The rat elastase I regulatory element is an enhancer that directs correct cell specificity and developmental onset of expression in transgenic mice

Breaking enhancers to gain insights into developmental defects

Despite ground-breaking genetic studies that have identified thousands of risk variants for developmental diseases, how these variants lead to molecular and cellular phenotypes remains a gap in knowledge. Many of these variants are non-coding and occur at enhancers, which orchestrate key regulatory programs during development. The prevailing paradigm is that non-coding variants alter the activity of enhancers, impacting gene expression programs, and ultimately contributing to disease risk. A key obstacle to progress is the systematic functional characterization of non-coding variants at scale, especially since enhancer activity is highly specific to cell type and developmental stage. Here, we review the foundational studies of enhancers in developmental disease and current genomic approaches to functionally characterize developmental enhancers and their variants at scale. In the coming decade, we anticipate systematic enhancer perturbation studies to link non-coding variants to molecular mechanisms, changes in cell state, and disease phenotypes.

The Promoter and Multiple Enhancers of the pou4f3 Gene Regulate Expression in Inner Ear Hair Cells

Few enhancers that target gene expression to inner ear hair cells (HCs) have been identified. Using transgenic analysis of enhanced green fluorescent protein (eGFP) reporter constructs and bioinformatics, we evaluated the control of pou4f3 gene expression, since it is expressed only in HCs within the inner ear and continues to be expressed throughout life. An 8.5-kb genomic DNA fragment 5' to the start codon, containing three regions of high cross-species homology, drove expression in all embryonic and neonatal HCs, and adult vestibular and inner HCs, but not adult outer HCs. Transgenes with 0.4, 0.8, 2.5, or 6.5 kb of 5' DNA did not produce HC expression. However, addition of the region from 6.5 to 7.2 kb produced expression in vestibular HCs and neonatal basal turn outer HCs, which also implicated the region from 7.2 to 8.5 kb in inner and apical outer HC expression. Deletion of the region from 0.4 to 5.5 kb 5' from the 8.5-kb construct did not affect HC expression, further indicating lack of HC regulatory elements. When the region from 1 to 0.4 kb was replaced with the minimal promoter of the Ela1 gene, HC expression was maintained but at a drastically reduced level. Bioinformatics identified regions of highly conserved sequence outside of the 8.5 kb, which contained POU4F3-, GFI1-, and LHX3-binding sites. These regions may be involved in maintaining POU4F3 expression in adult outer HCs. Our results identify separate enhancers at various locations that direct expression to different HC types at different ages and determine that 0.4 kb of upstream sequence determines expression level. These data will assist in the identification of mutations in noncoding, regulatory regions of this deafness gene.

BMP-7 Induces Adult Human Pancreatic Exocrine-to-Endocrine Conversion

The exocrine pancreas can give rise to endocrine insulin-producing cells upon ectopic expression of key transcription factors. However, the need for genetic manipulation remains a translational hurdle for diabetes therapy. Here we report the conversion of adult human nonendocrine pancreatic tissue into endocrine cell types by exposure to bone morphogenetic protein 7. The use of this U.S. Food and Drug Administration-approved agent, without any genetic manipulation, results in the neogenesis of clusters that exhibit high insulin content and glucose responsiveness both in vitro and in vivo. In vitro lineage tracing confirmed that BMP-7-induced insulin-expressing cells arise mainly from extrainsular PDX-1(+), carbonic anhydrase II(-) (mature ductal), elastase 3a (acinar)(-) , and insulin(-) subpopulations. The nongenetic conversion of human pancreatic exocrine cells to endocrine cells is novel and represents a safer and simpler alternative to genetic reprogramming.

Molecular analysis of the first intron in the bovine myostatin gene

To study the mechanism of transcription and expression of the myostatin gene, we cloned and analyzed the sequence of the bovine myostatin gene promoter and first intron from Qinchuan and Red Angus cattle, then constructed eukaryotic expression vectors encoding the GFP vector by replacing the CMV promoter with the bovine myostatin promoter using PCR method, thereby obtaining an expression vector coding GFP report gene with first intron (identified as pEGFP-MSTNPro-intron1). By transfecting C2C12 cells with the vectors, we then compared the effect on GFP gene expression of the promoter and normal first intron of Qinchuan and Red Angus cattle with that from the promoter and a Qinchuan allele with a 16 base pair insertion. After 48 h incubation, fluorescent indices (FIs), which indicate the expression rate and intensity of gene GFP expression, were analyzed by flow cytometry (FCM). Results showed that Qinchuan sequence homology of promoter was 99% with Red Angus, that Qinchuan first intron sequence homology was 99.51% with Red Angus and that first intron homologies of Qinchuan and Red Angus were 99.08 and 99.02%, respectively, with Accession No.AF320998 in GenBank. Expression of the GFP gene did not differ significantly between preparations using the Qinchuan versus Red Angus promoter. Preparations with a construct that included the first intron had higher GFP gene expression in C2C12 cells than those whose construct lacked the first intron (P < 0.05 or P < 0.01). However, there was no significant difference (P > 0.05) in gene expression between normal first intron and 16 bp insertion first intron (+16 bp) preparations.

Pancreatic acinar cell-specific overexpression of group 1B phospholipase A2 exacerbates diet-induced obesity and insulin resistance in mice

Genome-wide association studies have identified significant association between polymorphisms of the Group 1B phospholipase A(2) (PLA2G1B) gene and central obesity in humans. Previous studies have shown that Pla2g1b inactivation decreases post-prandial lysophospholipid absorption, and as a consequence increases hepatic fatty acid oxidation and protects against diet-induced obesity and glucose intolerance in mice. The present study showed that transgenic mice with pancreatic acinar cell-specific overexpression of the human PLA2G1B gene gained significantly more weight and displayed elevated insulin resistance characteristics, such as impaired glucose tolerance, compared with wild-type (WT) mice, when challenged with a high-fat/carbohydrate diet. Pre- and post-prandial plasma β-hydroxybutyrate levels were also lower, indicative of decreased hepatic fatty acid oxidation, in the hypercaloric diet-fed PLA2G1B transgenic mice. These, along with earlier observations of Pla2g1b-null mice, document that Pla2g1b expression level is an important determinant of susceptibility to diet-induced obesity and diabetes, suggesting that the relationship between PLA2G1B polymorphisms and obesity may be due to differences in PLA2G1B expression levels between these individuals. The ability of pancreas-specific overexpression of PLA2G1B to promote obesity and glucose intolerance suggests that target phospholipase activity in the digestive tract with non-absorbable inhibitors should be considered as a therapeutic option for metabolic disease therapy.

Involvement of autophagy in trypsinogen activation within the pancreatic acinar cells

Autophagy is mostly a nonselective bulk degradation system within cells. Recent reports indicate that autophagy can act both as a protector and killer of the cell depending on the stage of the disease or the surrounding cellular environment (for review see Cuervo, A.M. 2004. Trends Cell Biol. 14:70–77). We found that cytoplasmic vacuoles induced in pancreatic acinar cells by experimental pancreatitis were autophagic in origin, as demonstrated by microtubule-associated protein 1 light chain 3 expression and electron microscopy experiments. To analyze the role of macroautophagy in acute pancreatitis, we produced conditional knockout mice lacking the autophagy-related 5 gene in acinar cells. Acute pancreatitis was not observed, except for very mild edema in a restricted area, in conditional knockout mice. Unexpectedly, trypsinogen activation was greatly reduced in the absence of autophagy. These results suggest that autophagy exerts devastating effects in pancreatic acinar cells by activation of trypsinogen to trypsin in the early stage of acute pancreatitis through delivering trypsinogen to the lysosome.

