Structure and regulation of the sheep metallothionein-Ia gene

Recombinant Adeno-Associated Viral Vectors (rAAV)-Vector Elements in Ocular Gene Therapy Clinical Trials and Transgene Expression and Bioactivity Assays

Inherited retinal dystrophies and optic neuropathies cause chronic disabling loss of visual function. The development of recombinant adeno-associated viral vectors (rAAV) gene therapies in all disease fields have been promising, but the translation to the clinic has been slow. The safety and efficacy profiles of rAAV are linked to the dose of applied vectors. DNA changes in the rAAV gene cassette affect potency, the expression pattern (cell-specificity), and the production yield. Here, we present a library of rAAV vectors and elements that provide a workflow to design novel vectors. We first performed a meta-analysis on recombinant rAAV elements in clinical trials (2007-2020) for ocular gene therapies. We analyzed 33 unique rAAV gene cassettes used in 57 ocular clinical trials. The rAAV gene therapy vectors used six unique capsid variants, 16 different promoters, and six unique polyadenylation sequences. Further, we compiled a list of promoters, enhancers, and other sequences used in current rAAV gene cassettes in preclinical studies. Then, we give an update on pro-viral plasmid backbones used to produce the gene therapy vectors, inverted terminal repeats, production yield, and rAAV safety considerations. Finally, we assess rAAV transgene and bioactivity assays applied to cells or organoids in vitro, explants ex vivo, and clinical studies.

IL-10 modulates depressive-like behavior

The role of pro-inflammatory cytokines in psychiatric disorders has been the focus of great research attention in recent years. Paradoxically, the same is not true for anti-inflammatory cytokines. In the present study, we assessed the behavioral profile of animals with altered expression of the anti-inflammatory cytokine IL-10. We performed a battery of tests to assess anxiety, depressive-like and cognitive behaviors in mice overexpressing IL-10 (PMT10) and IL-10(-/-) animals; in the later mice we also tested the behavioral effect of IL-10 administration. In the forced-swimming test, IL-10(-/-) females displayed increased depressive-like behavior; importantly, this phenotype was reverted by the injection of IL-10. Moreover, mice overexpressing IL-10 presented a decreased depressive-like behavior. Despite the presence of a similar trend, male animals did not reach significant differences in depressive-like behavior. Assessment in the open-field showed that the absence of IL-10 decreased the percentage of time spent in the center of the arena in both male and female mice, while male animals overexpressing IL-10 revealed an opposite behavior. For both sexes, imbalance in IL-10 levels did not affect spatial reference memory. In conclusion, variations in IL-10 expression are associated with an altered depressive-like behavior, but do not influence cognitive performance. Interestingly, IL-10 imbalance produced more profound behavioral changes in females than in male animals. This is in accordance with clinical data demonstrating an increased susceptibility of women to mood disorders, suggesting an interplay between anti-inflammatory cytokines and sexual steroids.

Gene-specific requirement of a nuclear protein, IkappaB-zeta, for promoter association of inflammatory transcription regulators

Expression of many inflammatory genes is induced through activation of the transcription factor NF-kappaB. In contrast to the advanced understanding of cytoplasmic control of NF-kappaB activation, its regulation in the nucleus has not been fully understood despite its importance in selective gene expression. We previously identified an inducible nuclear protein, IkappaB-zeta, and demonstrated that this molecule is indispensable for the expression of a group of NF-kappaB-regulated genes. In this study, we established a unique gene induction system, in which IkappaB-zeta is expressed independently of inflammatory stimuli, to specifically investigate the molecular basis underlying IkappaB-zeta-mediated gene activation. We show that in the presence of IkappaB-zeta other primary response genes are dispensable for the expression of the target secondary response genes. ChIP analyses revealed that IkappaB-zeta is required for stimulus-induced recruitment of NF-kappaB onto the target promoter in a gene-specific manner. Surprisingly, IkappaB-zeta is also necessary for the gene-selective promoter recruitment of another inflammatory transcription factor, C/EBPbeta, and the chromatin remodeling factor Brg1. We propose a new gene regulatory mechanism underlying the selective expression of inflammatory genes.

