Regulation and expression of a growth arrest-specific gene (gas5) during growth, differentiation, and development

The time-course analysis of gene expression during wound healing in mouse skin

RNA analysis has been applied to forensic work to determine wound age. We investigated mRNA expression using quantitative RT-PCR of ten genes, including c-fos, fosB, mitogen-activated protein kinase phosphatase-1 (MKP-1), CD14, chemokine (C-C motif) ligand 9 (CCL9), placenta growth factor (PlGF), mast cell protease-5 (MCP-5), growth arrest specific 5 (Gas5), beta-2 microglobulin (B2M) and major urinary protein-1 (MUP-1), in terms of repair response in adult mice. The expression level of c-fos, fosB and MKP-1 transcripts increased drastically, peaked within 1h, and that of the CD14 and CCL9 transcripts peaked from 12 to 24h. An increase in PlGF and MCP-5 mRNA appeared on about day 5. Gas5, B2M and MUP-1 transcripts showed no significant change. Each gene had differentially expressional patterns with time-course. Our result implied that the observation of the 7 genes in wounded skin could serve to aid in the accurate diagnosis of wound age.

GAS5, a non-protein-coding RNA, controls apoptosis and is downregulated in breast cancer

Effective control of both cell survival and cell proliferation is critical to the prevention of oncogenesis and to successful cancer therapy. Using functional expression cloning, we have identified GAS5 (growth arrest-specific transcript 5) as critical to the control of mammalian apoptosis and cell population growth. GAS5 transcripts are subject to complex post-transcriptional processing and some, but not all, GAS5 transcripts sensitize mammalian cells to apoptosis inducers. We have found that, in some cell lines, GAS5 expression induces growth arrest and apoptosis independently of other stimuli. GAS5 transcript levels were significantly reduced in breast cancer samples relative to adjacent unaffected normal breast epithelial tissues. The GAS5 gene has no significant protein-coding potential but expression encodes small nucleolar RNAs (snoRNAs) in its introns. Taken together with the recent demonstration of tumor suppressor characteristics in the related snoRNA U50, our observations suggest that such snoRNAs form a novel family of genes controlling oncogenesis and sensitivity to therapy in cancer.

Overlapping BXSB congenic intervals, in combination with microarray gene expression, reveal novel lupus candidate genes

The BXSB mouse strain is an important model of glomerulonephritis observed in systemic lupus erythematosus (SLE). Linkage studies have successfully identified disease-susceptibility intervals; however, extracting the identity of the susceptibility gene(s) in such regions is the crucial next step. Congenic mouse strains present a defined genetic resource that is highly amenable to microarray analysis. We have performed microarray analysis using a series of chromosome 1 BXSB congenic mice with partially overlapping disease-susceptibility intervals. Simultaneous comparison of the four congenic lines allowed the identification of expression differences associated with both the initiation and progression of disease. Thus, we have identified a number of novel SLE disease gene candidates and have confirmed the identity of Ifi202 as a disease candidate in the BXSB strain. Sequencing of the promoter regions of Gas5 has revealed polymorphisms in the BXSB strain, which may account for the differential expression profile. Furthermore, the combination of the microarray results with the different phenotypes of these mice has allowed the identification of a number of expression differences that do not necessarily map to the congenic interval, but may be implicated in disease pathways.

Molecular approaches to developmental malformations using analogous forms of valproic acid

The teratogenic potential of valproic acid has been well established both in experimental models and in human clinical studies. Evidence from many previous studies has shown that VPA is an appropriate drug model for studying chemical structure-teratogenicity relationships. Using molecular techniques of DNA microarray (GeneChip system) or quantitative real-time polymerase chain reaction with low teratogenic VPA analogs as comparative control drugs, we attempted to identify the genes involved with the molecular mechanisms of VPA teratogenicity in the neural tube and the axial skeleton of the mouse embryo. The recent development of DNA microarray enables a genome-wide approach to the identification of genes correlated with the teratogenicity of chemicals (teratogenomics). The VPA-induced changes in gene expression seen during mouse embryogenesis provides information for understanding how VPA disrupts normal embryonic development, and also provides leads for the development of safer medicines.

