Combinatorial regulation by promoter and intron 1 regions of the metallothionein SpMTA gene in the sea urchin embryo

Phenotypic and genetic differentiation in young-of-the-year common sole (Solea solea) at differentially contaminated nursery grounds

Growth-related characters, condition factor, and genetic differentiation were investigated for a single cohort of young-of-the-year (YOY) sole within and among nurseries with differing levels of heavy metals (Cd, Cu and Zn) contamination in the two Charentais Straits, Bay of Biscay, France. Analyses were performed when individuals recruited (May), then after a full summer spent in each nursery (October). Levels of phenotypic and genetic diversity were compared, together with genetic differentiation at a candidate metallothionein (MT) locus and three putatively neutral microsatellite loci. No phenotypic or genetic differentiation was detected among nurseries in May, but significant variation at each phenotypic trait and at the multilocus level in October (P < 0.001). Single locus analysis demonstrated that only the MT locus was significantly differentiated among nurseries, whether corrected for null alleles or not (θ=0.0401 and θ(corr.FreeNA)=0.0326, respectively; P < 0.001). Results indicate that phenotypic differences among YOY sole nurseries present a molecular correlate acting at identical spatio-temporal scales among nurseries, potentially reflecting differential selective pressure among nurseries in response to contamination.

The bean PvSR2 gene produces two transcripts by alternative promoter usage

The bean (Phaseolus vulgaris) stress-related gene number 2 (PvSR2) is heavy metal-inducible. Here, the intron of PvSR2 (I-PvSR) within the coding sequence was isolated and characterized. I-PvSR exhibited a weak and constitutive promoter activity and enhanced the PvSR2 promoter activity in transiently transformed tobacco protoplasts. The transcription start site of I-PvSR promoter was mapped 72 bp upstream of the 3'-splice site. The shorter PvSR2 transcript (768nt) in bean is generated from this intronic promoter and lacks the last 56 bases of 3'-end sequence of longer PvSR2 transcript (829nt) by utilizing an alternative polyadenylation site. Quantitative competitive PCR analysis further revealed that two transcripts were differently accumulated in response to Hg(2+)-exposure and the longer transcript was more abundant than the shorter one. These results demonstrate an additional non-metal inducible transcription of PvSR2 via alternative intronic promoter usage and provide new insights into expression mechanism of metal inducible gene.

Genomic organization, promoter characterization and expression profiles of an antiviral gene PmAV from the shrimp Penaeus monodon

Diseases caused by viruses are the greatest challenge to worldwide shrimp aquaculture. PmAV is the first antiviral gene identified from the shrimp and its mRNA level is up-regulated in response to viral infection (Luo et al., 2003). The transcriptional regulation of PmAV is critical since the expression of this gene is regulated in response to viral stimuli. In this study, we show that the Penaeus monodon PmAV gene contains four exons, separated by three introns. The 5'-flanking sequence of PmAV gene consists of a typical TATA box, several potential regulatory elements, and a compound microsatellite repeat as well. Interestingly, a TATA box and several regulatory elements also exist in the first intron (intron 1). Both intron 1 and the microsatellite are involved in transcriptional regulation of the PmAV gene. PmAV promoter activity depends on the existence of intron 1 while the microsatellite in 5'-flanking sequence acts as a negative regulative element. In addition, using Real-time PCR, we found that PmAV was highly expressed in the hepatopancreas and was up-regulated from the second day post-infection with the increase of viral load. These results extend our previous findings and provide insights into the molecular regulation of PmAV gene expression, which will be helpful for shrimp viral disease control.

Metallothionein cDNA, promoter, and genomic sequences of the tropical green mussel, Perna viridis

The primary structure of the cDNA and metallothionein (MT) genomic sequences of the tropical green mussel (Perna viridis) was determined. The complete cDNA sequences were obtained using degenerate primers designed from known metallothionein consensus amino acid sequences from the temperate species Mytilus edulis. The amino acid sequences of P. viridis metallothionein deduced from the coding region consisted of 72 amino acids with 21 cysteine residues and 9 Cys-X-Cys motifs corresponding to Type I MT class of other species. Two different genomic sequences coding for the same mRNA were obtained. Each putative gene contained a unique 5'UTR and two unique introns located at the same splice sites. The promoters for both genes were different in length and both contained metal responsive elements and active protein-binding sites. The structures of the genomic clones were compared with those of other species. J. Exp. Zool. 284:445-453, 1999.

