Mammalian SWI/SNF collaborates with a polycomb-associated protein to regulate male germline transcription in the mouse.

A deficiency in BRG1, the catalytic subunit of the SWI/SNF chromatin remodeling complex, results in a meiotic arrest during spermatogenesis. Here, we explore the causative mechanisms. BRG1 is preferentially enriched at active promoters of genes essential for spermatogonial pluripotency and meiosis. In contrast, BRG1 is also associated with the repression of somatic genes. Chromatin accessibility at these target promoters is dependent upon BRG1. These results favor a model in which BRG1 coordinates spermatogenic transcription to ensure meiotic progression. In spermatocytes, BRG1 interacts with SCML2, a testis-specific PRC1 factor that is associated with the repression of somatic genes. We present evidence to suggest that BRG1 and SCML2 concordantly regulate genes during meiosis. Furthermore, BRG1 is required for the proper localization of SCML2 and its associated deubiquitylase, USP7, to the sex chromosomes during pachynema. SCML2-associated mono-ubiquitylation of histone H2A lysine 119 (H2AK119ub1) and acetylation of histone lysine 27 (H3K27ac) are elevated in Brg1cKO testes. Coincidentally, the PRC1 ubiquitin ligase RNF2 is activated while a histone H2A/H2B deubiquitylase USP3 is repressed. Thus, BRG1 impacts the male epigenome by influencing the localization and expression of epigenetic modifiers. This mechanism highlights a novel paradigm of cooperativity between SWI/SNF and PRC1.

Repression of the soma-specific transcriptome by Polycomb-repressive complex 2 promotes male germ cell development.

Polycomb-repressive complex 2 (PRC2) catalyzes the methylation of histone H3 Lys27 (H3K27) and functions as a critical epigenetic regulator of both stem cell pluripotency and somatic differentiation, but its role in male germ cell development is unknown. Using conditional mutagenesis to remove the core PRC2 subunits EED and SUZ12 during male germ cell development, we identified a requirement for PRC2 in both mitotic and meiotic germ cells. We observed a paucity of mutant spermatogonial stem cells (SSCs), which appears independent of repression of the known cell cycle inhibitors Ink4a/Ink4b/Arf. Moreover, mutant spermatocytes exhibited ectopic expression of somatic lamins and an abnormal distribution of SUN1 proteins on the nuclear envelope. These defects were coincident with abnormal chromosome dynamics, affecting homologous chromosome pairing and synapsis. We observed acquisition of H3K27me3 on stage-specific genes during meiotic progression, indicating a requirement for PRC2 in regulating the meiotic transcriptional program. Together, these data demonstrate that transcriptional repression of soma-specific genes by PRC2 facilitates homeostasis and differentiation during mammalian spermatogenesis.

EZH1 in germ cells safeguards the function of PRC2 during spermatogenesis.

We previously reported the requirement of Polycomb Repressive Complex 2 (PRC2) for spermatogenesis through transcriptional repression of somatic genes and meiosis-specific genes. To characterize how PRC2's two methyltransferase subunits, EZH1 and EZH2, regulate histone H3 lysine 27 (H3K27) methylation during germ cell development, we generated mouse models with a germline ablation of EZH1 and/or EHZ2. Only the combined loss of EZH1 and EZH2 caused a depletion of global H3K27me3 marks and meiotic arrest in spermatocytes. Genome-wide analysis of H3K27me3 in spermatogenic cells revealed that a noncanonical EZH1-PRC2 could establish and maintain this histone mark on somatic genes and certain meiotic genes. Consistent with it having active enhancers in testis, Ezh1 was not only abundant in highly differentiated spermatocytes but also in actively proliferating progenitor and stem germ cells. Taken together, our findings suggest that the expression level of Ezh1 determines the restoration of H3K27 methylation in the absence of the canonical EZH2-PRC2.

Key mediators of somatic ATR signaling localize to unpaired chromosomes in spermatocytes.

