Temporal and tissue-specific expression of the proto-oncogene c-fos during development in Xenopus laevis

Expression analysis of microRNAs and mRNAs in ovarian granulosa cells after microcystin-LR exposure

Microcystin is a cyclic heptapeptide compounds which could cause female mammals' reproductive toxicity. Ovarian granulosa cells (GCs) are essential for the growth and development of follicles. In this study, after mouse granulosa cells (mGCs) treated with microcystin-LR (MC-LR) for 48 h, microRNAs (miRNAs) and mRNAs microarray technology were adopted to detect the expression of miRNAs and mRNAs. The results showed that 125 miRNAs and 283 mRNAs changed significantly, including 50 miRNAs down-regulated (fold change < -1.2), 75 miRNAs up-regulated (fold change > 1.2), 162 mRNAs down-regulated (fold change < -1.15) and 121 mRNAs up-regulated (fold change > 1.15) in treated group compared with the control group. Functional analysis showed that significant changed miRNAs and mRNAs are mainly involved in proliferation, apoptosis, immunity, metabolism and other biological processes of mGCs. By KEGG pathways analysis, we found that differentially expressed miRNAs and mRNAs mainly participated in apoptosis, formation of cancer, proliferation, production of hormones and other related signal pathways. miRNA-gene network analysis indicated that miR-29b-3p, miR-29a-3p, miR-29c-3p, miR-1906, miR-182-5p, growth factor receptor bound protein 2-associated protein 2 (Gab2), FBJ osteosarcoma oncogene (Fos), insulin-like growth factor 1 (Igf1), mannosidase 1, alpha (Man1a) are key miRNAs and genes. The microarray results were validated by real-time fluorescent quantitative PCR (qRT-PCR).

Oocyte-Specific Expression of Mouse MEX3C652AA in the Ovary and Its Potential Role in Regulating Maternal Fos mRNA

Currently, the human MEX3C gene is known to encode an RNA-binding protein of 659 amino acid residues. Here we show that the MEX3C gene has alternative splicing forms giving rise to multiple MEX3C variants, and some cells express MEX3C transcripts coding for short MEX3C isoforms but not transcripts for MEX3C(659AA) MEX3C(659AA) functions as an adaptor protein for Exportin 1 (XPO1)-mediated nuclear export since it increases the cytoplasmic distribution of poly(A)(+) RNA and since addition of the nuclear export signal (NES) sequence to a short MEX3C isoform MEX3C(464AA) confers similar cytoplasmic poly(A)(+) RNA accumulation activity as MEX3C(659AA) FOS mRNA is a potential MEX3C target mRNA. One mechanism by which MEX3C(659AA) could regulate FOS mRNA is by promoting its nuclear export. Overexpressing MEX3C(659AA) significantly increased FOS mRNA expression, whereas mutating the NES of MEX3C(659AA) and treating cells with leptomycin B to inhibit XPO1-mediated nuclear export attenuated FOS upregulation. FOS mRNA is unstable in somatic cells but less so in oocytes; how it is stabilized in the oocytes is unknown. Transcripts for the mouse counterpart of human MEX3C(659AA) (MEX3C(652AA)) are specifically expressed in developing oocytes in the ovary, although total Mex3c transcripts are expressed in both granulosa cells and oocytes. The specific expression of this long MEX3C isoform in oocytes and its ability to enhance FOS mRNA nuclear export and stability all suggest that MEX3C(659AA) is an RNA-binding protein that preserves maternal FOS mRNA in oocytes.

A novel mouse c-fos intronic promoter that responds to CREB and AP-1 is developmentally regulated in vivo

Background

The c-fos proto-oncogene is an archetype for rapid and integrative transcriptional activation. Innumerable studies have focused on the canonical promoter, located upstream from the transcriptional start site. However, several regulatory sequences have been found in the first intron.

Methodology/Principal Findings

Here we describe an extremely conserved region in c-fos first intron that contains a putative TATA box, and functional TRE and CRE sites. This fragment drives reporter gene activation in fibroblasts, which is enhanced by increasing intracellular calcium and cAMP and by cotransfection of CREB or c-Fos/c-Jun expression vectors. We produced transgenic mice expressing a lacZ reporter controlled by the intronic promoter. Lac Z expression of this promoter is restricted to the developing central nervous system (CNS) and the mesenchyme of developing mammary buds in embryos 12.5 days post-conception, and to brain tissue in adults. RT-QPCR analysis of tissue mRNA, including the anlage of the mammary gland and the CNS, confirms the existence of a novel, nested mRNA initiated in the first intron.

Conclusions/Significance

Our results provide evidence for a novel, developmentally regulated promoter in the first intron of the c-fos gene.