Molecular and genetic ecotoxicologic approaches to aquatic environmental bioreporting

Molecular and population genetic ecotoxicologic approaches are being developed for the utilization of arthropods as bioreporters of heavy metal mixtures in the environment. The explosion of knowledge in molecular biology, molecular genetics, and biotechnology provides an unparalleled opportunity to use arthropods as bioreporter organisms. Interspecific differences in aquatic arthropod populations have been previously demonstrated in response to heavy metal insult in the Arkansas River (AR) California Gulch Superfund site (CGSS). Population genetic analyses were conducted on the mayfly Baetis tricaudatus. Genetic polymorphisms were detected in polymerase chain reaction amplified 16S mitochondrial rDNA (a selectively neutral gene) of B tricaudatus using single-strand conformation polymorphism analysis. Genetic differences may have resulted from impediments to gene flow in the population caused by mortality arising from exposure to heavy metal mixture pollution. In laboratory studies a candidate metal-responsive mucinlike gene, which is metal and dose specific, has been identified in Chironomus tentans and other potential AR-CGSS bioreporter species. Population genetic analyses using the mucinlike gene may provide insight into the role of this selectable gene in determining the breeding structure of B. tricaudatus in the AR-CGSS and may provide mechanistic insight into determinants of aquatic arthropod response to heavy metal insult. Metal-responsive (MR) genes and regulatory sequences are being isolated, characterized, and assayed for differential gene expression in response to heavy metal mixture pollution in the AR-CGSS. Identified promoter sequences can then be engineered into previously developed MR constructs to provide sensitive in vitro assays for environmental bioreporting of heavy metal mixtures. The results of the population genetic studies are being entered into an AR geographic information system that contains substantial biological, chemical, and geophysical information. Integrated spatial, structural, and temporal analyses of these parameters will provide invaluable information concerning environmental determinants that restrict or promote gene flow in bioreporter populations.

An intronic enhancer is required for deflagellation-induced transcriptional regulation of a Chlamydomonas reinhardtii dynein gene

Chlamydomonas reinhardtii flagellar regeneration is accompanied by rapid induction of genes encoding a large set of flagellar structural components and provides a model system to study coordinate gene regulation and organelle assembly. After deflagellation, the abundance of a 70-kDa flagellar dynein intermediate chain (IC70, encoded by ODA6) mRNA increases approximately fourfold within 40 min and returns to predeflagellation levels by approximately 90 min. We show by nuclear run-on that this increase results, in part, from increased rates of transcription. To localize cis induction elements, we created an IC70 minigene and measured accumulation, in C. reinhardtii, of transcripts from the endogenous gene and from introduced promoter deletion constructs. Clones containing 416 base pairs (bp) of 5'- and 2 kilobases (kb) of 3'-flanking region retained all sequences necessary for a normal pattern of mRNA abundance change after deflagellation. Extensive 5'- and 3'- flanking region deletions, which removed multiple copies of a proposed deflagellation-response element (the tub box), did not eliminate induction, and the IC70 5'-flanking region alone did not confer deflagellation responsiveness to a promoterless arylsulfatase (ARS) gene. Instead, an intron in the IC70 gene 5'-untranslated region was found to contain the deflagellation response element. These results suggest that the tub box does not play an essential role in deflagellation-induced transcriptional regulation of this dynein gene.

Promoter structure and activity of type 1 rice metallothionein-like gene

A novel stress-inducible metallothionein-like gene from rice, designated as rgMT-1 (rice genomic metallothionein-like gene-1), was isolated and sequenced. From the sequence analysis of its 5'-flanking region, two putative TATA boxes, one CAAT box, and several short sequences homologous to regulatory cis-elements previously reported were identified. Two direct repeats, one 10 bp in length (CAAAATCAAA) and the other 11 bp (GTGAAAATACT), respectively, were also found. By transient GUS (beta-glucuronidase) assay, the expression of GUS, in vitro, was enhanced by the presence of the rgMT-1 intron. The critical region which controls the basal transcription was shown to lie between -73 and -36 upstream of rgMT-1, in which one of the two putative TATA boxes was located. The promoter activity was lost completely when both putative TATA boxes were deleted. This is the first report describing the genomic structure and regulation of a monocotyledonous metallothionein-like gene critical to the response of stress.

Metallothionein gene expression in embryos of the sea urchin Lytechinus pictus

The metallothionein (MT) gene LpMT1 of the sea urchin Lytechinus pictus was characterized. The primary transcript of 3042 nucleotides includes four exons, as uniquely observed for other sea urchin MT genes, which are spliced to form a messenger RNA of 605 nucleotides. The deduced LpMT1 protein sequence includes 69 amino acids, more than observed for other MT proteins. For a high level of inducible activity, the LpMT1 promoter requires sequence elements in addition to the canonical regulatory elements identified for mammalian MT promoters. The promoter of the closely related LpMT2 gene is very active in spite of its lack of a distinctive poly(C) element included in a sequence tract required for fully induced activity of the LpMT1 promoter. In contrast to embryos of the sea urchin S. purpuratus in which MT mRNAs are restricted to the aboral ectoderm of uninduced embryos, no spatially preferential accumulation of MT mRNAs in L. pictus embryos was observed. The cisacting regulatory elements required for MT gene activity and the spatial specificity of MT gene expression in sea urchin embryos are considered. The LpMT1 and LpMT2 promoters constitute promiscuous promoters that can be induced to a high level of activity.