Identification of early-responsive genes correlated to valproic acid-induced neural tube defects in mice

BACKGROUND

Valproic acid (VPA) causes the failure of neural tube closure in newborn mice. However, the molecular mechanism of its teratogenesis is unknown. This study was conducted to investigate the genomewide effects of VPA disruption of normal neural tube development in mice.

METHODS

Microarray analysis was performed on the head part of NMRI mouse embryos treated for 1 hr with VPA on gestational day (GD) 8. Subsequently, we attempted to isolate genes that changed in correlation with the teratogenic action of VPA by employing reduced teratogenic VPA analogs, valpromide (VPD) and valnoctamide (VCD), in a real-time PCR study.

RESULTS

Microarray results demonstrated that during neurulation, many genes, some of whose functions are known and some unknown, were either increased or decreased after VPA injection. Some genes were affected by VPD or VCD in the same way as VPA, but others were not changed by the analogs. In this way, our system identified 11 increased and 20 decreased genes. Annotation analysis revealed that the increased genes included gadd45b, ier5, per1, phfl3, pou3f1, and sox4, and the decreased genes included ccne2, ccnl, gas5, egr2, sirt1, and zfp105.

CONCLUSIONS

These findings demonstrate that expression changes in genes having roles in the cell cycle and apoptosis pathways of neural tube cells were strongly expected to relate to the teratogenic, but not antiepileptic, activity of VPA. Our approach has allowed the expansion of the catalog of molecules immediately affected by VPA in the developing neural tube.

Genes involved in nonpermissive temperature-induced cell differentiation in Sertoli TTE3 cells bearing temperature-sensitive simian virus 40 large T-antigen

Sertoli TTE3 cells, derived from transgenic mice bearing temperature-sensitive simian virus 40 large T (tsSV40LT)-antigen, proliferated continuously at a permissive temperature (33 degrees C) whereas inactivation of the large T-antigen by a nonpermissive temperature (39 degrees C) led to differentiation as judged by elevation of transferrin. To clarify the detailed mechanisms of differentiation, we investigated the time course of changes in gene expression using cDNA microarrays. Of the 865 genes analyzed, 14 genes showed increased levels of expression. Real-time quantitative PCR revealed that the mRNA levels of p21(waf1), milk fat globule membrane protein E8, heat-responsive protein 12, and selenoprotein P were markedly elevated. Moreover, the differentiated condition induced by the nonpermissive temperature significantly increased mRNA levels of these four genes in several cell lines from the transgenic mice bearing the oncogene. The present results regarding changes in gene expression will provide a basis for a further understanding of molecular mechanisms of differentiation in both Sertoli cells and cell lines transformed by tsSV40LT-antigen.

GeneChip analysis of hippocampal gene expression profiles of short- and long-attack-latency mice: Technical and biological implications

To gain insight into the molecular mechanisms underlying the behavioral differences between two mouse lines genetically selected for long and short attack latency (LAL and SAL mice, respectively), we have recently applied the large-scale gene expression profiling method known as serial analysis of gene expression (SAGE) to generate hippocampal gene expression profiles of these mice. The aim of the present study is to extend and validate the SAGE expression profile of hippocampi of LAL and SAL mice using GeneChips (Affymetrix, Santa Clara, CA; one array per mouse, n = 5 per mouse line). As was the case with SAGE, GeneChips detect only medium- to high-abundance genes in the hippocampus. Extensive analysis of GeneChip data using very stringent parameters shows differential expression of 122 genes, all except one of which were expressed at higher levels in LAL mice (P < 0.01). As predicted by SAGE, our data indicate higher expression of several cytoskeleton genes in LAL mice, suggesting longer axonal and dendritic projections in the hippocampus of these mice. This is consistent with our tentative model, in which the behavioral differences between LAL and SAL mice may be related to structural differences in the hippocampus. In addition, a group of 76 genes with diverse biological function and 46 expressed sequence tags (ESTs) were all expressed at higher levels in LAL mice. A novel finding in this study was the significantly lower expression of only a single gene, growth arrest-specific gene (gas5), in LAL mice. As gas5 does not encode a protein but several small nuclear RNAs, our data suggest that small RNAs may contribute to the molecular mechanisms underlying the extreme behavioral differences between LAL and SAL mice.