Noggin elicits retinal fate in Xenopus animal cap embryonic stem cells

Driving specific differentiation pathways in multipotent stem cells is a main goal of cell therapy. Here we exploited the differentiating potential of Xenopus animal cap embryonic stem (ACES) cells to investigate the factors necessary to drive multipotent stem cells toward retinal fates. ACES cells are multipotent, and can be diverged from their default ectodermal fate to give rise to cell types from all three germ layers. We found that a single secreted molecule, Noggin, is sufficient to elicit retinal fates in ACES cells. Reverse-transcription polymerase chain reaction, immunohistochemistry, and in situ hybridization experiments showed that high doses of Noggin are able to support the expression of terminal differentiation markers of the neural retina in ACES cells in vitro. Following in vivo transplantation, ACES cells expressing high Noggin doses form eyes, both in the presumptive eye field region and in ectopic posterior locations. The eyes originating from the transplants in the eye field region are functionally equivalent to normal eyes, as seen by electrophysiology and c-fos expression in response to light. Our data show that in Xenopus embryos, proper doses of a single molecule, Noggin, can drive ACES cells toward retinal cell differentiation without additional cues. This makes Xenopus ACES cells a suitable model system to direct differentiation of stem cells toward retinal fates and encourages further studies on the role of Noggin in the retinal differentiation of mammalian stem cells.

The Bv8 gene from Bombina orientalis: molecular cloning, genomic organization and functional characterization of the promoter

Bv8 is a secreted peptide from Bombina variegata skin glands with a molecular mass close to 8kDa that is conserved in fish, amphibians and mammals. Bv8 has diverse regulatory roles, including an involvement in hematopoiesis and immunomodulation. Here we report the genomic organization of the gene from Bombina orientalis coding for the Bv8 homolog (Bo8). It contains three exons separated by two large introns. Several putative transcription factor binding sites have been identified in the promoter sequence. Functional analysis of this region was performed using a yeast genetic system. The results indicate that the transcription factors AP-1, NF-kappaB and NFAT are involved in the regulation of the expression of Bo8. Hence, amphibians are a useful model for the study of transcriptional regulation of all Bv8 homologs.

Cloning and sequence analysis of the self-fertilizing fish Rivulus marmoratus immediate early gene c-fos

We have cloned the proto-oncogene c-fos from a self-fertilizing fish Rivulus marmoratus (Cyprinodontiformes, Rivulidae) after screening of R. marmoratus lambdaGEM-11 genomic DNA library, and sequenced over 12 kb including all exons, introns and the promoter region. The R. marmoratus c-fos gene consisted of one noncoding exon and four exons with high similarity to those of fugu and mammals. We sequenced approximately 7 kb of the R. marmoratus c-fos gene promoter region to gain a better understanding of the molecular anatomy of the immediate response of this gene upon cellular damage. In the promoter region, R. marmoratus c-fos gene has seven xenobiotic response elements (XREs) and eight metal response elements (MREs) as well as two estradiol (E2), 4 NFkappaB, 2 CarG, 2 prolactin (PRL) motifs and one pit1 site, while the 3'-UTR of this gene contains the estrogen response element (ERE). The seven XRE and eight MRE motifs raise the possibility of its regulation by exposure to environmental pollutants. In this paper, we discuss the gene structure of R. marmoratus c-fos gene and compare its promoter region with those of other organisms' c-fos genes. We propose its potential use in ecotoxicology.

Distinct enhancers regulate skeletal and cardiac muscle-specific expression programs of the cardiac alpha-actin gene in Xenopus embryos

During vertebrate embryonic development, cardiac and skeletal muscle originates from distinct precursor populations. Despite the profound structural and functional differences in the striated muscle tissue they eventually form, such progenitors share many features such as components of contractile apparatus. In vertebrate embryos, the alpha-cardiac actin gene encodes a major component of the myofibril in both skeletal and cardiac muscle. Here, we show that expression of Xenopus cardiac alpha-actin in the myotomes and developing heart tube of the tadpole requires distinct enhancers within its proximal promoter. Using transgenic embryos, we find that mutations in the promoter-proximal CArG box and 5 bp downstream of it specifically eliminate expression of a GFP transgene within the developing heart, while high levels of expression in somitic muscle are maintained. This sequence is insufficient on its own to limit expression solely to the myocardium, such restriction requiring multiple elements within the proximal promoter. Two additional enhancers are active in skeletal muscle of the embryo, either one of which has to interact with the proximal CArG box for correct expression to be established. Transgenic reporters containing multimerised copies of CArG box 1 faithfully detect most sites of SRF expression in the developing embryo as do equivalent reporters containing the SRF binding site from the c-fos promoter. Significantly, while these motifs possess a different A/T core within the CC(A/T)(6)GG consensus and show no similarity in flanking sequence, each can interact with a myotome-specific distal enhancer of cardiac alpha-actin promoter, to confer appropriate cardiac alpha-actin-specific regulation of transgene expression. Together, these results suggest that the role of CArG box 1 in the cardiac alpha-actin gene promoter is to act solely as a high-affinity SRF binding site.

