Bex1, a gene with increased expression in parthenogenetic embryos, is a member of a novel gene family on the mouse X chromosome

BEX2 is poor prognostic factor and required for cancer stemness in gastric cancer

Gastric cancer is the fifth most common malignancy worldwide. However, targeted therapy for advanced gastric cancer is still limited. Here, we report BEX2 (Brain expressed X-linked 2) as a poor prognostic factor in two gastric cancer cohorts. BEX2 expression was increased in spheroid cells, and its knockdown decreased aldefluor activity and cisplatin resistance. BEX2 was found to upregulate CHRNB2 (Cholinergic Receptor Nicotinic Beta 2 Subunit) expression, a cancer stemness-related gene, in a transcriptional manner, and the knockdown of which also decreases aldefluor activity. Collectively, these data are suggestive of the role of BEX2 in the malignant process of gastric cancer, and as a promising therapeutic target.

Cancer-associated fibroblast-derived exosomal miR-18b promotes breast cancer invasion and metastasis by regulating TCEAL7

Studies have shown that cancer-associated fibroblasts (CAFs) play an irreplaceable role in the occurrence and development of tumors. Therefore, exploring the action and mechanism of CAFs on tumor cells is particularly important. In this study, we compared the effects of CAFs-derived exosomes and normal fibroblasts (NFs)-derived exosomes on breast cancer cells migration and invasion. The results showed that exosomes from both CAFs and NFs could enter into breast cancer cells and CAFs-derived exosomes had a more enhancing effect on breast cancer cells migration and invasion than NFs-derived exosomes. Furthermore, microRNA (miR)-18b was upregulated in CAFs-derived exosomes, and CAFs-derived exosomes miR-18b can promote breast cancer cell migration and metastasis by specifically binding to the 3'UTR of Transcription Elongation Factor A Like 7 (TCEAL7). The miR-18b-TCEAL7 pathway promotes nuclear Snail ectopic activation by activating nuclear factor-kappa B (NF-κB), thereby inducing epithelial-mesenchymal transition (EMT) and promoting cell invasion and metastasis. Moreover, CAFs-derived exosomes miR-18b could promote mouse xenograft model tumor metastasis. Overall, our findings suggest that CAFs-derived exosomes miR-18b promote nuclear Snail ectopic by targeting TCEAL7 to activate the NF-κB pathway, thereby inducing EMT, invasion, and metastasis of breast cancer. Targeting CAFs-derived exosome miR-18b may be a potential treatment option to overcome breast cancer progression.

Analyzing differentially expressed genes and pathways of Bex2-deficient mouse lung via RNA-Seq

Bex2 is well known for its role in the nervous system, and is associated with neurological disorders, but its role in the lung’s physiology is still not reported. To elucidate the functional role of Bex2 in the lung, we generated a Bex2 knock-out (KO) mouse model using the CRISPR-Cas9 technology and performed transcriptomic analysis. A total of 652 genes were identified as differentially expressed between Bex2^-/- and Bex2^+/+ mice, out of which 500 were downregulated, while 152 were upregulated genes. Among these DEGs, Ucp1, Myh6, Coxa7a1, Myl3, Ryr2, RNaset2b, Npy, Enob1, Krt5, Myl2, Hba-a2, and Nrob2 are the most prominent genes. Myl2, was the most downregulated gene, followed by Npy, Hba-a2, Rnaset2b, nr0b2, Klra8, and Ucp1. Tcte3, Eno1b, Zfp990, and Pcdha9 were the most upregulated DEGs. According to gene enrichment analysis, PPAR pathway, cardiac muscle contraction, and cytokine-cytokine receptor interaction were the most enriched pathways. Besides, the nuclear factor-κB signaling pathway and hematopoietic cell linage pathways were also enriched. Chronic obstructive pulmonary disease (COPD) is enriched among KEGG disease pathways. RT-qPCR assays confirmed the RNA-Seq results. This study opens a new window toward the biological functions of Bex2 in different systems.

BEX2 is required for maintaining dormant cancer stem cell in hepatocellular carcinoma

Cancer stem cells (CSCs) are responsible for therapy resistance and share several properties with normal stem cells. Here, we show that brain‐expressed X‐linked gene 2 (BEX2), which is essential for dormant CSCs in cholangiocarcinoma, is highly expressed in human hepatocellular carcinoma (HCC) lesions compared with the adjacent normal lesions and that in 41 HCC cases the BEX2^high expression group is correlated with a poor prognosis. BEX2 localizes to Ki67‐negative (nonproliferative) cancer cells in HCC tissues and is highly expressed in the dormant fraction of HCC cell lines. Knockdown of BEX2 attenuates CSC phenotypes, including sphere formation ability and aldefluor activity, and BEX2 overexpression enhances these phenotypes. Moreover, BEX2 knockdown increases cisplatin sensitivity, and BEX2 expression is induced by cisplatin treatment. Taken together, these data suggest that BEX2 induces dormant CSC properties and affects the prognosis of patients with HCC.

BEX2 suppresses mitochondrial activity and is required for dormant cancer stem cell maintenance in intrahepatic cholangiocarcinoma

Cancer stem cells (CSCs) define a subpopulation of cancer cells that are resistant to therapy. However, little is known of how CSC characteristics are regulated. We previously showed that dormant cancer stem cells are enriched with a CD274^low fraction of cholangiocarcinoma cells. Here we found that BEX2 was highly expressed in CD274^low cells, and that BEX2 knockdown decreased the tumorigenicity and G₀ phase of cholangiocarcinoma cells. BEX2 was found to be expressed predominantly in G₀ phase and starvation induced the USF2 transcriptional factor, which induced BEX2 transcription. Comprehensive screening of BEX2 binding proteins identified E3 ubiquitin ligase complex proteins, FEM1B and CUL2, and a mitochondrial protein TUFM, and further demonstrated that knockdown of BEX2 or TUFM increased mitochondria-related oxygen consumption and decreased tumorigenicity in cholangiocarcinoma cells. These results suggest that BEX2 is essential for maintaining dormant cancer stem cells through the suppression of mitochondrial activity in cholangiocarcinoma.

Downregulation of TCEAL7 expression induces CCND1 expression in non-small cell lung cancer

Transcription Elongation Factor A-like 7 (TCEAL7) was first reported as a candidate tumor suppressor gene because of its inactivation in ovarian cancer as a result of promoter methylation. Down-regulation of the TCEAL7 gene expression was also associated with other cancers such as endometrial, breast, brain, prostate, gastric cancers, glioblastoma and linked to tumor phenotypes and clinical outcomes. However, there is no report in the literature investigating the role of TCEAL7 in non-small cell lung cancer. Cyclin D1 is an important molecule in the transition from G1 to S phase of the cell cycle, and is frequently deregulated in cancers. Cylin D1 (CCND1) gene is amplified or overexpressed in a variety of tumors. In our previous study we reported that CCND1 over-expression was not associated with amplification in non-small cell lung cancer. Recently, it has been reported that TCEAL7 regulates CCND1 expression through myc-binding E-box sequences. The aim of this study was to investigate the expression of TCEAL7 gene in non-small cell lung cancer and to determine its effect on the CCND1 expression level. For this purpose, expression levels of TCEAL7 and CCND1 genes were investigated in 50 patients with non-small cell lung cancer by quantitative real time polymerase chain reaction (qRT-PCR). TCEAL7 was under-expressed (68%) in non-small cell lung cancer tumor tissues while CCND1 was over-expressed (42%). The TCEAL7 levels negatively correlated with increased CCND1 expression (p = 0.002).