Transcriptional autoregulation controls pancreatic Ptf1a expression during development and adulthood

The basic helix-loop-helix (bHLH) transcription factor PTF1a is critical to the development of the embryonic pancreas. It is required early for the formation of the undifferentiated tubular epithelium of the nascent pancreatic rudiment and then becomes restricted to the differentiating acinar cells, where it directs the transcriptional activation of the secretory digestive enzyme genes. Here we report that the complex temporal and spatial expression of Ptf1a is controlled by at least three separable gene-flanking regions. A 14.8-kb control domain immediately downstream of the last Ptf1a exon is highly conserved among mammals and directs expression in the dorsal part of the spinal cord but has very little activity in the embryonic or neonatal pancreas. A 13.4-kb proximal promoter domain initiates limited expression in cells that begin the acinar differentiation program. The activity of the proximal promoter domain is complemented by an adjacent 2.3-kb autoregulatory enhancer that is able to activate a heterologous minimal promoter with high-level penetrance in the pancreases of transgenic mice. During embryonic development, the enhancer initiates expression in the early precursor epithelium and then superinduces expression in acinar cells at the onset of their development. The enhancer contains two evolutionarily conserved binding sites for the active form of PTF1a, a trimeric complex composed of PTF1a, one of the common bHLH E proteins, and either RBPJ or RBPJL. The two sites are essential for acinar cell-specific transcription in transfected cell lines and mice. In mature acinar cells, the enhancer and PTF1a establish an autoregulatory loop that reinforces and maintains Ptf1a expression. Indeed, the trimeric PTF1 complex forms dual autoregulatory loops with the Ptf1a and Rbpjl genes that may maintain the stable phenotype of pancreatic acinar cells.

Mutagenesis in rodents using the L1 retrotransposon

LINE1 (L1) retrotransposons are genetic elements that are present in all mammalian genomes. L1s are active in both humans and mice, and are capable of copying themselves and inserting the copy into a new genomic location. These de novo insertions occasionally result in disease. Endogenous L1 retrotransposons can be modified to increase their activity and mutagenic power in a variety of ways. Here we outline the advantages of using modified L1 retrotransposons for performing random mutagenesis in rodents and discuss several potential applications.

Preexisting pancreatic acinar cells contribute to acinar cell, but not islet beta cell, regeneration

It has been suggested that pancreatic acinar cells can serve as progenitors for pancreatic islets, a concept with substantial implications for therapeutic efforts to increase insulin-producing beta cell mass in patients with diabetes. We report what we believe to be the first in vivo lineage tracing approach to determine the plasticity potential of pancreatic acinar cells. We developed an acinar cell-specific inducible Cre recombinase transgenic mouse, which, when mated with a reporter strain and pulsed with tamoxifen, resulted in permanent and specific labeling of acinar cells and their progeny. During various time periods of observation and using several models to provoke injury, we failed to observe any chase of the labeled cells into the endocrine compartment, indicating that acinar cells do not normally transdifferentiate into islet beta cells in vivo in adult mice. In contrast, we observed a substantial role for replication of preexisting acinar cells in the regeneration of new acinar cells after partial pancreatectomy. These results indicate that mature acinar cells harbor a facultative acinar but not endocrine progenitor capacity.

Lineage tracing and characterization of insulin-secreting cells generated from adult pancreatic acinar cells

Although several studies have suggested that insulin-secreting cells can be generated in vitro from cells residing in adult exocrine pancreas, neither the origin of these cells nor their precise insulin secretory properties was obtained. We show here that insulin-secreting cells can be derived from adult mouse pancreatic exocrine cells by suspension culture in the presence of EGF and nicotinamide. The frequency of insulin-positive cells was only 0.01% in the initial preparation and increased to approximately 5% in the culture conditions. Analysis by the Cre/loxP-based direct cell lineage tracing system indicates that these newly made cells originate from amylase/elastase-expressing pancreatic acinar cells. Insulin secretion is stimulated by glucose, sulfonylurea, and carbachol, and potentiation by glucagon-like peptide-1 also occurs. Insulin-containing secretory granules are present in these cells. In addition, we found that the enzymatic dissociation of pancreatic acini itself leads to activation of EGF signaling, and that inhibition of EGF receptor kinase blocks the transdifferentiation. These data demonstrate that pancreatic acinar cells can transdifferentiate into insulin-secreting cells with secretory properties similar to those of native pancreatic beta cells, and that activation of EGF signaling is required in such transdifferentiation.

An mSin3A interaction domain links the transcriptional activity of KLF11 with its role in growth regulation

KLF11 is a biochemical paradigm for a subset of proteins that repress transcription via a Mad1-like mSin3A interacting domain (SID). The biological role of these proteins and the significance of their biochemical activity, however, remain to be established. We report that KLF11 is downregulated in human cancers, inhibits cell growth in vitro and in vivo, and suppresses neoplastic transformation. Transgenic mice for KLF11 display a downregulation of genes encoding the oxidative stress scavengers SOD2 and Catalase1. Chromatin immunoprecipitation assays confirm that, indeed, these genes are bonafide targets of KLF11. KLF11 expression renders cells more sensitive to oxidative drugs, an effect that is rescued by infection with recombinant adenoviruses expressing SOD2 and Catalase1. KLF11-regulated functions require the Mad1-like SID, indicating that these target genes involved in these phenomena are regulated via this corepressor system. These results demonstrate that SID-containing KLF repressor proteins can inhibit cell growth and neoplastic transformation, and outline for the first time cellular and molecular mechanisms by which these functions may be achieved.

Improved glucose tolerance and acinar dysmorphogenesis by targeted expression of transcription factor PDX-1 to the exocrine pancreas

The homeodomain protein PDX-1 is critical for pancreas development and is a key regulator of insulin gene expression. PDX-1 nullizygosity and haploinsufficiency in mice and humans results in pancreatic agenesis and diabetes, respectively. At embryonic day (e) 10.5, PDX-1 is expressed in all pluripotential gut-derived epithelial cells destined to differentiate into the exocrine and endocrine pancreas. At e15, PDX-1 expression is downregulated in exocrine cells, but remains high in endocrine cells. The aim of this study was to determine whether targeted overexpression of PDX-1 to the exocrine compartment of the developing pancreas at e15 would allow for respecification of the exocrine cells. Transgenic (TG) mice were generated in which PDX-1 was expressed in the exocrine pancreas using the exocrine-specific elastase-1 promoter. These mice exhibited a marked dysmorphogenesis of the exocrine pancreas, manifested by increased rates of replication and apoptosis in acinar cells and a progressive fatty infiltration of the exocrine pancreas with age. Interestingly, the TG mice exhibited improved glucose tolerance, but absolute beta-cell mass was not increased. These findings indicate that downregulation of PDX-1 is required for the proper maintenance of the exocrine cell phenotype and that upregulation of PDX-1 in acinar cells affects beta-cell function. The mechanisms underlying these observations remain to be elucidated.