The gene structure of the Drosophila melanogaster homolog of the human proto-oncogene fos

The Drosophila melanogaster homolog of the human proto-oncogene fos is Dfos. It is the only fos homolog in the Drosophila genome. Fos functions as a subunit of the heterodimeric transcription factor AP-1. There are two models of the Dfos gene. The first comes from a cDNA sequence of Dfos (Perkins et al., Genes Dev. 4 (1990) 822). The second is from the gene sequence published by the Drosophila genome project (Adams et al., Science 287 (2000) 2185), and there are notable contradictions between the two models. The promoter and the 5' end of the transcript sequence were not identified in either model. In this paper, we present the gene structure of Dfos and identify the promoter. This promoter has an initiator and a downstream promoter element sequence, but lacks a TATA box. Through comparison of the mRNA and genomic DNA sequences, three introns varying in length from 66 bp to 17.57 kb were found and verified by RT-PCR. The Dfos gene is 21.2 kb in length, giving a transcript of 3438 bp, coding for a predicted protein of 595 amino acids. The 3' untranslated region is confirmed to be 1092 bp in length.

Noggin upregulates Fos expression by a calcium-mediated pathway in amphibian embryos

In amphibia, noggin, one of the neural inducers expressed in the Spemann organizer, acts by neutralizing the effects of bone morphogenetic protein-4 (BMP-4). It is shown that noggin is able to activate L-type calcium channels. The fos proto-oncogene is known to be induced within minutes by calcium signaling. Here it is reported that in animal cap explants of the amphibian Pleurodeles waltl, noggin can induce upregulation of a FOS-related protein in a calcium-dependent manner. Specific inhibition of the dihydropyridine sensitive L-type calcium channels blocked both calcium influx and the induction of FOS-related protein. When animal cap explants were treated with caffeine in order to release calcium from an internal store or with a specific agonist of the L-type calcium channels, FOS-related protein could be detected in cell nuclei by 5 or 15 min, respectively. Additionally, the calcium calmodulin kinase inhibitor. KN62, could block the upregulation of FOS-related protein induced by agents that increased intracellular calcium ([Ca2+]i). The present results suggest that transcription factors from the FOS family are downstream targets of neural inducer noggin.

RNase A activity in Japanese quail oocytes

The presence of RNase A activity was studied in vitro in homogenates of quail oocytes and early embryos using [3H]poly(U) as a substrate. The activity was measured by adsorption of the undegraded substrate onto DE-81 filter paper discs and by chromatographic separation on a Sephadex G-50 column. RNase A activity examined by these methods was almost undetectable in quail previtellogenic, vitellogenic and ovulated oocytes as well as in the embryos from laid eggs. It is estimated to be about 1.1 x 10(-5) Kunitz units per ovulated oocyte. Higher activity starts to appear in gastrulating embryos. These findings are discussed in relation to other studies demonstrating the high stability of maternal RNA during early development, especially in growing oocytes.

Cloning and characterization of human phosphatase inhibitor-2 (IPP-2) sequences

cDNA clones similar to rabbit muscle phosphatase inhibitor-2 (IPP-2) were isolated from human libraries. On Northern blots two transcripts of approximately 2kbp and approximately 4kbp were detected in all tissues tested. Analysis of cDNA sequences showed that the longer transcripts were similar to the shorter clones but contained extended 3' ends. The human nucleotide sequence was highly homologous (94% identity) to the rabbit IPP-2 sequence and encoded a peptide of 205 amino acids. IPP-2 sequences were highly conserved throughout vertebrates. Southern hybridization results were consistent with the existence of a family of related IPP-2 sequences in the human genome. Most of these are likely to be pseudogenes, since all of the cDNA clones examined could have originated from a single gene. By in situ hybridization IPP-2 sequences were mapped to several different human chromosomes. We sequenced one gene located in the major histocompatibility complex (MHC) on Chromosome (Chr) 6 that contained the entire coding region of IPP-2.