Posttranscriptional and posttranslational regulation of C/EBP delta in G0 growth-arrested mammary epithelial cells

Previous work from our laboratory demonstrated that CCAAT/enhancer-binding protein delta (C/EBP delta) functions in the initiation and maintenance of G(0) growth arrest in mouse mammary epithelial cells (MECs). In this report, we investigated the posttranscriptional and posttranslational regulation of C/EBP delta in G(0) growth-arrested mouse MECs. The results of transcriptional inhibitor studies demonstrated that the C/EBP delta mRNA exhibits a relatively short half-life in G(0) growth-arrested mouse MECs (t(1/2) approximately 35 min). In contrast, C/EBP delta mRNA has a longer half-life in G(0) growth-arrested mouse fibroblast cells (t(1/2) >100 min). Oligo/RNase H cleavage analysis and rapid amplification of cDNA ends-poly(A) test both confirmed the short C/EBP delta mRNA half-life observed in MECs and demonstrated that the C/EBP delta mRNA poly(A) tail is relatively short (approximately 100 nucleotides). In addition, the poly(A) tail length was not shortened during C/EBP delta mRNA degradation, which suggested a deadenylation-independent pathway. The C/EBP delta protein also exhibited a relatively short half-life in G(0) growth-arrested mouse MECs (t(1/2) approximately 120 min). The C/EBP delta protein was degraded in a ubiquitin-dependent manner, primarily in the nucleus, during G(0) growth arrest. In conclusion, these studies indicated that the C/EBP delta mRNA and protein content are under tight regulation in G(0) growth-arrested mouse MECs, despite the general concept that G(0) growth arrest is associated with a decrease in cellular activity.

Non-coding ribonucleic acids--a class of their own?

Non-coding ribonucleic acids (RNAs) do not contain a peptide-encoding open reading frame and are therefore not translated into proteins. They are expressed in all phyla, and in eukaryotic cells they are found in the nucleus, cytoplasm, and mitochondria. Non-coding RNAs either can exert structural functions, as do transfer and ribosomal RNAs, or they can regulate gene expression. Non-coding RNAs with regulatory functions differ in size ranging from a few nucleotides to over 100 kb and have diverse cell- or development-specific functions. Some of the non-coding RNAs associate with human diseases. This chapter summarizes the current knowledge about regulatory non-coding RNAs.

Gene expression profiling in the midbrain of striatal 6-hydroxydopamine-injected mice

In order to clarify mechanisms underlying dopaminergic neuronal death in Parkinson's disease (PD), a gene expression profiling study was performed in a rodent model of PD. In this model, mice are intrastriatally injected with 6-hydroxydopamine (6-OHDA) and dopaminergic neurons in the substantia nigra (SN) gradually die by retrograde degeneration. The SN were removed 2 h, 24 h, or 14 days after 6-OHDA administration. Levels of mRNAs related to cell death or survival were quantified using adaptor-tagged competitive PCR (ATAC-PCR). The cyclin D1 gene showed an immediate increase in mRNA expression. After 24 h, when dopaminergic neurons were under intense degeneration, levels of caspase 8 mRNA and p53 apoptosis effecter related to pmp 22 (PERP) mRNA increased and, conversely, FAS mRNA decreased. After 14 days, when the degeneration was attenuated, levels of PERP mRNA and serum- and glucocorticoid-regulated kinase (SGK) mRNA still increased. SGK has a similarity to AKT, which is an important molecule involved in nerve growth factor signal transduction. AKT mRNA levels are low in dopaminergic neurons. These results suggest that an increase in cyclin D1 mRNA triggers dopaminergic neurons to enter an abnormal cell cycle, which leads to neuronal degeneration and cell death, possibly induced by PERP and caspase 8. In addition to cell death-related genes, several survival-related genes are activated. SGK might function as a key enzyme for the survival of dopaminergic neurons.