A 500-bp region, approximately 40 kb upstream of the human CYP19 (aromatase) gene, mediates placenta-specific expression in transgenic mice

In humans, aromatase P450 (product of CYP19 gene), which catalyzes conversion of C19 steroids to estrogens, is expressed in a number of tissues, including ovary, adipose, and syncytiotrophoblast of the placenta. The 5' untranslated regions of CYP19 mRNA transcripts in these tissues are encoded by different tissue-specific first exons, which are spliced onto a common site just upstream of the translation initiation site in exon II. In placenta, the 5' untranslated region of CYP19 mRNA transcripts is encoded by exon I.1, which lies approximately 40 kb upstream of exon II. To map genomic sequences required for placenta-specific CYP19 expression, fusion genes containing 2,400 and 501 bp of placenta-specific exon I.1 5' flanking DNA linked to the human growth hormone gene (hGH), as reporter, were introduced into transgenic mice. Expression of CYP19(I.1):hGH fusion genes containing as little as 501 bp of 5' flanking DNA was placenta-specific and developmentally regulated. Furthermore, transgene expression occurred specifically in the labyrinthine trophoblast of the mouse placenta, which contains syncytial cells that may be analogous to the human syncytiotrophoblast. We show that a relatively small segment of DNA (approximately 500 bp) >40 kb upstream of the protein coding region of a human gene is able to direct expression in an appropriate tissue- and cell-specific manner in transgenic mice. These findings suggest that 5' flanking DNA within 501 bp of exon I.1 of the human CYP19 gene contains cis-acting elements that bind placenta-specific transcription factors that are conserved between humans and mice.

Cooperation between elements of an organ-specific transcriptional enhancer in animals

The elastase I gene enhancer that specifies high levels of pancreatic transcription comprises three functional elements (A, B, and C). When assayed individually in transgenic mice, homomultimers of A are acinar cell specific, those of B are islet specific, and those of C are inactive. To determine how the elements interact in the elastase I enhancer and to investigate further the role of the C element, we have examined the activity of the three possible combinations of synthetic double elements in transgenic animals. Combining the A and B elements reconstitutes the exocrine plus endocrine specificity of the intact enhancer with an increased activity in acinar cells compared with that in the A homomultimer. The B element therefore plays a dual role: in islet cells it is capable of activating transcription, whereas in acinar cells it is inactive alone but greatly augments the activity specified by the A element. The C element augments the activity of either the A or B element without affecting their pancreatic cell type specificity. The roles of each element were verified by examining the effects of mutational inactivation of each element within the context of the elastase I enhancer. These results demonstrated that when tested in animals, the individual enhancer elements can perform discrete, separable functions that combine additively for cell type specificity and cooperatively for the overall strength of a multielement stage- and site-specific transcriptional enhancer.

Binding sites for hepatocyte nuclear factor 3 beta or 3 gamma and pancreas transcription factor 1 are required for efficient expression of the gene encoding pancreatic alpha-amylase

Efficient expression of genes under the control of alpha-amylase 2 5'-flanking sequences in exocrine pancreatic cells requires, in addition to the pancreas transcription factor 1 binding site (M. Cockell, B.J. Stevenson, M. Strubin, O. Hagenbüchle, and P. K. Wellauer, Mol. Cell. Biol. 9:2464-2476, 1989), another cis-acting element at positions -60 to -86. This DNA element, which contains an AT-rich core, site for nuclear proteins present not only in the pancreas but also in other tissues and cell lines derived from the endoderm. Purification of binding activities from pancreatic cells by DNA affinity chromatography reveals several distinct proteins ranging in size from 45 to 54 kDa (p45, p47/48, and p54). All of these proteins interact with the specific DNA sequence upon renaturation in vitro. Protein sequencing, electrophoretic mobility shift assay, and immunoblot analyses identify p54 and p47/48 as members of the hepatocyte nuclear factor 3 (HNF3 [forkhead]) family of transcription factors. p54 belongs to the subfamily of HNF3 beta proteins, while p47/48 binding activity includes HNF3 gamma. The cDNAs for two HNF3 beta proteins differing only in N-terminal amino acid sequences were isolated from a pancreatic cDNA library. The mRNAs encoding the two protein species accumulate to different steady-state levels in poly(A)+ RNA of pancreatic cells. Our results support a model by which the pancreas-specific expression of the alpha-amylase gene is mediated by a combination of cell-specific and cell lineage-specific transcription factors.

Visualization and ablation of phenylethanolamine N-methyltransferase producing cells in transgenic mice

We cloned and sequenced the mouse phenylethanolamine N-methyltransferase (PNMT) gene which encodes the enzyme that catalyses the conversion of norepinephrine to epinephrine. The ability of various length sequences flanking the mouse or human PNMT genes to direct expression of reporter genes in transgenic mice was examined. We show that 9 kb of 5' flanking sequences from the cloned mouse PNMT gene can direct expression of the Escherichia coli beta-galactosidase (lacZ) gene to predicted regions of the adrenal, eye and brain in the adult transgenic mouse. The transgene was also expressed during development, in the myelencephalon, adrenal medulla and dorsal root ganglia. PNMT-producing cells were ablated by expression of the diphtheria toxin (DT-A) gene driven by the human PNMT promoter, resulting in abnormalities in the adrenal medulla, eye and testis. The hPNMT8 kb-DT-A line presents a model with which to examine the developmental ramifications of deletion of PNMT-producing cell populations from the adrenal medulla and retina.

A single element of the elastase I enhancer is sufficient to direct transcription selectively to the pancreas and gut

The elastase I (EI) gene is expressed at high levels in the exocrine pancreas and at lower levels in other regions of the gut. The transcriptional enhancer of the EI gene, from nucleotides -205 to -72, recapitulates the expression of the endogenous gene in transgenic mice; it directs not only pancreatic acinar cell expression of a human growth hormone (hGH) transgene but also expression to the stomach, duodenum, and colon. This pattern of selective expression limited to the gastroenteropancreatic organ system is specified by the A element, one of three functional elements in the EI enhancer. When multimerized, the A element directed expression of a hGH reporter gene selectively to the pancreas, stomach, and intestine in transgenic mice. Immunofluorescent localization of hGH indicated that the A element multimer transgenes were expressed in the acinar cells of the pancreas as well as in Brunner's gland cells of the duodenum. The A element binds a pancreatic acinar cell-specific factor, PTF1. Our results show that while the A element is responsible for directing tissue and cell type specificity, other elements of the enhancer must be involved in the regulation of the level of gene expression.

A single element of the elastase I enhancer is sufficient to direct transcription selectively to the pancreas and gut

The elastase I (EI) gene is expressed at high levels in the exocrine pancreas and at lower levels in other regions of the gut. The transcriptional enhancer of the EI gene, from nucleotides -205 to -72, recapitulates the expression of the endogenous gene in transgenic mice; it directs not only pancreatic acinar cell expression of a human growth hormone (hGH) transgene but also expression to the stomach, duodenum, and colon. This pattern of selective expression limited to the gastroenteropancreatic organ system is specified by the A element, one of three functional elements in the EI enhancer. When multimerized, the A element directed expression of a hGH reporter gene selectively to the pancreas, stomach, and intestine in transgenic mice. Immunofluorescent localization of hGH indicated that the A element multimer transgenes were expressed in the acinar cells of the pancreas as well as in Brunner's gland cells of the duodenum. The A element binds a pancreatic acinar cell-specific factor, PTF1. Our results show that while the A element is responsible for directing tissue and cell type specificity, other elements of the enhancer must be involved in the regulation of the level of gene expression.

A C/EBP-binding site in the transferrin promoter is essential for expression in the liver but not the brain of transgenic mice

The gene for the iron-binding protein transferrin is transcribed at a high level in liver hepatocytes but is also active in several other cell types, including oligodendrocytes in the brain. Enhancer elements between bp -560 and -44 of the transferrin gene promoter specifically activated transcription from a heterologous promoter in transgenic mouse liver and brain. Within this region, a potent cis-acting element between bp -98 and -83 was found to be essential for gene activity in both cultured hepatocytes and transgenic mouse liver. The -98 to -83 element contains a CCAAT sequence and is specifically bound by a nuclear factor from mouse liver that is homologous to rat liver C/EBP (CAAT enhancer-binding protein). Point mutations within this binding site inhibit factor binding and abolish transcription in transfected hepatoma cells. When placed in the context of the 3,000-bp transferrin promoter, the C/EBP binding site mutation causes a complete loss of transcription in transgenic mouse liver; however, transgene expression in the brain of the same animals was unaffected. These results suggest a modular structure for the transferrin promoter and demonstrate that deletions or specific point mutations can be used to generate transgene promoters with an activity more restricted than that of their endogenous counterparts.