Characterization of metallothioneins (MT-I and MT-II) in the yak

The cDNA-encoding sequences for yak metallothionein isoforms I (MT-I) and II (MT-II) were amplified and cloned by reverse-transcription PCR to characterize the nucleotide sequence and protein structure of metallothionein in the yak. The cDNA sequences of MT-I and MT-II were subjected to BLAST searching at the National Center for Biotechnology Information, and the results indicated that the nucleotide sequences of yak MT-I and MT-II, when compared among different species of mammals, are highly conserved. The yak open reading frames have a length of 183 nucleotides, which encode for yak MT-I and MT-II proteins of 61 AA, respectively. Analysis of hydrophobicity, trans-membrane region, and signal peptides suggested that metallothioneins of the yak are nonsecretory proteins. There were several conserved tripeptide sequences, such as C-X-C, C-C-X-C-C, and C-X-X-C (X designates AA excluding cysteine in MT-I and MT-II), and they are highly conserved in their evolution. By homologous comparative modeling, we predicted the molecular spatial structures of yak MT-I and MT-II, which are composed of alpha- and beta-domains that are linked by the conserved tripeptide Lys(30)-Lys(31)-Ser(32) (KKS).

Identification of Nd1, a novel murine kelch family protein, involved in stabilization of actin filaments

We isolated Nd1, a novel kelch family gene that encodes two forms of proteins, Nd1-L and Nd1-S. Nd1-L contains a BTB/POZ domain in its N terminus and six kelch repeats in the C terminus. Nd1-S has the BTB/POZ domain but lacks the six kelch repeats. Nd1-L but not Nd1-S mRNA is detected ubiquitously in normal mouse tissues. Nd1-L and Nd1-S proteins can form a dimer through the BTB/POZ domain. Nd1-L colocalizes with actin filaments detected using a confocal microscope, and its kelch repeats bind to them in vitro. Overexpression of Nd1-L in NIH3T3 cells delayed cell growth by affecting the transition of cytokinesis. Furthermore, the overexpression prevented NIH3T3 cells from cell death induced by actin destabilization but not by microtubule dysfunction. These data suggest that Nd1-L functions as a stabilizer of actin filaments as an actin-binding protein and may play a role in the dynamic organization of the actin cytoskeleton.

Evidence for early cytotoxic aggregates in transgenic mice for human transthyretin Leu55Pro

Familial amyloidotic polyneuropathy (FAP) is a lethal autosomal dominant disorder characterized by systemic extracellular deposition of transthyretin (TTR) amyloid fibrils. Several groups have generated transgenic mice carrying human TTR Val30Met, the most common mutation in FAP. To study amyloidogenicity and cytotoxicity of different TTRs, we produced transgenic mice expressing human TTR Leu55Pro, one of the most aggressive FAP-related mutations. TTR deposition and presence of amyloid fibrils was investigated and compared to animals carrying the human TTR Val30Met gene kept under the same conditions. Deposition in a C57BL/6J background (TTR-Leu55Pro mice) and in a TTR-null background [TTR-Leu55Pro X TTR-knockout (KO) mice] was compared. Animals in a C57BL/6J background presented early (1 to 3 months) nonfibrillar TTR deposition but amyloid was absent. In a TTR-null background, presence of amyloid fibrils was detected starting at 4 to 8 months with a particular involvement of the gastrointestinal tract and skin. This data suggested that TTR homotetramers are more prone to fibril formation than TTR murine wild-type/human mutant heterotetramers. The nature of the deposited material was further investigated by immunocytochemistry. Both amorphous aggregates and small TTR fibrils were present in TTR-Leu55Pro X TTR-KO transgenics. We observed that these TTR deposits mimic the toxic effect of TTR deposits in FAP: animals with TTR deposition, present approximately twofold increased levels of nitrotyrosine in sites related to deposition. The TTR-Leu55Pro X TTR-KO mice here described are an important tool for the dual purpose of investigating factors involved in amyloidogenesis and in cytotoxicity of deposited TTR.