Isolation and properties of Gas8, a growth arrest-specific gene regulated during male gametogenesis to produce a protein associated with the sperm motility apparatus

Growth arrest-specific (Gas) genes are expressed during serum starvation or contact inhibition of cells grown in culture. Here we report the isolation and characterization of Gas8, a novel gene identified on the basis of its growth arrest-specific expression in murine fibroblasts. We show that production of Gas8 mRNA and protein occurs in adult mice predominantly in the testes, where expression is regulated during postmeiotic development of male gametocytes. Whereas a low level of Gas8 mRNA was detected by Northern blotting in testes of murine male neonates and young adolescents, Gas8 mRNA increased rapidly postmeiotically. In adult males, both Gas8 mRNA and protein reached steady state levels in testes that were 10-fold higher than in other tissues. Immunohistochemical analyses showed that Gas8 protein accumulates in gametocytes as they approach the lumen of seminiferous tubules and is localized to the cytoplasm of round spermatids, the tails of elongating spermatids, and mature spermatid tail bundles protruding into the lumen; in epididymal spermatozoa Gas8 protein was present in the flagella. However, premeiotic murine gametocytes lacked detectable Gas8 protein, as did seminiferous tubules in biopsy specimens from seven human males having cytological evidence of non-obstructive azoospermia secondary to Sertoli cell-only syndrome. Our findings, which associate Gas8 production developmentally with the later stages of spermatogenesis and spatially with the sperm motility apparatus, collectively suggest that this growth arrest-specific gene product may have a role in sperm motility. This postulated role for Gas8 is supported by our observation that highly localized production of Gas8 protein occurs also in the cilia of epithelial cells lining pulmonary bronchi and fallopian tubes and by the flagellar association of a Trypanosoma brucei ortholog of Gas8.

Differential expression of ribosomal L31, Zis, gas-5 and mitochondrial mRNAs following oxidant induction of proliferative vascular smooth muscle cell phenotypes

Treatment of cultured vascular smooth muscle cells (vSMCs) with benzo(a)pyrene (BaP), a prooxidant present in the particulate phase of tobacco smoke, induces highly proliferative (i.e. atherogenic) phenotypes. Critical early target genes in vSMCs have been identified, but patterns of gene expression following repeated cycles of carcinogen treatment in vivo have yet to be evaluated. In the present study, male Sprague-Dawley rats (175-200 g) were given weekly injections of BaP (10 mg/kg) for 8 weeks to induce atherogenic phenotypes. At the end of this atherogenic regimen, vSMCs were established in serial culture and monitored for patterns of proliferative activity and gene expression. vSMCs isolated from BaP-treated animals (hence forth referred to as BaP cells) exhibited constitutively increased growth rates, and marked enhancement of proliferation in response to serum mitogens. Differential display polymerase chain reaction (DD-PCR) and Northern blot analyses revealed that mRNAs for ribosomal protein L31 and Zis genes were suppressed, while gas-5 and mitochondrial mRNAs were overexpressed in BaP cells relative to control mRNA populations. In situ hybridization experiments in vascular tissue confirmed these alterations in vivo. This is the first report linking expression of these genes to proliferative dysregulation during the course of experimentally-induced atherogenesis.

Chipping away at complex behavior: transcriptome/phenotype correlations in the mouse brain

Highly parallel gene expression profiling has the potential to provide new insight into the molecular mechanisms of complex brain diseases and behavioral traits. We review how gene expression profiling in various brain regions of inbred mouse strains has been used to identify genes that may contribute to strain-specific phenotypes. New data, which demonstrate the use of gene expression profiling in combination with behavioral testing to identify candidate genes involved in mediating variation in running wheel activity, are also presented. These and other studies suggest that a combination of gene expression profiling and more traditional genetic approaches, such as quantitative trait locus analysis, can be used to identify genes responsible for specific neurobehavioral phenotypes.

COP-1, a member of the CCN family, is a heparin-induced growth arrest specific gene in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) hyperplasia is responsible for the failure of 15-30% of vascular surgical procedures such as coronary artery bypass grafts and angioplasties. We and others have shown that heparin suppresses VSMC proliferation in vivo and in cell culture. We hypothesize that heparin inhibits VSMC proliferation by binding to cell surface receptors, resulting in selective modulation of mitogenic signal transduction pathways and altered transcription of a specific subset of growth regulatory genes. To test this idea, we used subtractive hybridization to identify differentially expressed mRNAs in heparin-treated and untreated VSMC. We identified a heparin induced mRNA identical to Cop-1, a member of the CCN family of proteins which are secreted, cysteine-rich modular proteins involved in growth regulation and migration. Cop-1 from smooth muscle cells appears to have a different expression pattern and possibly different functions than Cop-1 from other cells. Cop-1 mRNA is expressed at high levels in quiescent VSMC and at low levels in proliferating VSMC, an expression pattern highly characteristic of growth arrest specific genes. Cop-1 mRNA is expressed at high levels in heparin treated VSMC and COP-1 protein is secreted into culture medium. In tissues, Cop-1 expression is observed in the uninjured rat aorta suggesting a possible role for Cop-1 in vivo. We found PDGF, but not EGF, inhibits the expression of Cop-1 in VSMC. Neither TGF-beta nor interferon-beta, two inhibitors of VSMC proliferation, were able to induce Cop-1 expression. In addition, heparin does not induce Cop-1 mRNA in endothelial cells and VSMC resistant to the antiproliferative effect of heparin. Conditioned medium from cells over-expressing COP-1 protein inhibits VSMC proliferation in culture. Together, our data indicate that COP-1 may play a role in the antiproliferative mechanism of action of heparin.