A C/EBP-binding site in the transferrin promoter is essential for expression in the liver but not the brain of transgenic mice

The gene for the iron-binding protein transferrin is transcribed at a high level in liver hepatocytes but is also active in several other cell types, including oligodendrocytes in the brain. Enhancer elements between bp -560 and -44 of the transferrin gene promoter specifically activated transcription from a heterologous promoter in transgenic mouse liver and brain. Within this region, a potent cis-acting element between bp -98 and -83 was found to be essential for gene activity in both cultured hepatocytes and transgenic mouse liver. The -98 to -83 element contains a CCAAT sequence and is specifically bound by a nuclear factor from mouse liver that is homologous to rat liver C/EBP (CAAT enhancer-binding protein). Point mutations within this binding site inhibit factor binding and abolish transcription in transfected hepatoma cells. When placed in the context of the 3,000-bp transferrin promoter, the C/EBP binding site mutation causes a complete loss of transcription in transgenic mouse liver; however, transgene expression in the brain of the same animals was unaffected. These results suggest a modular structure for the transferrin promoter and demonstrate that deletions or specific point mutations can be used to generate transgene promoters with an activity more restricted than that of their endogenous counterparts.

Distal regulatory elements from the mouse metallothionein locus stimulate gene expression in transgenic mice

DNA regions of 10 and 7 kb that flank the mouse metallothionein II (MT-II) and MT-I genes, respectively, were combined with a minimally marked MT-I (MT-I*) gene and tested in transgenic mice. This construct resulted in (i) position-independent expression of MT-I* mRNA and copy number-dependent expression, (ii) levels of hepatic MT-I mRNA per cell per transgene that were about half that derived from endogenous MT-I genes, (iii) appropriate regulation by metals and hormones, and (iv) tissue distribution of transgene mRNA that resembled that of endogenous MT-I mRNA. These features were not observed when MT-I* was tested without the flanking regions. These MT-I flanking sequences also improved the expression of rat growth hormone reporter genes, with or without introns, that were under the control of the MT-I promoter. Moreover, they enhanced expression from two of four heterologous promoters/enhancers that were tested. Deletion analysis indicated that regions known to have DNase I-hypersensitive sites were necessary but not sufficient for high-level expression. These data suggest that the DNA regions flanking the mouse MT-I and MT-II genes have functions like the locus control regions described for other genes.

Distal regulatory elements from the mouse metallothionein locus stimulate gene expression in transgenic mice

DNA regions of 10 and 7 kb that flank the mouse metallothionein II (MT-II) and MT-I genes, respectively, were combined with a minimally marked MT-I (MT-I*) gene and tested in transgenic mice. This construct resulted in (i) position-independent expression of MT-I* mRNA and copy number-dependent expression, (ii) levels of hepatic MT-I mRNA per cell per transgene that were about half that derived from endogenous MT-I genes, (iii) appropriate regulation by metals and hormones, and (iv) tissue distribution of transgene mRNA that resembled that of endogenous MT-I mRNA. These features were not observed when MT-I* was tested without the flanking regions. These MT-I flanking sequences also improved the expression of rat growth hormone reporter genes, with or without introns, that were under the control of the MT-I promoter. Moreover, they enhanced expression from two of four heterologous promoters/enhancers that were tested. Deletion analysis indicated that regions known to have DNase I-hypersensitive sites were necessary but not sufficient for high-level expression. These data suggest that the DNA regions flanking the mouse MT-I and MT-II genes have functions like the locus control regions described for other genes.

Analysis of the mouse protamine 1 promoter in transgenic mice

Protamines are small arginine-rich proteins that package DNA in spermatozoa. The mouse protamine 1 (Prm-1) gene is transcribed exclusively in post-meiotic spermatids. To identify elements in the Prm-1 promoter required for spermatid-specific transcription, we generated transgenic mice by microinjection of transgenes containing Prm-1 5' flanking sequences with 5' truncations or internal deletions of conserved sequences linked to a marked Prm-1 gene. We also tested Prm-1 promoter regions with a heterologous human growth hormone reporter gene. We conclude that a 113-bp region can direct spermatid-specific transcription and we have defined sequences within this region that are essential for proper function. These results will facilitate the isolation and characterization of transcription factors essential for post-meiotic gene expression.

Erythroid expression and DNAaseI-hypersensitive sites of the carbonic anhydrase 1 gene

The carbonic anhydrase 1 gene is expressed in adult human and mouse erythroid cells and colon epithelia from two distinct promoters. We have explored the erythroid promoter for cis-acting sequences involved in transcription using DNAaseI as a probe. Two DNAaseI-hypersensitive sites (DHS-1 and DHS-2) have been identified in the distal erythroid promoter in CA1-expressing erythroleukaemic cells. These sites are present at low levels in K562 cells, which have a foetal/embryonic phenotype and do not express CA1. DHS-1 and DHS-2 are not present in non-erythroid cells, including colon cells, which express CA1 from the proximal colon promoter. DHS-1 and DHS-2 were also generated in an heterologous CA1 gene containing 5 kb of erythroid promoter sequence after transfection into erythroid cells, including K562 cells. These transfection studies showed that both this fragment, and an abbreviated 817 bp promoter fragment which contains only DHS-1, were sufficient to confer erythroid-specific expression to a reporter gene. These promoters were active in cell lines expressing CA1 and in K562 cells. This latter observation implies that a developmental repressor factor is both present in K562 cells and binds to a cis-acting sequence that is absent from the sequence 5 kb upstream of the erythroid transcription start site.

Use of transgenic mice to map cis-acting elements in the intestinal fatty acid binding protein gene (Fabpi) that control its cell lineage-specific and regional patterns of expression along the duodenal-colonic and crypt-villus axes of the gut epithelium

The mouse intestinal epithelium is able to establish and maintain complex lineage-specific, spatial, and temporal patterns of gene expression despite its rapid and continuous renewal. A multipotent stem cell located near the base of each intestinal crypt gives rise to progeny which undergo amplification and allocation to either enterocytic, Paneth cell, goblet cell, or enteroendocrine cell lineages. Differentiation of these four lineages occurs during their geographically ordered migration along the crypt-villus axis. Gut stem cells appear to have a "positional address" which is manifested by differences in the differentiation programs of their lineal descendants along the duodenal-colonic (cephalocaudal) axis. We have used the intestinal fatty acid binding protein gene (Fabpi) as a model to identify cis-acting elements which regulate cell- and region-specific patterns of gene expression in the gut. Nucleotides -1178 to +28 of rat Fabpi direct a pattern of expression of a reporter (human growth hormone [hGH]) which mimics that of mouse Fabpi (a) steady-state levels of hGH mRNA are highest in the distal jejunum of adult transgenic mice and fall progressively toward both the duodenum and the mid-colon; and (b) hGH is confined to the enterocytic lineage and first appears as postmitotic, differentiating cells exit the crypt and migrate to the base of small intestinal villi or their colonic homologs, the surface epithelial cuffs. Nucleotides -103 to +28, which are highly conserved in rat, mouse and human Fabpi, are able to correctly initiate transgene expression in late fetal life, restrict hGH to the enterocytic lineage, and establish an appropriate cephalocaudal gradient of reporter expression. This cephalocaudal gradient is also influenced by cis-acting elements located between nucleotides -1178 and -278, and -277 and -185 that enhance and suppress (respectively) expression in the ileum and colon and by element(s) located upstream of nucleotide -277 that are needed to sustain high levels of hGH production after weaning. Nucleotides -277 to -185 contain part of a domain conserved between the three orthologous Fabpi genes (nucleotides -240 to -159), a 24-bp element (nucleotides -212 to -188) that binds nuclear factors present in colonic but not small intestinal epithelial cells, and a portion of a CCAAT/enhancer binding protein footprint (C/EBP alpha, nucleotides -188 to -167). Removal of nucleotides -277 to -185 (yielding I-FABP-184 to +28/hGH+3) results in inappropriate expression of hGH in proliferating and nonproliferating epithelial cells located in the mid and upper portions of duodenal, jejunal, ileal, and colonic crypts without affecting the "shape" of the cephalocaudal gradient of transgene expression.(ABSTRACT TRUNCATED AT 400 WORDS)