Molecular functions of brain expressed X-linked 2 (BEX2) in malignancies

Over the last decade there has been growing evidence that Brain Expressed X-Linked 2 (BEX2) has a significant role in the process of carcinogenesis. Collectively, available studies suggest a pro-oncogenic function for this gene in multiple malignancies, including breast, colorectal and hepatocellular cancers in addition to brain tumors. The identification of BEX2 in breast cancer resulted from gene expression microarray studies. Subsequent studies showed that BEX2 promotes breast cancer cell growth and survival by modulating the mitochondrial apoptotic pathway and G1 cell cycle. In this process, BEX2 has cross-talk with the NF-κB, c-Jun/JNK and ErbB2 pathways. Of note, several studies have found a pro-oncogenic function for BEX2 in other malignancies associated with a similar signaling function to that observed in breast cancer. In brain tumors, BEX2 promotes cell migration and invasion in oligodendroglioma and glioblastoma cells. In addition, BEX2 expression protects glioma cells against apoptosis mediated through the JNK pathway and is required for glioma cell proliferation through the NF-κB p65. Furthermore, it has been shown that BEX2 promotes cell proliferation through the JNK/c-Jun pathway and regulates JNK/c-Jun phosphorylation in colorectal cancer. Most recently, it has been demonstrated that BEX2 expression is required for cell proliferation and Hepatitis B Virus-mediated development of hepatocellular carcinoma. Therefore, a pro-oncogenic function for BEX2 is supported by reproducible data in multiple malignancies and the NF-κB and JNK/c-Jun pathways are commonly regulated by BEX2 in this process. In view of these findings, targeting BEX2 may provide an attractive therapeutic strategy in multiple malignancies.

A pivotal role of BEX1 in liver progenitor cell expansion in mice

Background

The activation and expansion of bipotent liver progenitor cells (LPCs) are indispensable for liver regeneration after severe or chronic liver injury. However, the underlying molecular mechanisms regulating LPCs and LPC-mediated liver regeneration remain elusive.

Methods

Hepatic brain-expressed X-linked 1 (BEX1) expression was evaluated using microarray screening, real-time polymerase chain reaction, immunoblotting and immunofluorescence. LPC activation and liver injury were studied following a choline-deficient, ethionine-supplemented (CDE) diet in wild-type (WT) and Bex1^−/− mice. Proliferation, apoptosis, colony formation and hepatic differentiation were examined in LPCs from WT and Bex1^−/− mice. Peroxisome proliferator-activated receptor gamma was detected in Bex1-deficient LPCs and mouse livers, and was silenced to analyse the expansion of LPCs from WT and Bex1^−/− mice.

Results

Hepatic BEX1 expression was increased during CDE diet-induced liver injury and was highly elevated primarily in LPCs. Bex1^−/− mice fed a CDE diet displayed impaired LPC expansion and liver regeneration. Bex1 deficiency inhibited LPC proliferation and enhanced LPC apoptosis in vitro. Additionally, Bex1 deficiency inhibited the colony formation of LPCs but had no effect on their hepatic differentiation. Mechanistically, BEX1 inhibited peroxisome proliferator-activated receptor gamma to promote LPC expansion.

Conclusion

Our findings indicate that BEX1 plays a pivotal role in LPC activation and expansion during liver regeneration, potentially providing novel targets for liver regeneration and chronic liver disease therapies.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0905-2) contains supplementary material, which is available to authorized users.

Induction of Bex genes by curcumin is associated with apoptosis and activation of p53 in N2a neuroblastoma cells

Brain expressed X-linked (Bex) genes are newer group of pro-apoptotic genes. Role of any Bex gene in neuroblastoma and Bex4 and Bex6 in any cancer is completely unknown. Re-expression of all endogenous Bex genes by any nutraceutical is also unknown. Therefore, we investigated the induction of all endogenous Bex genes and associated mechanisms by curcumin using N2a, an aggressive neuroblastoma cell line. Curcumin induced all endogenous Bex genes prior to apoptosis in N2a cells in a dose- and time-dependent manner. Wortmannin (PI-3Kinases inhibitor), SP600125 (JNK inhibitor) and pifithrin-α (p53 inhibitor) abrogated curcumin-mediated induction of Bex genes. Inhibition of curcumin-mediated induction of Bex genes by pifithrin-α also inhibited N2a cells apoptosis suggesting, a direct role of Bex genes in N2a cells apoptosis and involvement of p53 in Bex genes induction. Curcumin treatment activated p53 through hyperphosphorylation at serine 15 before Bex genes induction indicating Bex genes are novel downstream targets of p53. Collectively, curcumin, a safe nutraceutical has the potential to induce all endogenous Bex genes to harness their anti-cancer properties in neuroblastoma cells. Re-expression of Bex genes by curcumin acts as tumor suppressors and may provide alternate strategy to treat neuroblastomas and other cancers with silenced Bex genes.

Oncogenic microtubule hyperacetylation through BEX4-mediated sirtuin 2 inhibition

Five brain-expressed X-linked (BEX) gene members (BEX1–5) are arranged in tandem on chromosome X, and are highly conserved across diverse species. However, little is known about the function and role of BEX. This study represents a first attempt to demonstrate the molecular details of a novel oncogene BEX4. Among BEX proteins, BEX4 localizes to microtubules and spindle poles, and interacts with α-tubulin (α-TUB) and sirtuin 2 (SIRT2). The overexpression of BEX4 leads to the hyperacetylation of α-TUB by inhibiting SIRT2-mediated deacetylation. Furthermore, we found BEX4 expression conferred resistance to apoptotic cell death but led to acquisition of aneuploidy, and also increased the proliferating potential and growth of tumors. These results suggest that BEX4 overexpression causes an imbalance between TUB acetylation and deacetylation by SIRT2 inhibition and induces oncogenic aneuploidy transformation.

BEX1 acts as a tumor suppressor in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease of the myeloid lineage. About 35% of AML patients carry an oncogenic FLT3 mutant making FLT3 an attractive target for treatment of AML. Major problems in the development of FLT3 inhibitors include lack of specificity, poor response and development of a resistant phenotype upon treatment. Further understanding of FLT3 signaling and discovery of novel regulators will therefore help to determine additional pharmacological targets in FLT3-driven AML. In this report, we identified BEX1 as a novel regulator of oncogenic FLT3-ITD-driven AML. We showed that BEX1 expression was down-regulated in a group of AML patients carrying FLT3-ITD. Loss of BEX1 expression resulted in poor overall survival (hazard ratio, HR = 2.242, p = 0.0011). Overexpression of BEX1 in mouse pro-B and myeloid cells resulted in decreased FLT3-ITD-dependent cell proliferation, colony and tumor formation, and in increased apoptosis in vitro and in vivo. BEX1 localized to the cytosolic compartment of cells and significantly decreased FLT3-ITD-induced AKT phosphorylation without affecting ERK1/2 or STAT5 phosphorylation. Our data suggest that the loss of BEX1 expression in FLT3-ITD driven AML potentiates oncogenic signaling and leads to decreased overall survival of the patients.

Brain-Expressed X-linked (BEX) proteins in human cancers

The Brain-Expressed X-linked (BEX) family proteins are comprised of five human proteins including BEX1, BEX2, BEX3, BEX4 and BEX5. BEX family proteins are expressed in a wide range of tissues and are known to play a role in neuronal development. Recent studies suggest a role of BEX family proteins in cancers. BEX1 expression is lost in a subgroup of patients with acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). Expression of BEX1 controls cell surface receptor signaling and restores imatinib response in resistant cells. BEX2 is overexpressed in a group of breast cancer patients and also in gliomas. Increased BEX2 expression led to enhanced NF-κB signaling as well as cell proliferation. Although BEX2 acts as tumor promoter in a subset of breast cancer, BEX3 expression displayed an opposite role. Overexpression of BEX3 resulted in inhibition of tumor formation in breast cancer mouse xenograft models. The role of BEX4 and BEX5 in cancer has not yet been defined. Collectively this suggests that BEX family members have distinct roles in cancers. While BEX1 and BEX3 act as tumor suppressors, BEX2 seems to act as an oncogene.