The gas 5 gene shows four alternative splicing patterns without coding for a protein

The murine gas5 gene was originally isolated based on its preferential expression in the growth arrest phase of the cell cycle. This gene contains 12 exons from which two alternatively spliced transcripts have been initially identified. More recently, it has been reported that both human and murine gas5 genes contain in their introns sequences homologous to the small nucleolar RNAs involved in the processing of ribosomal RNA. Here we report on the identification and analysis of the expression pattern of two novel alternatively spliced mouse gas5 mRNAs which contain no obvious open reading frame (ORF). Using antibodies generated against the putative amino acid sequence deduced from the gas5 cDNAs, we were not able to detect any Gas5 protein in cultured cells or murine tissues extracts. Even more definitive evidence that the gas5 gene may not encode a protein was obtained by cloning and sequencing the rat gas5 gene which revealed that the putative ORF is interrupted by a stop codon after the first 13 amino acids.

Characterization of a novel quiescence responsive element downregulated by v-Src in the promoter of the neuroretina specific QR1 gene

The neuroretina is a functional unit of the central nervous system which arises through successive steps of division, growth arrest and differentiation of neuroectodermal precursors. Postmitotic quail neuroretina (QNR) cells are conditionally induced to divide upon infection with temperature sensitive mutants of Rous sarcoma virus (RSV), since QNR cell division can be arrested by either inactivating p60v-Src at the nonpermissive temperature (41 degrees C) or by serum deprivation at 37 degrees C. We are studying the transcriptional control of QR1, a neuroretina specific gene, whose expression is down-regulated in proliferating cells at 37 degrees C and is fully restored when these cells are made quiescent. We previously showed that this quiescence specific upregulation implicates a promoter region named A box, which binds Maf transcription factors. We report the identification of the C box, a second promoter sequence that activates QR1 transcription in non dividing cells. This sequence is able to form two DNA-protein complexes, one of which (C4) is predominantly detected in growth arrested NR cells. We identified the DNA binding site for C4 and described mutations that abolish both C4 binding and promoter activity in quiescent cells. Moreover, we show that a multimerized C box is able to stimulate a heterologous promoter in non dividing cells and constitutes, therefore, a novel quiescence responsive enhancer. Finally, we report that QR1 transcriptional response to cell quiescence requires cooperation between the C box and A box.

Detection of a novel quiescence-dependent protein kinase

We have identified a cell quiescence-specific 33-kDa cytoplasmic protein kinase (p33(QIK), Quiescence-Induced Kinase) based on induction of p33(QIK)-specific kinase activity of cells growth-arrested in the quiescent phase and deactivation upon entry into the cell cycle. Blockage of macromolecular synthesis prevents p33(QIK) from deactivation, indicating a requirement of newly synthesized regulators for deactivation of p33(QIK) during G(0)/G(1) transition. Stress shock induces additional increases of p33(QIK) activity in a quiescence-dependent manner that correlates with induction of apoptosis. Using a specific antibody to Krs1/Mst2 protein, we found that p33(QIK) is related to p63(Krs1) and is distinguishable from a 36-kDa protein kinase, which is induced through proteolytic modification of activated p63(Krs1) in proliferating cells undergoing apoptosis. p33(QIK) is constantly expressed in quiescent, proliferating, and apoptotic quiescent cells. Regulation of p33(QIK) activity involves protein phosphorylation/dephosphorylation in a proteolysis-independent manner. Regulation of p33(QIK) and related p63(Krs1) and p36 appears to involve distinct pathways in quiescent and proliferating cells, respectively. Our results illustrate the relevance of p33(QIK) activity for cell quiescence that may provide a new insight into signaling pathways regulated in cells during quiescence and quiescence-related apoptosis.