Organ injury associated with extrathymic induction of immune tolerance in doubly transgenic mice

The developmental fate of autoreactive T cells encountering extrathymically expressed self-antigen was studied in a doubly transgenic mouse model system where pancreatic acinar cells expressed H-2Ld and T cells expressed an antigen receptor (2C TCR) specific for H-2Ld. Thymocytes bearing 2C TCR differentiated normally. They were positively selected without evidence of intrathymic clonal deletion. Survival of H-2Ld-bearing skin allografts was significantly prolonged in pancreatic H-2Ld singly and doubly transgenic mice, consistent with an in vivo state of T-cell tolerance. The mechanism of tolerance induction was determined and found to have two components. First, up to 80% of peripheral CD8+2C TCR+ T cells were eliminated. Second, those T cells which escaped elimination had a significantly reduced proliferative response to H-2Ld. Thus, autoreactive T cells can be made self-tolerant through interaction with self-antigen located extrathymically. This is accomplished by a reduction in the percentage of autoreactive T cells as well as by a reduction in the functional capacity of residual T cells. Surprisingly, although pancreatic lymphocytic infiltration and organ injury were absent in exocrine tissue of singly transgenic mice, it was present in doubly transgenic mice. This suggests that when the percentage of autoreactive T cells is high, tolerance induction can be associated with an inflammatory infiltrate in extrathymic tissue where self-antigen is presented.

Functional dissection of the lck proximal promoter

The lck gene encodes a protein tyrosine kinase that participates in lymphocyte-specific signal transduction pathways. Previous studies have established that lck transcription is regulated by two distinct promoter elements termed proximal (or 3') and distal (or 5'). The proximal promoter is active almost exclusively in thymocytes and becomes inactive later during T-cell maturation. To dissect the mechanisms responsible for lck gene regulation, we generated transgenic animals bearing 5' truncations in the proximal promoter element. Sequences between -584 and +37 with respect to the proximal promoter transcription start site act to direct tissue-specific and temporally correct transcription of either a tagged version of the lck gene itself or a heterologous reporter sequence (lacZ). This region contains binding sites for at least five distinct nuclear proteins, of which one is found only in cells that support proximal lck promoter activity and a second appears only in nonexpressing cells. Interestingly, the transcribed region of the lck gene contains positive control elements that can substantially boost expression from minimal (-130 bp) proximal promoter constructs. These results provide a basis for the biochemical dissection of transcriptional regulators that act at defined points during T-cell development.

Functional dissection of the lck proximal promoter

The lck gene encodes a protein tyrosine kinase that participates in lymphocyte-specific signal transduction pathways. Previous studies have established that lck transcription is regulated by two distinct promoter elements termed proximal (or 3') and distal (or 5'). The proximal promoter is active almost exclusively in thymocytes and becomes inactive later during T-cell maturation. To dissect the mechanisms responsible for lck gene regulation, we generated transgenic animals bearing 5' truncations in the proximal promoter element. Sequences between -584 and +37 with respect to the proximal promoter transcription start site act to direct tissue-specific and temporally correct transcription of either a tagged version of the lck gene itself or a heterologous reporter sequence (lacZ). This region contains binding sites for at least five distinct nuclear proteins, of which one is found only in cells that support proximal lck promoter activity and a second appears only in nonexpressing cells. Interestingly, the transcribed region of the lck gene contains positive control elements that can substantially boost expression from minimal (-130 bp) proximal promoter constructs. These results provide a basis for the biochemical dissection of transcriptional regulators that act at defined points during T-cell development.

A mouse oocyte-specific protein that binds to a region of mZP3 promoter responsible for oocyte-specific mZP3 gene expression

The gene encoding mZP3, the mouse sperm receptor, is expressed exclusively in growing oocytes during oogenesis. To investigate the molecular basis of oocyte-specific mZP3 gene expression, we generated several lines of mice harboring a transgene that contains 470 bp of mZP3 gene 5'-flanking sequence (nucleotides -470 to +10) fused to the firefly luciferase gene coding region. Three of four expressing transgenic lines exhibited luciferase activity only in growing oocytes, suggesting that the 470-bp fragment is sufficient to direct Iocyte-specific expression of the luciferase gene. Results of DNase I footprinting and gel mobility shift assays suggested the presence of an ovary-specific protein that binds to a small region (nucleotides-99 to -86) within the 470-bp fragment of the mZP3 promoter, with 5'-G(G/A)T(G/A)A-3' representing the minimal sequence required for binding. Southwestern (DNA-protein) gel blots revealed the presence of an oocyte-specific, approximately 60,000-Mr protein, called OSP-1, that binds to the minimal sequence. Changes in levels of OSP-1 during oogenesis and early cleavage are consistent with the pattern of mZP3 gene expression during these developmental stages in mice. Therefore, OSP-1 may be a mammalian oocyte-specific transcription factor involved in regulating oocyte-specific mZP3 gene expression.

A mouse oocyte-specific protein that binds to a region of mZP3 promoter responsible for oocyte-specific mZP3 gene expression

The gene encoding mZP3, the mouse sperm receptor, is expressed exclusively in growing oocytes during oogenesis. To investigate the molecular basis of oocyte-specific mZP3 gene expression, we generated several lines of mice harboring a transgene that contains 470 bp of mZP3 gene 5'-flanking sequence (nucleotides -470 to +10) fused to the firefly luciferase gene coding region. Three of four expressing transgenic lines exhibited luciferase activity only in growing oocytes, suggesting that the 470-bp fragment is sufficient to direct Iocyte-specific expression of the luciferase gene. Results of DNase I footprinting and gel mobility shift assays suggested the presence of an ovary-specific protein that binds to a small region (nucleotides-99 to -86) within the 470-bp fragment of the mZP3 promoter, with 5'-G(G/A)T(G/A)A-3' representing the minimal sequence required for binding. Southwestern (DNA-protein) gel blots revealed the presence of an oocyte-specific, approximately 60,000-Mr protein, called OSP-1, that binds to the minimal sequence. Changes in levels of OSP-1 during oogenesis and early cleavage are consistent with the pattern of mZP3 gene expression during these developmental stages in mice. Therefore, OSP-1 may be a mammalian oocyte-specific transcription factor involved in regulating oocyte-specific mZP3 gene expression.