Regulation of heme oxygenase-2 by glucocorticoids in neonatal rat brain: characterization of a functional glucocorticoid response element

Heme oxygenase-2 (HO-2) is constitutively expressed in mammalian tissues; together with HO-1 (HSP32) it catalyzes the cleavage of heme to produce biliverdin IX alpha, CO and Fe. Detection of a consensus sequence of the glucocorticoid response element (GRE) in the promoter region of the HO-2 gene prompted the present study which has investigated the role of glucocorticoids (Gcs) in the regulation of HO-2 protein and transcript development in the newborn rat brain and has examined the promoter activity of the GRE in HeLa cells. Using in situ hybridization histochemistry, we noted a pronounced increase in signal for HO-2 mRNA in the brain of 14-day-old rats postnatally treated with corticosterone (5 microg/g, 4 x, starting 24-36 h after birth). And, using immunohistochemistry, a striking increase in neuronal HO-2 immunostaining in treated brains was detected. The HO-2 GRE was tested for responsiveness to dexamethasone (DX) using both a promoterless CAT expression vector, and a heterologous promoter containing luciferase expression vector in HeLa cells. The HO-2 promoter containing the GRE and transcription start site induced CAT reporter gene activity in response to DX, whereas mutation or deletion in the GRE abolished hormone responsiveness. Similarly, constructs containing the GRE conferred responsiveness to DX in an orientation-independent manner and increased relative luciferase activity. Further, specific binding of glucocorticoid receptor protein to the GRE was observed; binding could be competed out only by excess cold GRE and not by mutated HO-2 GRE, or AP1. HO-2 mRNAs (approximately 1.3 and approximately 1.9 kb) increased in HeLa cells treated with DX (5 microM), the level reached a maximum at 24 h. DX did not effect HO-1 mRNA level. The increase in the HO-2 transcript was accompanied by an increase in HO-2 protein, as assessed by Western blot analysis, and an increase in HO activity, as measured by bilirubin formation. Also, an increase in intensity of immunostaining was noted in DX-treated HeLa cells. We conclude that the GRE present in the HO-2 gene promoter region is functional, and propose the direct involvement of the adrenal glucocorticoids in modulation of HO-2 gene expression. In the context of biological functions of heme degradation products, we suggest that this regulation may be of significance, particularly to the neurons.

WEE1-like CDK tyrosine kinase mRNA level is regulated temporally and spatially in sea urchin embryos

A cDNA from the sea urchin Strongylocentrotus purpuratus encodes a 624 amino acid polypeptide (WEE1S.purp) with a high degree of similarity to the Mik1 and Wee1 protein tyrosine kinases. These kinases act as negative regulators of mitosis by inactivating cyclin-dependent kinases (CDK). Wee1 activity varies during the cell-cycle, and is generated only when required. The pattern of WEE1S.purp mRNA expression was examined temporally and spatially in sea urchin embryos. Only a trace amount of WEE1S.purp mRNA is present in the egg and through the fifth cell cycle post-fertilization. During the next three cycles to the mid-blastula stage, its concentration rises transiently to 2.5 x 10(4) transcripts per embryo. Its developmental profile during this early period is the inverse of that reported for cyclin mRNAs, which are at a high level in the egg and through the fifth cell cycle, then decline upon further development. WEE1S.purp mRNA in the gastrula and pluteus stages becomes restricted to cells engaged in DNA replication, including the endoderm (gut), oral ectoderm, and arm rudiments. It is absent from the aboral ectoderm, which lacks cycling cells. In the pluteus larva of the species Lytechinus pictus, WEE1 mRNA was detected in the arm rudiments during cellular proliferation and arm elongation, but not after the completion of the arms. Putative regulatory motifs in the sea urchin Wee1-like cDNA suggest a capacity for rapid turnover of both its mRNA and protein: The WEE1S.purp mRNA 3' UTR contains 13 AUUUA pentamers, which have been characterized as determinants of mRNA lability; and the N-terminal domain of the predicted WEE1S.purp polypeptide is enriched in S/TP-containing, potential kinase-target sites, as well as high-value "PEST' sequences, associated with protein lability. The developmental appearance of WEE1S.purp mRNA may coincide with the introduction of a gap phase in the cell cycle. Its spatial pattern during embryogenesis appears to reflect distinct programs of regulated cell cycling in differentiating tissues.