Meiotic silencing of unpaired chromatin (MSUC) occurs during the first meiotic prophase, as chromosomes that fail to pair are sequestered into a transcriptionally repressive nuclear domain. This phenomenon is exemplified by the heterologous sex chromosomes of male mammals, where the ATR DNA damage response kinase is crucial for this silencing event. However, the mechanisms underlying the initiation of MSUC remain unknown. Here, we show that essential components of ATR signaling in murine somatic cells are spatially confined to unpaired chromosomes in spermatocytes, including the ATR-dependent phosphorylation of the single-stranded DNA (ssDNA)-binding complex replication protein A (RPA) and the checkpoint kinase CHK1. These observations support a model in which ssDNA plays a central role in the recruitment of ATR during MSUC, and provide a link to meiotic progression through activation of CHK1.

RBBP4 dysfunction reshapes the genomic landscape of H3K27 methylation and acetylation and disrupts gene expression.

RBBP4 is a subunit of the chromatin remodeling complexes known as Polycomb repressive complex 2 and histone deacetylase 1/2-containing complexes. These complexes are responsible for histone H3 lysine 27 methylation and deacetylation, respectively. How RBBP4 modulates the functions of these complexes remains largely unknown. We generated viable Rbbp4 mutant alleles in mouse embryonic stem cell lines by CRISPR-Cas9. The mutations disrupted Polycomb repressive complex 2 assembly and H3K27me3 establishment on target chromatin and altered histone H3 lysine 27 acetylation genome wide. Moreover, Rbbp4 mutant cells underwent dramatic changes in transcriptional profiles closely tied to the deregulation of H3K27ac. The alteration of H3K27ac due to RBBP4 dysfunction occurred on numerous cis-regulatory elements, especially putative enhancers. These data suggest that RBBP4 plays a central role in regulating histone H3 lysine 27 methylation and acetylation to modulate gene expression.

PDCD2 is essential for inner cell mass development and embryonic stem cell maintenance.

PDCD2 is a conserved eukaryotic protein implicated in cell cycle regulation by virtue of its interactions with HCFC1 and the NCOR1/SIN3A corepressor complex. Pdcd2 transcripts are enriched in ES cells and other somatic stem cells, and its ortholog is essential for hematopoietic stem cell maintenance in Drosophila. To characterize the physiological role(s) of mammalian PDCD2, we created a disruption allele in mice. Pdcd2(-/-) embryos underwent implantation but did not undergo further development. Inner cell masses (ICMs) from Pdcd2(-/-) blastocysts failed to outgrow in vitro. Furthermore, embryonic stem cells (ESCs) require PDCD2 as demonstrated by the inability to generate Pdcd2(-/-) ESCs in the absence of an ectopic transgene. Upon differentiation of ESCs by retinoic acid treatment or LIF deprivation, PDCD2 levels declined. In conjunction with prior studies, these results indicate that in vivo, PDCD2 is critical for blastomere and ESC maintenance by contributing to the regulation of genes in a manner essential to the undifferentiated state of these cells.

Low-Se Diet Can Affect Sperm Quality and Testicular Glutathione Peroxidase-4 activity in Rats.

This study aimed to observe the influence of selenium (Se) deficiency on sperm quality and selenoprotein expression in rats. Four-week male Wista rats were randomly divided into three groups: Se-A, Se-L, and Se-D (respectively for Se- adequate, low, and deficient group). After 9 weeks, the rats were sacrificed by anesthesia, with the cauda epididymidis quickly fetched for sperm count, motility, and deformity. Meanwhile the blood, liver, brain, heart, and testis were collected for Se and biochemical analysis. It was found that the rats in Se-D had poor growth, while the Se concentrations in blood, liver, and heart for Se-D decreased significantly, compared with Se-A and Se-L (p < 0.01). But no significant difference was observed in testis and brain and also no statistical significance for sperm count. The sperm motility for Se-A (63.07%) was significantly higher than Se-L (53.91%) and Se-D (54.15%). Deformities were observed in both Se-L and Se-D. Both glutathione peroxidases (GPxs) and selenoprotein-P (SEPP1) levels in plasma and tissues of Se-D were significantly lower than those of Se-A and Se-L (p < 0.01). The SEPP1 levels in heart and brain of Se-L were lower than Se-A (p < 0.01). There was no statistical difference for GPx1 between Se-A and Se-L. The GPx4 level in testis of Se-L was lower than Se-A (p < 0.05). However, the SEPP1 in plasma, liver, testis, and the GPx3 level in plasma of Se-L were higher than those of Se-A (p < 0.05 or p < 0.01). Our results show that dietary Se deficiency could reduce GPx4 and SEPP1 expression in testis, which further influence sperm motility and may cause sperm deformity. Selenoprotein expression in some tissues of Se-L was higher than that of Se-A, but sperm quality and GPx4 expression in testis were not improved for Se-L. Low active pseudoselenoproteins might be synthesized in low-Se condition. The underlying mechanism needs to be further investigated.