Exocrine pancreas transcription factor 1 binds to a bipartite enhancer element and activates transcription of acinar genes

Exocrine pancreas (XP) enhancers, which contain a conserved core sequence, are active only in XP cells. A core enhancer-binding activity also appears to be restricted to XP nuclei. Here we describe the properties of a factor, purified approximately 100,000-fold from pancreas nuclei, which displays core enhancer-binding activity. It is not identical to previously characterized factors and is termed exocrine pancreas transcription factor 1 (XPF-1). In the highly purified preparation, only a single major protein of 60 kDa was detected by silver staining on sodium dodecyl sulfate-gels and by UV cross-linking. XPF-1 binds to the core enhancer of all tested XP genes and not to a mutant sequence which is inactive in vivo. High-affinity binding sites are bipartite. The results of competition binding and UV-cross-linking assays suggest that XPF-1 interacts with both motifs. XPF-1 selectively stimulates transcription of core enhancer templates in an in vitro transcription system. We hypothesize that XPF-1 plays a role in activation of the transcription of XP-specific genes.

Exocrine pancreas transcription factor 1 binds to a bipartite enhancer element and activates transcription of acinar genes

Exocrine pancreas (XP) enhancers, which contain a conserved core sequence, are active only in XP cells. A core enhancer-binding activity also appears to be restricted to XP nuclei. Here we describe the properties of a factor, purified approximately 100,000-fold from pancreas nuclei, which displays core enhancer-binding activity. It is not identical to previously characterized factors and is termed exocrine pancreas transcription factor 1 (XPF-1). In the highly purified preparation, only a single major protein of 60 kDa was detected by silver staining on sodium dodecyl sulfate-gels and by UV cross-linking. XPF-1 binds to the core enhancer of all tested XP genes and not to a mutant sequence which is inactive in vivo. High-affinity binding sites are bipartite. The results of competition binding and UV-cross-linking assays suggest that XPF-1 interacts with both motifs. XPF-1 selectively stimulates transcription of core enhancer templates in an in vitro transcription system. We hypothesize that XPF-1 plays a role in activation of the transcription of XP-specific genes.

Regulatory regions of rat insulin I gene necessary for expression in transgenic mice

Ten transgenic mouse lines harboring the -346/-103 fragment of the rat insulin I enhancer linked to a heterologous promoter and a reporter gene (Eins-Ptk-CAT construct) were produced. Expression of the hybrid transgene was essentially observed in pancreas and to a lesser extent in brain. These results indicate that the rat insulin I promoter is dispensable for pancreatic expression. This insulin gene sequence is the shortest fragment described as conferring tissue-specific expression in transgenic mice. Two short homologous sequences in the rat insulin I enhancer fragment used, IEB2 and IEB1, have been described as playing a dominant role in the regulation of HIT hamster insulinoma cell-specific transcription of the insulin gene (1). We investigated whether the combination of IEB2 and IEB1 sequences is sufficient to confer specific expression in transgenic mice to a IEB2-IEB1-Ptk-CAT gene construct. No CAT activity was observed neither in pancreas nor in any other organ examined in 19 different transgenic mice. Moreover in transient expression experiments in RIN2A rat insulinoma cells, the IEB sequences had a very weak or no enhancer activity. These observations contribute to the conclusion that DNA regulatory elements other than the IEB sequences are necessary for gene expression in vivo.

Transactivation of pancreas-specific gene sequences in somatic cell hybrids

Enhancer/promoter elements from two pancreas-specific genes, those encoding amylase and elastase, were ligated to the bacterial GPT gene. The resulting construct can be used to select for expression of gene products which activate these pancreas-specific promoters in hybrid cells. The selectable GPT construct was stably transferred into several cell lines either directly or by cotransfection with pSV2Neo. GPT was expressed when transferred to pancreatic cell lines but not when transferred to GPT-fibroblast (L) cells or hepatoma cells. When the transformed L cells and hepatoma cells were fused with pancreatic cell lines, GPT was activated in the hybrid cells. Endogenous pancreas-specific genes from the L-cell and hepatoma parents were also activated in the hybrids. In addition, a pancreas-specific nuclear protein, PTF1, was produced in pancreatic and hybrid cells, correlating with GPT expression. The transformed L cells and hepatoma cells thus contained a nonexpressed construct which could be activated in trans by factors present in pancreatic cells. The hepatoma hybrid also continued to produce albumin, demonstrating the coexpression of liver and pancreas-specific genes in the hybrid-cell population. Cell lines carrying the amylase/elastase/GPT construct may be useful as a selection system for cloning of pancreatic transcription activators.

Transactivation of pancreas-specific gene sequences in somatic cell hybrids

Enhancer/promoter elements from two pancreas-specific genes, those encoding amylase and elastase, were ligated to the bacterial GPT gene. The resulting construct can be used to select for expression of gene products which activate these pancreas-specific promoters in hybrid cells. The selectable GPT construct was stably transferred into several cell lines either directly or by cotransfection with pSV2Neo. GPT was expressed when transferred to pancreatic cell lines but not when transferred to GPT-fibroblast (L) cells or hepatoma cells. When the transformed L cells and hepatoma cells were fused with pancreatic cell lines, GPT was activated in the hybrid cells. Endogenous pancreas-specific genes from the L-cell and hepatoma parents were also activated in the hybrids. In addition, a pancreas-specific nuclear protein, PTF1, was produced in pancreatic and hybrid cells, correlating with GPT expression. The transformed L cells and hepatoma cells thus contained a nonexpressed construct which could be activated in trans by factors present in pancreatic cells. The hepatoma hybrid also continued to produce albumin, demonstrating the coexpression of liver and pancreas-specific genes in the hybrid-cell population. Cell lines carrying the amylase/elastase/GPT construct may be useful as a selection system for cloning of pancreatic transcription activators.

Binary system for regulating transgene expression in mice: targeting int-2 gene expression with yeast GAL4/UAS control elements

We have developed a binary transgenic system that activates an otherwise silent transgene in the progeny of a simple genetic cross. The system consists of two types of transgenic mouse strains, targets and transactivators. A target strain bears a transgene controlled by yeast regulatory sequences (UAS) that respond only to the yeast transcriptional activator GAL4. A transactivator strain expresses an active GAL4 gene that can be driven by any selected promoter. The current paradigm uses the murine growth factor int-2 cDNA as the target gene and the GAL4 gene driven by the mouse mammary tumor virus long terminal repeat as the transactivator. Both target and transactivator strains are phenotypically normal. By contrast, the bigenic offspring of these two strains express high levels of the target int-2 gene in each organ expressing the GAL4 transactivator. They also display a characteristic dominant int-2 phenotype that consists of epithelial hyperplasia in mammary and salivary glands, as well as prostatic and epididymal hypertrophy, which results in male sterility.

Expression from the transferrin gene promoter in transgenic mice

Transferrin is an iron-binding protein that is expressed as a major product in liver and secreted into the plasma. To study the tissue-specific regulatory regions of this gene, the genomic mouse transferrin (mTf) gene was cloned and characterized by partial sequence analysis and S1 nuclease mapping of the transcriptional start site. Fusion genes containing the transferrin gene promoter and 5'-flanking sequences were ligated to the human growth hormone (hGH) gene and used to produce transgenic mice. A deletion construct containing the -581 to +50 region of the transferrin gene was sufficient to direct a high level of liver-specific expression resembling endogenous transferrin gene expression. Deletion to -139 base pairs of 5'-flanking sequence gave a construct which retained liver specificity, but the magnitude of expression decreased severalfold. These results demonstrate the presence of a liver-specific transcriptional element between -139 and +50 and suggest the presence of a distal element between -581 and -139 that can further increase expression. Surprisingly, fusion constructs containing -3 kilobase pairs (kb) of 5'-flanking sequence gave higher levels of mRNA in nonhepatic tissues than did either the -581 or -139 construct. Further studies indicated that the high levels of circulating hGH in these transgenic mice specifically induced the endogenous transferrin and albumin genes in liver and also stimulated the normally low levels of expression of the endogenous transferrin gene in brain, heart, kidney, and muscle. A mutated hGH gene that does not produce active growth hormone was fused to the -3- to +50-kb transferrin sequences to produce the -3-kb mTf-hGX construct. A liver-specific pattern of expression was observed in transgenic mice harboring the -3-kb mTf-hGX construct, and this mutated transgene was shown to be induced four- to sevenfold by either bovine or human growth hormone. These results demonstrate the presence of a growth hormone-responsive element between -3 and +50 kb in the 5'-flanking region of the mTf gene promoter.

