Expression of a foreign gene in a line of transgenic mice is modulated by a chromosomal position effect

Digestion and utilization of plant-based diets by transgenic pigs secreting β-glucanase, xylanase, and phytase in their salivary glands

Novel transgenic (TG) pigs co-expressing three microbial enzymes, β-glucanase, xylanase, and phytase, in their salivary glands were previously generated, which exhibited reduced phosphorus and nitrogen emissions and improved growth performances. In the present study, we attempted to explore the age-related change of the TG enzymic activity, the residual activity of the enzymes in the simulated gastrointestinal tract, and the effect of the transgenes on the digestion of nitrogen and phosphorus content in the fiber-rich, plant-based diets. Results showed that all the three enzymes were stably expressed over the growing and finishing periods in the F2 generation TG pigs. In simulated gastric juice, all the three enzymes exhibited excellent gastrointestinal environment adaptability. The apparent total tract digestibility of phosphorus was increased by 69.05% and 499.64%, while fecal phosphate outputs were decreased by 56.66% and 37.32%, in the TG pigs compared with the wild-type littermates fed with low non-starch polysaccharides diets and high fiber diets, respectively. Over half of available phosphorus and water-soluble phosphorus in fecal phosphorus were reduced. We also found the performance of phosphorus, calcium, and nitrogen retention rates were significantly improved, resulting in faster growth performance in TG pigs. The results indicate that TG pigs can effectively digest the high-fiber diets and exhibit good growth performance compared with wild type pigs.

Neurosecretory Protein GL Promotes Normotopic Fat Accumulation in Male ICR Mice

Neurosecretory protein GL (NPGL) is a small secretory protein identified in the hypothalamus of birds and mammals. We recently reported that NPGL exerts obesogenic effects in obesity-prone C57BL6/J mice. However, whether NPGL elicits adiposity in different mouse strains is poorly understood. In this study, we generated transgenic mice overexpressing Npgl using the ICR strain (Npgl Tg mice) to elucidate the obesogenic effects of NPGL in different strains. Npgl Tg mice showed increased white adipose tissue (WAT) mass. Although the mass of brown adipose tissue (BAT) was slightly altered in Npgl Tg mice, hypertrophy of lipid droplets was also observed in BAT. In contrast, fat accumulation was not induced in the liver, with the upregulation of mRNAs related to hepatic lipolysis. These results support the hypothesis that NPGL causes obesity in several strains and species. This report highlights the pivotal role of NPGL in fat accumulation in adipose tissues and contributes to the elucidation of the biological mechanisms underlying obesity and metabolic diseases in heterogeneous populations.

Transgenic mice overexpressing the LH receptor in the female reproductive system spontaneously develop endometrial tumour masses

The receptor for the luteinizing hormone (LH-R) is aberrantly over expressed in cancers of the reproductive system. To uncover whether LH-R over expression has a causative role in cancer, we generated a transgenic (TG) mouse which overexpresses the human LH-R (hLH-R) in the female reproductive tract, under the control of the oviduct-specific glycoprotein (OGP) mouse promoter (mogp-1). The transgene was highly expressed in the uterus, ovary and liver, but only in the uterus morphological and molecular alterations (increased proliferation and trans-differentiation in the endometrial layer) were detected. A transcriptomic analysis on the uteri of young TG mice showed an up regulation of genes involved in cell cycle control and a down regulation of genes related to the immune system and the metabolism of xenobiotics. Aged TG females developed tumor masses in the uteri, which resembled an Endometrial Cancer (EC). Microarray and immunohistochemistry data indicated the deregulation of signaling pathways which are known to be altered in human ECs. The analysis of a cohort of 126 human ECs showed that LH-R overexpression is associated with early-stage tumors. Overall, our data led support to conclude that LH-R overexpression may directly contribute to trigger the neoplastic transformation of the endometrium.

What do you mean, "epigenetic"?

Interest in the field of epigenetics has increased rapidly over the last decade, with the term becoming more identifiable in biomedical research, scientific fields outside of the molecular sciences, such as ecology and physiology, and even mainstream culture. It has become increasingly clear, however, that different investigators ascribe different definitions to the term. Some employ epigenetics to explain changes in gene expression, others use it to refer to transgenerational effects and/or inherited expression states. This disagreement on a clear definition has made communication difficult, synthesis of epigenetic research across fields nearly impossible, and has in many ways biased methodologies and interpretations. This article discusses the history behind the multitude of definitions that have been employed since the conception of epigenetics, analyzes the components of these definitions, and offers solutions for clarifying the field and mitigating the problems that have arisen due to these definitional ambiguities.

Analysis of the sericin1 promoter and assisted detection of exogenous gene expression efficiency in the silkworm Bombyx mori L

In genetics, the promoter is one of the most important regulatory elements controlling the spatiotemporal expression of a target gene. However, most studies have focused on core or proximal promoter regions, and information on regions that are more distant from the 5′-flanking region of the proximal promoter is often lacking. Here, approximately 4-kb of the sericin1 (Ser1) promoter was predicted to contain many potential transcriptional factor binding sites (TFBSs). Transgenic experiments have revealed that more TFBSs included in the promoter improved gene transcription. However, multi-copy proximal Ser1 promoter combinations did not improve gene expression at the transcriptional level. Instead, increasing the promoter copy number repressed transcription. Furthermore, a correlation analysis between two contiguous genes, firefly luciferase (FLuc) and EGFP, was conducted at the transcriptional level; a significant correlation was obtained regardless of the insertion site. The ELISA results also revealed a significant correlation between the transcriptional and translational EGFP levels. Therefore, the exogenous gene expression level can be predicted by simply detecting an adjacent EGFP. In conclusion, our results provide important insights for further investigations into the molecular mechanisms underlying promoter function. Additionally, a new approach was developed to quickly screen transgenic strains that highly express exogenous genes.

The aflatoxin-detoxifizyme specific expression in mouse parotid gland

The aflatoxin-detoxifizyme (ADTZ) gene derived from Armillariella tabescens was cloned into parotid gland-specific expression vector (pPSPBGPneo) to construct the parotid gland-specific vector expressing ADTZ (pPSPBGPneo-ADTZ). Transgenic mice were generated by microinjection and identified by using PCR and Southern blotting analysis. PCR and Southern blotting analysis showed that total six transgenic mice carried the ADTZ gene were generated. RT-PCR analysis indicated that the expression of ADTZ mRNA could be detected only in parotid glands of the transgenic mice. The ADTZ activity in the saliva was found to be 3.72 ± 1.64 U/mL. After feeding a diet containing aflatoxin B1 (AFB1) for 14 days, the effect of ADTZ on serum biochemical indexes and AFB1 residues in serum and liver of mice were evaluated. The results showed that total protein and globulin contents in the test treatment (transgenic mice) produced ADTZ were significantly higher than that of the positive control, while alanine aminotransferase and aspartate aminotransferase activity in serum of the test treatment (transgenic mice) were remarkably lower compared to that of the positive control (P < 0.05). Moreover, AFB1 residues in serum and liver of the test treatment (transgenic mice) were significantly lower compared with that of the positive control (P < 0.05). These results in the study confirmed that ADTZ produced in transgenic mice could reduce, even eliminate the negative effects of AFB1 on mice.