Transgene and host growth hormone gene expression in pituitary and nonpituitary tissues of normal and growth hormone transgenic salmon

Growth hormone (GH) gene expression has been examined in control and transgenic coho salmon containing a transgene comprised of the sockeye salmon GH1 gene under the control of the MT-B promoter from the same species. This transgene dramatically enhances the growth of salmonids, and raises serum GH levels some forty-fold. Transcript levels from this transgene were detected by RT-PCR using construct-specific GH primers in all tissues examined (liver, kidney, skin, intestine, stomach, muscle, spleen, pyloric caeca), and ranged from 0.1 - 9.4 pg/50 microg total RNA in different tissues as estimated by dot blot analysis. Interestingly, GH gene expression was also observed in intestine of control coho salmon by RT-PCR capable of detecting host and transgene transcripts using general primers. Sequence analysis of the intestinal GH mRNA from controls indicated it was derived from the coho GH2 gene. GH mRNA abundance analyzed by northern analysis indicates lower levels are found in large (400-500 g) than small transgenic salmon (20-21 g). No molecular evidence for transgene expression was obtained in tissues from transgenic fry, despite an obvious increase in size relative to control siblings, suggesting very low levels of transgene expression early in development. GH mRNA levels (per microg RNA) were also examined in the pituitary gland, and were found to be significantly lower (P < 0.01) in transgenic coho compared to nontransgenic animals of the same size. Pituitary glands of transgenic animals were also smaller than control animals of the same size, and pituitary size, expressed as a proportion of body weight, decreased with body size in transgenic but not control animals. These results imply that pituitary GH expression is regulated by negative feed-back controls as occurs in other vertebrate systems. GH mRNA was examined in pituitary glands by whole-mount in situ hybridization, and, whereas overall levels appeared reduced in transgenic animals, the site of hybridization did not differ between transgenic and control glands.

Repression of c-myc transcription by Blimp-1, an inducer of terminal B cell differentiation

Transcription of c-myc in plasma cells, which are terminally differentiated B cells, is repressed by plasmacytoma repressor factor. This factor was identified as Blimp-1, known for its ability to induce B cell differentiation. Blimp-1 repressed c-myc promoter activity in a binding site-dependent manner. Treatment of BCL1 lymphoma cells with interleukin-2 (IL-2) plus IL-5 induced Blimp-1 and caused a subsequent decline in c-Myc protein. Ectopic expression of Blimp-1 in Abelson-transformed precursor B cells repressed endogenous c-Myc and caused apoptosis; Blimp-1-induced death was partially overcome by ectopic expression of c-Myc. Thus, repression of c-myc is a component of the Blimp-1 program of terminal B cell differentiation.

Biphasic response of the metallothionein promoter to ultraviolet radiation in human melanoma cells

Because metallothionein (MT) is elevated and may be protective in UV-irradiated skin, we have studied the effects of UV and other agents on MT transcription using the sheep MT 1A promoter, linked to the beta-galactosidase gene and stably transfected into human cell lines. beta-galactosidase reporter activity was inducible by adding Zn2+ ions to the medium (100 microM for 2-4 h). Two differentiating agents, butyric acid and azelaic bishydroxamic acid (ABHA), significantly increased the response to Zn2+ in a melanoma cell line (MM96L-gal). UVB (280-315 nm) had two distinct, time-dependent effects. During the first 4 h after irradiation, high doses of UVB inhibited induction by Zn2+, an effect that was made more acute by simultaneous exposure to the differentiating agents. These changes in reporter activity were not due to alterations in Zn2+ transport into the cell. The UVB-depressed MT response subsequently recovered and by 24 h was double the control, yet remained sensitive to ABHA. Reporter activity in transfected HeLa cells differed from that in MM96L, being depressed 4 and 24 h after UVB and insensitive to ABHA at both times. Galactosidase reporter activity driven by non-MT promoters was not affected by these treatments. Dependence of MT transcriptional activity on UV-related DNA damage could be inferred because equitoxic UVC (254 nm) affected the response to Zn2+ in a similar fashion, whereas UVA, cisplatin and a methylating agent had no effect. The MT response was partly dependent on the PKC signal transduction pathway because it was inhibited by phorbol ester in HeLa, and by bisindolyl maleimide in HeLa and MM96L. The biphasic MT transcriptional response may model a signal transduction pathway that gives an early, depressed response to acute UV damage, with exacerbation by concurrent differentiation stimuli, but switches to a positive, cell-specific and potentially protective response at later times.