The DNA-binding activity of transcription factor PTF1 parallels the synthesis of pancreas-specific mRNAs during mouse development

We have studied the expression of the alpha-amylase, trypsin, and elastase II genes in the acinar pancreas during mouse development. Transcriptional control is the major mechanism by which the differential accumulation of alpha-amylase, trypsin, and elastase II mRNAs is determined during late embryogenesis. The synthesis of pancreatic mRNAs is detected around day 15 of gestation and involves most if not all acinar cells. The DNA-binding activity of the pancreas-specific transcription factor PTF1, which binds to enhancers of genes expressed in this tissue, is detected for the first time at day 15 of gestation. The appearance of the factor at this early stage of development suggests that it plays an important role during pancreas differentiation.

The DNA-binding activity of transcription factor PTF1 parallels the synthesis of pancreas-specific mRNAs during mouse development

We have studied the expression of the alpha-amylase, trypsin, and elastase II genes in the acinar pancreas during mouse development. Transcriptional control is the major mechanism by which the differential accumulation of alpha-amylase, trypsin, and elastase II mRNAs is determined during late embryogenesis. The synthesis of pancreatic mRNAs is detected around day 15 of gestation and involves most if not all acinar cells. The DNA-binding activity of the pancreas-specific transcription factor PTF1, which binds to enhancers of genes expressed in this tissue, is detected for the first time at day 15 of gestation. The appearance of the factor at this early stage of development suggests that it plays an important role during pancreas differentiation.

Peripheral tolerance to allogeneic class II histocompatibility antigens expressed in transgenic mice: evidence against a clonal-deletion mechanism

To examine the effects of aberrant expression of class II major histocompatibility complex (MHC) proteins on tolerance development, transgenic mice expressing the I-Ad genes under control of the pancreatic elastase promoter were produced. Such transgenic mice express I-Ad exclusively on exocrine pancreas, without expression in thymus or by lymphocytes. No spontaneous development of autoimmune reactivity toward exocrine pancreas was found in transgene-expressing mice of an H-2b background even though such mice could produce in vitro allogeneic responses against I-Ad. When T cells from nontransgenic H-2b mice as well as transgenic H-2b mice were activated in vitro by I-Ad allogeneic stimulator cells and transferred to transgenic mice, an intense, destructive lymphocytic infiltrate specific for exocrine pancreas developed. These findings suggest that aberrant class II MHC expression alone may not trigger autoimmune reactions. Rather, the unresponsiveness to allogenic class II MHC may result from the inability of exocrine pancreas to initiate primary responses by T cells.

Muscle creatine kinase sequence elements regulating skeletal and cardiac muscle expression in transgenic mice

Muscle creatine kinase (MCK) is expressed at high levels only in skeletal and cardiac muscle tissues. Previous in vitro transfection studies of skeletal muscle myoblasts and fibroblasts had identified two MCK enhancer elements and one proximal promoter element, each of which exhibited expression only in differentiated skeletal muscle. In this study, we have identified several regions of the mouse MCK gene that are responsible for tissue-specific expression in transgenic mice. A fusion gene containing 3,300 nucleotides of MCK 5' sequence exhibited chloramphenicol acetyltransferase activity levels that were more than 10(4)-fold higher in skeletal muscle than in other, nonmuscle tissues such as kidney, liver, and spleen. Expression in cardiac muscle was also greater than in these nonmuscle tissues by 2 to 3 orders of magnitude. Progressive 5' deletions from nucleotide -3300 resulted in reduced expression of the transgene, and one of these resulted in a preferential decrease in expression in cardiac tissue relative to that in skeletal muscle. Of the two enhancer sequences analyzed, only one directed high-level expression in both skeletal and cardiac muscle. The other enhancer activated expression only in skeletal muscle. These data reveal a complex set of cis-acting sequences that have differential effects on MCK expression in skeletal and cardiac muscle.

Expression from the transferrin gene promoter in transgenic mice

Transferrin is an iron-binding protein that is expressed as a major product in liver and secreted into the plasma. To study the tissue-specific regulatory regions of this gene, the genomic mouse transferrin (mTf) gene was cloned and characterized by partial sequence analysis and S1 nuclease mapping of the transcriptional start site. Fusion genes containing the transferrin gene promoter and 5'-flanking sequences were ligated to the human growth hormone (hGH) gene and used to produce transgenic mice. A deletion construct containing the -581 to +50 region of the transferrin gene was sufficient to direct a high level of liver-specific expression resembling endogenous transferrin gene expression. Deletion to -139 base pairs of 5'-flanking sequence gave a construct which retained liver specificity, but the magnitude of expression decreased severalfold. These results demonstrate the presence of a liver-specific transcriptional element between -139 and +50 and suggest the presence of a distal element between -581 and -139 that can further increase expression. Surprisingly, fusion constructs containing -3 kilobase pairs (kb) of 5'-flanking sequence gave higher levels of mRNA in nonhepatic tissues than did either the -581 or -139 construct. Further studies indicated that the high levels of circulating hGH in these transgenic mice specifically induced the endogenous transferrin and albumin genes in liver and also stimulated the normally low levels of expression of the endogenous transferrin gene in brain, heart, kidney, and muscle. A mutated hGH gene that does not produce active growth hormone was fused to the -3- to +50-kb transferrin sequences to produce the -3-kb mTf-hGX construct. A liver-specific pattern of expression was observed in transgenic mice harboring the -3-kb mTf-hGX construct, and this mutated transgene was shown to be induced four- to sevenfold by either bovine or human growth hormone. These results demonstrate the presence of a growth hormone-responsive element between -3 and +50 kb in the 5'-flanking region of the mTf gene promoter.

Binding of a pancreatic nuclear protein is correlated with amylase enhancer activity

The mouse amylase gene Amy-2.2 is expressed at high levels specifically in the acinar cells of the pancreas. The region between -172 and -110 of this gene includes sequence elements common to pancreas-specific genes. Nuclear proteins with specific affinity for this region were partially purified from rat pancreas. The consensus element of another pancreas-specific gene, elastase 1, competes for protein binding to the amylase sequences. Binding was localized by DNase I protection to the sequence -156 to -122. Site-directed mutagenesis of this sequence resulted in concomitant loss of protein binding and enhancer activity. Photo-affinity labelling of pancreatic nuclear extracts identified one predominant binding protein with a molecular weight of approximately 75 kDa. The data indicate that binding of this nuclear protein is essential for the enhancer activity of this pancreas-specific element.