Identification of a growth arrest specific (gas 5) gene by differential display as a candidate gene for determining susceptibility to hyperthermia-induced exencephaly in mice

Neural tube defects (NTDs) are among the most common congenital malformations, affecting approximately 1 per 1,000 liveborn infants in the United States [Nakano, 1973; Richards et al., 1972]. Maternal exposure to hyperthermia, either through recreational sources or due to an infectious agent, is thought to account for approximately 10% of observed NTD cases. The specific genes conferring susceptibility or resistance to hyperthermia-induced NTDs have not been identified. This study used differential display-polymerase chain reaction (DD-PCR) to characterize alterations in gene expression in the anterior embryonic neural tube of two highly inbred murine strains (SWV/Fnn, LM/Bc/Fnn) known to differ in their genetically determined susceptibility to heat-induced NTDs. Herein, we report the neural tube-specific differential expression of the growth arrest specific (gas 5) gene in the highly susceptible SWV/Fnn strain during neural tube closure (NTC). Although the expression of gas 5 did not appear to be altered by the teratogenic heat treatment, its spatial and strain-specific pattern of expression makes it an excellent candidate gene responsible for the observed genetic differences in NTD susceptibility between these two inbred murine strains.

Noncoding RNA genes

Some genes produce RNAs that are functional instead of encoding proteins. Noncoding RNA genes are surprisingly numerous. Recently, active research areas include small nucleolar RNAs, antisense riboregulator RNAs, and RNAs involved in X-dosage compensation. Genome sequences and new algorithms have begun to make systematic computational screens for noncoding RNA genes possible.

Expression of the growth arrest genes (GAS and GADD) changes during organogenesis in the rat fetus

Mammalian cells mount an active response to nutrient limitation by overexpressing the growth arrest specific (GAS) and the growth arrest and DNA damage (GADD) genes. During embryogenesis in rats, there are quantitative and temporal differences in GAS and GADD gene expression during the development of the placenta, heart and kidney. Genes associated with the inhibition of DNA synthesis (p53 and GAS1) were predominantly expressed during the early stages of development, whereas those genes associated with inhibition of protein synthesis [GADD153 (also known as CHOP-10 or Ddit3) and C/EBP-beta] were more highly expressed during the later stages. The GADD45 gene was expressed throughout development. There were distinct periods of GAS3 and GAS6 gene expression during the development of the placenta, heart and kidneys, which is consistent with the proposed roles of these genes in cell interactions. These results show that there is a change in the expression of genes associated with the negative regulation of growth as the fetus develops.

Regulatory signals in messenger RNA: determinants of nutrient–gene interaction and metabolic compartmentation

Nutrition has marked influences on gene expression and an understanding of the interaction between nutrients and gene expression is important in order to provide a basis for determining the nutritional requirements on an individual basis. The effects of nutrition can be exerted at many stages between transcription of the genetic sequence and production of a functional protein. This review focuses on the role of post-transcriptional control, particularly mRNA stability, translation and localization, in the interactions of nutrients with gene expression. The effects of both macronutrients and micronutrients on regulation of gene expression by post-transcriptional mechanisms are presented and the post-transcriptional regulation of specific genes of nutritional relevance (glucose transporters, transferrin, selenoenzymes, metallothionein, lipoproteins) is described in detail. The function of the regulatory signals in the untranslated regions of the mRNA is highlighted in relation to control of mRNA stability, translation and localization and the importance of these mRNA regions to regulation by nutrients is illustrated by reference to specific examples. The localization of mRNA by signals in the untranslated regions and its function in the spatial organization of protein synthesis is described; the potential of such mechanisms to play a key part in nutrient channelling and metabolic compartmentation is discussed. It is concluded that nutrients can influence gene expression through control of the regulatory signals in these untranslated regions and that the post-transcriptional regulation of gene expression by these mechanisms may influence nutritional requirements. It is emphasized that in studies of nutritional control of gene expression it is important not to focus only on regulation through gene promoters but also to consider the possibility of post-transcriptional control.

