Characterization of three optional promoters in the 5' region of the human aldolase A gene

Bcr-Abl regulation of sphingomyelin synthase 1 reveals a novel oncogenic-driven mechanism of protein up-regulation

Bcr-Abl (break-point cluster region-abelson), the oncogenic trigger of chronic myelogenous leukemia (CML), has previously been shown to up-regulate the expression and activity of sphingomyelin synthase 1 (SMS1), which contributes to the proliferation of CML cells; however, the mechanism by which this increased expression of SMS1 is mediated remains unknown. In the current study, we show that Bcr-Abl enhances the expression of SMS1 via a 30-fold up-regulation of its transcription. Of most interest, the Bcr-Abl-regulated transcription of SMS1 is initiated from a novel transcription start site (TSS) that is just upstream of the open reading frame. This shift in TSS utilization generates an SMS1 mRNA with a substantially shorter 5' UTR compared with its canonical mRNA. This shorter 5' UTR imparts a 20-fold greater translational efficiency to SMS1 mRNA, which further contributes to the increase of its expression in CML cells. Therefore, our study demonstrates that Bcr-Abl increases SMS1 protein levels via 2 concerted mechanisms: up-regulation of transcription and enhanced translation as a result of the shift in TSS utilization. Remarkably, this is the first time that an oncogene-Bcr-Abl-has been demonstrated to drive such a mechanism that up-regulates the expression of a functionally important target gene, SMS1.-Moorthi, S., Burns, T. A., Yu, G.-Q., Luberto, C. Bcr-Abl regulation of sphingomyelin synthase 1 reveals a novel oncogenic-driven mechanism of protein up-regulation.

Overexpression of Six1 gene suppresses proliferation and enhances expression of fast-type muscle genes in C2C12 myoblasts

Sine oculis homeobox 1 (Six1) homeodomain transcription factor is implicated in the genesis of muscle fiber type diversity, but its regulatory mechanisms on the formation of muscle fiber type are still poorly understood. To elucidate the biological roles of Six1 gene in muscle fiber formation, we established C2C12 cell line overexpressing Six1 and determined the effects of forced Six1 expression on muscle-specific genes expression, cell proliferation, and cell cycles. Our results indicated that Six1 overexpression could significantly promote the expression of fast-type muscle genes Atp2a1, Srl, and Mylpf. Furthermore, Six1 overexpressing C2C12 cells displayed a relative lower proliferative potential, and cell cycle analysis showed that Six1 exerted its role in cell cycle primarily through the regulation of G1/S and G2/M phases. In conclusion, Six1 plays an essential role in modulation of the fast-twitch muscle fiber phenotype through up-regulating fast-type muscle genes expression, and it could suppress the proliferation of muscle cells.

Six1 and Eya1 expression can reprogram adult muscle from the slow-twitch phenotype into the fast-twitch phenotype

Muscle fibers show great differences in their contractile and metabolic properties. This diversity enables skeletal muscles to fulfill and adapt to different tasks. In this report, we show that the Six/Eya pathway is implicated in the establishment and maintenance of the fast-twitch skeletal muscle phenotype. We demonstrate that the MEF3/Six DNA binding element present in the aldolase A pM promoter mediates the high level of activation of this promoter in fast-twitch glycolytic (but not in slow-twitch) muscle fibers. We also show that among the Six and Eya gene products expressed in mouse skeletal muscle, Six1 and Eya1 proteins accumulate preferentially in the nuclei of fast-twitch muscles. The forced expression of Six1 and Eya1 together in the slow-twitch soleus muscle induced a fiber-type transition characterized by the replacement of myosin heavy chain I and IIA isoforms by the faster IIB and/or IIX isoforms, the activation of fast-twitch fiber-specific genes, and a switch toward glycolytic metabolism. Collectively, these data identify Six1 and Eya1 as the first transcriptional complex that is able to reprogram adult slow-twitch oxidative fibers toward a fast-twitch glycolytic phenotype.