Generation of c-Myc transgenic pigs for autosomal dominant polycystic kidney disease

After several decades of research, autosomal dominant polycystic kidney disease (ADPKD) is still incurable and imposes enormous physical, psychological, and economic burdens on patients and their families. Murine models of ADPKD represent invaluable tools for studying this disease. These murine forms of ADPKD can arise spontaneously, or they can be induced via chemical or genetic manipulations. Although these models have improved our understanding of the etiology and pathogenesis of ADPKD, they have not led to effective treatment strategies. The mini-pig represents an effective biomedical model for studying human diseases, as the pig's human-like physiological processes help to understand disease mechanisms and to develop novel therapies. Here, we tried to generate a transgenic model of ADPKD in pigs by overexpressing c-Myc in kidney tissue. Western-blot analysis showed that c-Myc was overexpressed in the kidney, brain, heart, and liver of transgenic pigs. Immunohistochemical staining of kidney tissue showed that exogenous c-Myc predominantly localized to renal tubules. Slightly elevated blood urea nitrogen levels were observed in transgenic pigs 1 month after birth, but no obvious abnormalities were detected after that time. In the future, we plan to subject this model to renal injury in an effort to promote ADPKD progression.

Regulatory consequences of gene translocation in bacteria

Gene translocations play an important role in the plasticity and evolution of bacterial genomes. In this study, we investigated the impact on gene regulation of three genome organizational features that can be altered by translocations: (i) chromosome position; (ii) gene orientation; and (iii) the distance between a target gene and its transcription factor gene (‘target-TF distance’). Specifically, we quantified the effect of these features on constitutive expression, transcription factor binding and/or gene expression noise using a synthetic network in Escherichia coli composed of a transcription factor (LacI repressor) and its target gene (yfp). Here we show that gene regulation is generally robust to changes in chromosome position, gene orientation and target-TF distance. The only demonstrable effect was that chromosome position alters constitutive expression, due to changes in gene copy number and local sequence effects, and that this determines maximum and minimum expression levels. The results were incorporated into a mathematical model which was used to quantitatively predict the responses of a simple gene network to gene translocations; the predictions were confirmed experimentally. In summary, gene translocation can modulate constitutive gene expression levels due to changes in chromosome position but it has minimal impact on other facets of gene regulation.

Coupling mammalian cell surface display with somatic hypermutation for the discovery and maturation of human antibodies

A novel approach has been developed for the isolation and maturation of human antibodies that replicates key features of the adaptive immune system by coupling in vitro somatic hypermutation (SHM) with mammalian cell display. SHM is dependent on the action of the B cell specific enzyme, activation-induced cytidine deaminase (AID), and can be replicated in non-B cells through expression of recombinant AID. A library of human antibodies, based on germline V-gene segments with recombined human regions was used to isolate low-affinity antibodies to human β nerve growth factor (hβNGF). These antibodies, initially naïve to SHM, were subjected to AID-directed SHM in vitro and selected using the same mammalian cell display system, as illustrated by the maturation of one of the antibodies to low pM K(D). This approach overcomes many of the previous limitations of mammalian cell display, enabling direct selection and maturation of antibodies as full-length, glycosylated IgGs.

Bioluminescence imaging captures the expression and dynamics of endogenous p21 promoter activity in living mice and intact cells

To interrogate endogenous p21(WAF1/CIP1) (p21) promoter activity under basal conditions and in response to various forms of stress, knock-in imaging reporter mice in which expression of firefly luciferase (FLuc) was placed under the control of the endogenous p21 promoter within the Cdkn1a gene locus were generated. Bioluminescence imaging (BLI) of p21 promoter activity was performed noninvasively and repetitively in mice and in cells derived from these mice. We demonstrated that expression of FLuc accurately reported endogenous p21 expression at baseline and under conditions of genotoxic stress and that photon flux correlated with mRNA abundance and, therefore, bioluminescence provided a direct readout of p21 promoter activity in vivo. BLI confirmed that p53 was required for activation of the p21 promoter in vivo in response to ionizing radiation. Interestingly, imaging of reporter cells demonstrated that p53 prevents the extracellular signal-regulated kinase/mitogen-activated protein kinase pathway from activating p21 expression when quiescent cells are stimulated with serum to reenter the cell cycle. In addition, low-light BLI identified p21 expression in specific regions of individual organs that had not been observed previously. This inducible p21(FLuc) knock-in reporter strain will facilitate imaging studies of p53-dependent and -independent stress responses within the physiological context of the whole animal.

One-step knockin for inducible expression in mouse embryonic stem cells

Transgenesis enables the elucidation of gene function; however, constant transgene expression is not always desired. The tetracycline responsive system was devised to turn on and off transgene expression at will. It has two components: a doxycycline (dox)-controlled transactivator (TA) and an inducible expression cassette. Integration of these transgenes requires two transfection steps usually accomplished by sequential random integration. Unfortunately, random integration can be problematic due to chromatin position effects, integration of variable transgene units, and mutation at the integration site. Therefore, targeted transgenesis and knockin were developed to target the TA and the inducible expression cassette to a specific location, but these approaches can be costly in time, labor, and money. Here, we describe a one-step Cre-mediated knockin system in mouse embryonic stem cells that positions the TA and inducible expression cassette to a single location. Using this system, we show dox-dependent regulation of eGFP at the DNA topoisomerase 3β promoter. Because Cre-mediated recombination is used in lieu of gene targeting, this system is fast and efficient.

Heterochromatinization as a potential mechanism of nickel-induced carcinogenesis

Epigenetics refers to heritable patterns of gene expression that do not depend on alterations of the genomic DNA sequence. Nickel compounds have demonstrated carcinogenicity without any associated mutagenesis, suggesting that its mechanism of carcinogenesis is epigenetic in nature. One such potential mechanism is the heterochromatinization of chromatin within a region of the genome containing a gene sequence, inhibiting any further molecular interactions with that underlying gene sequence and effectively inactivating that gene. We report here the observation, by atomic force microscopy and circular dichroism spectropolarimetry, that nickel ion (Ni(2+)) condenses chromatin to a greater extent than the natural divalent cation of the cell, magnesium ion (Mg(2+)). In addition, we use a model experimental system that incorporates a transgene, the bacterial xanthine guanine phosphoribosyl transferase gene (gpt), differentially near, and far from, a heterochromatic region of the genome, in two cell lines, the Chinese hamster V79-derived G12 and G10 cells, respectively, to demonstrate by a DNase I protection assay that nickel treatement protects the gpt gene sequence from DNase I exonuclease digestion in the G12 cells, but not in the G10 cells. We conclude that condensation of chromatin by nickel is a potential mechanism of nickel-mediated gene regulation.

The changing role of cell culture in the generation of transgenic livestock

Transgenesis may allow the generation of farm animals with altered phenotype, animal models for research and animal bioreactors. Although such animals have been produced, the time and expense involved in generating transgenic livestock and then evaluating the transgene expression pattern is very restrictive. If questions about the ability and efficiency of expression could be asked solely in vitro rapid progress could be achieved. Unfortunately, experiments addressing transcriptional control in vitro have proved unreliable in their ability to indicate whether a transgene will be transcribed or not. However, initial studies suggest that cell culture may be able to predict in vivo post-transcriptional events. We review these issues and propose that strategies which engineer the transgene integration site could enhance the probability for efficient expression. This approach has now become feasible with the development of techniques allowing animals to be generated from somatic cells by nuclear transfer. The important step in this procedure is the use of cells grown in culture as the source of genetic information, allowing the selection of specific transgene integration events. This technology which has dramatically increased the potential use of transgenic livestock for both agricultural and biotechnological applications, is based on standard cell culture methodology. We are now at the start of a new era in large animal transgenics.

A mammalian artificial chromosome engineering system (ACE System) applicable to biopharmaceutical protein production, transgenesis and gene-based cell therapy

Mammalian artificial chromosomes (MACs) provide a means to introduce large payloads of genetic information into the cell in an autonomously replicating, non-integrating format. Unique among MACs, the mammalian satellite DNA-based Artificial Chromosome Expression (ACE) can be reproducibly generated de novo in cell lines of different species and readily purified from the host cells' chromosomes. Purified mammalian ACEs can then be re-introduced into a variety of recipient cell lines where they have been stably maintained for extended periods in the absence of selective pressure. In order to extend the utility of ACEs, we have established the ACE System, a versatile and flexible platform for the reliable engineering of ACEs. The ACE System includes a Platform ACE, containing >50 recombination acceptor sites, that can carry single or multiple copies of genes of interest using specially designed targeting vectors (ATV) and a site-specific integrase (ACE Integrase). Using this approach, specific loading of one or two gene targets has been achieved in LMTK(-) and CHO cells. The use of the ACE System for biological engineering of eukaryotic cells, including mammalian cells, with applications in biopharmaceutical production, transgenesis and gene-based cell therapy is discussed.

