Expression of transforming growth factor-beta 3 by embryonal carcinoma cells, parietal endoderm-like cells and early mouse embryos

Co-expression analysis of fetal weight-related genes in ovine skeletal muscle during mid and late fetal development stages

BACKGROUND

Muscle development and lipid metabolism play important roles during fetal development stages. The commercial Texel sheep are more muscular than the indigenous Ujumqin sheep.

RESULTS

We performed serial transcriptomics assays and systems biology analyses to investigate the dynamics of gene expression changes associated with fetal longissimus muscles during different fetal stages in two sheep breeds. Totally, we identified 1472 differentially expressed genes during various fetal stages using time-series expression analysis. A systems biology approach, weighted gene co-expression network analysis (WGCNA), was used to detect modules of correlated genes among these 1472 genes. Dramatically different gene modules were identified in four merged datasets, corresponding to the mid fetal stage in Texel and Ujumqin sheep, the late fetal stage in Texel and Ujumqin sheep, respectively. We further detected gene modules significantly correlated with fetal weight, and constructed networks and pathways using genes with high significances. In these gene modules, we identified genes like TADA3, LMNB1, TGF-β3, EEF1A2, FGFR1, MYOZ1, and FBP2 correlated with fetal weight.

CONCLUSION

Our study revealed the complex network characteristics involved in muscle development and lipid metabolism during fetal development stages. Diverse patterns of the network connections observed between breeds and fetal stages could involve some hub genes, which play central roles in fetal development, correlating with fetal weight. Our findings could provide potential valuable biomarkers for selection of body weight-related traits in sheep and other livestock.

Isolation and characterization of the murine transforming growth factor-beta2 promoter

This report describes the isolation and characterization of the 5' flanking region of the murine transforming growth factor beta-2 (TGF-beta2) gene. A genomic clone containing the promoter region of the gene was isolated after screening a bacteriophage P1 genomic library. The resulting clone was sequenced and compared to promoters for the human and chicken TGF-beta2 genes. The sequence located near the transcription start site is highly conserved. It includes a TATA box, an E-box, and a largely conserved CRE/ATF site. A series of murine TGF-beta2 promoter/reporter constructs was generated to identify regulatory regions of the gene. As in the case of the human TGF-beta2 gene, sequences just upstream of the TATA box, including the CRE/ATF site, actively stimulate the murine TGF-beta2 promoter. However, unlike the human TGF-beta2 gene, the 5' flanking region of the murine TGF-beta2 gene contains a long alternating purine/pyrimidine repeat that unexpectedly exerts a strong positive effect on its promoter. This is of particular interest since alternating purine/pyrimidine repeats in other promoters have been observed to be inhibitory.

Transcriptional activation of the type II transforming growth factor-beta receptor gene upon differentiation of embryonal carcinoma cells

Previously, it has been shown that differentiation of embryonal carcinoma (EC) cells turns on the expression of functional transforming growth factor type-beta receptors. Here, we show that the type II receptor (TbetaR-II) gene is activated at the transcriptional level when EC cells differentiate. We show that the differentiated cells, but not the parental EC cells, express transcripts for TbetaR-II. In addition, the expression of TbetaR-II promoter/reporter gene constructs are elevated dramatically when EC cells differentiate and we identify at least two positive and two negative regulatory regions in the 5' flanking region of the TbetaR-II gene. Moreover, we identify a cAMP response element/activating transcription factor site that acts as a positive cis-regulatory element in the TbetaR-II promoter, and we demonstrate that the transcription factor ATF-1 binds to this site and strongly stimulates the expression of the TbetaR-II promoter/reporter gene constructs when ATF-1 is overexpressed in EC-derived differentiated cells. Equally important, we identify a negative regulatory element in a 53-base pair region that had previously been shown to inhibit strongly the expression of TbetaR-II promoter/reporter gene constructs. Specifically, we demonstrate that this region, which contains an inverted CCAAT box motif, binds the transcription factor complex NF-Y (also referred to as CBF) in vitro. Furthermore, expression of a dominant-negative NF-YA mutant protein, which prevents DNA binding by NF-Y, enhances TbetaR-II promoter expression. Together, these studies suggest that the transcription factors ATF-1 and NF-Y play important roles in the regulation of the TbetaR-II gene.