Bex3 Dimerization Regulates NGF-Dependent Neuronal Survival and Differentiation by Enhancing trkA Gene Transcription

The development of the nervous system is a temporally and spatially coordinated process that relies on the proper regulation of the genes involved. Neurotrophins and their receptors are directly responsible for the survival and differentiation of sensory and sympathetic neurons; however, it is not fully understood how genes encoding Trk neurotrophin receptors are regulated. Here, we show that rat Bex3 protein specifically regulates TrkA expression by acting at the trkA gene promoter level. Bex3 dimerization and shuttling to the nucleus regulate the transcription of the trkA promoter under basal conditions and also enhance nerve growth factor (NGF)-mediated trkA promoter activation. Moreover, qChIP assays indicate that Bex3 associates with the trkA promoter within a 150 bp sequence, immediately upstream from the transcription start site, which is sufficient to mediate the effects of Bex3. Consequently, the downregulation of Bex3 using shRNA increases neuronal apoptosis in NGF-dependent sensory neurons deprived of NGF and compromises PC12 cell differentiation in response to NGF. Our results support an important role for Bex3 in the regulation of TrkA expression and in NGF-mediated functions through modulation of the trkA promoter.

Brain expressed and X-linked (Bex) proteins are intrinsically disordered proteins (IDPs) and form new signaling hubs

Intrinsically disordered proteins (IDPs) are abundant in complex organisms. Due to their promiscuous nature and their ability to adopt several conformations IDPs constitute important points of network regulation. The family of Brain Expressed and X-linked (Bex) proteins consists of 5 members in humans (Bex1-5). Recent reports have implicated Bex proteins in transcriptional regulation and signaling pathways involved in neurodegeneration, cancer, cell cycle and tumor growth. However, structural and biophysical data for this protein family is almost non-existent. We used bioinformatics analyses to show that Bex proteins contain long regions of intrinsic disorder which are conserved across all members. Moreover, we confirmed the intrinsic disorder by circular dichroism spectroscopy of Bex1 after expression and purification in E. coli. These observations strongly suggest that Bex proteins constitute a new group of IDPs. Based on these findings, together with the demonstrated promiscuity of Bex proteins and their involvement in different signaling pathways, we propose that Bex family members play important roles in the formation of protein network hubs.

Β-catenin is involved in Bex2 down-regulation induced glioma cell invasion/migration inhibition

Previously, we found that brain expressed X-linked gene 2 (Bex2) regulates the invasion/migration ability of glioma cells. However, the mechanism of this effect remains unknown. In current study, we reported that Bex2 down-regulation inhibited glioma cell migration and invasion by decreasing the nucleus and cytoplasm protein level of β-catenin. We found that the protein levels of Bex2 and β-catenin were up-regulated and showed direct correlation in glioma tissues. Bex2 down-regulation significantly decreased β-catenin protein levels but not its mRNA levels. Furthermore, the decreased protein level of β-catenin was located in the nucleus and cytoplasm but not in the cell membrane. Further study found that the effects of Bex2 down-regulation on the invasion and migration of glioma cell could be reversed by β-catenin over-expression. Taken together, Bex2 affects the invasion and migration ability of glioma cells by regulating β-catenin.

Epigenetic disruptions of histone signatures for the trophectoderm and inner cell mass in mouse parthenogenetic embryos

Epigenetic asymmetry has been shown to be associated with the first lineage allocation event in preimplantation development, that is, the formation of the trophectoderm (TE) and inner cell mass (ICM) lineages in the blastocyst. Since parthenogenesis causes aberrant segregation between the TE and ICM lineages, we examined several development-associated histone modifications in parthenotes, including those involved in (i) transcriptional activation [acetylated histone H3 lysine 9 (H3K9Ac) and lysine 14 (H3K14Ac), trimethylated histone H3 lysine 4 (H3K4Me3), and dimethylated histone H3 arginine 26 (H3R26Me2)] and (ii) transcriptional repression [trimethylated histone H3 lysine 9 (H3K9Me3) and lysine 27 (H3K27Me3), and mono-ubiquitinated histone H2A lysine 119 (H2AK119u1)]. Here, we report that in parthenotes, H3R26Me2 expression decreased from the morula stage, while expression patterns and levels of H3K9Ac, H3K27Me3, and H2AK119u1 were unchanged until the blastocyst stage; whereas H3K14Ac, H3K4Me3, and H3K9Me3 showed normal patterns and levels of expressions. Relative to the decrease of H3K9Ac in the ICM and increase in the TE of parthenotes, we detected reduced expression of TAT-interactive protein 60 acetyltransferase and histone deacetylase 1 deacetylase in the ICM and TE of parthenotes, respectively. Relative to the decrease of H3R26Me2, we also observed decreased expression of coactivator-associated arginine methyltransferase 1 methyltransferase and increased expression of the Wnt effector transcription factor 7L2 and miR-181c microRNA in parthenotes. Furthermore, relative to the decrease in H3K27Me3 and H2AK119u1, we found increased phosphorylation of Akt1 and enhancer of zeste homolog 2 in parthenogenetic TE. Therefore, our findings that histone signatures are impaired in parthenotes provide a mechanistic explanation for aberrant lineage segregation and TE defects.

Gene targeting study reveals unexpected expression of brain-expressed X-linked 2 in endocrine and tissue stem/progenitor cells in mice

Identification of genes specifically expressed in stem/progenitor cells is an important issue in developmental and stem cell biology. Genome-wide gene expression analyses in liver cells performed in this study have revealed a strong expression of X-linked genes that include members of the brain-expressed X-linked (Bex) gene family in stem/progenitor cells. Bex family genes are expressed abundantly in the neural cells and have been suggested to play important roles in the development of nervous tissues. However, the physiological role of its individual members and the precise expression pattern outside the nervous system remain largely unknown. Here, we focused on Bex2 and examined its role and expression pattern by generating knock-in mice; the enhanced green fluorescence protein (EGFP) was inserted into the Bex2 locus. Bex2-deficient mice were viable and fertile under laboratory growth conditions showing no obvious phenotypic abnormalities. Through an immunohistochemical analysis and flow cytometry-based approach, we observed unique EGFP reporter expression patterns in endocrine and stem/progenitor cells of the liver, pyloric stomach, and hematopoietic system. Although Bex2 seems to play redundant roles in vivo, these results suggest the significance and potential applications of Bex2 in studies of endocrine and stem/progenitor cells.

Bex2 controls proliferation of human glioblastoma cells through NF-κB signaling pathway

Glioblastoma is the most common and fatal human brain malignancy in adults with highly proliferative capacity. Despite advances in surgery and adjuvant therapy, the median survival of patients has changed little over recent decades. Identifying molecules critical for glioma development is significant for devising effective targeted therapy. We previously reported that Bex2, a member of the brain expressed X-linked gene family, promoted the progression of glioma by promoting cell proliferation. In the present study, we investigated the main mechanism of Bex2 promoting the proliferation of glioblastoma cells. We found that Bex2 downregulation inhibited glioma cell proliferation and the expression of NF-κB p65, but Bex2 overexpression promoted them. Similarly, the proliferation of glioma cells was inhibited by p65 downregulation but increased by p65 overexpression. In addition, Bex2 overexpression-induced cell proliferation was abolished by p65 downregulation. Furthermore, Bex2 with nuclear localization signal deleted no longer promoted p65 expression. In conclusion, this study demonstrates that Bex2 promotes proliferation of human glioblastoma cells via NF-κB signaling pathway and Bex2 nuclear location is critical for p65 expression.

Decreased expression of transcription elongation factor A-like 7 is associated with gastric adenocarcinoma prognosis

Background

We sought to investigate the expression levels and prognosis value of TCEAL7 in primary gastric cancer.