A new beta-lactoglobulin-based vector targets luciferase cDNA expression to the mammary gland of transgenic mice

A beta-lactoglobulin (BLG)/luciferase gene vector (p907), composed of a luciferase intronless gene inserted between the second and sixth BLG exons was constructed. Stable transfections of CID-9 cells with this vector, as well as with a series of additional vectors, were performed to define regulatory regions within the BLG sequence, and the contribution of the SV40 polyadenylation (PA) site to luciferase expression. A relatively low level of luciferase activity was supported by vector p907. It was partially rescued by vector p906, in which the BLG 3' region, downstream of the luciferase cDNA, was replaced with the SV40 PA site. Flanking the SV40 region of vector p906, at its 3' end, with BLG sequences of exon 6/intron 6/exon 7 and the 3' region of the gene resulted in vector p904. This vector supported the highest luciferase activity, 10 times or 2.5 times higher than that measured in cells transfected with vectors p907 and p906, respectively. The induced activity supported by vector p904 is attributed to interaction between the SV40 PA site and elements of the distal part of the BLG 3' flanking sequences. The BLG 5' regulatory region of vector p904 encompasses a 3-kb promoter sequences. Deletion of 935 bp of its proximal end resulted in a 60% decrease in luciferase activity. Reduced activity was also seen with vector p915 lacking sequences of exon 1/intron 1/exon 2. This decrease could not be rescued with heterologous sequences of insulin intron 1, inserted upstream of the luciferase cDNA. Two sets of transgenic mice carrying vectors p907 and p904 were generated. Vector p907 supported only marginal luciferase activity in the mammary gland of all transgenic mice tested and luciferase RNA could not be detected by northern analysis. In contrast, 50% of the transgenic mice carrying vector p904 expressed luciferase RNA in the mammary gland and tissue-specific, hormonal-dependent activity was determined. However, the new p904 vector was not able to insulate the transgene from surrounding host DNA sequences, as reflected by its copy number-independent manner of expression. Nevertheless, vector p904 may represent a valuable tool for the expression of cDNAs in the mammary gland of transgenic animals.

Production of transgenic rodents by the microinjection of cloned DNA into fertilized one-cell eggs

Transgenic technologies that enable rapid movement between genotype and phenotype through specific loss-of-function, overexpression, or misexpression phenotypes will be crucial in the elucidation of gene sequences emerging from genome projects. This article describes detailed procedures for the generation of transgenic mice and rats by the injection of cloned DNA into the pronuclei of fertilized one-cell eggs.

A hybrid bovine beta-casein/bGH gene directs transgene expression to the lung and mammary gland of transgenic mice

We investigated spatial and temporal expression of bGH controlled by two different sizes (1.8 kb and 15 kb) of 5'-flanking sequences of the bovine beta-casein in transgenic mice. In the 1.8-kb promoter-containing mice, bGH expression was specifically confined to lung and mammary gland at lactation. While mammary gland expression was highly variable depending on the lines, lung expression was relatively constant with a high level in most lines. Moreover, this dual-tissue specificity of bGH expression was consistently retained in all of the 15 kb-promoter-containing mice, although a low ectopic expression was sometimes detected in salivary gland or brain. During mammary gland development in the 1.8-kb promoter-containing mice was mammary gland expression first detected at lactation, following the bovine rather than murine pattern of beta-casein expression. In contrast, lung expression was almost constant regardless of mammary gland developmental state or sex. Therefore, it can be concluded that a combination of the bovine beta-casein promoter and bGH gene directs a distinct dual-tissue specific bGH expression with different regulatory mechanisms between mammary gland and lung and as little as 1.8-kb promoter is sufficient for the proper regulation of the bovine beta-casein gene in mammary gland.

Intron-independent association of splicing factors with active genes

The cell nucleus is organized as discrete domains, often associated with specific events involved in chromosome organization, replication, and gene expression. We have examined the spatial and functional relationship between the sites of heat shock gene transcription and the speckles enriched in splicing factors in primary human fibroblasts by combining immunofluorescence and fluorescence in situ hybridization (FISH). The hsp90alpha and hsp70 genes are inducibly regulated by exposure to stress from a low basal level to a high rate of transcription; additionally the hsp90alpha gene contains 10 introns whereas the hsp70 gene is intronless. At 37 degrees C, only 30% of hsp90alpha transcription sites are associated with speckles whereas little association is detected with the hsp70 gene, whose constitutive expression is undetectable relative to the hsp90alpha gene. Upon exposure of cells to heat shock, the heavy metal cadmium, or the amino acid analogue azetidine, transcription at the hsp90alpha and hsp70 gene loci is strongly induced, and both hsp transcription sites become associated with speckles in >90% of the cells. These results reveal a clear disconnection between the presence of intervening sequences at specific gene loci and the association with splicing factor-rich regions and suggest that subnuclear structures containing splicing factors are associated with sites of transcription.

The human pH aldolase A promoter directs widespread but muscle-predominant expression in transgenic mice

In order to identify regulatory elements that direct widespread in vivo expression of a linked gene, we have examined one of the human aldolase A alternative promoters, the ubiquitous pH promoter, which is active in most foetal and adult tissues. We have used the pH promoter region to drive expression of an heterologous CAT reporter gene in transgenic mice. We show that a short 820 bp pH promoter fragment is able to confer a ubiquitous and reproducible activity pattern on the CAT reporter gene in most of the transgenic lines analysed, with a particularly high level of expression in adult skeletal muscle. Activity of this transgene was detected from early embryonic stages. Therefore, this pH promoter region appears to be a powerful tool to direct ubiquitous and early expression of a transgene in vivo. Deletion analysis revealed that: (i) the region between -651 and -369 bp relative to the pH promoter transcription start site includes DNA elements capable of overriding effects of the surrounding chromatin at the integration site, (ii) the region between -285 and -211 bp is involved in pH promoter tissue-specific expression pattern in skeletal muscle and/or nervous tissues, (iii) the region located between -211 and -108 bp is necessary for its ubiquitous and muscle-predominant activity and (iv) the most proximal region downstream from -108 bp is still sufficient to confer an activity in brain and lung.

Tissue specific and vitamin D responsive gene expression in bone

Studies of gene expression in bone have adopted a number of molecular approaches that seek to determine those cis and trans-acting factors responsible for the development and physiological regulation of this unique tissue. The majority of studies have been performed in vitro, focussing on the expression of genes such as osteocalcin, bone sialoprotein and type I collagen which demonstrate restricted or altered expression patterns in osteoblasts. These studies have demonstrated a large number of cis and trans acting factors that modulate the tissue specific and vitamin D responsive expression of these genes. These include the response elements and regions mediating basal and vitamin D dependent transcription of these genes as well as some of the transcription factors that bind to these regions and the nucleosomal organisation of these genes within a nuclear framework. In vivo studies, including the introduction of transgenes into transgenic mice, extend these in vitro observations within a physiological context. However, in part due to limitations in each approach, these in vitro and in vivo studies are yet to accurately define all the necessary cis and trans-acting factors required for tissue specific and vitamin D responsive gene expression. Advances have been made in identifying many cis-acting regions within the flanking regions of these genes that are responsible for their restricted expression patterns, but a vector incorporating all the necessary cis-acting regions capable of directing gene expression independent of integration site has not yet been described. Similarly, trans-acting factors that determine the developmental destiny of osteoblast progenitors and the restricted expression of these genes remain elusive and, despite advances in the understanding of protein-DNA interactions at vitamin D response elements contained within these genes, further intermediary factors that interact with the transcriptional machinery to modulate vitamin D responsiveness need to be identified.