Transcriptional regulation of the TGF-beta 2 gene in choriocarcinoma cells and breast carcinoma cells: differential utilization of Cis-regulatory elements

Previous studies have shown that the transcription of the TGF-beta 2 gene is controlled by at least one negative and two positive regulatory regions in differentiated cells derived from both embryonal carcinoma cells and embryonic stem cells. The use of TGF-beta 2 promoter/reporter gene constructs has also identified a CRE/ATF motif near the TATA box that appears to heavily influence the transcription of the TGF-beta 2 gene. In this study, two choriocarcinoma cell lines, JAR and JEG-3, and the breast cancer cell line, MCF-7, were used to determine whether differences exist in the transcriptional regulation of the TGF-beta 2 gene. We demonstrated that both similarities and differences exist in the transcriptional regulation of this gene. Common to all cells examined to date, the positive regulatory region just upstream of the TATA box contains an essential CRE/ATF motif that binds at least one transcription factor, ATF-1, in gel mobility shift assays. However, we did not detect ATF-2 binding to this site with any of the nuclear extracts used. We also determined that the effect of the region between -187 and -78 (relative to the transcription start site) is cell type dependent. Previous studies have shown that this region acts to reduce the activity of the TGF-beta 2 promoter in differentiated cells derived from embryonal carcinoma cells and embryonic stem cells. In direct contrast, this region acts as a strong positive regulatory region in JAR, JEC-3, and MCF-7 cells. The mechanisms responsible for these differing effects remain to be established. Interestingly, this region does not appear to contain sequence motifs that bind known transcription factors. Thus, this region is likely to bind one or more novel transcription factors or contain novel recognition sites for known transcription factors.

Cis-regulatory elements and transcription factors involved in the regulation of the transforming growth factor-beta 2 gene

Embryonal carcinoma (EC) cells and embryonic stem (ES) cells provide useful model systems for studying differentiation during early mammalian development. Previous studies have demonstrated that differentiation of two restricted mouse EC cell lines is accompanied by activation of the TGF-beta 2 gene. Moreover, one negative and two positive regulatory regions upstream of the transcription start site were identified, which appear to play key roles in the transcriptional regulation of the human TGF-beta 2 gene. In this report, we demonstrate that the same three regulatory regions strongly influence the activity of the TGF-beta 2 promoter in differentiated cells derived from the multipotent human EC cell line, NT2/D1, and from the murine totipotent ES cell line, CCE. We also determined that the same three regions are active in the regulation of the TGF-beta 2 gene in the murine parietal endoderm-like cell line, PYS-2. However, an additional negative regulatory region appears to contribute to the regulation of the TGF-beta 2 gene in PYS-2 cells. Last, mutation of a CRE/ATF element located just upstream of the transcription start site of the TGF-beta 2 gene reduces significantly the activity of the TGF-beta 2 promoter in the differentiated cells. However, in contrast to our previous findings, our gel mobility shift analyses demonstrate that this CRE/ATF element is bound by similar proteins in nuclear extracts prepared from undifferentiated and differentiated mouse EC cells as well as from undifferentiated human EC cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of the transforming growth factor-beta 2 gene promoter in embryonal carcinoma cells and their differentiated cells: differential utilization of transcription factors

Previous studies demonstrated that differentiation of embryonal carcinoma (EC) cells increases the expression of the TGF-beta 2 gene and identified a CRE/ATF-like motif in the TGF-beta 2 promoter that is necessary for its activity. This suggested that differentiation may increase the transcription of this gene by differential binding of transcription factors to the CRE/ATF-like motif. To test this possibility, we performed gel mobility shift analysis using double-stranded oligodeoxynucleotides containing the TGF-beta 2 CRE/ATF-like motif and nuclear extracts prepared from F9 EC cells and F9-differentiated cells. We determined that the DNA/protein complexes formed by the EC nuclear extracts, but not the complexes formed by differentiated cell nuclear extracts, are recognized and supershifted by an ATF-1 specific antibody. This observation is consistent with our Western immunoblot analysis that detects AFT-1 in the EC cells, but not in their differentiated counterparts. In addition, we provide evidence that protein phosphorylation influences the formation of complexes between F9 nuclear proteins and the CRE/ATF-like motif. Together, our studies identify a likely role for the CRE/ATF-like motif in the regulation of TGF-beta 2 and suggest that this site binds one set of nuclear proteins in EC cells, where the gene is not expressed, and a different set of nuclear proteins in the differentiated cells, where the gene is expressed.

Transforming growth factor-beta 1 in reproduction and development

Expression patterns of TGF-beta s during embryogenesis and in adult reproductive organs, as well as the activities of these molecules in in vitro assays of biological processes relating to reproduction and development, have suggested that TGF-beta s may play a role in both reproductive function and embryonic development. To investigate the function of TGF-beta 1 in vivo, the murine TGF-beta 1 gene was disrupted by gene targeting, and animals that lacked TGF-beta 1 activity were generated. Homozygous mutant animals were obtained which exhibited a multifocal inflammatory disease. However, the observed numbers of homozygous mutant offspring were less than expected, suggesting the occurrence of some type of prenatal lethality. This paper reviews the proposed role of the TGF-beta s in reproductive and developmental processes and discusses observations obtained from the TGF-beta 1 gene-targeting experiments as they relate to these processes.