Methods and Results

We investigated TCEAL7 and other homologous five members of the TCEAL family expression in normal gastricepithelial cell line and gastric cancer cell lines using real-time quantitative PCR. Furthermore, we examined the expression of TCEAL7 in 39 paired cancerous and matched adjacent noncancerous gastric mucosa tissues by real-time quantitative PCR and western blotting. Moreover, we analyzed TCEAL7 expression in 406 gastric cancer patients using immunohistochemistry. The relationships between the TCEAL7 expression levels, the clinicopathological factors, and patient survival were investigated. RT- qPCR data showed that mRNA expression level of TCEAL7 was significantly lower in the gastric cancer cell lines comparing with the levels of other five members of the TCEAL family. Results also revealed decreased TCEAL7 mRNA (P = 0.025) and protein (P = 0.012) expression in tumor tissue samples compared with matched adjacent non-tumor tissue samples. Immunohistochemical staining data showed that TCEAL7 expression was significantly decreased in 43.3% of gastric adenocarcinoma cases. The result also showed that the low TCEAL7 expression was significantly correlated with female, larger tumor size, higher histological grade and worse nodal status. Kaplan–Meier survival curves revealed that the reduced expression of TCEAL7 was associated with a poor prognosis in gastric adenocarcinoma patients (P<0.001). Based on a univariate analysis that included all 406 patients, TCEAL7 expression was found to have statistically significant associations with overall survival (P<0.001). Multivariate analysis also demonstrated that TCEAL7 expression (P = 0.009), age, tumor size, histological grade, lymphovascular invasion, T stage, N stage and M stage were independent risk factors in the prognosis of gastric cancer patients.

Conclusions

Our study suggests that TCEAL7 might serve as a candidate tumor suppressor and a potential prognostic biomarker in gastric carcinogenesis.

X-linked gene transcription patterns in female and male in vivo, in vitro and cloned porcine individual blastocysts

To determine the presence of sexual dimorphic transcription and how in vitro culture environments influence X-linked gene transcription patterns in preimplantation embryos, we analyzed mRNA expression levels in in vivo-derived, in vitro-fertilized (IVF), and cloned porcine blastocysts. Our results clearly show that sex-biased expression occurred between female and male in vivo blastocysts in X-linked genes. The expression levels of XIST, G6PD, HPRT1, PGK1, and BEX1 were significantly higher in female than in male blastocysts, but ZXDA displayed higher levels in male than in female blastocysts. Although we found aberrant expression patterns for several genes in IVF and cloned blastocysts, similar sex-biased expression patterns (on average) were observed between the sexes. The transcript levels of BEX1 and XIST were upregulated and PGK1 was downregulated in both IVF and cloned blastocysts compared with in vivo counterparts. Moreover, a remarkable degree of expression heterogeneity was observed among individual cloned embryos (the level of heterogeneity was similar in both sexes) but only a small proportion of female IVF embryos exhibited variability, indicating that this phenomenon may be primarily caused by faulty reprogramming by the somatic cell nuclear transfer (SCNT) process rather than in vitro conditions. Aberrant expression patterns in cloned embryos of both sexes were not ameliorated by treatment with Scriptaid as a potent HDACi, although the blastocyst rate increased remarkably after this treatment. Taken together, these results indicate that female and male porcine blastocysts produced in vivo and in vitro transcriptional sexual dimorphisms in the selected X-linked genes and compensation of X-linked gene dosage may not occur at the blastocyst stage. Moreover, altered X-linked gene expression frequently occurred in porcine IVF and cloned embryos, indicating that X-linked gene regulation is susceptible to in vitro culture and the SCNT process, which may eventually lead to problems with embryonic or placental defects.

Bex2 regulates cell proliferation and apoptosis in malignant glioma cells via the c-Jun NH2-terminal kinase pathway

The function of Bex2, a member of the Brain Expressed X-linked gene family, in glioma is controversial and its mechanism is largely unknown. We report here that Bex2 regulates cell proliferation and apoptosis in malignant glioma cells via the c-Jun NH2-terminal kinase (JNK) pathway. The expression level of Bex2 is markedly increased in glioma tissues. We observed that Bex2 over-expression promotes cell proliferation, while down-regulation of Bex2 inhibits cell growth. Furthermore, Bex2 down-regulation promotes cell apoptosis and activates the JNK pathway; these effects were abolished by administration of the JNK specific inhibitor, SP600125. Thus, Bex2 may be an important player during the development of glioma.

Transcriptional dynamics of the sex chromosomes and the search for offspring sex-specific antigens in sperm

The ability to pre-select offspring sex via separation of X- and Y-bearing sperm would have profound ramifications for the animal husbandry industry. No fully satisfactory method is as yet available for any species, although flow sorting is commercially viable for cattle. The discovery of antigens that distinguish X- and Y-bearing sperm, i.e. offspring sex-specific antigens (OSSAs), would allow for batched immunological separation of sperm and thus enable a safer, more widely applicable and high-throughput means of sperm sorting. This review addresses the basic processes of spermatogenesis that have complicated the search for OSSAs, in particular the syncytial development of male germ cells, and the transcriptional dynamics of the sex chromosomes during and after meiosis. We survey the various approaches taken to discover OSSA and propose that a whole-genome transcriptional approach to the problem is the most promising avenue for future research in the field.

In vivo-derived horse blastocysts show transcriptional upregulation of developmentally important genes compared with in vitro-produced horse blastocysts

In vitro-produced (IVP) equine blastocysts can give rise to successful pregnancies, but their morphology and developmental rate differ from those of in vivo-derived equine blastocysts. The aim of the present study was to evaluate this difference at the genetic level. Suppression subtractive hybridisation (SSH) was used to construct a cDNA library enriched for transcripts preferentially expressed in in vivo-derived equine blastocysts compared with IVP blastocysts. Of the 62 different genes identified in this way, six genes involved in embryonic development (BEX2, FABP3, HSP90AA1, MOBKL3, MCM7 and ODC) were selected to confirm this differential expression by reverse transcription–quantitative real-time polymerase chain reaction (RT-qPCR). Using RT-qPCR, five genes were confirmed to be significantly upregulated in in vivo-derived blastocysts (i.e. FABP3, HSP90AA1 (both P < 0.05), ODC, MOBKL3 and BEX2 (P < 0.005 for all three)), confirming the results of the SSH. There was no significant difference in MCM7 expression between IVP and in vivo-derived blastocysts. In conclusion, five genes that are transcriptionally upregulated in in vivo-derived equine blastocysts compared with IVP blastocysts have been identified. Because of their possible importance in embryonic development, the expression of these genes can be used as a marker to evaluate in vitro embryo production systems in the horse.

BEX2 has a functional interplay with c-Jun/JNK and p65/RelA in breast cancer

Background

We have previously demonstrated that BEX2 is differentially expressed in breast tumors and has a significant role in promoting cell survival and growth in breast cancer cells. BEX2 expression protects breast cancer cells against mitochondrial apoptosis and G1 cell cycle arrest. In this study we investigated the transcriptional regulation of BEX2 and feedback mechanisms mediating the cellular function of this gene in breast cancer.

Results

We found a marked induction of BEX2 promoter by c-Jun and p65/RelA using luciferase reporter assays in MCF-7 cells. Furthermore, we confirmed the binding of c-Jun and p65/RelA to the BEX2 promoter using a chromatin immunoprecipitation assay. Importantly, transfections of c-Jun or p65/RelA in MCF-7 cells markedly increased the expression of BEX2 protein. Overall, these results demonstrate that BEX2 is a target gene for c-Jun and p65/RelA in breast cancer. These findings were further supported by the presence of a strong correlation between BEX2 and c-Jun expression levels in primary breast tumors. Next we demonstrated that BEX2 has a feedback mechanism with c-Jun and p65/RelA in breast cancer. In this process BEX2 expression is required for the normal phosphorylation of p65 and IκBα, and the activation of p65. Moreover, it is necessary for the phosphorylation of c-Jun and JNK kinase activity in breast cancer cells. Furthermore, using c-Jun stable lines we showed that BEX2 expression is required for c-Jun mediated induction of cyclin D1 and cell proliferation. Importantly, BEX2 down-regulation resulted in a significant increase in PP2A activity in c-Jun stable lines providing a possible underlying mechanism for the regulatory effects of BEX2 on c-Jun and JNK.