Complementation of reduced survival, hypotension, and renal abnormalities in angiotensinogen-deficient mice by the human renin and human angiotensinogen genes

The aim of this study was to determine whether elements of the human renin-angiotensin system (RAS) could functionally replace elements of the mouse RAS by complementing the reduced survival and renal abnormalities observed in mice carrying a gene-targeted deletion of the mouse angiotensinogen gene (mAgt). Double transgenic mice containing the human renin (HREN) and human angiotensinogen (HAGT) genes were bred to mice heterozygous for the mAgt deletion and the compound heterozygotes were identified and intercrossed. The resulting progeny (n = 139) were genotyped at each locus and the population was stratified into two groups: the first containing both human transgenes (RA+) and the second containing zero or one, but not both human transgenes (RA-). Despite appropriate Mendelian ratios of RA- mice that were wildtype (+/+), heterozygous (+/-), and homozygous (-/-) for the deletion of mAgt at birth, there was reduced survival of RA- mAgt-/- mice to adulthood (P < 0.001 by chi2). In contrast, we observed appropriate Mendelian ratios of RA+ mAgt+/+, RA+ mAgt+/-, and RA+ mAgt-/- mice at birth and in adults (P > 0.05 by chi2). These results demonstrate that the presence of both human transgenes rescues the postnatal lethality in mAgt-/- mice. The renal histopathology exhibited by RA- mAgt-/- mice, including thickened arterial walls, severe fibrosis, lymphocytic infiltration, and atrophied parenchyma, was also rescued in the RA+ mAgt-/- mice. Direct arterial blood pressure recordings in conscious freely moving mice revealed that BP (in mmHg) varied proportionally to mAgt gene copy number in RA+ mice (approximately 20 mmHg per mAgt gene copy, P < 0.001). BP in RA+ mAgt-/- mice (132+/-3, n = 14) was intermediate between wild-type (RA- mAgt+/+, 105+/-2, n = 9) and RA+ mAgt+/+ (174+/-3, n = 10) mice. These studies establish that the human renin and angiotensinogen genes can functionally replace the mouse angiotensinogen gene, and provides proof in principle that we can examine the regulation of elements of the human RAS and test the significance of human RAS gene variants by a combined transgenic and gene targeting approach.

Contrasting effects of the SATB1 core nuclear matrix attachment region and flanking sequences of the keratin 18 gene in transgenic mice

The 2.3 kb and 3.5 kb of DNA that flank the human keratin 18 (K18) gene and synthetic nuclear matrix attachment regions (MAR) composed of the binding sites for the SATB1 nuclear protein were fused to a reporter gene that utilizes the mouse metallothionein promoter and the human growth hormone gene (MThGH). Transgenic mice were generated from both constructions and the control MThGH gene to test K18 and SATB1 MAR sequences for the ability to insulate the reporter gene from integration site-specific position effects. The MThGH control gene was variably expressed in brain, heart, intestine, kidney, liver, and testes, confirming previous studies. In contrast, the MThGH gene insulated by the K18 flanking sequences was expressed in the same tissues of four independent transgenic animals at levels correlated with the copy number except for intestine. The average level of expression on a per gene basis of the K18 insulated gene was from 9- to 49-fold higher than the control. The MThGH gene linked to the SATB1 MAR sequences was completely repressed in the brains and kidneys of all six transgenic mice. However, expression was nearly as efficient in testes as the K18-insulated gene. Both the SATB1 MAR and the K18 flanking sequences confer position-independent transcriptional status on the reporter gene in some or many tissues. However, the effects are stimulatory for the K18 elements and generally suppressive for the SATB1 MAR elements.

Nonrandom gene organization: structural arrangements of specific pre-mRNA transcription and splicing with SC-35 domains

This work demonstrates a highly nonrandom distribution of specific genes relative to nuclear domains enriched in splicing factors and poly(A)+ RNA, and provides evidence for the direct involvement of these in pre-mRNA metabolism. As investigated in hundreds of diploid fibroblasts, human collagen I alpha 1 and beta-actin DNA/RNA showed a very high degree of spatial association with SC-35 domains, whereas three nontranscribed genes, myosin heavy chain, neurotensin, and albumin, showed no such preferential association. Collagen I alpha 1 RNA accumulates within the more central region of the domain, whereas beta-actin RNA localizes at the periphery. A novel approach revealed that collagen RNA tracks are polarized, with the entire gene at one end, on the edge of the domain, and the RNA extending into the domain. Intron 26 is spliced within the RNA track at the domain periphery. Transcriptional inhibition studies show both the structure of the domain and the gene's relationship to it are not dependent upon the continued presence of accumulated collagen RNA, and that domains remaining after inhibition are not just storage sites. Results support a model reconciling light and electron microscopic observations which proposes that transcription of some specific genes occurs at the border of domains, which may also function in the assembly or distribution of RNA metabolic components. In contrast to the apparently random dispersal of total undefined hnRNA synthesis through interdomain space, transcription and splicing for some genes occurs preferentially at specific sites, and a high degree of individual pre-mRNA metabolism is compartmentalized with discrete SC-35 domains.

Position independent expression and developmental regulation is directed by the beta myosin heavy chain gene's 5' upstream region in transgenic mice

Transgenic mice generated with constructs containing 5.6 kb of the beta myosin heavy chain (MyHC) gene's 5' flanking region linked to the cat reporter gene express the transgene at high levels. In all 47 lines analyzed, tissue-specific accumulation of chloramphenicol acetyltransferase was found at levels proportional to the number of integrated transgene copies. Deletion constructs containing only 0.6 kb of 5' upstream region showed position effects in transgenic mice and did not demonstrate copy number dependence although transgene expression remained muscle-specific. The 5.6 kb 5' upstream region conferred appropriate developmental control of the transgene to the cardiac compartment and directs copy number dependent and position independent expression. Lines generated with a construct in which three proximal cis-acting elements were mutated showed reduced levels of transgene expression, but all maintained their position independence and copy number dependence, suggesting the presence of distinct regulatory mechanisms.

Carcinogenic nickel silences gene expression by chromatin condensation and DNA methylation: a new model for epigenetic carcinogens

A transgenic gpt+ Chinese hamster cell line (G12) was found to be susceptible to carcinogenic nickel-induced inactivation of gpt expression without mutagenesis or deletion of the transgene. Many nickel-induced 6-thioguanine-resistant variants spontaneously reverted to actively express gpt, as indicated by both reversion assays and direct enzyme measurements. Since reversion was enhanced in many of the nickel-induced variant cell lines following 24-h treatment with the demethylating agent 5-azacytidine, the involvement of DNA methylation in silencing gpt expression was suspected. This was confirmed by demonstrations of increased DNA methylation, as well as by evidence indicating condensed chromatin and heterochromatinization of the gpt integration site in 6-thioguanine-resistant cells. Upon reversion to active gpt expression, DNA methylation and condensation are lost. We propose that DNA condensation and methylation result in heterochromatinization of the gpt sequence with subsequent inheritance of the now silenced gene. This mechanism is supported by direct evidence showing that acute nickel treatment of cultured cells, and of isolated nuclei in vitro, can indeed facilitate gpt sequence-specific chromatin condensation. Epigenetic mechanisms have been implicated in the actions of some nonmutagenic carcinogens, and DNA methylation changes are now known to be important in carcinogenesis. This paper further supports the emerging theory that nickel is a human carcinogen that can alter gene expression by enhanced DNA methylation and compaction, rather than by mutagenic mechanisms.