Introduction and expression of the bacterial glyoxylate cycle genes in transgenic mice

The glyoxylate cycle, catalysed by two unique enzymes: isocitrate lyase (ICL; EC 4.1.3.1) and malate synthase (MS; EC 4.1.3.2), is necessary for the net conversion of acetate into glucose. This metabolic pathway operates in microorganisms, higher plants and nematodes. Two bacterial genes, encoding ICL and MS, were modified in order to introduce them into the mouse germ line. The ovine metallothionein-Ia (MT-Ia) promoter-ace B gene-ovine growth hormone (GH) gene (3' GH sequence) construct was fused to the ovine, MT-Ia promoter-ace A gene-ovine GH gene (3' GH sequence). Therefore, in this single DNA sequence, both ace A and ace B are under independent MT-Ia promoter control and can be induced by zinc. Transgenic mice were generated by pronuclear microinjection of the ace B-ace A gene construct. We now report the establishment of four mouse lines carying these two transgenes. Studies on the progeny of these lines indicate that one line (No. 91) is expressing both genes at the mRNA and enzyme levels in the liver and intestine, whereas another line (No. 66) has a much lower expression. Both enzyme activities were detected in the liver and intestine at levels up to 25% of those measured in fully derepressed Escherichia coli cells.

Analysis of regulatory elements flanking metallothionein genes in Cd-tolerant fish (pike and stone loach)

From genomic libraries constructed for both pike and stone loach, clones were isolated containing the metallothionein genes from these two species of cadmium-tolerant fish. A single copy metallothionein gene was identified in each species by Southern blot analysis. Sequencing revealed that each gene consisted of three exons followed by polyadenylation signals at the 3' end. In the 5' flanking region, putative metal responsive elements were identified both close to the transcription start site and clustered distally approx. 500 bp upstream. Neither gene locus showed any homology with the glucocorticoid or interferon responsive elements that have been identified in mammalian species. The significance of the absence of such responsive elements and their replacement by additional metal responsive elements in the same location of the 5'-flanking region of the MT genes is discussed in relation to the organisation of the MT gene loci in (the Cd-sensitive) rainbow trout and higher mammalian species.

Introduction and expression of the bacterial genes cysE and cysK in eukaryotic cells

The coding sequences of the cysE and cysK genes from Escherichia coli, which encode the enzymes of the cysteine biosynthetic pathway, namely, serine acetyltransferase (EC 2.3.1.30) and O-acetylserine sulfhydrylase (or cysteine synthase [EC 4.2.99.8]), were modified for expression in eukaryotic cells and introduced into murine L cells. A number of fusion genes comprising the cysE or cysK coding sequences joined to the promoter of the ovine metallothionein-Ia (MT-Ia) gene and various portions of the ovine growth hormone (GH) gene were prepared. Significant differences in the level of transcription were observed, depending on the amount and arrangement of the GH gene sequences used, the highest levels being obtained with the constructs MTCE10 and MTCK7, which contained only the GH 3' untranslated gene sequences. These two constructs were fused to produce the gene MTCEK1. In this single DNA sequence, each bacterial gene is under independent MT-Ia promoter control. Expression of the cysK sequence in this construct (MT-Ia promoter-cysE-3' GH sequence-MT-Ia promoter-cysK-3' GH sequence) was elevated compared with expression of the cysK gene in MTCK7. However, expression of the cysE sequence in MTCEK1 was only 40% of that of the cysE gene cloned into MTCE10. The double-promoter configuration, which enhances the expression of the second gene in MTCEK1, is proposed as a model for the modification of bacterial genes in general.

Zinc-specific activation of a HeLa cell nuclear protein which interacts with a metal responsive element of the human metallothionein-IIA gene

Transcription of metallothionein genes is activated by heavy metals such as zinc and cadmium, and a DNA element called metal responsive element (MRE) is essential for this process. By mobility-shift assay, we identified a HeLa-cell nuclear protein which specifically binds to MREa of human metallothionein-IIA gene. This protein, named ZRF (zinc-regulatory factor), is present in the cells untreated with heavy metals. Zinc is essential for, and increases in a dose-dependent manner, the binding of ZRF to MREa. Other heavy metals which can also induce metallothioneins, including cadmium, copper and mercury, do not activate ZRF. A MREa-containing oligonucleotide that can bind ZRF confers heavy metal-inducibility to a heterologous promoter, suggesting that ZRF is a zinc-dependent transcriptional activator. In addition to the MRE core sequence, the surrounding sequences are also important for both ZRF binding in vitro, and zinc-dependent transcriptional activation in vivo. MREa by itself responds not only to zinc but also to other metallothionein-inducing heavy metals, indicating that the ZRF protein, not the MREa sequence, is responsible for the zinc specificity.