High resolution mapping and positional cloning of ENU-induced mutations in the Rw region of mouse chromosome 5.

BACKGROUND: Forward genetic screens in mice provide an unbiased means to identify genes and other functional genetic elements in the genome. Previously, a large scale ENU mutagenesis screen was conducted to query the functional content of a ~50 Mb region of the mouse genome on proximal Chr 5. The majority of phenotypic mutants recovered were embryonic lethals. RESULTS: We report the high resolution genetic mapping, complementation analyses, and positional cloning of mutations in the target region. The collection of identified alleles include several with known or presumed functions for which no mutant models have been reported (Tbc1d14, Nol14, Tyms, Cad, Fbxl5, Haus3), and mutations in genes we or others previously reported (Tapt1, Rest, Ugdh, Paxip1, Hmx1, Otoe, Nsun7). We also confirmed the causative nature of a homeotic mutation with a targeted allele, mapped a lethal mutation to a large gene desert, and localized a spermiogenesis mutation to a region in which no annotated genes have coding mutations. The mutation in Tbc1d14 provides the first implication of a critical developmental role for RAB-GAP-mediated protein transport in early embryogenesis. CONCLUSION: This collection of alleles contributes to the goal of assigning biological functions to all known genes, as well as identifying novel functional elements that would be missed by reverse genetic approaches.

Calculation of an Adequate Intake (AI) Value and Safe Range of Selenium (Se) for Chinese Infants 0-3 Months Old Based on Se Concentration in the Milk of Lactating Chinese Women with Optimal Se Intake.

The required selenium intake for optimal health in Chinese residents was published in 2014. However, the adequate intake (AI) value for Chinese infants 0-3 months old is not established. This study assessed the current selenium nutritional status of 264 lactating Chinese women from three geographical locations with different Se levels (Liangshan in Sichuan province, Enshi in Hubei province, and Xicheng District in Beijing), to screen mothers with optimal Se intake, and to modify the AI value of Se for Chinese infants 0-3 months old. Milk and plasma Se concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS) and glutathione peroxidase 3 (GPx3), and plasma selenoprotein P (SEPP1) was measured by ELISA. Daily Se intake (Y, µg/day) in lactating Chinese woman was calculated from plasma Se concentrations (X, µg/L) using the formula logY = 1.623 log(X) + 3.433. Plasma Se concentrations in lactating Chinese women were 78.19 ± 25.71, 112.48 ± 24.57, and 183.83 ± 45.81 µg/L from Se-deficient, Se-moderate, and seleniferous areas, respectively. Se intakes calculated from concentrations of plasma Se were 45.6 ± 21.69, 80.03 ± 27.69, and 223.10 ± 50.95 µg/day, respectively. An optimal dietary Se intake is not lower than the recommended nutrient intake (RNI) but not more than the tolerable upper intake level (UL). A range of 78-400 µg Se/day was defined as the optimal daily Se intake for lactating Chinese women. The percentages of mothers within this range in Sichuan, Beijing, and Enshi were 8.11, 45.13, and 6.06%, respectively. Based on milk Se concentrations of mothers with optimal daily Se intake, the adequate Se intake value and a safe range for Chinese infants 0-3 months of age were calculated as 15.29 and 8-35 µg Se/day, respectively. The Se status of Chinese lactating women has improved, particularly in traditionally Se-deficient and Se-toxic regions. A safe range for daily Se intake in Chinese infants may be regarded as a guideline for infant formula.

EZH2 variants differentially regulate polycomb repressive complex 2 in histone methylation and cell differentiation.