Overexpression of Gs alpha protein in the hearts of transgenic mice

Alterations in beta-adrenergic receptor-Gs-adenylyl cyclase coupling underlie the reduced catecholamine responsiveness that is a hallmark of human and animal models of heart failure. To study the effect of altered expression of Gs alpha, we overexpressed the short isoform of Gs alpha in the hearts of transgenic mice, using a rat alpha-myosin heavy chain promoter. Gs alpha mRNA levels were increased selectively in the hearts of transgenic mice, with a level 38 times the control. Despite this marked increase in mRNA, Western blotting identified only a 2.8-fold increase in the content of the Gs alpha short isoform, whereas Gs activity was increased by 88%. The discrepancy between Gs alpha mRNA and Gs alpha protein levels suggests that the membrane content of Gs alpha is posttranscriptionally regulated. The steady-state adenylyl cyclase catalytic activity was not altered under either basal or stimulated conditions (GTP + isoproterenol, GTP gamma S, NaF, or forskolin). However, progress curve studies did show a significant decrease in the lag period necessary for GppNHp to stimulate adenylyl cyclase activity. Furthermore, the relative number of beta-adrenergic receptors binding agonist with high affinity was significantly increased. Our data demonstrate that a relatively small increase in the amount of the coupling protein Gs alpha can modify the rate of catalyst activation and the formation of agonist high affinity receptors.

Ectopic expression of beta-lactoglobulin transgenes

Genomic constructs comprising the ovine beta-lactoglobulin gene are expressed in a position-independent manner in the mammary gland of transgenic mice. In some lines however, constitutive low-level transgene expression was detected in all other tissues. This ectopic expression presumably represents a position-dependent phenomenon since it was observed in only a proportion (40%) of the lines generated. Different lines of BLG transgenic mice displayed similar temporal patterns of ectopic expression. This pattern differed from that of BLG in the mammary gland. These data imply that the DNA elements that direct position-independent expression of beta-lactoglobulin transgenes in the mammary gland do not have the ability to insulate them from position effects in other tissues. Furthermore, the relatively high frequency and constitutive nature of ectopic expression suggests that transgene integration may not be totally random.

Expression of bacterial cysteine biosynthesis genes in transgenic mice and sheep: toward a new in vivo amino acid biosynthesis pathway and improved wool growth

It is possible to improve wool growth through increasing the supply of cysteine available for protein synthesis and cell division in the wool follicle. As mammals can only synthesise cysteine indirectly from methionine via trans-sulphuration, expression of transgenes encoding microbial cysteine biosynthesis enzymes could provide a more efficient pathway to cysteine synthesis in the sheep. If expressed in the rumen epithelium, the abundant sulphide, produced by ruminal microorganisms and normally excreted, could be captured for conversion to cysteine. This paper describes the characterisation of expression of the cysteine biosynthesis genes of Salmonella typhimurium, cysE, cysM and cysK, and linked cysEM, cysME and cysKE genes as transgenes in mice and sheep. The linked transgenes were constructed with each gene driven by a separate promoter, either with the Rous sarcoma virus long terminal repeat (RSVLTR) promoter or the mouse phosphoglycerate kinase-1 (mPgk-1) promoter, and with human growth hormone (hGH) polyadenylation sequences. Transgenesis of mice with the RSVLTR-cysE gene afforded tissue-specific, heritable expression of the gene. Despite high levels of expression in a number of tissues, extremely low levels of expression occurred in the stomach and small intestine. Results of a concurrent sheep transgenesis experiment using the RSVLTR-cysEM and -cysME linked transgenes revealed that the RSVLTR promoter was inadequate for expression in the rumen. Moreover, instability of transgenes containing the RSVLTR sequence was observed. Expression of mPgk-cysME and -cysKE linked transgenes in most tissues of the mice examined, including the stomach and small intestine, suggested this promoter to be a better candidate for expression of these transgenes in the analogous tissues of sheep. However, a subsequent sheep transgenesis experiment indicated that use of the mPgk-1 promoter, active ubiquitously and early in development, may be inappropriate for expression of the cysteine biosynthesis transgenes. In summary, these results indicate that enzymically active bacterial cysteine biosynthesis gene products can be coexpressed in mammalian cells in vivo but that expression of the genes should be spatio-temporally restricted to the adult sheep rumen epithelium.

Immunotoxin-mediated conditional disruption of specific neurons in transgenic mice

We have developed a transgenic approach, termed immunotoxin-mediated cell targeting (IMCT), to ablate conditionally selective neurons in the brain with the cytotoxic activity of immunotoxins. Transgenic mice were created that express the human interleukin 2 receptor alpha subunit (IL-2R alpha) under the control of the dopamine beta-hydroxylase (DBH) gene promoter. The animals were treated intracerebroventricularly with a recombinant immunotoxin, anti-Tac(Fv)-PE40, which selectively kills animal cells bearing human IL-2R alpha. The immunotoxin caused a characteristic behavioral abnormality only in the transgenic mice. This was accompanied by a dramatic loss of DBH-containing neurons and a significant decrease in DBH activity and norepinephrine levels in various regions of the brain. IMCT should provide a general technique to create animal models of human neurodegenerative disorders by targeting neurons or other cell types.

Restricted tissue-specific but correct developmental expression mediated by a short human alpha 1AT promoter fragment in transgenic mice

The tissue-specific and developmental pattern of expression controlled by the proximal promoter (position-348 to +15) derived from the human alpha-1-antitrypsin (h alpha 1AT) gene was studied in transgenic mice. The short promoter segment was linked to the chloramphenicol acetyltransferase (CAT) reporter gene. The transgene showed highly specific expression in the liver and the correct developmental pattern of regulation. Interestingly, this short promoter targets expression to the liver with a greater specificity than that reported for larger alpha 1AT promoter fragments.

Analysis of a 70 kb segment of DNA containing the human zeta and alpha-globin genes linked to their regulatory element (HS-40) in transgenic mice

We have ligated two cosmids through an oligonucleotide linker to produce a single fragment spanning 70 kb of the human alpha-globin cluster, in which the alpha-like globin genes (zeta 2, alpha 2 and alpha 1), their regulatory element (HS-40) and erythroid-specific DNase I hypersensitive sites accurately retain their normal genomic organization. The zeta (embryonic) and alpha (embryonic, fetal and adult) globin genes were expressed in all 17 transgenic embryos. Similarly, all fetal and adult mice from seven transgenic lines that contained one or more copies of the fragment, produced up to 66% of the level of endogenous mouse alpha-globin mRNA. However, as for smaller constructs containing these elements, human alpha-globin expression was not copy number dependent and decreased by 1.5-9.0 fold during development. These findings suggest that either it is not possible to obtain full regulation of human alpha-globin expression in transgenic mice or, more likely, that additional alpha-globin regulatory elements lie beyond the 70 kb segment of DNA analysed.

Chromosomal position effects in chicken lysozyme gene transgenic mice are correlated with suppression of DNase I hypersensitive site formation

The complete chicken lysozyme gene locus is expressed copy number dependently and at a high level in macrophages of transgenic mice. Gene expression independent of genomic position can only be achieved by the concerted action of all cis regulatory elements located on the lysozyme gene domain. Position independency of expression is lost if one essential cis regulatory region is deleted. Here we compared the DNase I hypersensitive site (DHS) pattern formed on the chromatin of position independently and position dependently expressed transgenes in order to assess the influence of deletions within the gene domain on active chromatin formation. We demonstrate, that in position independently expressed transgene all DHSs are formed with the authentic relative frequency on all genes. This is not the case for position dependently expressed transgenes. Our results show that the formation of a DHS during cellular differentiation does not occur autonomously. In case essential regulatory elements of the chicken lysozyme gene domain are lacking, the efficiency of DHS formation on remaining cis regulatory elements during myeloid differentiation is reduced and influenced by the chromosomal position. Hence, no individual regulatory element on the lysozyme domain is capable of organizing the chromatin structure of the whole locus in a dominant fashion.