The first intron of the mouse neurofilament light gene (NF-L) increases gene expression

Neurofilament expression is developmentally and post-transcriptionally controlled. Using transient transfection assays in mouse L cells, we demonstrate that the expression of the mouse neurofilament light subunit (NF-L) is influenced by intron sequences. NF-L expression was decreased twenty fold upon deletion of the three intron sequences. Elements contained principally within a 350 bp region of intron 1 were responsible for enhanced NF-L expression. Enhancement of expression did not occur when intron I was placed 3' to a heterologous chloramphenicol acetyl transferase (CAT) gene whose expression was driven by NF-L 5' sequences. The intron enhancement of NF-L expression was not promoter-specific and also occurred with the mouse sarcoma virus (MSV) LTR promoter. These data suggest intron sequences may be important in regulating NF gene expression.

Spatial regulation of SpMTA metallothionein gene expression in sea urchin embryos by a regulatory cassette in intron 1

The SpMTA metallothionein (MT) gene of the sea urchin Strongylocentrotus purpuratus is restricted in its expression to the aboral ectoderm in gastrulae and pluteus larvae. The proximal 1.6 kb of the 5'-flanking region together with the 1.12-kb first intron of the SpMTA gene are sufficient for its correct cell-type specific expression in transgenic embryos. This restricted spatial expression is largely eliminated by deletion of an interior 405-bp region in the intron. Within this region is a 295-bp, genomically repetitive, transposon-like segment (Nemer et al., 1993), containing several sequence motifs highly homologous to posited regulatory elements in the promoters of other genes (Thiebaud et al., 1990). The P3A and P5 sites in this apparent regulatory cassette were shown through competition to bind with relatively high affinities the same nuclear factors, bound by their counterpart sites in the CyIIIa actin promoter.

Functional analysis of the proximal 5'-flanking region of the N-methyl-D-aspartate receptor subunit gene, NMDAR1

The NMDAR1 receptor subunit is a common subunit of N-methyl-D-aspartate receptors. We have previously characterized 3 kilobases (kb) of 5'-flanking sequence of the NMDAR1 gene and now report on the ability of this region to direct transcription of a reporter gene and on its interaction with nuclear proteins. The sequence 356 base pairs (bp) 5' of the first nucleotide of codon 1 was sufficient to express a luciferase reporter gene in rat PC12 pheochromocytoma cells. Additional sequences upstream of nucleotide -356 influenced the activity approximately 2-fold. A labeled 112-bp fragment (position -356 to -245) formed six complexes (C1A and -B, C2A and -B, and C3A and -B), grouped as three double bands, with nuclear extracts from PC12 cells. Competition with Sp1 oligonucleotides abolished formation of C2A and -B and C3A and -B complexes. Sp1 antibody recognized the C3A complex in supershift experiments. Prior immunoprecipitation of nuclear extracts with Sp1 antibody abolished formation CA2 and -B and C3A and -B complexes. Purified Sp1 protein alone did not form a C3A complex but potentiated its formation when PC12 nuclear extract was added. A GC-rich sequence in this fragment was protected from DNase I digestion by nuclear extract. These results suggest that a 356-bp sequence comprises the NMDAR1 basal promoter, and that NMDAR1 gene expression may be regulated by Sp1-like nuclear factors.

Purification and characterisation of recombinant sea urchin metallothionein expressed in Escherichia coli

Metallothioneins (MT) are metalloproteins expressed tissue specifically during the development of the sea urchin, Strongylocentrotus pururatus. To explore their structural and functional features and to compare them with those of the evolutionary distant mammalian MTs, one isoform (MTA) was obtained as the cadmium-containing form, from synthetic cDNA heterologously expressed in Escherichia coli. The purified protein was identified as the desired product by a combination of peptide-map analysis, amino acid sequence analysis and ion-spray mass spectroscopy. The existence of seven 113Cd NMR resonances revealed that the recombinant protein binds seven Cd ions/molecule. The position of the NMR resonances (605-695 ppm) and the electronic absorption features suggest that the sea urchin MTA, like the mammalian MTs, possesses tetrahedrally coordinated cadmium-thiolate clusters. With its large Stokes' radius, sea urchin MTA resembles the mammalian forms, suggesting a comparable elongated molecular shape. Measurements by spectrophotometric pH titration of cadmium binding by the recombinant protein suggest that it possesses two metal-thiolate clusters of distinctly different stability. At pH 7 the average apparent association constant for Cd2+ in the clusters is about 20-times weaker in sea urchin MTA than in rabbit MT-2.

Promoter analysis meets pattern formation: transcriptional regulatory genes in sea urchin embryogenesis

Analyses of spatial and temporal gene control mechanisms in the sea urchin embryo have identified several important trans-regulatory factors, including some that are related to known developmental control genes of the fly and mouse. Recent advances in gene perturbation technologies, including the use of antisense oligonucleotides to target mRNAs in early-stage embryos, as well as the injection of mRNAs into zygotes to express genes ectopically, have made it possible to test the functions of such factors directly.