BACKGROUND: Polycomb repressive complex 2 (PRC2) is responsible for establishing and maintaining histone H3K27 methylation during cell differentiation and proliferation. H3K27 can be mono-, di-, or trimethylated, resulting in differential gene regulation. However, it remains unknown how PRC2 specifies the degree and biological effects of H3K27 methylation within a given cellular context. One way to determine PRC2 specificity may be through alternative splicing of Ezh2, PRC2's catalytic subunit, during cell differentiation and tissue maturation. RESULTS: We fully characterized the alternative splicing of Ezh2 in somatic cells and male germ cells and found that Ezh's exon 14 was differentially regulated during mitosis and meiosis. The Ezh2 isoform containing exon 14 (ex14-Ezh2) is upregulated during cell cycle progression, consistent with a role in maintaining H3K27 methylation during chromatin replication. In contrast, the isoform lacking exon 14 (ex14D-Ezh2) was almost exclusively present in spermatocytes when new H3K27me2 is established during meiotic differentiation. Moreover, Ezh2's transcript is normally controlled by E2F transcription activators, but in spermatocytes, Ezh2's transcription is controlled by the meiotic regulator MYBL1. Compared to ex14-EZH2, ex14D-EZH2 has a diminished efficiency for catalyzing H3K27me3 and promotes embryonic stem cell differentiation. CONCLUSIONS: Ezh2's expression is regulated at transcriptional and post-transcriptional levels in a cellular context-dependent manner. EZH2 variants determine functional specificity of PRC2 in histone methylation during cell proliferation and differentiation.

Selenium in infant formula milk.

Formula-based animal milk is an alternative source of infant nutrition in many cases when breastfeeding is unacceptable or inaccessible; however, these replacements often have low selenium levels. The composition of infant formula milk should be as close as possible to that of human breast milk, both in content and chemical speciation. Selenium is an essential trace element for infants. Generally, human breast milk is the ideal food to ensure adequate infant Se intake. However, to date, sodium selenite or sodium selenate has been used as selenium supplementation in infant formula milk in most countries. This inorganic Se, which is not a natural component of food, may not be the optimal speciation for Se supplementation in infant formula milk. Advances in speciation in foods, especially in animal milk, suggest that future proposals for selenium speciation in human breast milk can lead to discussions regarding the most favorable methods of selenium supplementation in infant formula milk.

[Detection of the genetically modified organisms in genetically modified soybean and maize by polymerase chain reaction method].

A method for the detection of the (genetically modified organism GMOs) in genetically modified soybean (Round-up Ready soybean, RR soybean) and maize(Bt-176 maize) is described. The polymerase chain reaction (PCR) method is discussed with the genetically modified soybean and maize whose contents are known. The detection limit can be 0.1%, that is to say, we can detect the GMO in the food whose content is only 0.1%, the detection method is just a screening method. The procedure includes: (1) extraction of genomic DNA of maize and soybean, (2) amplification of the inserted genes, CaMV35S promoter and the NOS terminator inserted by means of the polymerase chain reaction (PCR) method, (3) amplification of the specific genes of maize and soybean in order to determine that the samples are maize and soybean, (4) characterization and confirmation of the PCR products by restriction enzyme analysis and the electrophoresis on agarose gel. The RR soybean contains CaMV35S promoter and NOS terminator, and the Bt-176 maize contains only CaMV35S promoter. Due to the high content of the starch in maize, the effect of the electrophororesis is not so good as of the soybean's.

[Studies on comparing the toxicity between sodium selenite and selenomethionine in rats].

OBJECTIVE: To compare the toxicity between sodium selenite and selenomethionine (SeM) and to investigate the indicators of selenium toxicity. METHODS: Weanling Wistar rats of both sexes were randomly divided into seven groups, 14 rats each group. One group was fed basal diet and the others were fed basal diets containing 3, 6, 10 mg greater than that of SeM and female rats were more sensitive to excessive selenium than male rats. Se/kg added as sodium selenite or SeM for 12 weeks. RESULTS: Histopathological changes of the liver were observed in rats on Se 3 mg/kg diets while the decreasing of body weight occurred in rats on 6 Se mg/kg diet. Among the rats fed Se 6, 10 mg/kg diet, the body weight of rats in selenite-treated groups was lower than that of rats in SeM-treated groups. At the 3 or 6 mg/kg Se level, the rats fed SeM suffered slighter hepatic damage than those fed sodium selenite and in male rats slighter than female rats. The abnormal change of ratio of liver weight to body weight was found to be more obvious both in female rats and in selenite-treated rats. GPX activity in liver of female rats reduced with the increase of Se level in diets. However, GPX activity in RBC, plasma, kidneys and liver showed an ascending tendency with the increasing level of dietary Se. CONCLUSION: The minimum dose of intoxication of Se in diet may be around 3 mg/kg. The toxicity of selenite is greater than that of SeM and female rats were more sensitive to excessive selenium than male rats.