The growth arrest genes gas5, gas6, and CHOP-10 (gadd153) are expressed in the mouse preimplantation embryo

The gas and gadd family of genes, known collectively as the growth arrest genes, are associated with the negative control of mammalian cell growth. The steady-state levels of their mRNAs are increased by three to fivefold when exponentially multiplying cells are exposed to a variety of stresses including inadequate nutrition or the removal of serum. Reverse transcription-polymerase chain reaction (RT-PCR) has been used to analyze growth arrest gene expression in the preimplantation mouse embryo. The gas5, gas6, and CHOP-10 (gadd153, Ddit3) genes were expressed from the eight-cell stage onward. The gas2 and gas3 genes associated with apoptosis were not expressed. Embryos were cultured in kSOM medium and a semiquantitative RT-PCR method was used to measure the relative gene expression using beta-actin mRNA as a reference. The ratio of gas5 to beta-actin mRNA was high at the eight-cell stage and fell three to fivefold during development. The decline in the gas5:beta-actin ratio corresponded to the activation of true cell growth (cytokinesis). The gas6:beta-actin ratio was low at the eight-cell stage and increased by twofold as the blastocyst formed. CHOP-10 was expressed at a constant level throughout development. Embryos that had developed in vivo were compared with the equivalent blastocyst-stage embryos cultured in kSOM medium. There were no significant differences in the ratio of CHOP-10, gas5, or gas6 mRNAs relative to beta-actin. These results suggest that these genes are expressed as part of normal early embryonic development. The potential roles of the growth arrest genes are discussed.

Functional genomics in mice by tagged sequence mutagenesis

Most mammalian genes will soon be characterized as cDNA sequences with little information about their function. To utilize this sequence information for large-scale functional studies, a gene trap retrovirus shuttle vector has been developed to disrupt genes expressed in murine embryonic stem (ES) cells. A library of mutant clones was isolated, and regions of genomic DNA adjacent to 400 independent provirus inserts were cloned and sequenced. The flanking sequences, designated 'promoter-proximal sequence tags', or PSTs, identified 63 specific genes and anonymous cDNAs disrupted as a result of virus integration. The efficiency of tagged sequence mutagenesis suggests that many of the 10,000-20,000 genes expressed in ES cells can be targeted, providing defined mutations for the analysis of gene functions in vivo. In addition, PSTs provide the first expressed sequence tags derived from genomic DNA, and define gene features such as exon boundaries and promoters that are missing from cDNA sequences.

Site-specific ribose methylation of preribosomal RNA: a novel function for small nucleolar RNAs

Eukaryotic cells contain many fibrillarin-associated small nucleolar RNAs (snoRNAs) that possess long complementarities to mature rRNAs. Characterization of 21 novel antisense snoRNAs from human cells followed by genetic depletion and reconstitution studies on yeast U24 snoRNA provides evidence that this class of snoRNAs is required for site-specific 2'-O-methylation of preribosomal RNA (pre-rRNA). Antisense sno-RNAs function through direct base-pairing interactions with pre-rRNA. The antisense element, together with the D or D' box of the snoRNA, provide the information necessary to select the target nucleotide for the methyltransfer reaction. The conclusion that sno-RNAs function in covalent modification of the sugar moieties of ribonucleotides demonstrates that eukaryotic small nuclear RNAs have a more versatile cellular function than earlier anticipated.

Purification and stability characterization of a cell regulatory sialoglycopeptide inhibitor

Previous attempts to physically separate the cell cycle inhibitory and protease activities in preparations of a purified cell regulatory sialoglycopeptide (CeReS) inhibitor were largely unsuccessful. Gradient elution of the inhibitor preparation from a DEAE HPLC column separated the cell growth inhibitor from the protease, and the two activities have been shown to be distinct and non-overlapping. The additional purification increased the specific biological activity of the CeReS preparation by approximately two-fold. The major inhibitory fraction that eluted from the DEAE column was further analyzed by tricine-SDS-PAGE and microbore reverse phase HPLC and shown to be homogeneous in nature. Two other fractions separated by DEAE HPLC, also devoid of protease activity, were shown to be inhibitory to cell proliferation and most likely represented modified relatives of the CeReS inhibitor. The highly purified CeReS was chemically characterized for amino acid and carbohydrate composition and the role of the carbohydrate in cell proliferation inhibition, stability, and protease resistance was assessed.