The use of transgenic animals to study the role of growth factors in endocrinology

Transgenesis is identified as being of special interest in the study of growth factors where their multicellular origins and complex interactions make them particularly difficult to characterize using classical experimental approaches developed to investigate hormones originating in specialized cells in discrete glands. Through allowing molecular 'tinkering' in intact animals, transgenesis enables specific growth factors to be 'ablated or replaced' from specific tissues and organs and target cell response and impact of modulatory factors such as binding proteins to be explored in the intact animal. To the endocrinologist, the potential applications of such technology are legend. This chapter provides a brief overview of the technique and provides linkages to the rapidly developing body of literature in establishing transgenesis in growth factor research.

Analysis of hepatic copper, zinc, metallothionein and metallothionein-Ia mRNA in developing sheep

The concentrations of zinc, copper, metallothionein and metallothionein-Ia mRNA in sheep livers during development was determined. It was found that early sheep foetuses (30-40 days gestation) had very high concentrations of hepatic zinc (2305 +/- 814 micrograms/g dry mass), and that these levels declined steadily to 644 +/- 304 micrograms/g near to term. The copper concentrations in the foetal livers were not higher than those in the adult. The concentrations of metallothionein and metallothionein-Ia mRNA were also very high in the foetal livers and declined steadily during gestation from 261 +/- 94 molecules/pg RNA to 71 +/- 18 molecules/pg near to term. Metallothionein-Ia mRNA concentrations were closely correlated with hepatic zinc concentrations but not with copper. Metallothionein concentrations also decreased during gestation: e.g. 3044 micrograms/g (wet mass) in one foetus on day 34 of gestation to 862 micrograms/g on day 125. After birth, however, the concentrations of metallothionein declined to less than 100 micrograms/g and this decline occurred despite the presence of significant quantities of mRNA. The ratio of metallothionein/metallothionein-Ia mRNA decreased from 1.3 to 3.2 x 10(5) molecules metallothionein/molecule of metallothionein-Ia mRNA during gestation to between 0.28-0.64 x 10(5) molecules/molecule in the postnatal animals. We conclude that the major function of metallothioneins in the foetal liver is protection of the liver against the potentially toxic accumulation of zinc. In the postnatal sheep there appears to be a decreased synthesis or increased degradation of metallothionein.

Regulation of expression of a sheep metallothionein 1a-sheep growth hormone fusion gene in transgenic mice

Transgenic mice containing a sheep metallothionein 1a-sheep growth hormone fusion gene exhibited low, tissue-specific basal levels of transgene mRNA expression, resulting in slightly elevated levels of circulating growth hormone that did not lead to a detectable increase in growth. After zinc stimulation, high levels of transgene mRNA expression were induced in a number of tissues; these levels correlated with increased levels of circulating growth hormone, resulting in growth increases of up to 1.5 times the levels of controls and unstimulated transgenic mice. After removal of the zinc stimulus, transgene expression and circulating growth hormone concentrations returned to basal levels. Additional evidence from the pattern of developmental expression of the transgene suggests that zinc is the main regulator of this promoter in mice. The demonstrated regulation and low basal level of expression of the sheep metallothionein 1a promoter make it a candidate for use in other mouse transgenic studies and for use in transgenic livestock, in which regulation of expression is essential.

Structure of an ectodermally expressed sea urchin metallothionein gene and characterization of its metal-responsive region

The metallothionein-A gene in the metallothionein gene family of the sea urchin Strongylocentrotus purpuratus (SpMTA gene) was sequenced and found to contain three coding exons plus a 3' entirely noncoding exon. Putative alpha and beta MT domains were encoded, by its exons 2 and 3, respectively, in reverse of the order in vertebrate metallothionein genes. The SpMTA promoter was characterized through the expression of recombinant constructs containing various portions of the proximal 678-base-pair (bp) 5'-flanking region of the SpMTA gene. Zygotes injected with constructs were cultured to the blastula stage in the presence of a heavy-metal chelator and then incubated in the presence or absence of cadmium. The longest constructs were expressed only when heavy-metal ion was present. Two putative metal-responsive elements (MREs a and b) within 240 bp of the transcription start site resembled mammalian MREs in their critical 8-bp cores (TGCRCNCS) and in their locations relative to each other and to the TATA box. Elimination of activity by site-specific mutations in MREs a and b, separately or in both, identified them as metal regulatory elements. Thus, MRE recognition in this invertebrate resembles that in vertebrates. Upstream sites with single-mismatched MREs neither acted as MREs nor amplified the activity of MREs a and b. The SpMTA, Spec1, and CyIIIa actin genes, which have the same ectodermal specificity, have common DNA elements at relatively similar locations in their promoter regions; however, these elements are insufficient in themselves to promote gene expression.