Induction of cytoplasmic factors that bind to the 3' AU-rich region of human interferon beta mRNA during early development of Xenopus laevis

Certain endogenous Xenopus mRNAs, carrying a destabilizing 3' AU-rich sequence, are unusually very stable in oocytes and become unstable only after fertilization. In addition, heterologous short lived mRNA, containing 3' AU-rich sequences, appear to be very stable when injected into Xenopus oocytes. In the present study, a human interferon beta (hu-IFN beta) mRNA, carrying the destabilizing 3' AU-rich element, was used as a probe to identify Xenopus proteins that specifically bind to the 3' AU-rich element as well as to study their relative levels during early embryonic development. While three major proteins that specifically bind to the 3' AU-rich element were detected in human SV80 cells, that naturally express hu-IFN beta (proteins termed AU-F1, F2 and F3), only two proteins, migrating similarly to the SV80 AU-F1 and AU-F3, were detected in cytoplasmic extracts from Xenopus oocytes or eggs. Following fertilization, the intensity of the Xenopus AU-F1 and AU-F3 proteins increased considerably and a new protein, corresponding to SV80 AU-F2, was also detected. Cyclohexamide applied either at the morula or at the early blastula stages reduced the intensity of the AU-binding factors, while actinomycin D did not, indicating that the levels of these factors during these stages are regulated posttranscriptionally. In contrast, application of each of these metabolic inhibitors at the late blastula stage increased the intensity of the AU-binding proteins. The possible function of these AU-binding factors in regulating the expression and half life of AU-rich mRNAs is discussed.

Isolation and characterization of SRF accessory proteins

Many genes which are regulated by growth factors contain a common regulatory element, the serum response element (SRE). Activation of transcription by the SRE involves a ternary complex formed between a ubiquitous factor, serum response factor (SRF), and a second protein, p62/TCF. We used a yeast genetic screen to isolate cDNAs encoding a protein, SAP-1, with the DNA binding properties of p62/TCF. The SAP-1 sequence contains three regions of homology to the previously uncharacterized Elk-1 protein, which also acts as an SRF accessory protein. Only two of these regions are required for cooperative interactions with SRF in the ternary complex. The third contains several conserved sites for the MAP kinases, whose activity is regulated in response to growth factor stimulation. We discuss the potential role of these proteins in regulation of the c-fos SRE.

The serum response element and an AP-1/ATF sequence immediately downstream co-operate in the regulation of c-fos transcription

Transcription of the c-fos gene is activated in response to a wide variety of extracellular stimuli and several cis-acting transcriptional control elements have been characterized. One of these elements is called the serum response element (SRE) and here we investigate an interaction between this element and an AP-1/ATF-like sequence immediately downstream from the SRE. In growing cells these sequences activate transcription in an additive fashion whereas in quiescent cells they co-operate to repress transcription. This co-operation is disrupted upon separation of the elements which also alters the response of the elements to serum or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) stimulation of quiescent cells. This separation also results in an increase of transcription in growing cells. A consensus AP-1 DNA-binding site can substitute for the AP-1/ATF-like sequence present in the c-fos promoter to activate transcription in an additive fashion with the SRE in growing cells, and co-operate in repression in quiescent cells. These observations show that any interaction that may be occurring between proteins binding to these elements results in a different pattern of transcriptional control in growing and quiescent cells. Alternatively, different proteins (or modified proteins) may complex with these sequences in the two different states of cell growth.

Characterization of SAP-1, a protein recruited by serum response factor to the c-fos serum response element

We used a yeast genetic screen to isolate cDNAs that encode a protein, SRF accessory protein-1 (SAP-1), that is recruited to the c-fos serum response element (SRE) as part of a ternary complex that includes serum response factor (SRF). SAP-1 requires DNA-bound SRF for ternary complex formation and makes extensive DNA contacts to the 5' side of SRF, but does not bind DNA autonomously. Ternary complex formation by SAP-1 requires only the DNA-binding domain of SRF, which can be replaced by that of the related yeast protein MCM1. We isolated cDNAs encoding two forms of SAP-1 protein, SAP-1a and SAP-1b, which differ at their C termini. Both SAP-1 proteins contain three regions of striking homology with the elk-1 protein, including an N-terminal ets domain. Ternary complex formation by SAP-1 requires both the ets domain and a second conserved region 50 amino acids to its C-terminal side. SAP-1 has similar DNA binding properties to the previously characterized HeLa cell protein p62/TCF.

Functions of maternal mRNA in early development

In this review, the types of mRNAs found in oocytes and eggs of several animal species, particularly Drosophila, marine invertebrates, frogs, and mice, are described. The roles that proteins derived from these mRNAs play in early development are discussed, and connections between maternally inherited information and embryonic pattern are sought. Comparisons between genetically identified maternally expressed genes in Drosophila and maternal mRNAs biochemically characterized in other species are made when possible. Regulation of the meiotic and early embryonic cell cycles is reviewed, and translational control of maternal mRNA following maturation and/or fertilization is discussed with regard to specific mRNAs.