Secretion of transforming growth factor-beta isoforms by embryonic stem cells: isoform and latency are dependent on direction of differentiation

Murine embryonic stem (ES) cells are maintained in an undifferentiated state when cultured in medium conditioned by Buffalo rat liver (BRL) cells. BRL conditioned medium (CM) contains a differentiation inhibitory activity (DIA) that is synonymous with leukemia inhibitory factor (LIF). ES cells in monolayer culture can be induced to differentiate by addition of all-trans retinoic acid (RA) to the BRL CM, when they mainly form cells resembling parietal endoderm, or by culture in medium not conditioned by BRL cells. ES cells thus deprived of LIF/DIA differentiate spontaneously to a cell type that expresses Brachyury (T), a marker of early mesoderm. Northern blot analyses have shown previously that transcripts for transforming growth factor beta 1 (TGF-beta 1) are detected in undifferentiated cells while transcripts for TGF-beta 2 and TGF-beta 3 only become detectable after differentiation. We have now determined levels of TGF-beta protein in CM and in the extracellular matrix (ECM) and have used neutralizing antibodies specific for TGF-beta 1 and TGF-beta 2 that do not react with recombinant human TGF-beta 3 to determine the isoform secreted. Using the growth inhibition of mink lung CCL64 cells as a bioassay for TGF-beta activity, we demonstrate that undifferentiated ES cells secrete latent TGF-beta 1 into the medium but no activity is found in their ECM. Cells induced to differentiate with RA contain TGF-beta 2 in both active and latent forms in their CM. Likewise their ECM contains TGF-beta 2 as the sole isoform. ES cells deprived of LIF/DIA secrete both TGF-beta 1 and TGF-beta 2 isoforms in their CM but TGF-beta-like activity remains after addition of neutralizing antibodies for TGF-beta 1 and TGF-beta 2. This active TGF beta is the major component of the TGF-beta activity in this CM. By contrast, ECM from LIF/DIA deprived cells contains only the TGF-beta 1 and beta 2 isoforms. The remaining activity in CM correlates with high expression of TGF-beta 3 by Northern blot analysis in these cells. We speculate that TGF-beta 3 is secreted by these cells and may be activated more efficiently and/or in a different manner to TGF-beta 1 and TGF-beta 2, since it is present in CM only in its active form.

Transforming growth factor-beta in the early mouse embryo: implications for the regulation of muscle formation and implantation

In a search for functions of transforming growth factor-beta during early embryonic development we used two different experimental approaches. In the first we made use of embryonic stem (ES) cells. ES cells in culture differentiate to derivatives of all three germ layers and mimic some aspects of organogenesis when grown as aggregates in suspension to form embryoid bodies. Differentiation proceeds further when the embryoid bodies attach to suitable substrates. Muscle and neuronal cells are among the most readily identified cell types then formed. We examined the effect of all-trans retinoic acid (RA) and members of the transforming growth factor-beta family (TGF-beta 1, TGF-beta 2) under these conditions in an assay where single aggregates formed in hanging microdrops in medium supplemented with serum depleted of lipophilic substances which would include retinoids. Endoderm-like cells formed under all conditions tested. RA at concentrations of 10(-8) M and 10(-7) M induced the formation of neurons but in the absence of RA or at concentrations up to 10(-9) M, neurons were not observed. Instead, beating muscle formed in about one-third of the plated aggregates; this was greatly reduced when RA concentrations increased above 10(-9) M. Immunofluorescent staining for muscle specific myosin showed that two muscle cell types could be distinguished: elongated, non-contractile myoblasts and mononucleate flat cells. The mononucleate flat cells appeared to correspond with rhythmically contracting muscle. The number of non-contractile myoblasts increased 3-fold over controls in the presence of 10(-9) M RA. TGF-beta s increased the number of contractile and non-contractile muscle cells by a factor 3 to 7 over controls, depending on the TGF-beta isoform added and the muscle cell type formed. TGF-beta 2 also invariably increased the rate at which contracting muscle cells were first observed in replated aggregates. The stimulatory effect of TGF-beta s on the formation of mononucleate flat cells was completely abrogated by RA at 10(-9) M while the number of myoblasts under similar conditions was unchanged. These data suggest that a complex interplay between retinoids and TGF-beta isoforms may be involved in regulation of differentiation in early myogenesis. In the second approach, neutralizing polyclonal rabbit antibodies specific for TGF-beta 2 were injected into the cavity of mouse blastocysts 3.5 days post coîtum (pc). After 1 day in culture, embryos were transferred to pseudopregnant females. The number of decidua, embryos and resorptions were counted at day 8.5-9.5 pc.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential regulation of the transforming growth factor type-beta 2 gene promoter in embryonal carcinoma cells and their differentiated cells