Differentiation-driven nucleolar association of the mouse imprinted Kcnq1 locus.

The organization of the genome within the mammalian nucleus is nonrandom, with physiologic processes often concentrated in specific three-dimensional domains. This organization may be functionally related to gene regulation and, as such, may play a role in normal development and human disease processes. However, the mechanisms that participate in nuclear organization are poorly understood. Here, we present data characterizing localization of the imprinted Kcnq1 alleles. We show that nucleolar association of the paternal allele (1) is stimulated during the differentiation of trophoblast stem cells, (ii) is dependent upon the Kcnq1ot1 noncoding RNA, (3) does not require polycomb repressive complex 2, and (4) is not sufficient to preclude transcription of imprinted genes. Although nucleolar positioning has been proposed as a mechanism to related to gene silencing, we find that silencing and perinucleolar localization through the Kcnq1ot1 noncoding RNA are separable events.

An allelic series uncovers novel roles of the BRCT domain-containing protein PTIP in mouse embryonic vascular development.

Pax transactivation domain-interacting protein (PTIP, or PAXIP1) is required for mouse development and has been implicated in DNA damage responses and histone modification. However, the physiological roles of PTIP during embryogenesis remain unclear due to early embryonic lethality of null mutants. We describe two N-ethyl N-nitrosourea-induced hypomorphic missense alleles of Ptip, each of which alters one of the six encoded BRCT domains. Phenotypic characterization of these mutants revealed important functions of PTIP in vasculogenesis and chorioplacental development that appear unrelated to activities in DNA repair or global histone modification. The results of gene expression profiling and in vitro angiogenesis assays indicated that PTIP modulates a transcriptional program, centered around Vegfa, that drives the migration of endothelial cells to properly form the embryonic vasculature. These and other data suggest that PTIP has multiple functions, one of which is to promote the formation of transcriptional complexes that provide specificity of developmental gene expression.

Development of insulin resistance and obesity in mice overexpressing cellular glutathione peroxidase.

Insulin resistance, a hallmark of type 2 diabetes, is associated with oxidative stress. However, the role of reactive oxygen species or specific antioxidant enzymes in its development has not been tested under physiological conditions. The objective of our study was to investigate the impact of overexpression of glutathione peroxidase 1 (GPX1), an intracellular selenoprotein that reduces hydrogen peroxide (H(2)O(2)) in vivo, on glucose metabolism and insulin function. The GPX1-overexpressing (OE) and WT male mice (n = 80) were fed a selenium-adequate diet (0.4 mg/kg) from 8 to 24 weeks of age. Compared with the WT, the OE mice developed (P < 0.05) hyperglycemia (117 vs. 149 mg/dl), hyperinsulinemia (419 vs. 1,350 pg/ml), and elevated plasma leptin (5 vs. 16 ng/ml) at 24 weeks of age. Meanwhile, these mice were heavier (37 vs. 27 g, P < 0.001) and fatter (37% vs. 17% fat, P < 0.01) than the WT mice. At 30-60 min after an insulin challenge, the OE mice had 25% less (P < 0.05) of a decrease in blood glucose than the WT mice. Their insulin resistance was associated with a 30-70% reduction (P < 0.05) in the insulin-stimulated phosphorylations of insulin receptor (beta-subunit) in liver and Akt (Ser(473) and Thr(308)) in liver and soleus muscle. Here we report the development of insulin resistance in mammals with elevated expression of an antioxidant enzyme and suggest that increased GPX1 activity may interfere with insulin function by overquenching intracellular reactive oxygen species required for insulin sensitizing.