The Eukaryotic Promoter Database EPD: the impact of in silico primer extension

The Eukaryotic Promoter Database (EPD) is an annotated non-redundant collection of eukaryotic POL II promoters, experimentally defined by a transcription start site (TSS). There may be multiple promoter entries for a single gene. The underlying experimental evidence comes from journal articles and, starting from release 73, from 5' ESTs of full-length cDNA clones used for so-called in silico primer extension. Access to promoter sequences is provided by pointers to TSS positions in nucleotide sequence entries. The annotation part of an EPD entry includes a description of the type and source of the initiation site mapping data, links to other biological databases and bibliographic references. EPD is structured in a way that facilitates dynamic extraction of biologically meaningful promoter subsets for comparative sequence analysis. Web-based interfaces have been developed that enable the user to view EPD entries in different formats, to select and extract promoter sequences according to a variety of criteria and to navigate to related databases exploiting different cross-references. Tools for analysing sequence motifs around TSSs defined in EPD are provided by the signal search analysis server. EPD can be accessed at http://www.epd. isb-sib.ch.

Muscle electrotransfer as a tool for studying muscle fiber-specific and nerve-dependent activity of promoters

Muscle electrotransfer has recently become a promising tool for efficient delivery of plasmids and transgene expression in skeletal muscle. This technology has been mainly applied to use of muscle as a bioreactor for production of therapeutic proteins. However, it remains to be determined whether muscle electrotransfer may also be accurately used as an alternative tool to transgenesis for studying aspects of muscle-specific gene control that must be explored in fully mature muscle fibers in vivo, such as fiber specificity and nerve dependence. It was also not known to what extent the initial electrical stimulations alter muscle physiology and gene expression. Therefore, optimized conditions of skeletal muscle electroporation were first tested for their effects on muscles of transgenic mice harboring a pM310-CAT transgene in which the CAT reporter gene was under control of the fast IIB fiber-specific and nerve-dependent aldolase A pM promoter. Surprisingly, electrostimulation led to a drastic but transient shutdown of pM310-CAT transgene expression concomitant with very transient activation of MyoD and, mostly, with activation of myogenin, suggesting profound alterations in transcriptional status of the electroporated muscle. Return to a normal transcriptional state was observed 7-10 days after electroporation. Therefore, we investigated whether a reporter construct placed under control of pM could exhibit fiber-specific expression 10 days after electrotransfer in either fast tibialis anterior or slow soleus muscle. We show that not only fiber specificity, but also nerve dependence, of a pM-driven construct can be reproduced. However, after electrotransfer, pM displayed a less tight control than previously observed for the same promoter when integrated in a chromatin context.

Characterization of multiple promoters in the human carboxylesterase 2 gene

Carboxylesterases are a broad class of enzymes important in the detoxification of many ester- or amide-bond containing xenobiotics. They also activate analgesics, anticancer prodrugs, and other biologically active compounds, such as cocaine and heroin. The objective of this work was to identify the CES2 gene structure, complex 5' untranslated regions and three potential promoters for the initiation of transcription in different human tissues. Using bioinformatics and progressive reverse transcriptase-polymerase chain reaction, we found that the 5' untranslated region is more than 1100 bases longer than previously reported. Rapid amplification of cDNA ends showed three distinctive transcription start sites at -74, -629 and -1187. DNA fragments upstream of each of the three transcription start sites were found to be transcriptionally active in HepG2 cells. The distal promoter is active in both orientations, suggesting its potential role in the transcription of another gene, CGI-128, located immediately upstream to the distal promoter in the opposite direction with respect to CES2. Hybridization analyses showed that CES2 is highly expressed in the heart, skeletal muscle, colon, spleen, kidney and liver, but considerably less expressed in fetal tissues (e.g. fetal heart, kidney, spleen, and liver) and cancer cells. It is also evident that the distal promoter is responsible for low level expression of the gene in many tissues, whereas the other two promoters are tissue specific. These findings shed some light on CES2 gene regulation, a gene important in the metabolism of many drugs.