Expression of gax, a growth arrest homeobox gene, is rapidly down-regulated in the rat carotid artery during the proliferative response to balloon injury

gax is a recently described homeobox gene whose expression in the adult is largely confined to cardiovascular tissues, gax has been shown to be rapidly down-regulated in cultured vascular smooth muscle cells (VSMC) upon stimulation by serum or platelet-derived growth factor. The temporal profile of gax expression in vitro matches that of two families of growth arrest genes: the gas genes and the gadd genes. All of these genes are expressed at their highest levels in quiescent cells and are down-regulated following mitogen activation. Here we report that gax is also down-regulated in vivo in the vascular wall in response to endothelial denudation by balloon angioplasty. The reduction in steady state levels of gax mRNA is transient and occurs with a similar time course to that seen in vitro. The down-regulation of gax in response to balloon injury mirrors the up-regulation seen in a number of early response genes such as c-myc and c-fos. This report is the first to document the in vivo expression of a growth arrest gene which regulates proliferation of vascular smooth muscle cells. In addition, in contrast with previous reports which have demonstrated up-regulation of several genes following balloon injury and/or angioplasty, the present report demonstrates the down-regulation of a regulatory gene within hours of balloon injury. The characteristics of gax suggest it may be required to maintain the gene expression of proteins in VSMC that are associated with the nonproliferative or contractile phenotype in smooth muscle cells.

Cellular biology of tubulointerstitial growth

The study of tubular growth has certainly become more complex since Pierre-Rayers's time and is progressing toward a molecular dissection of regulatory events. Understanding the mechanisms of tubular growth is important, because these cells represent the bulk of the nephron, and there is convincing evidence of a link between tubular hypertrophy and the progression of renal disease with irreversible tubulointerstitial fibrosis as an end point. Two tubular growth responses can be distinguished: hypertrophy and hyperplasia. These fundamentally different patterns of growth indicate that diverse molecular mechanisms may be involved in inducing distinct growth responses. It is likely that cytokines and polypeptide growth factors play a role in tubular hypertrophy and hyperplasia. Probably, a combination of growth factors including inhibitory polypeptides like TGF beta, rather than a single factor, is necessary for differentiated tubular growth responses. Such factors bind to their receptors, and signals are transduced to the nucleus by various second messengers involving protein kinases, cyclic nucleotides, Ca++, and inositolphosphates. The phosphorylation of nuclear trans-acting factors resulting in an expression of immediate early genes may be the common pathway of many of these mediators. Finally, whether the cell is to proliferate or to remain in the G1-phase of the cell cycle is determined by the very complex cascade phosphorylation of kinases and their associations with different cyclins. How the induction of immediate early genes is linked to events of the cell cycle is currently incompletely understood. Negative regulation of growth through protein growth suppressors like the retinoblastoma gene product or the expression of special genes only during cell rest may be mandatory for the fine tuning of tubular growth.

Negative regulators of cell proliferation

Cell proliferation is governed by the influence of both mitogens and inhibitors. Although cell contact has long been thought to play a fundamental role in cell cycling regulation, and negative regulators have long been suspected to exist, their isolation and purification has been complicated by a variety of technical difficulties. Nevertheless, over recent years an ever-expanding list of putative negative regulators have emerged. In many cases, their biological inhibitory activities are consistent with density-dependent growth inhibition. Most likely their interactions with mitogenic agents, at an intracellular level, are responsible for either mitotic arrest or continued cell cycling. A review of naturally occurring cell growth inhibitors is presented with an emphasis on those factors shown to be residents of the cell surface membrane. Particular attention is focused on a cell surface sialoglycopeptide, isolated from intact bovine cerebral cortex cells, which has been shown to inhibit the proliferation of an unusually wide range of target cells. The glycopeptide arrest cells obtained from diverse species, both fibroblasts and epithelial cells, and a broad variety of transformed cells. Signal transduction events and a limited spectrum of cells that are refractory to the sialoglycopeptide have provided insight into the molecular events mediated by this cell surface inhibitor.

Fibrositis/fibromyalgia syndrome in the workplace

A recent major epidemic of localized fibrositis/fibromyalgia syndrome occurring in the workplaces of Australia is reviewed. The clinical features are described and the important provoking factors are detailed. A neurogenic model is proposed to explain this localized phenomena and also encompass primary generalized fibrositis/fibromyalgia syndrome.