The DNA rearrangement associated with facioscapulohumeral muscular dystrophy involves a heterochromatin-associated repetitive element: implications for a role of chromatin structure in the pathogenesis of the disease

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant form of muscular dystrophy. The FSHD locus has been linked to the most distal genetic markers on the long arm of chromosome 4. Recently, a probe was identified that detects an EcoRI fragment length polymorphism which segregates with the disease in most FSHD families. Within the EcoRI fragment lies a tandem array of 3.2 kb repeats. In several familial cases and four independent sporadic FSHD mutations, the variation in size of the EcoRI fragment was due to a decrease in copy number of the 3.2 kb repeats. To gain further insight into the relationship between the tandem array and FSHD, a single 3.2 kb repeat unit was characterized. Fluorescence in situ hybridization (FISH) demonstrates that the 3.2 kb repeat cross-hybridizes to several regions of heterochromatin in the human genome. In addition, DNA sequence analysis of the repeat reveals a region which is highly homologous to a previously identified family of heterochromatic repeats, LSau. FISH on interphase chromosomes demonstrates that the tandem array of 3.2 kb repeats lies within 215 kb of the 4q telomere. Together, these results suggest that the tandem array of 3.2 kb repeats, tightly linked to the FSHD locus, is contained in heterochromatin adjacent to the telomere. In addition, they are consistent with the hypothesis that the gene responsible for FSHD may be subjected to position effect variegation because of its proximity to telomeric heterochromatin.

Alu sequence involvement in transcriptional insulation of the keratin 18 gene in transgenic mice

The human keratin 18 (K18) gene is expressed in a variety of adult simple epithelial tissues, including liver, intestine, lung, and kidney, but is not normally found in skin, muscle, heart, spleen, or most of the brain. Transgenic animals derived from the cloned K18 gene express the transgene in appropriate tissues at levels directly proportional to the copy number and independently of the sites of integration. We have investigated in transgenic mice the dependence of K18 gene expression on the distal 5' and 3' flanking sequences and upon the RNA polymerase III promoter of an Alu repetitive DNA transcription unit immediately upstream of the K18 promoter. Integration site-independent expression of tandemly duplicated K18 transgenes requires the presence of either an 825-bp fragment of the 5' flanking sequence or the 3.5-kb 3' flanking sequence. Mutation of the RNA polymerase III promoter of the Alu element within the 825-bp fragment abolishes copy number-dependent expression in kidney but does not abolish integration site-independent expression when assayed in the absence of the 3' flanking sequence of the K18 gene. The characteristics of integration site-independent expression and copy number-dependent expression are separable. In addition, the formation of the chromatin state of the K18 gene, which likely restricts the tissue-specific expression of this gene, is not dependent upon the distal flanking sequences of the 10-kb K18 gene but rather may depend on internal regulatory regions of the gene.

Alu sequence involvement in transcriptional insulation of the keratin 18 gene in transgenic mice

The human keratin 18 (K18) gene is expressed in a variety of adult simple epithelial tissues, including liver, intestine, lung, and kidney, but is not normally found in skin, muscle, heart, spleen, or most of the brain. Transgenic animals derived from the cloned K18 gene express the transgene in appropriate tissues at levels directly proportional to the copy number and independently of the sites of integration. We have investigated in transgenic mice the dependence of K18 gene expression on the distal 5' and 3' flanking sequences and upon the RNA polymerase III promoter of an Alu repetitive DNA transcription unit immediately upstream of the K18 promoter. Integration site-independent expression of tandemly duplicated K18 transgenes requires the presence of either an 825-bp fragment of the 5' flanking sequence or the 3.5-kb 3' flanking sequence. Mutation of the RNA polymerase III promoter of the Alu element within the 825-bp fragment abolishes copy number-dependent expression in kidney but does not abolish integration site-independent expression when assayed in the absence of the 3' flanking sequence of the K18 gene. The characteristics of integration site-independent expression and copy number-dependent expression are separable. In addition, the formation of the chromatin state of the K18 gene, which likely restricts the tissue-specific expression of this gene, is not dependent upon the distal flanking sequences of the 10-kb K18 gene but rather may depend on internal regulatory regions of the gene.

Transcriptional insulation of the human keratin 18 gene in transgenic mice

Expression of the 10-kb human keratin 18 (K18) gene in transgenic mice results in efficient and appropriate tissue-specific expression in a variety of internal epithelial organs, including liver, lung, intestine, kidney, and the ependymal epithelium of brain, but not in spleen, heart, or skeletal muscle. Expression at the RNA level is directly proportional to the number of integrated K18 transgenes. These results indicate that the K18 gene is able to insulate itself both from the commonly observed cis-acting effects of the sites of integration and from the potential complications of duplicated copies of the gene arranged in head-to-tail fashion. To begin to identify the K18 gene sequences responsible for this property of transcriptional insulation, additional transgenic mouse lines containing deletions of either the 5' or 3' distal end of the K18 gene have been characterized. Deletion of 1.5 kb of the distal 5' flanking sequence has no effect upon either the tissue specificity or the copy number-dependent behavior of the transgene. In contrast, deletion of the 3.5-kb 3' flanking sequence of the gene results in the loss of the copy number-dependent behavior of the gene in liver and intestine. However, expression in kidney, lung, and brain remains efficient and copy number dependent in these transgenic mice. Furthermore, herpes simplex virus thymidine kinase gene expression is copy number dependent in transgenic mice when the gene is located between the distal 5'- and 3'-flanking sequences of the K18 gene. Each adult transgenic male expressed the thymidine kinase gene in testes and brain and proportionally to the number of integrated transgenes. We conclude that the characteristic of copy number-dependent expression of the K18 gene is tissue specific because the sequence requirements for transcriptional insulation in adult liver and intestine are different from those for lung and kidney. In addition, the behavior of the transgenic thymidine kinase gene in testes and brain suggests that the property of transcriptional insulation of the K18 gene may be conferred by the distal flanking sequences of the K18 gene and, additionally, may function for other genes.

Transcriptional insulation of the human keratin 18 gene in transgenic mice

Expression of the 10-kb human keratin 18 (K18) gene in transgenic mice results in efficient and appropriate tissue-specific expression in a variety of internal epithelial organs, including liver, lung, intestine, kidney, and the ependymal epithelium of brain, but not in spleen, heart, or skeletal muscle. Expression at the RNA level is directly proportional to the number of integrated K18 transgenes. These results indicate that the K18 gene is able to insulate itself both from the commonly observed cis-acting effects of the sites of integration and from the potential complications of duplicated copies of the gene arranged in head-to-tail fashion. To begin to identify the K18 gene sequences responsible for this property of transcriptional insulation, additional transgenic mouse lines containing deletions of either the 5' or 3' distal end of the K18 gene have been characterized. Deletion of 1.5 kb of the distal 5' flanking sequence has no effect upon either the tissue specificity or the copy number-dependent behavior of the transgene. In contrast, deletion of the 3.5-kb 3' flanking sequence of the gene results in the loss of the copy number-dependent behavior of the gene in liver and intestine. However, expression in kidney, lung, and brain remains efficient and copy number dependent in these transgenic mice. Furthermore, herpes simplex virus thymidine kinase gene expression is copy number dependent in transgenic mice when the gene is located between the distal 5'- and 3'-flanking sequences of the K18 gene. Each adult transgenic male expressed the thymidine kinase gene in testes and brain and proportionally to the number of integrated transgenes. We conclude that the characteristic of copy number-dependent expression of the K18 gene is tissue specific because the sequence requirements for transcriptional insulation in adult liver and intestine are different from those for lung and kidney. In addition, the behavior of the transgenic thymidine kinase gene in testes and brain suggests that the property of transcriptional insulation of the K18 gene may be conferred by the distal flanking sequences of the K18 gene and, additionally, may function for other genes.