Identification of a cell-specific DNA-binding activity that interacts with a transcriptional activator of genes expressed in the acinar pancreas

Footprint analysis of the 5'-flanking regions of the alpha-amylase 2, elastase 2, and trypsina genes, which are expressed in the acinar pancreas, showed multiple sites of protein-DNA interaction for each gene. Competition experiments demonstrated that a region from each 5'-flanking region interacted with the same cell-specific DNA-binding activity. We show by in vitro binding assays that this DNA-binding activity also recognizes a sequence within the 5'-flanking regions of elastase 1, chymotrypsinogen B, carboxypeptidase A, and trypsind genes. Methylation interference and protection studies showed that the DNA-binding activity recognized a bipartite motif, the subelements of which were separated by integral helical turns of DNA. The alpha-amylase 2 cognate sequence was found to enhance in vivo transcription of its own promoter in a cell-specific manner, which identified the DNA-binding activity as a transcription factor (PTF 1). The observation that PTF 1 bound to DNA sequences that have been defined as transcriptional enhancers by others suggests that this factor is involved in the coordinate expression of genes transcribed in the acinar pancreas.

Muscle creatine kinase sequence elements regulating skeletal and cardiac muscle expression in transgenic mice

Muscle creatine kinase (MCK) is expressed at high levels only in skeletal and cardiac muscle tissues. Previous in vitro transfection studies of skeletal muscle myoblasts and fibroblasts had identified two MCK enhancer elements and one proximal promoter element, each of which exhibited expression only in differentiated skeletal muscle. In this study, we have identified several regions of the mouse MCK gene that are responsible for tissue-specific expression in transgenic mice. A fusion gene containing 3,300 nucleotides of MCK 5' sequence exhibited chloramphenicol acetyltransferase activity levels that were more than 10(4)-fold higher in skeletal muscle than in other, nonmuscle tissues such as kidney, liver, and spleen. Expression in cardiac muscle was also greater than in these nonmuscle tissues by 2 to 3 orders of magnitude. Progressive 5' deletions from nucleotide -3300 resulted in reduced expression of the transgene, and one of these resulted in a preferential decrease in expression in cardiac tissue relative to that in skeletal muscle. Of the two enhancer sequences analyzed, only one directed high-level expression in both skeletal and cardiac muscle. The other enhancer activated expression only in skeletal muscle. These data reveal a complex set of cis-acting sequences that have differential effects on MCK expression in skeletal and cardiac muscle.

Tolerance in transgenic mice expressing class II major histocompatibility complex on pancreatic acinar cells

To study the nature of tolerance to antigens not expressed by cells of the lymphoid system, expression of class II MHC I-E was targeted to the acinar cells of the exocrine pancreas in transgenic mice (elastase [EL]-I-E). Despite the absence of detectable I-E in the thymus of EL-I-E transgenic mice, both thymocytes and peripheral T lymphocytes were tolerant to I-E, and the pancreas was free of autoimmune infiltrates. Nontolerant T cells adoptively transferred into irradiated or T-depleted transgenic mice rapidly destroy the I-E+ components of the pancreas; however, adoptive transfer of nontolerant T lymphocytes into nonirradiated transgenic mice do not. These results suggest that tolerance in transgenic mice is maintained by some peripheral tolerance mechanism. However, further studies indicate that tolerance in transgenic mice is not maintained by specific Ts cells. For example, cell mixing experiments both in vitro and in vivo fail to reveal dominant unresponsiveness. Furthermore, nontolerant T cells injected into otherwise unmanipulated EL-I-E mice can be primed in situ (by injections of I-E+ spleen cells) to destroy the I-E+ acinar cells.

Identification of a cell-specific DNA-binding activity that interacts with a transcriptional activator of genes expressed in the acinar pancreas

Footprint analysis of the 5'-flanking regions of the alpha-amylase 2, elastase 2, and trypsina genes, which are expressed in the acinar pancreas, showed multiple sites of protein-DNA interaction for each gene. Competition experiments demonstrated that a region from each 5'-flanking region interacted with the same cell-specific DNA-binding activity. We show by in vitro binding assays that this DNA-binding activity also recognizes a sequence within the 5'-flanking regions of elastase 1, chymotrypsinogen B, carboxypeptidase A, and trypsind genes. Methylation interference and protection studies showed that the DNA-binding activity recognized a bipartite motif, the subelements of which were separated by integral helical turns of DNA. The alpha-amylase 2 cognate sequence was found to enhance in vivo transcription of its own promoter in a cell-specific manner, which identified the DNA-binding activity as a transcription factor (PTF 1). The observation that PTF 1 bound to DNA sequences that have been defined as transcriptional enhancers by others suggests that this factor is involved in the coordinate expression of genes transcribed in the acinar pancreas.

Expression of the third member of the serum amyloid A gene family in mouse adipocytes

Three homologous genes that code for three related proteins comprise the serum amyloid A (SAA) family in the mouse. Endotoxin induces equally vigorous expression of mRNAs for the three SAA genes in liver. In extrahepatic tissues SAA1 and/or SAA2 mRNAs have been found only in kidney and intestine, however, SAA3 is expressed in all extrahepatic tissues thus far examined. This observation raised the question: is SAA3 mRNA expressed by a single cell system dispersed throughout all tissues, or by differentiated cells of each tissue? This question was explored in various tissues by in situ hybridization with a single-stranded cRNA probe specific for SAA3 mRNA. We found expression in the liver of SAA3 mRNA by other cells as well as by hepatocytes. A common feature among extrahepatic tissues was SAA3 mRNA expression in adipocytes. SAA3 mRNA was also found in two nonadipose cells, Leydig cells of the testis, and some of the cells located in parafollicular zones of the spleen.

Interactions between the promoter and first intron are involved in transcriptional control of alpha 1(I) collagen gene expression

The first intron of the human collagen alpha 1(I) gene contains several positively and negatively acting elements. We have studied the transcription of collagen-human growth hormone fusion genes, containing deletions and rearrangements of collagen intronic sequences, by transient transfection of chick tendon fibroblasts and NIH 3T3 cells. In chick tendon fibroblasts, but not in 3T3 cells, inversion of intronic sequences containing a previously studied 274-base-pair segment, A274, resulted in markedly reduced human growth hormone mRNA levels as determined by an RNase protection assay. This inhibitory effect was largely alleviated when deletions were introduced in the collagen promoter of plasmids containing negatively oriented intronic sequences. Evidence for interaction of the promoter with the intronic segment, A274, was obtained by gel mobility shift assays. We suggest that promoter-intron interactions, mediated by DNA-binding proteins, regulate collagen gene transcription. Inversion of intronic segments containing critical interactive elements might then lead to an altered geometry and reduced activity of a transcriptional complex in those cells with sufficiently high levels of appropriate transcription factors. We further suggest that the deleted promoter segment plays a key role in directing DNA interactions involved in transcriptional control.

Interactions between the promoter and first intron are involved in transcriptional control of alpha 1(I) collagen gene expression

The first intron of the human collagen alpha 1(I) gene contains several positively and negatively acting elements. We have studied the transcription of collagen-human growth hormone fusion genes, containing deletions and rearrangements of collagen intronic sequences, by transient transfection of chick tendon fibroblasts and NIH 3T3 cells. In chick tendon fibroblasts, but not in 3T3 cells, inversion of intronic sequences containing a previously studied 274-base-pair segment, A274, resulted in markedly reduced human growth hormone mRNA levels as determined by an RNase protection assay. This inhibitory effect was largely alleviated when deletions were introduced in the collagen promoter of plasmids containing negatively oriented intronic sequences. Evidence for interaction of the promoter with the intronic segment, A274, was obtained by gel mobility shift assays. We suggest that promoter-intron interactions, mediated by DNA-binding proteins, regulate collagen gene transcription. Inversion of intronic segments containing critical interactive elements might then lead to an altered geometry and reduced activity of a transcriptional complex in those cells with sufficiently high levels of appropriate transcription factors. We further suggest that the deleted promoter segment plays a key role in directing DNA interactions involved in transcriptional control.