Conclusions

This study shows that BEX2 has a functional interplay with c-Jun and p65/RelA in breast cancer. In this process BEX2 is a target gene for c-Jun and p65/RelA and in turn regulates the phosphorylation/activity of these proteins. These suggest that BEX2 is involved in a novel feedback mechanism with significant implications for the biology of breast cancer.

Polymorphisms in TCEAL7 and risk of epithelial ovarian cancer

OBJECTIVE

We have previously shown that TCEAL7 (transcription elongation factor A (SII)-like 7) is epigenetically down-regulated in the majority of epithelial ovarian cancers. We now examine the hypothesis that inherited alterations in TCEAL7 play a role in the etiology of ovarian cancer.

METHODS

A two-site case-control study of 930 cases of ovarian cancer and 1037 controls, frequency-matched on residence, age and race, was conducted. Six informative SNPs (tagSNPs and putative-functional SNPs) were genotyped. Logistic regression was used to adjust for potential confounders and determine if inherited variation at this locus was associated with risk of ovarian cancer in general and among cases with invasive disease and serous histology. Gene-level principal component and haplotype analyses were also conducted.

RESULTS

None of the SNPs or haplotypes studied were significantly associated with ovarian cancer risk overall. However, among the 440 invasive serous cases, the minor alleles for three correlated SNPs were significantly associated with reduced risk (p-values<0.05), summarized gene-level variation was weakly associated with reduced risk (p-value=0.05), and the predominant haplotype was less common among cases than controls (0.36 v 0.40, p-value=0.05), consistent with single-SNP results.

CONCLUSION

TCEAL7 polymorphisms may play a role in the development of invasive serous ovarian cancers. Follow-up molecular and replication studies are warranted.

Adaptive evolution and frequent gene conversion in the brain expressed X-linked gene family in mammals

This work examines the molecular evolution of a brain-expressed X-linked gene family in the mammalian genomes of human, chimp, macaque, mouse, rat, dog, and cow. The gene structures are well conserved across family members and among the mammals in that all five members have three exons with the first two exons untranslated. Furthermore, the five members are arranged tandemly on chromosome X with Bex5, Bex1, Bex2 on the negative strand and Bex4, Bex3 on the positive strand, and this physical arrangement remains conserved among species. Sequence analyses indicate that gene conversion has been frequent and ongoing among Bex1-4, occurring in multiple species independently. All gene conversions in different species between Bex1 and Bex4, and between Bex2 and Bex3, appear to be limited to the upstream regions of the third exon, whereas the gene conversions occurred independently in different species between Bex1 and Bex2 and cover only the third exon. Bex5 appears to have little exchange of genetic information with other members, possibly due to its distance from other members. The GC content decreases from 5'-UTR, intron 1, intron 2, coding region, to 3'-UTR, reflecting faithfully the frequency of gene conversion in different regions of the Bex genes. Sequence analyses also suggest that both relaxed selective constraint and positive selection have acted on the Bex members after duplication. In particular, Bex3 shows strong evidence of positive selection and seems to have evolved a new gene function after gene duplication.

BEX2 is overexpressed in a subset of primary breast cancers and mediates nerve growth factor/nuclear factor-kappaB inhibition of apoptosis in breast cancer cell lines

We have identified a novel subtype of estrogen receptor (ER)-positive breast cancers with improved outcome after tamoxifen treatment and characterized by overexpression of the gene BEX2. BEX2 and its homologue BEX1 have highly correlated expression and are part of a cluster enriched for ER response and apoptosis genes. BEX2 expression is induced after estradiol (E2) treatment with a peak at 3 h, suggesting BEX2 is an estrogen-regulated gene. BEX2 belongs to a family of genes, including BEX1, NGFRAP1 (alias BEX3), BEXL1 (alias BEX4), and NGFRAP1L1 (alias BEX5). Both BEX1 and NGFRAP1 interact with p75NTR and modulate nerve growth factor (NGF) signaling through nuclear factor-kappaB (NF-kappaB) to regulate cell cycle, apoptosis, and differentiation in neural tissues. In breast cancer cells, NGF inhibits C2-induced apoptosis through binding of p75NTR and NF-kappaB activation. Here, we show that BEX2 expression is necessary and sufficient for the NGF-mediated inhibition (through NF-kappaB activation) of C2-induced apoptosis. We also show that BEX2 modulates apoptosis of breast cancer cells in response to E2 (50 nmol/L) and tamoxifen (5 and 10 micromol/L). Furthermore, BEX2 overexpression enhances the antiproliferative effect of tamoxifen at pharmacologic dose (1 micromol/L). These data suggest that a NGF/BEX2/NF-kappaB pathway is involved in regulating apoptosis in breast cancer cells and in modulating response to tamoxifen in primary tumors.

The TSC1 gene product hamartin interacts with NADE

Hamartomatous brain lesions are a hallmark of brain pathology of tuberous sclerosis complex (TSC). To elucidate the mechanism of tumor development in the brain of TSC, we identified NADE (p75NTR-associated cell death executor) as an interactor for TSC1 gene product hamartin using a yeast two-hybrid system. In a pull-down assay, endogenous NADE was purified with the immobilized coiled-coil domain (CCD) of hamartin from the PC12h cell lysate. Immunofluorescence and immunoprecipitation confirmed the interaction of hamartin and NADE in cultured neurons and mouse brain lysate. Hamartin constitutively associated with NADE to prevent its proteasomal degradation. Suppression of hamartin with TSC1 small interfering RNA (siRNA) caused reduction of NADE and failed to lead to NGF-induced apoptosis in PC12h cells. These results indicate that hamartin binds to NADE to regulate neuronal cell function and loss of this association is likely to contribute to the brain pathology in TSC.

Expression profiling of the mouse early embryo: reflections and perspectives

The laboratory mouse model plays important roles in our understanding of early mammalian development and provides an invaluable model for human early embryos, which are difficult to study for ethical and technical reasons. A comprehensive collection of cDNA clones, their sequences, and complete genome sequence information, which have been accumulated over the past two decades, reveal even further the value of the mouse models. Here, the progress in global gene expression profiling in early mouse embryos and, to some extent, stem cells is reviewed and future directions and challenges are discussed. The discussions include the restatement of global gene expression profiles as a snapshot of cellular status, and subsequent distinction between the differentiation state and physiological state of the cells. The discussions then extend to the biological problems that can be addressed only through global expression profiling, including a bird's-eye view of global gene expression changes, molecular index for developmental potency, cell lineage trajectory, microarray-guided cell manipulation, and the possibility of delineating gene regulatory cascades and networks.

Rex3 (reduced in expression 3) as a new tumor marker in mouse hepatocarcinogenesis

In a previous microarray expression analysis, Rex3, a gene formerly not linked to tumor formation, was found to be highly overexpressed in both Ctnnb1-(beta-Catenin) and Ha-ras-mutated mouse liver tumors. Subsequent analyses by in situ hybridization and real-time PCR confirmed a general liver tumor-specific overexpression of the gene (up to 400-fold). To investigate the role of Rex3 in liver tumors, hepatoma cells were transfected with FLAG- and Myc-tagged Rex3 expression vectors. Rex3 was shown to be exclusively localized to the cytoplasm, as determined by fluorescence microscopy and Western blotting. However, forced overexpression of Rex3 did not significantly affect proliferation or stress-induced apoptosis of transfected mouse hepatoma cells. Rex3 mRNA was determined in primary hepatocytes in culture by real-time PCR. In primary mouse hepatocytes, expression of Rex3 increased while cells dedifferentiated in culture. This effect was abolished when hepatocytes were maintained in a differentiated state. Furthermore, expression of Rex3 decreased in mouse liver with age of mice and the expression profile was highly correlated to that of the tumor markers alpha-fetoprotein and H19. The findings suggest a role of Rex3 as a marker for hepatocyte differentiation/dedifferentiation processes and tumor formation.