An opportunistic promoter sharing regulatory sequences with either a muscle-specific or a ubiquitous promoter in the human aldolase A gene

The human aldolase A gene is transcribed from three different promoters, pN, pM, and pH, all of which are clustered within a small 1.6-kbp DNA domain. pM, which is highly specific to adult skeletal muscle, lies in between pN and pH, which are ubiquitous but particularly active in heart and skeletal muscle. A ubiquitous enhancer, located just upstream of pH start sites, is necessary for the activity of both pH and pN in transient transfection assays. Using transgenic mice, we studied the sequence controlling the muscle-specific promoter pM and the relations between the three promoters and the ubiquitous enhancer. A 4.3-kbp fragment containing the three promoters and the ubiquitous enhancer showed an expression pattern consistent with that known in humans. In addition, while pH was active in both fast and slow skeletal muscles, pM was active only in fast muscle. pM activity was unaltered by the deletion of a 1.8-kbp region containing the ubiquitous enhancer and the pH promoter, whereas pN remained active only in fast skeletal muscle. These findings suggest that in fast skeletal muscle, a tissue-specific enhancer was acting on both pN and pM, whereas in other tissues, the ubiquitous enhancer was necessary for pN activity. Finally, a 2.6-kbp region containing the ubiquitous enhancer and only the pH promoter was sufficient to bring about high-level expression of pH in cardiac and skeletal muscle. Thus, while pH and pM function independently of each other, pN, remarkably, shares regulatory elements with each of them, depending on the tissue. Importantly, expression of the transgenes was independent of the integration site, as originally described for transgenes containing the beta-globin locus control region.

An opportunistic promoter sharing regulatory sequences with either a muscle-specific or a ubiquitous promoter in the human aldolase A gene

The human aldolase A gene is transcribed from three different promoters, pN, pM, and pH, all of which are clustered within a small 1.6-kbp DNA domain. pM, which is highly specific to adult skeletal muscle, lies in between pN and pH, which are ubiquitous but particularly active in heart and skeletal muscle. A ubiquitous enhancer, located just upstream of pH start sites, is necessary for the activity of both pH and pN in transient transfection assays. Using transgenic mice, we studied the sequence controlling the muscle-specific promoter pM and the relations between the three promoters and the ubiquitous enhancer. A 4.3-kbp fragment containing the three promoters and the ubiquitous enhancer showed an expression pattern consistent with that known in humans. In addition, while pH was active in both fast and slow skeletal muscles, pM was active only in fast muscle. pM activity was unaltered by the deletion of a 1.8-kbp region containing the ubiquitous enhancer and the pH promoter, whereas pN remained active only in fast skeletal muscle. These findings suggest that in fast skeletal muscle, a tissue-specific enhancer was acting on both pN and pM, whereas in other tissues, the ubiquitous enhancer was necessary for pN activity. Finally, a 2.6-kbp region containing the ubiquitous enhancer and only the pH promoter was sufficient to bring about high-level expression of pH in cardiac and skeletal muscle. Thus, while pH and pM function independently of each other, pN, remarkably, shares regulatory elements with each of them, depending on the tissue. Importantly, expression of the transgenes was independent of the integration site, as originally described for transgenes containing the beta-globin locus control region.

The mouse beta-globin locus control region: hypersensitive sites 3 and 4

The human beta-globin LCR plays a key role in the transcriptional regulation of the beta-globin locus and comprises four erythroid specific DNase I hypersensitive sites, designated 5'HS1-4. We have now isolated genomic clones containing 5'HS3 and 5'HS4 of the mouse beta-globin LCR. 5'HS3 and 5'HS4 are located 15 kb and 22 kb upstream of the mouse epsilon y-globin gene, respectively. Sequence analysis of murine 5'HS3 and 5'HS4 reveals a significant degree of sequence conservation with their human homologues, including the presence of recognition sites for functionally relevant transcription factors. 5'HS3 and 5'HS4 regions were found to form hypersensitive sites in nuclei from murine erythroid cells, but not in nuclei from a variety of nonerythroid haematopoietic cell lines. Analysis of different mouse strains revealed the existence of a polymorphism that alters the spacing between 5'HS3 and 5'HS4. Taken together, our results emphasize the extent of evolutionary conservation and complexity of mammalian beta-globin LCRs. Finally, the cloning of mouse 5'HS3 and 5'HS4 will facilitate the molecular analysis of LCR function in the mouse model.

Position-independent expression of the ovine beta-lactoglobulin gene in transgenic mice

The major milk whey protein of sheep, beta-lactoglobulin (BLG), is expressed specifically in the mammary gland in a developmentally regulated pattern. To identify the cis-acting DNA regions involved in the regulation of BLG expression, resected gene constructs were analysed in transgenic mice. BLG transgenes which contain at least the proximal 406 bp of the 5' flanking region were expressed in all mice analysed, at levels related to transgene copy number, and thus were expressed in a position-independent manner. Expression was restricted to the mammary gland, except in a few lines where low-level expression was also detected in the salivary gland. In these mice, BLG transgenes were expressed during pregnancy and lactation in the appropriate temporal pattern. Further resection of the 5' proximal region to -146 bp resulted in a dramatically reduced frequency of expression, without affecting tissue specificity, while a construct which retained only 79 bp of 5' flanking region was not expressed. Chromatin analysis of isolated sheep nuclei showed that the promoter resides within a DNAaseI-hypersensitive region in the mammary gland but not in the liver. A BLG transgene displayed a similar tissue-specific pattern of DNAaseI hypersensitivity in mice. These data demonstrate an essential role of the proximal DNAaseI-hypersensitive sequences for position-independent expression of the BLG gene.

The herpes simplex virus type 1 thymidine kinase is expressed in the testes of transgenic mice under the control of a cryptic promoter

We reported previously that the herpes simplex virus type 1 (HSV-1) thymidine kinase reporter gene (tk) was expressed in the testes of transgenic mice when coupled to the promoter of a liver-specific mouse major urinary protein (MUP) gene. Here we show that HSV-1 tk is also expressed in the testis when coupled to a MUP pseudogene promoter, to a truncated MUP promoter that is not active in the liver, and to the promoter of the bovine thyroglobulin gene. Furthermore, HSV-1 tk itself was expressed in the testis, although its normal expression had been disabled by removing an upstream regulator of transcription. In every case, the same multiple transcripts were observed, with their 5' ends located downstream of the normal HSV-1 tk translation initiation codon. We conclude that the transcription of HSV-1 tk in the testis is directed by a cryptic TATA box-independent promoter located in the coding region of the gene. The longest HSV-1 thymidine kinase (TK) polypeptides synthesized in the testis were shorter than full-length TK and probably result from translational initiation at Met46 and Met60, the second and third ATG codons of the tk reading frame. Male mice of most transgenic lines were sterile, and the severity of the lesion in spermatogenesis was directly related to the level of TK expression. In the most highly expressing lines, sperm counts were low and morphologically defective sperm were common. In other sterile lines, TK was expressed at a lower level and sperm counts were normal but sperm motility was greatly reduced. Lines with the lowest levels of HSV-1 TK expression were fertile. HSV-1 TK was expressed in germ line cells, mainly in the haploid spermatids. However, low-level HSV-1 TK activity was found in the testis before the first germ cells entered meiosis, showing that if expression is confined to the germ cells, it also occurs in spermatogonia.