Previous studies have shown that EC cells do not express detectable levels of TGF-beta 2 or its mRNA until they differentiate. This suggested that differentiation influences the transcription of the TGF-beta 2 gene in this model system. To address this possibility, we have examined the activity of the TGF-beta 2 promoter in EC cells and their differentiated cells using gene constructs containing various portions of the TGF-beta 2 promoter inserted upstream of the reporter gene, chloramphenicol acetyltransferase (CAT). We determined that the level of CAT increases approximately ninefold when EC cells were induced to differentiate. Our studies also indicate that the TGF-beta 2 promoter contains at least two positive regulatory elements that are separated by a negative regulatory element. Finally, we have identified a CRE/ATF-like site that appears to be responsible for a positive regulatory element located between -77 and -40.

Localization and binding of transforming growth factor-beta isoforms in mouse preimplantation embryos and in delayed and activated blastocysts

The stage and cell-specific accumulation of mammalian isoforms of transforming growth factor-beta (TGF-beta 1, TGF-beta 2, and TGF-beta 3) and TGF-beta binding were examined in the preimplantation embryo and in progesterone (P4)-treated delayed or P4 plus estradiol-17 beta (E2)-treated activated blastocysts in the mouse. Immunocytochemical studies revealed that while all three immunoreactive TGF-beta isoforms were present in one-cell embryos, very little or no immunostaining was observed in two-cell embryos. However, distinct immunostaining of these isoforms was again observed in four-cell embryos and persisted through the blastocyst stage. Among the isoforms studied, TGF-beta 2 immunostaining showed a unique pattern in late morulae. In many of these morulae, the staining was primarily observed in outside cells. However, in blastocysts, immunostaining for all three isoforms was present both in the inner cell mass (ICM) and trophectoderm (Tr). Immunostaining in sectioned blastocysts and immunosurgically isolated ICMs confirmed immunostaining in Tr and ICM cells. To ascertain whether preimplantation embryos can produce TGF-beta isoforms, immunostaining was performed in embryos grown in vitro from two-cell stage in simple balanced salt solution. Immunoreactive TGF-beta s 1-3 were present in embryos at all stages of development examined (four-cell embryos through blastocysts). The virtual absence of immunoactive TGF-beta s in two-cell embryos but their accumulation in embryos at later stages of development in vitro provides evidence that these growth factors were produced by embryos. In order to assess at what stages of development preimplantation embryos could be responsive to TGF-beta s, specific binding of [125I]TGF-beta 1 and [125I]TGF-beta 2 was performed in embryos and examined by autoradiography. Low levels of binding were first detected in eight-cell embryos. The binding increased in morulae followed by a further increase in blastocysts. Analysis of binding of [125I]TGF-beta 2 in immunosurgically isolated ICMs indicated that binding was primarily evident in Tr cells. Affinity labeling of TGF-beta 1 or TGF-beta 2 in Day 4 blastocysts revealed three classes of binding proteins with approximate molecular sizes of 65 kDa (type I), 90 kDa (type II), and greater than 250 kDa (type III), in addition to a doublet of 130 and 140 kDa proteins. This observation is similar to those reported for other cell types. The data suggest that embryos are likely to be responsive to TGF-beta s after the third cleavage.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression of fibroblast growth factor receptors by embryonal carcinoma cells and early mouse embryos

We have previously shown that differentiation of embryonal carcinoma (EC) cells leads to both increased binding of FGF (fibroblast growth factor) and suppression of k-FGF expression. In the current study, we examined the expression of FGF receptors by EC cells, EC-derived differentiated cells and early mammalian embryos using the technique of reverse transcription-polymerase chain reaction (RT-PCR). We determined that both mouse, F9, and human, NT2/D1, EC cells as well as their differentiated counterparts express transcripts for two forms of FGF receptors, bek (bacterially expressed kinase) and flg (fms-like gene). In addition, we determined that mouse blastocysts express flg transcripts. The presence of FGF receptor transcripts in early embryos and the previous finding of FGF-related activity in medium conditioned by mouse blastocysts argue that the FGF family plays important roles during early mammalian development.