Bex1, a novel interactor of the p75 neurotrophin receptor, links neurotrophin signaling to the cell cycle

A screening for intracellular interactors of the p75 neurotrophin receptor (p75NTR) identified brain-expressed X-linked 1 (Bex1), a small adaptor-like protein of unknown function. Bex1 levels oscillated during the cell cycle, and preventing the normal cycling and downregulation of Bex1 in PC12 cells sustained cell proliferation under conditions of growth arrest, and inhibited neuronal differentiation in response to nerve growth factor (NGF). Neuronal differentiation of precursors isolated from the brain subventricular zone was also reduced by ectopic Bex1. In PC12 cells, Bex1 overexpression inhibited the induction of NF-kappaB activity by NGF without affecting activation of Erk1/2 and AKT, while Bex1 knockdown accelerated neuronal differentiation and potentiated NF-kappaB activity in response to NGF. Bex1 competed with RIP2 for binding to the p75NTR intracellular domain, and elevating RIP2 levels restored the ability of cells overexpressing Bex1 to differentiate in response to NGF. Together, these data establish Bex1 as a novel link between neurotrophin signaling, the cell cycle, and neuronal differentiation, and suggest that Bex1 may function by coordinating internal cellular states with the ability of cells to respond to external signals.

Human Bex2 interacts with LMO2 and regulates the transcriptional activity of a novel DNA-binding complex

Human Bex2 (brain expressed X-linked, hBex2) is highly expressed in the embryonic brain, but its function remains unknown. We have identified that LMO2, a LIM-domain containing transcriptional factor, specifically interacts with hBex2 but not with mouse Bex1 and Bex2. The interaction was confirmed both by pull-down with GST-hBex2 and by coimmunoprecipitation assays in vivo. Using electrophoretic mobility shift assay, we have demonstrated the physical interaction of hBex2 and LMO2 as part of a DNA-binding protein complex. We have also shown that hBex2 can enhance the transcriptional activity of LMO2 in vivo. Furthermore, using mammalian two-hybrid analysis, we have identified a neuronal bHLH protein, NSCL2, as a novel binding partner for LMO2. We then showed that LMO2 could up-regulate NSCL2-dependent transcriptional activity, and hBex2 augmented this effect. Thus, hBex2 may act as a specific regulator during embryonic development by modulating the transcriptional activity of a novel E-box sequence-binding complex that contains hBex2, LMO2, NSCL2 and LDB1.

Characterization of the Bex gene family in humans, mice, and rats

To better understand the development of ventral mesencephalic dopamine neurons, we performed subtractive hybridization screens to find ventral mesencephalic genes expressed at rat embryonic day 10 when these neurons begin to differentiate. The most commonly identified genes in these screens were members of the Bex (Brain expressed X-linked) gene family, rat Bex1 (Rex3), and a novel gene, rat Bex4. After identifying these genes, we then sought to characterize the Bex gene family. Two additional novel Bex genes (human Bex5 and mouse Bex6) were discovered through genomic databases. Bex5 is present in humans and monkeys, but not rodents, while Bex6 exists in mice, but not humans. Bex4 and Bex5 are localized to the X chromosome, are expressed in brain, and are similar in sequence. Bex4 and Bex5 are 54% and 56% identical to human Bex3 (pHGR74, NADE). Mouse Bex6 is on chromosome 16 and is 67% identical to mouse Bex4. Human Bex gene expression was studied with tissue expression arrays probed with specific oligonucleotides. Human Bex1 and Bex2 have similar expression patterns in the central nervous system with high levels in pituitary, cerebellum, and temporal lobe, and Bex1 is widely expressed outside of the central nervous system with high expression in the liver. Human Bex4 is highly expressed in heart, skeletal muscle, and liver, while Bex3 and Bex5 are more widely expressed. The subcellular localization of the Bex proteins varies from nuclear (rat Bex1) to cytoplasmic (rat Bex3, human Bex5, and mouse Bex6) and to both nuclear and cytoplasmic (rat Bex2 and rat Bex4). Rat Bex3, rat Bex4, human Bex5, and mouse Bex6 are degraded by the proteasome, while rat Bex1 or Bex2 are not. Rat Bex3 protein can likely bind transition metals through a histidine-rich domain. Because this gene family was originally named Bex and because these genes are unified by sequence similarity and gene structure, we believe the Bex nomenclature should prevail over nomenclature based on function (NADE) that has not been extended to the other Bex genes. We conclude that the Bex gene family members are highly homologous but differ in their expression patterns, subcellular localization, and degradation by the proteasome.

Mammalian BEX, WEX and GASP genes: coding and non-coding chimaerism sustained by gene conversion events

BACKGROUND

The identification of sequence innovations in the genomes of mammals facilitates understanding of human gene function, as well as sheds light on the molecular mechanisms which underlie these changes. Although gene duplication plays a major role in genome evolution, studies regarding concerted evolution events among gene family members have been limited in scope and restricted to protein-coding regions, where high sequence similarity is easily detectable.

RESULTS

We describe a mammalian-specific expansion of more than 20 rapidly-evolving genes on human chromosome Xq22.1. Many of these are highly divergent in their protein-coding regions yet contain a conserved sequence motif in their 5' UTRs which appears to have been maintained by multiple events of concerted evolution. These events have led to the generation of chimaeric genes, each with a 5' UTR and a protein-coding region that possess independent evolutionary histories. We suggest that concerted evolution has occurred via gene conversion independently in different mammalian lineages, and these events have resulted in elevated G+C levels in the encompassing genomic regions. These concerted evolution events occurred within and between genes from three separate protein families ('brain-expressed X-linked' [BEX], WWbp5-like X-linked [WEX] and G-protein-coupled receptor-associated sorting protein [GASP]), which often are expressed in mammalian brains and associated with receptor mediated signalling and apoptosis.

CONCLUSION

Despite high protein-coding divergence among mammalian-specific genes, we identified a DNA motif common to these genes' 5' UTR exons. The motif has undergone concerted evolution events independently of its neighbouring protein-coding regions, leading to formation of evolutionary chimaeric genes. These findings have implications for the identification of non protein-coding regulatory elements and their lineage-specific evolution in mammals.

Transgenic Overexpression of Vascular Endothelial Growth Factor-B Isoforms by Endothelial Cells Potentiates Postnatal Vessel Growth In Vivo and In Vitro

Vascular endothelial growth factors (VEGFs) play significant roles in endothelial growth, survival, and function, and their potential use as therapeutic agents to promote the revascularization of ischemic tissues in being avidly explored. VEGF-A has received most attention, as it is a potent stimulator of vascular growth. Results in clinical trials of VEGF-A as a therapeutic agent have fallen short of high expectations because of serious edematous side effects caused by its activity in promoting vascular permeability. VEGF-B, a related factor, binds some of the VEGF-A receptors but not to VEGF receptor 2, which is implicated in the vascular permeability promoting activity of VEGF-A. Despite little in vitro evidence to date for the ability of Vegf-B to directly promote angiogenesis, recent data indicate that it may promote postnatal vascular growth in mice, suggesting that it may have potential therapeutic application. We have specifically studied the effects of VEGF-B on vascular growth in vivo and on angiogenesis in vitro by analyzing transgenic mice in which individual isoforms ( VEGFB 167 Tg and VEGFB 186 Tg) of VEGF-B are overexpressed in endothelial cells. VEGFB 167 Tg and VEGFB 186 Tg mice displayed enhanced vascular growth in the Matrigel assay in vivo and during cutaneous wound healing. In the aortic explant assay, explants from VEGFB 167 Tg and VEGFB 186 Tg mice displayed elevated vascular growth, suggesting a direct effect of VEGF-B isoforms in potentiating angiogenesis. These data support the use of VEGF-B as a therapeutic agent to promote vascular growth, in part, by potentiating angiogenesis. Furthermore, the lack of vascular permeability activity associated with either transgenic overexpression of the VEGF-B gene in endothelial cells or application of VEGF-B protein to the skin of mice in the Miles assay indicates that use of VEGF-B as a therapy should not be associated with edematous side effects.

