de-repression of these genes is accompanied by the loss of repressive heterochromatic marks such as H3K9 and H4K20 tri-methylation and impaired recruitment of repressive chromatin-modifying enzymes. Finally, analysis of the DNA methylation state of the Dmc1, Paqr6, and Rims3 promoters by bisulfite sequencing revealed that these genes are highly methylated in Sp3wt MEFs but are unmethylated in Sp3E₅₅₃D MEFs linking SUMOylation of Sp3 to tissue-specific CpG methylation. Our results establish SUMO conjugation to Sp3 as a molecular beacon for the assembly of repression machineries to maintain tissue-specific transcriptional gene silencing.

Cell type–specific gene expression patterns are largely regulated by positively or negatively acting transcription factors binding to promoter and enhancer elements. The ubiquitous transcription factor Sp3 represents a paradigm for a dual function transcription factor as it can activate and repress transcription. The repression function of Sp3 is mediated by attachment of a small protein designated SUMO to a single lysine residue. SUMOylation of Sp3 thus acts as a molecular switch that determines whether Sp3 acts as an activator or repressor. In this study, we have generated mice with a subtle mutation in the SUMO attachment site of Sp3. We found that several spermatocyte- and brain-specific genes that are silenced in non-testicular and extra-neuronal tissues of wild-type animals become aberrantly de-repressed in mice in which the SUMO attachment site of Sp3 is mutated. De-repression of these genes is accompanied with dramatic epigenetic changes including the loss of repressive histone methylation marks and, most significantly, loss of DNA methylation. Our findings suggest that SUMO modification of a transcription factor can act as a molecular beacon for the assembly of repression machineries to maintain tissue-specific transcriptional gene silencing in vivo.

SK3 channel expression during pregnancy is regulated through estrogen and Sp factor-mediated transcriptional control of the KCNN3 gene

Overexpression of the small-conductance calcium-activated K(+) channel 3 (SK3) in transgenic mice compromises parturition, suggesting that the SK3 channel plays a role in pregnancy. In wild-type mouse myometrium, expression of SK3 transcript and protein is significantly reduced during pregnancy, but the mechanism(s) responsible for this attenuation of channel expression is unknown. The promoter region of the SK3-encoding mouse KCNN3 gene contains two binding sites for specificity protein (Sp) transcription factors, two of which are expressed in the uterus: Sp1, which enhances gene transcription in response to estrogen; and Sp3, which competes for the same binding motif as Sp1 and can repress gene expression. We investigated the hypothesis that Sp1 and Sp3 regulate SK3 channel expression during pregnancy. In mouse myometrium, Sp1 expression was reduced during late gestation, whereas Sp3 expression levels were constant throughout pregnancy. Using a reporter system, we found that Sp1 overexpression resulted in a significant increase in SK3 promoter activation and that Sp3 cotransfection reduced promoter activation to basal levels. These findings indicate that Sp3 outcompetes Sp1 to decrease SK3 transcription. To determine whether high levels of estrogen in vivo can affect the regulation of SK3 protein levels by Sp factors, ovariectomized mice were implanted with a 17β-estradiol or placebo pellet for 3 wk; estrogen-treated mice had reduced uterine SK3 protein expression compared with placebo-treated counterparts. In human myometrial cells overexpressing Sp1, estrogen treatment stimulated expression of the SK3 transcript. Overall, our findings indicate that Sp1 and Sp3 compete to regulate SK3 channel expression during pregnancy in response to stimulation by estrogen.

The role of Sp1 and Sp3 in normal and cancer cell biology

Sp1 and Sp3 are transcription factors expressed in all mammalian cells. These factors are involved in regulating the transcriptional activity of genes implicated in most cellular processes. Dysregulation of Sp1 and Sp3 is observed in many cancers and diseases. Due to the amino acid sequence similarity of the DNA binding domains, Sp1 and Sp3 recognize and associate with the same DNA element with similar affinity. However, others and our laboratory demonstrated that these two factors possess different properties and exert different functional roles. Both Sp1 and Sp3 can interact with and recruit a large number of proteins including the transcription initiation complex, histone modifying enzymes and chromatin remodeling complexes, which strongly suggest that Sp1 and Sp3 are important transcription factors in the remodeling chromatin and the regulation of gene expression. In this review, the role of Sp1 and Sp3 in normal and cancer cell biology and the multiple mechanisms deciding the functional roles of Sp1 and Sp3 will be presented.