Structure of an ectodermally expressed sea urchin metallothionein gene and characterization of its metal-responsive region

The metallothionein-A gene in the metallothionein gene family of the sea urchin Strongylocentrotus purpuratus (SpMTA gene) was sequenced and found to contain three coding exons plus a 3' entirely noncoding exon. Putative alpha and beta MT domains were encoded, by its exons 2 and 3, respectively, in reverse of the order in vertebrate metallothionein genes. The SpMTA promoter was characterized through the expression of recombinant constructs containing various portions of the proximal 678-base-pair (bp) 5'-flanking region of the SpMTA gene. Zygotes injected with constructs were cultured to the blastula stage in the presence of a heavy-metal chelator and then incubated in the presence or absence of cadmium. The longest constructs were expressed only when heavy-metal ion was present. Two putative metal-responsive elements (MREs a and b) within 240 bp of the transcription start site resembled mammalian MREs in their critical 8-bp cores (TGCRCNCS) and in their locations relative to each other and to the TATA box. Elimination of activity by site-specific mutations in MREs a and b, separately or in both, identified them as metal regulatory elements. Thus, MRE recognition in this invertebrate resembles that in vertebrates. Upstream sites with single-mismatched MREs neither acted as MREs nor amplified the activity of MREs a and b. The SpMTA, Spec1, and CyIIIa actin genes, which have the same ectodermal specificity, have common DNA elements at relatively similar locations in their promoter regions; however, these elements are insufficient in themselves to promote gene expression.

Regulation of expression of a sheep metallothionein 1a-sheep growth hormone fusion gene in transgenic mice

Transgenic mice containing a sheep metallothionein 1a-sheep growth hormone fusion gene exhibited low, tissue-specific basal levels of transgene mRNA expression, resulting in slightly elevated levels of circulating growth hormone that did not lead to a detectable increase in growth. After zinc stimulation, high levels of transgene mRNA expression were induced in a number of tissues; these levels correlated with increased levels of circulating growth hormone, resulting in growth increases of up to 1.5 times the levels of controls and unstimulated transgenic mice. After removal of the zinc stimulus, transgene expression and circulating growth hormone concentrations returned to basal levels. Additional evidence from the pattern of developmental expression of the transgene suggests that zinc is the main regulator of this promoter in mice. The demonstrated regulation and low basal level of expression of the sheep metallothionein 1a promoter make it a candidate for use in other mouse transgenic studies and for use in transgenic livestock, in which regulation of expression is essential.

Structure of the rainbow trout metallothionein B gene and characterization of its metal-responsive region

The trout metallothionein (MT) genes consist of two members. We describe the structure of the first fish MT (tMT-B) gene which shows an overall resemblance but some remarkable differences with mammalian MT genes. The similarities included (i) tripartite structure of the gene, (ii) conservation of cysteine residues, and (iii) a TATAAA signal and two copies of metal-responsive elements (MREs). The differences consisted of (i) an AT-rich tMT-B promoter compared with highly GC-rich mammalian MT promoters and (ii) a lack of SP1-binding sites in the tMT-B promoter. Functional analysis of the tMT-B 5'-flanking region following fusion with the bacterial chloramphenicol acetyltransferase gene and its transfection into the rainbow trout hepatoma cell line revealed that sequences from positions -600 to +8 are sufficient for regulation by metals. Further deletion analyses of this fragment suggested that a minimum of 100 nucleotides upstream of the transcription initiation site are required for induction by cadmium and zinc. The tMT-B promoter was also functional in the human hepatoblastoma cell line, suggesting that an MT regulatory factor(s) is conserved in phylogenetically distant species like humans and fish.