Epigenetic silencing of TCEAL7 (Bex4) in ovarian cancer

Epigenetic silencing by hypermethylation of CpGs represents a mechanism of inactivation of tumor suppressors. Here we report on the cloning of a novel candidate tumor suppressor gene TCEAL7 inactivated by methylation in ovarian cancer. TCEAL codes for a 1.35 kb transcript that was previously reported to be downregulated in ovarian cancer by cDNA microarray and suppression subtraction cDNA (SSH) analyses. This report focuses on the elucidation of mechanisms associated with TCEAL7 downregulation. Expression of TCEAL7 is downregulated in a majority of ovarian tumors and cancer cell lines but induced by 5-aza-2'-deoxycytidine treatment in a dose-dependant manner, implicating methylation as a mechanism of TCEAL7 inactivation. Sequence analyses of bisufite-modified genomic DNA from somatic cell hybrids with either the active or the inactive human X chromosome reveal that TCEAL7 is subjected to X chromosome inactivation. Loss of TCEAL7 expression in primary tumors and cell lines correlates with methylation of a CpG site within the promoter. In vitro methylation of the CpG site suppresses promoter activity whereas selective demethylation of the SmaI site attenuates the suppression. Finally, re-expression of TCEAL7 in cancer cell lines induces cell death and reduces colony formation efficiency. These data implicate TCEAL7 as a cell death regulatory protein that is frequently inactivated in ovarian cancers, and suggest that it may function as a tumor suppressor.

Immunolocalization of Bex protein in the mouse brain and olfactory system

Bex proteins are expressed from a family of "brain expressed X-linked genes" that are closely linked on the X-chromosome. Bex1 and 2 have been characterized as interacting partners of the olfactory marker protein (OMP). Here we report the distribution of Bex1 and Bex2 mRNAs in several brain regions and the development and characterization of an antibody to mouse Bex1 protein that cross-reacts with Bex2 (but not Bex3), and its use to determine the cellular distribution of Bex proteins in the murine brain. The specificity of the antiserum was characterized by immunoprecipitation and Western blots of tissue and transfected cell extracts and by immunocytochemical analyses of cells transfected with either Bex1 or Bex2. Antibodies preabsorbed with Bex2 still recognize Bex1, while blocking with Bex1 eliminates all immunoreactivity to both Bex1 and Bex2. Bex immunoreactivity (ir) was primarily localized to neuronal cells within several regions of the brain, including the olfactory epithelium, bulb, peri/paraventricular nuclei, suprachiasmatic nucleus, arcuate nucleus, median eminence, lateral hypothalamic area, thalamus, hippocampus, and cerebellum. RT-PCR and in situ hybridization demonstrated the presence of Bex mRNA in several of these regions. Double-label immunocytochemistry indicates that Bex-ir is colocalized with OMP in mature olfactory receptor neurons (ORNs) and in the OMP-positive subpopulation of neurons in hypothalamus. This is the first anatomical mapping of Bex proteins in the mouse brain and their colocalization with OMP in ORNs and hypothalamus.

Bex3 associates with replicating mitochondria and is involved in possible growth control of F9 teratocarcinoma cells

Bex3 expression and possible function in growth control were studied. It was expressed in a limited number of organs, including gonads and hippocampal regions of the brain. Visualized by deconvolution microscopy as a GFP-fusion protein in F9 teratocarcinoma cells, Bex3 localized, along with concentrations of actin, at perinuclear mitochondria that were undergoing active DNA replication. Bex3 association with mitochondria required a nuclear export signal (NES) and the C-terminal four amino acids (CaaX box), and siRNA reduction of Bex3 levels led to slow or negligible growth rates of the F9 cells. Thus, Bex3 may be required in target tissues for mitochondrial function at a distinct phase of the cellular growth cycle.

The interaction of Bex and OMP reveals a dimer of OMP with a short half-life

Olfactory marker protein (OMP) participates in the olfactory signal transduction pathway. This is evident from the behavioral and electrophysiological deficits of OMP-null mice, which can be reversed by intranasal infection of olfactory sensory neurons with an OMP-expressing adenovirus. Bex, brain expressed X-linked protein, has been identified as a protein that interacts with OMP. We have now further characterized the interaction of OMP and Bex1/2 by in vitro binding assays and by immuno-coprecipitation experiments. OMP is a 19 kDa protein but these immunoprecipitation studies have revealed the unexpected presence of a 38 kDa band in addition to the expected 19 kDa band. Furthermore, the 38 kDa form was preferentially co-immunoprecipitated with Bex from cell extracts. In-gel tryptic digestion, mass spectrometry, and two-dimensional gel electrophoresis indicate that the 38 kDa protein behaves as a covalently cross-linked OMP-homodimer. The 38 kDa band was also identified in western blots of olfactory epithelium demonstrating its presence in vivo. The stabilities and subcellular localizations of the OMP-monomer and -dimer were studied in transfected cells. These results demonstrated that the OMP-dimer is much less stable than the monomer, and that while the monomer is present both in the nuclear and cytosolic compartments, the dimer is preferentially located in a Triton X-100 insoluble cytoskeletal fraction. These novel observations led us to hypothesize that regulation of the level of the rapidly turning-over OMP-dimer and its interaction with Bex1/2 is critical for OMP function in sensory transduction.

Differences between human and mouse embryonic stem cells

We compared gene expression profiles of mouse and human ES cells by immunocytochemistry, RT-PCR, and membrane-based focused cDNA array analysis. Several markers that in concert could distinguish undifferentiated ES cells from their differentiated progeny were identified. These included known markers such as SSEA antigens, OCT3/4, SOX-2, REX-1 and TERT, as well as additional markers such as UTF-1, TRF1, TRF2, connexin43, and connexin45, FGFR-4, ABCG-2, and Glut-1. A set of negative markers that confirm the absence of differentiation was also developed. These include genes characteristic of trophoectoderm, markers of germ layers, and of more specialized progenitor cells. While the expression of many of the markers was similar in mouse and human cells, significant differences were found in the expression of vimentin, beta-III tubulin, alpha-fetoprotein, eomesodermin, HEB, ARNT, and FoxD3 as well as in the expression of the LIF receptor complex LIFR/IL6ST (gp130). Profound differences in cell cycle regulation, control of apoptosis, and cytokine expression were uncovered using focused microarrays. The profile of gene expression observed in H1 cells was similar to that of two other human ES cell lines tested (line I-6 and clonal line-H9.2) and to feeder-free subclones of H1, H7, and H9, indicating that the observed differences between human and mouse ES cells were species-specific rather than arising from differences in culture conditions.