The herpes simplex virus type 1 thymidine kinase is expressed in the testes of transgenic mice under the control of a cryptic promoter

We reported previously that the herpes simplex virus type 1 (HSV-1) thymidine kinase reporter gene (tk) was expressed in the testes of transgenic mice when coupled to the promoter of a liver-specific mouse major urinary protein (MUP) gene. Here we show that HSV-1 tk is also expressed in the testis when coupled to a MUP pseudogene promoter, to a truncated MUP promoter that is not active in the liver, and to the promoter of the bovine thyroglobulin gene. Furthermore, HSV-1 tk itself was expressed in the testis, although its normal expression had been disabled by removing an upstream regulator of transcription. In every case, the same multiple transcripts were observed, with their 5' ends located downstream of the normal HSV-1 tk translation initiation codon. We conclude that the transcription of HSV-1 tk in the testis is directed by a cryptic TATA box-independent promoter located in the coding region of the gene. The longest HSV-1 thymidine kinase (TK) polypeptides synthesized in the testis were shorter than full-length TK and probably result from translational initiation at Met46 and Met60, the second and third ATG codons of the tk reading frame. Male mice of most transgenic lines were sterile, and the severity of the lesion in spermatogenesis was directly related to the level of TK expression. In the most highly expressing lines, sperm counts were low and morphologically defective sperm were common. In other sterile lines, TK was expressed at a lower level and sperm counts were normal but sperm motility was greatly reduced. Lines with the lowest levels of HSV-1 TK expression were fertile. HSV-1 TK was expressed in germ line cells, mainly in the haploid spermatids. However, low-level HSV-1 TK activity was found in the testis before the first germ cells entered meiosis, showing that if expression is confined to the germ cells, it also occurs in spermatogonia.

Rostrocaudal gradient of transgene expression in adult skeletal muscle

Transgenic mice were produced in which expression of the reporter gene chloramphenicol acetyltransferase (CAT) is controlled by regulatory elements of a rodent myosin light chain gene. CAT activity was readily detectable in muscles of these mice but negligible in a variety of nonmuscle tissues. Unexpectedly, levels of CAT expression varied greater than 100-fold from muscle to muscle, forming a gradient in which a muscle's position in the rostrocaudal axis was correlated with its level of CAT enzyme activity and abundance of CAT mRNA. Thus, rostral muscles (innervated by cranial nerves) had the lowest levels of CAT, thoracic muscles had intermediate levels, and caudal muscles (innervated through lumbar and sacral roots) had the highest levels. We established that myosin light chain sequences are responsible for the gradient of CAT expression but observed no strong gradient of endogenous myosin light chain expression. We argue that elements that are silent or masked by other sequences in their native context are revealed in the transgene and that the rostrocaudal gradient of gene expression they produce reveals the existence of a positionally graded endogenous regulator of gene expression. These transgenic mice provide evidence that cells in adult mammals retain "positional information" of a sort hitherto studied largely in embryos. The transgene they express may provide a means for determining how such positional values are generated and maintained.

Integration site-dependent expression of a transgene reveals specialized features of cells associated with neuromuscular junctions

After skeletal muscle is denervated, fibroblasts near neuromuscular junctions proliferate more than fibroblasts distant from synaptic sites, and they accumulate adhesive molecules such as tenascin (Gatchalian, C. L., M. Schachner, and J. R. Sanes. 1989. J. Cell Biol. 108:1873-1890). This response could reflect signals that arise perisynaptically after denervation, preexisting differences between perisynaptic and extrasynaptic fibroblasts, or both. Here, we describe a line of transgenic mice in which patterns of transgene expression provide direct evidence for differences between perisynaptic and extrasynaptic fibroblasts in normal muscle. Transgenic mice were generated using regulatory elements from a major histocompatibility complex (MHC) class I gene linked to the Escherichia coli beta-galactosidase (lacZ) gene. Expression of lacZ was detected histochemically. In each of eight lines, lacZ was detected in different subsets of cells, none of which included lymphocytes. In contrast, endogenous MHC is expressed in most tissues and at high levels in lymphocytes. Thus, the MHC gene sequences appeared inactive in the transgene, and lacZ expression was apparently controlled by genomic regulatory elements that were specific for the insertion site. In one line, cells close to the neuromuscular junction were lacZ positive in embryonic and young postnatal mice. Electron microscopy identified these cells as fibroblasts and Schwann cells associated with motor nerve terminals, as well as endoneurial fibroblasts, perineurial cells, and Schwann cells in the distal branches of motor nerves. No intramuscular cells greater than 200 microns from synaptic sites were lacZ positive. These results indicate that there are molecular differences between perisynaptic and extrasynaptic fibroblasts even in normal muscle and that diverse perisynaptic cell types share a specific pattern of gene expression.

Mutation in a reporter gene depends on proximity to and transcription of immunoglobulin variable transgenes

Somatic mutation in immunoglobulin genes is localized to a 2-kilobase region of DNA surrounding and including rearranged variable (V), diversity, and joining (J) gene segments encoding heavy and light chains. To examine the structural basis for targeted mutation, we developed an assay to score mutation on plasmid substrates by using a reporter gene: a bacterial gene encoding an amber-suppressor tRNA molecule was placed 3' of a rearranged kappa VJ gene within the boundaries of mutation. The reporter gene is exquisitely suited for mutational analysis because it is only 200 base pairs (bp), which should not greatly disrupt structure of the immunoglobulin locus, and gene function depends on secondary structure, which means mutation can be scored in many different nucleotide positions. The plasmid was used to make transgenic mice, which were then immunized. The shuttle vector was retrieved by plasmid rescue into an indicator strain of Escherichia coli that contained an amber mutation in its beta-galactosidase gene. Integrity of the tRNA molecule was monitored by colony color, which permitted many transformants to be screened visually. Mutations were not seen in DNA from a transfected B-cell line grown in vitro or in DNA from nonlymphoid tissue of transgenic mice, indicating that the reporter gene was stable during cell division and DNA manipulations. However, when the transgenic mice were immunized, DNA from splenic B cells contained point mutations in the reporter gene at a frequency of 10(-3) per transformant. Sequence analysis of 17 mutated transgenes revealed that the mutations were 1- and 2-bp deletions in the tRNA gene, and one plasmid had an additional 2-bp deletion in the V gene. In contrast, previous studies have shown that mutations in endogenous VJ genes are predominantly nucleotide substitutions and have only 6% deletions. Two other plasmid constructs were analyzed in transgenic lines: no mutations were found when the tRNA gene was placed distal to the VJ gene, and no mutations were seen when the immunoglobulin promoter was deleted. Although we lack direct evidence that the deletions in the tRNA gene are caused by the same mechanism that acts on VJ genes, we have shown that mutations in this assay occur in a manner consistent with immunoglobulin-specific mutation in that they are found in splenic B cells and not in tail tissue, depend on position next to the VJ gene, and require transcription of the VJ gene.

Epigenetic changes in the expression of the maize A1 gene in Petunia hybrida: role of numbers of integrated gene copies and state of methylation

The Petunia hybrida mutant RL01 is white flowering due to a genetic block in the anthocyanin pathway. The introduction of the maize A1 cDNA under the control of the CaMV 35S RNA promoter leads to the production of pelargonidin derivatives, resulting in a brick red flower phenotype. Among the transgenic petunia plants the pigmentation of the petals exhibited different expression patterns which could be categorized into the 'red', the 'variegated', and the 'white' phenotype. This system proved to be especially suitable for the investigation of gene expression by simply looking at the pigmentation pattern of the petals. The uniformity of floral pelargonidin pigmentation is inversely correlated with the number of integrated A1 copies. Furthermore, a correlation was found between the methylation status of the 35S RNA promoter and the instability of the floral pelargonidin coloration. The status of promoter methylation controlling the expression of the A1 gene seems to be influenced by the copy number and the chromosomal position of the transferred gene.