RFX2 is a candidate downstream amplifier of A-MYB regulation in mouse spermatogenesis

Background

Mammalian spermatogenesis involves formation of haploid cells from the male germline and then a complex morphological transformation to generate motile sperm. Focusing on meiotic prophase, some tissue-specific transcription factors are known (A-MYB) or suspected (RFX2) to play important roles in modulating gene expression in pachytene spermatocytes. The current work was initiated to identify both downstream and upstream regulatory connections for Rfx2.

Results

Searches of pachytene up-regulated genes identified high affinity RFX binding sites (X boxes) in promoter regions of several new genes: Adam5, Pdcl2, and Spag6. We confirmed a strong promoter-region X-box for Alf, a germ cell-specific variant of general transcription factor TFIIA. Using Alf as an example of a target gene, we showed that its promoter is stimulated by RFX2 in transfected cells and used ChIP analysis to show that the promoter is occupied by RFX2 in vivo. Turning to upstream regulation of the Rfx2 promoter, we identified a cluster of three binding sites (MBS) for the MYB family of transcription factors. Because testis is one of the few sites of A-myb expression, and because spermatogenesis arrests in pachytene in A-myb knockout mice, the MBS cluster implicates Rfx2 as an A-myb target. Electrophoretic gel-shift, ChIP, and co-transfection assays all support a role for these MYB sites in Rfx2 expression. Further, Rfx2 expression was virtually eliminated in A-myb knockout testes. Immunohistology on testis sections showed that A-MYB expression is up-regulated only after pachytene spermatocytes have clearly moved away from the tubule wall, which correlates with onset of RFX2 expression, whereas B-MYB expression, by contrast, is prevalent only in earlier spermatocytes and spermatogonia.

Conclusion

With an expanding list of likely target genes, RFX2 is potentially an important transcriptional regulator in pachytene spermatocytes. Rfx2 itself is a good candidate to be regulated by A-MYB, which is essential for meiotic progression. If Alf is a genuine RFX2 target, then A-myb, Rfx2, and Alf may form part of a transcriptional network that is vital for completion of meiosis and preparation for post-meiotic differentiation.

Differential expression of Rfx1-4 during mouse spermatogenesis

The regulatory factor X (RFX) family of transcription factors has been recently implicated in gene regulation during spermatogenesis. However, the relative expression of individual members during this developmental process is not completely characterized, particularly in the case of Rfx4, which has multiple transcript variants in the testis. We used reverse transcriptase-dependent real-time PCR, 5'-RACE cloning, and Western blotting to compare transcripts and protein levels for this family in cell populations from the three major phases of spermatogenesis (mitotic, meiotic, and haploid). Transcripts for Rfx1-4 were present at trace to low levels in spermatogonia prepared from 8-day-old mice. Transcripts for both Rfx2 and Rfx4 were elevated in mid-late pachytene spermatocytes; however, the dominant Rfx4 transcript present begins at a downstream exon and lacks the DNA binding domain. Transcripts for all four genes were elevated in early haploid cells (round spermatids). In these cells Rfx4 transcripts originate primarily from a newly described promoter with intron 1 but are expected to be translationally compromised due to a poorly situated start codon. Western blotting confirmed that RFX2 is greatly elevated beginning in meiosis and also confirmed that full-length RFX4 protein is not prevalent in mouse testis at any stage. These results imply that RFX2 is the most likely X box binding factor to influence novel gene expression during meiosis, that RFX1-3 may all play roles in haploid cells but that RFX4 is much less prevalent than implied by its high transcript levels.