Cloning, nucleotide sequence and molecular evolution of a rabbit processed metallothionein MT-2 pseudogene

A rabbit metallothionein-2 pseudogene (MT-2 psi) has been isolated from a partial rabbit genomic library. Its unusual sequence shows evidence of complex rearrangements involving recombination and deletion events. There are no intervening sequences, 3' poly A tract or 5' regulatory DNA sequences. The pseudogene is flanked by two sets of direct repeats (CT)3 GT(CT)4 and CTGG(G)CTC. They are most probably the sites of insertion of MT-2 psi in the rabbit genome. In addition, a number of repetitive DNA sequences are observed flanking the MT-2 psi gene. These are features of a processed retrogene.

Structure of the rainbow trout metallothionein B gene and characterization of its metal-responsive region

The trout metallothionein (MT) genes consist of two members. We describe the structure of the first fish MT (tMT-B) gene which shows an overall resemblance but some remarkable differences with mammalian MT genes. The similarities included (i) tripartite structure of the gene, (ii) conservation of cysteine residues, and (iii) a TATAAA signal and two copies of metal-responsive elements (MREs). The differences consisted of (i) an AT-rich tMT-B promoter compared with highly GC-rich mammalian MT promoters and (ii) a lack of SP1-binding sites in the tMT-B promoter. Functional analysis of the tMT-B 5'-flanking region following fusion with the bacterial chloramphenicol acetyltransferase gene and its transfection into the rainbow trout hepatoma cell line revealed that sequences from positions -600 to +8 are sufficient for regulation by metals. Further deletion analyses of this fragment suggested that a minimum of 100 nucleotides upstream of the transcription initiation site are required for induction by cadmium and zinc. The tMT-B promoter was also functional in the human hepatoblastoma cell line, suggesting that an MT regulatory factor(s) is conserved in phylogenetically distant species like humans and fish.

Differential expression of four linked sheep metallothionein genes

Regulation of the closely linked endogenous sheep MT-Ia, MT-Ib, MT-Ic and MT-II genes by heavy metals and dexamethasone was studied in cultured sheep fibroblasts. Only MT-II mRNA was detectable before addition of any inducer. Addition of copper, zinc or cadmium salts to the culture medium increased the level of each mRNA; however, the magnitude of this response varied greatly between the four metallothionein genes. Following induction, levels of MT-Ia mRNA were the highest, followed by MT-II and MT-Ic mRNAs. The MT-Ib mRNA was only present at low levels. Zinc and cadmium were found to be the most effective inducers of each gene. The maximal response of the sMT-Ia, Ib and II genes to copper was only 30% of zinc and cadmium. The sMT-Ic gene responded very weakly to copper, less than 5% of the levels achieved with zinc. Only the MT-II mRNA increased in response to dexamethasone. In the liver of sheep on normal diets, the levels of MT-Ia, Ic and II mRNAs were found to be unexpectedly high and comparable to induced levels in fibroblasts.

The sheep metallothionein gene family. Structure, sequence and evolutionary relationship of five linked genes

Southern blot analysis of the sheep genome revealed a metallothionein gene family with at least nine members. Two overlapping cosmid clones spanning approximately 67 kb and containing five metallothionein genes have been isolated. DNA sequence analysis reveals that one of these is a metallothionein II variant, three are metallothionein I variants and one is a truncated metallothionein pseudogene containing only the first exon. The predicted amino acid sequence was compared with previously reported amino acid composition data of sheep metallothioneins [Whanger, P. D., Oh, S.-H. & Deagen, J. T. (1981) J. Nutr. 111, 1207-1215], and this suggests that we have isolated the genes encoding the major protein isoforms found in the sheep liver. The promoter regions of these genes contain many conserved elements, among them metal-regulatory elements and putative glucocorticoid-responsive elements. However, there are a number of differences between these genes in the arrangement of these elements. Sequence comparisons indicate that the multiple metallothionein I genes and the pseudogene appear to have resulted from sequential duplication events, and a larger cluster of metallothionein I genes may have been disrupted leading to the formation of the pseudogene.

Cloning, nucleotide sequence and characterization of a New Zealand rabbit metallothionein-I gene

We have isolated a rabbit metallothionein-I gene from a lambda gt10 library. The coding sequence of this gene is interrupted by two introns occurring at amino acid positions 9 1/3 and 30 1/3. Comparison of the promoter sequence of this gene with the promoters of other metallothionein genes identified a number of oligonucleotide sequences which are recognized by trans-acting proteins involved in the regulation of these genes by heavy metals, glucocorticoids and alpha interferon.