Fiber-type specific and position-dependent expression of a transgene in limb muscles

We have previously shown that the proximal sequences of the human aldolase A fast-muscle-specific promoter (pM) are sufficient to target the expression of a linked CAT reporter gene to all fast, glycolytic trunk and limb muscles of transgenic mice (pM310CAT lines) in a manner mimicking the activity of the endogenous mouse promoter. When a NF1-binding site (motif M2) in this proximal regulatory region is mutated, the activity of the corresponding mM2 transgene is strongly affected but only in a some fast muscles. Here we show that the mutation of the M2 motif has only mild effects on pM activity in axial and proximal limb, while it drastically reduces this activity in both fore and hind limb distal muscles. At the cellular level, we show that both the pM310CAT and mM2 transgenes are highly expressed in fast glycolytic 2B fibers. However, by contrast to the pM310CAT transgene, whose expression is mainly restricted to fast glycolytic 2B fibers, the mM2 transgene is also active in a high proportion of 2X fibers. This result suggests that the M2 sequence could play a role in restricting the expression of pM to the 2B fibers. The variable expression of the mM2 transgene along the limb axis already exists at post-natal day 10 and seems to result from a change in the proportion of expressing fast fibers per muscle. Altogether, these results suggest that, although considered as phenotypically similar, different populations of fast glycolytic fibers exist, in which the requirement of the NF1 activity for pM expression varies according to the proximal versus distal position of the muscle along the limb axis.

Isolation and characterization of Xenopus laevis aldolase B cDNA and expression patterns of aldolase A, B and C genes in adult tissues, oocytes and embryos of Xenopus laevis

Following previous cloning and expression studies of Xenopus aldolase C (brain-type) and A (muscle-type) cDNAs, we cloned here two Xenopus aldolase B (liver-type) cDNAs (XALDB1 and XALDB2, 2447 and 1490 bp, respectively) using two different liver libraries. These cDNAs had very similar ORF with only one conservative amino acid substitution, but 3'-UTR of XALDB1 contained ca. 1 kb of unrelated reiterated sequence probably ligated during library construction as shown by genomic Southern blot analysis. In adult, aldolase B mRNA (ca. 1.8 kb) was expressed strongly in kidney, liver, stomach, intestine, moderately strongly in skin, and very weakly in all the other tissues including muscles and brain, which strongly express aldolase A and C mRNAs, respectively. In oocytes and early embryos, aldolase A and C mRNAs occurred abundantly as maternal mRNAs, but aldolase B mRNA occurred only at a residual level, and its strong expression started only after the late neurula stage, mainly in liver rudiment, pronephros, epidermis and proctodeum. Thus, active expression of the gene for aldolase B, involved in dietary fructose metabolism, starts only later during development (but before the feeding stage), albeit genes for aldolases A and C, involved in glycolysis, are expressed abundantly from early stages of embryogenesis, during which embryos develop depending on yolk as the only energy source.

The Na-G ion channel is transcribed from a single promoter controlled by distinct neuron- and Schwann cell-specific DNA elements

Na-G is a putative sodium (or cationic) channel expressed in neurons and glia of the PNS, in restricted neuronal subpopulations of the brain, and in several tissues outside the nervous system, like lung and adrenal medulla. To analyze the mechanisms underlying tissue-specific expression of this channel, we isolated the 5' region of the corresponding gene and show that Na-G mRNA transcription proceeds from a single promoter with multiple initiation sites. By transgenic mice studies, we demonstrate that 600 bp containing the Na-G proximal promoter region and the first exon are sufficient to drive the expression of a beta-galactosidase reporter gene in neurons of both CNS and PNS, whereas expression in Schwann cells depends on more remote DNA elements lying in the region between -6,500 and -1,050 bp upstream of the main transcription initiation sites. Crucial elements for lung-specific expression seem to be located in the region between -1,050 and -375 bp upstream of the promoter. Using in vivo footprint experiments, we demonstrate that several sites of the Na-G proximal promoter region are bound specifically by nuclear proteins in dorsal root ganglion neurons, as compared with nonexpressing hepatoma cells.

Developmental regulation of the aldolase A muscle-specific promoter during in vivo muscle maturation is controlled by a nuclear receptor binding element

During the post-natal period, skeletal muscles undergo important modifications leading to the appearance of different types of myofibers which exhibit distinct contractile and metabolic properties. This maturation process results from the activation of the expression of different sets of contractile proteins and metabolic enzymes, which are specific to the different types of myofibers. The muscle-specific promoter of the aldolase A gene (pM) is expressed mainly in fast-twitch glycolytic fibers in adult body muscles. We investigate here how pM is regulated during the post-natal development of different types of skeletal muscles (slow or fast-twitch muscles, head or body muscles). We show that pM is expressed preferentially in prospective fast-twitch muscles soon after birth; pM is up-regulated specifically in body muscles only later in development. This activation pattern is mimicked by a transgene which comprises only the 355 most proximal sequences of pM. Within this region, we identify a DNA element which is required for the up-regulation of the transgene during post-natal development in body muscles. Comparison of nuclear M1-binding proteins from young or adult body muscles show no qualitative differences. Distinct M1-binding proteins are present in both young and adult tongue nuclear extracts, compared to that present in gastrocnemius extracts.