Differential gene expressions in the visual cortex of postnatal day 1 versus day 21 rats revealed by suppression subtractive hybridization

The neonatal visual cortex is a highly plastic structure and its development is guided by visual experience during early postnatal life. Rats do not open their eyes until the end of the second postnatal week. We hypothesized that the expression of genes in the visual cortex would differ before and after eye opening. As a first step in uncovering these differences, we compared gene expressions in the visual cortex of postnatal days (PND) 1 and 21 rats. Suppression subtractive hybridization was performed using PND1 samples as the tester and PND21 as the driver. More than 30 genes were expressed at a higher level in PND1 than PND21 samples, but 5 fragments showed higher copies than others. PCR product of the five fragments was gel-purified and cloned into pCRII vectors. They showed significant homology to cDNA of genes: (A). clone MGC: 19375; (B). Type II iodothyronine 5'-deiodinase (D2); (C). reduced expression 3 gene; (D). lactosylceramide synthase; and (E). septin 4, respectively. Functions of A, C and E are unknown. By means of RACE PCR, three full-length cDNAs not reported previously in the rat were obtained for A, C and E, and we named them "expression genes 1, 2 and 3, respectively, in the rat visual cortex (EG1RVC, EG2RVC and EG3RVC)". EG1RVC was further characterized by Northern blots, in situ hybridization and in vitro transfection. These approaches confirmed that EG1RVC was expressed at a significantly higher level in PND1 than in PND21 visual cortical samples, and that transfected PC12 cells and primary neuronal cultures showed expression mainly in neuronal cell bodies. Our data indicate that genes expressed more abundantly on PND1 are associated with various metabolic pathways and enzymatic changes, and may play an important role in visual cortical development, growth and/or plasticity.

The role of neurotransmission and the Chopper domain in p75 neurotrophin receptor death signaling

The role of p75 neurotrophin receptor (p75NTR) in mediating cell death is now well characterized, however, it is only recently that details of the death signaling pathway have become clearer. This review focuses on the importance of the juxtamembrane Chopper domain region of p75NTR in this process. Evidence supporting the involvement of K+ efflux, the apoptosome (caspase-9, apoptosis activating factor-1, APAF-1, and Bcl-xL), caspase-3, c-jun kinase, and p53 in the p75NTR cell death pathway is discussed and regulatory roles for the p75NTR ectodomain and death domain are proposed. The role of synaptic activity is also discussed, in particular the importance of neutrotransmitter-activated K+ channels acting as the gatekeepers of cell survival decisions during development and in neurodegenerative conditions.

Two genome-wide linkage disequilibrium screens in Scandinavian multiple sclerosis patients

We report the first two genome-wide screens for linkage disequilibrium between putative multiple sclerosis (MS) susceptibility genes and genetic markers performed in the genetically homogenous Scandinavian population, using 6000 microsatellite markers and DNA pools of approximately 200 MS cases and 200 controls in each screen. Usable data were achieved from the same 3331 markers in both screens. Nine markers from eight genomic regions (1p33, 3q13, 6p21, 6q14, 7p22, 9p21, 9q21 and Xq22) were identified as potentially associated with MS in both screens.

Identification of members of the Bex gene family as olfactory marker protein (OMP) binding partners

Olfactory marker protein (OMP) expression is a hallmark of mature vertebrate olfactory receptor neurons (ORNs). Evidence for OMP function derives from altered behavioral and electrophysiological activities of OMP-KO mice. The molecular basis for the altered phenotype following the deletion of OMP is still unclear. Recent structural studies predict the involvement of OMP in protein-protein interaction. Here we report the identification of an OMP partner, Bex2, by phage-display screening of an olfactory mucosal cDNA-library. In situ hybridization demonstrates cellular co-localization of OMP mRNA with mRNAs for Bex1, Bex2, and Bex3 in ORNs of olfactory tissue of the mouse. The OMP/Bex interaction has been confirmed by demonstrating the chemical cross-linking of recombinant rat OMP with a synthetic peptide derived from the Bex amino acid sequence. The subcellular localization of Bex and OMP proteins was evaluated in transfected HEK293 cells. Bex is visualized in the nucleus and cytoplasm. Following co-transfection we observed the unexpected presence of some OMP in the nucleus along with Bex. Together, these data argue convincingly that we have identified Bex as an OMP partner whose further characterization will provide insight to the role of OMP and to the mechanism of the OMP/Bex interaction in ORN differentiation and function.

Nerve growth factor-dependent regulation of NADE-induced apoptosis

The p75 neurotrophin receptor (p75NTR) is a member of the tumor necrosis factor receptor (TNFR) superfamily, and can mediate both cell survival and cell death in response to nerve growth factor (NGF). Based on the structural and functional differences between p75NTR and the related receptors Fas or TNFR, it has been suggested that these receptors have distinct signaling functions. NADE (p75NTR-associated cell death executor) is a p75NTR-associated protein that mediates apoptosis in response to NGF by interacting with the cell death domain of p75NTR. NADE has at least four isoforms, designated as NADE2, NADE3, NADE4/Bex1, and NADE5/Bex2. NADE plays a role in NGF-induced apoptosis in oligodendrocytes and in zinc-induced neuronal death. In this review, we focus on the proapoptotic actions of NADE that regulate p75NTR signaling in response to NGF.

Olfactory marker protein (OMP) exhibits a beta-clam fold in solution: implications for target peptide interaction and olfactory signal transduction

Olfactory marker protein (OMP) is a ubiquitous, cytoplasmic protein found in mature olfactory receptor neurons of all vertebrates. Electrophysiological and behavioral studies demonstrate that it is a modulator of the olfactory signal transduction pathway. Here, we demonstrate that the solution structure of OMP, as determined by NMR studies, is a single globular domain protein comprised of eight beta-strands forming two beta-sheets oriented orthogonally to one another, thus exhibiting a "beta-clam" or "beta-sandwich" fold: beta-sheet 1 is comprised of beta3-beta8-beta1-beta2 and beta-sheet 2 contains beta6-beta5-beta4-beta7. Insertions include two, long alpha-helices located on opposite sides of the beta-clam and three flexible loops. The juxtaposition of beta-strands beta6-beta5-beta4-beta7-beta2-beta1-beta8-beta3 forms a continuously curved surface and encloses one side of the beta-clam. The "cleft" formed by the two beta-sheets is opposite to the closed end of the beta-clam. Using a peptide titration series, we have identified this cleft as the binding surface for a peptide derived from the Bex1 protein. The highly conserved Omega-loop structure adjacent to the Bex1 peptide-binding surface found in OMP may be the site of additional OMP-protein interactions related to its role in modulating olfactory signal transduction. Thus, the interaction between the OMP and Bex1 proteins could facilitate the interaction between OMP and other components of the olfactory signaling pathway.

Structure-function analysis of NADE: identification of regions that mediate nerve growth factor-induced apoptosis

Nerve growth factor (NGF) can induce apoptosis in neural cells via activation of the low affinity neurotrophin receptor p75NTR. NADE (p75NTR-associated cell death executor) is a p75NTR-associated protein that mediates apoptosis in response to NGF by interacting with the death domain of p75NTR in 293T, PC12, and nnr5 cells (Mukai, J., Hachiya, T., Shoji-Hoshino, S., Kimura, M. T., Nadano, D., Suvanto, P., Hanaoka, T., Li, Y., Irie, S., Greene, L. A., and Sato, T. A. (2000) J. Biol. Chem. 275, 17566-17570). We performed extensive mutational analysis on NADE, to better characterize its structural and functional features. Truncation of a minimal region, including amino acid residues 41-71 of NADE, was found to be sufficient to induce apoptosis. The designated regulatory region includes the C-terminal amino acid residues (72-112) and is essential for NGF-dependent regulation of NADE-induced apoptosis. Furthermore, the mutants with amino acid substitutions in the leucine-rich nuclear export signal (NES) sequence (residues 90-100) abolished the export of NADE from the nucleus to the cytoplasm. Mutation of the NES also abolished self-association of NADE, its interaction with p75NTR, and NGF-dependent apoptosis. Expression of a fragment of NADE (amino acid residues 81-124) blocked NGF-induced apoptosis in oligodendrocytes, suggesting that this region has a dominant negative effect on NGF/p75NTR-induced apoptosis. These studies identify distinct regions of NADE that are involved in regulating specific functions involved in p75NTR signal transduction.