Red blood cell enzymes and their clinical application

Red blood cell enzyme activities are measured mainly to diagnose hereditary nonspherocytic hemolytic anemia associated with enzyme anomalies. At least 15 enzyme anomalies associated with hereditary hemolytic anemia have been reported. Some nonhematologic disease can also be diagnosed by the measurement of red blood cell enzyme activities in the case in which enzymes of red blood cells and the other organs are under the same genetic control. Progress in molecular biology has provided a new perspective. Techniques such as the polymerase chain reaction and single-strand conformation polymorphism analysis have greatly facilitated the molecular analysis of erythroenzymopathies. These studies have clarified the correlation between the functional and structural abnormalities of the variant enzymes. In general, the mutations that induce an alteration of substrate binding site and/or enzyme instability might result in markedly altered enzyme properties and severe clinical symptoms.

Isolation and characterization of a novel promoter for the bovine growth hormone receptor gene

The use of alternative promoters represents an important mechanism for the regulation of growth hormone receptor (GHR) gene expression. Two promoters have been isolated previously for the GHR gene: the P1 promoter that drives liver-specific expression, and the P2 promoter that drives ubiquitous expression. In the present study, we isolated a third GHR promoter termed P3. The P3 promoter was GC-rich and TATA-less. The P3 promoter was able to drive the expression of a luciferase reporter gene in cell lines Hep G2, PLC/PRF/5, and BHK-21. In vivo, the P3 promoter initiated transcription from two major sites in exon 1C of the GHR gene in many tissues. In the adult bovine liver, the P3-transcribed GHR mRNA represented only 10% of the total GHR mRNA pool. In non-hepatic tissues such as kidney, skeletal muscle, mammary gland, and uterus, P3-transcribed GHR mRNA represented 30-40% of the total GHR mRNA pool. Within the bovine GHR gene, the P3 promoter was located immediately downstream from the P2 promoter. In transfected cells, the P2 promoter served as an enhancer for the P3 promoter. Existence and co-regulation of two ubiquitous promoters may be a mechanism for achieving a high level of expression of the GHR gene in multiple tissues.

Proximal sequences of the aldolase A fast muscle-specific promoter direct nerve- and activity-dependent expression in transgenic mice

Muscle activity is known to modulate the muscle fiber phenotype. Changes in muscle activity (normal or experimentally induced) lead to modifications of the expression status of several muscle-specific genes. However, the transcription regulatory elements involved in the adaptative response are mainly unknown. The aldolase A muscle-specific promoter, pM, is expressed in adult fast twitch muscle with a preferential expression in fast glycolytic-2B fibers. Its activity is induced during postnatal muscle maturation, suggesting a role of nerve and/or muscle activity. Indeed, denervation of gastrocnemius in newborn mice prevented the activation of the promoter in this muscle, despite the nerve-independent formation of 2B fibers. Although the nerve was necessary for pM onset during development, denervating the gastrocnemius in adults had only mild effects on pM activity. By contrast, a transgene including the pM proximal regulatory sequences that are sufficient to reproduce the 2B fiber-specific expression of the endogenous promoter was shown to be highly sensitive to both neonatal and adult denervation. Transgenes containing muscle-specific pM proximal promoter elements were used to delineate the regulatory elements involved in this response to innervation and changes in the contractile activity pattern. Nerve- and activity-dependent elements could be localized in the 130-base pair-long proximal promoter region of the human aldolase A gene.

Genomic sequences of aldolase C (Zebrin II) direct lacZ expression exclusively in non-neuronal cells of transgenic mice

Aldolase C is regarded as the brain-specific form of fructose-1, 6-bisphosphate aldolase whereas aldolase A is regarded as muscle-specific. In situ hybridization of mouse central nervous system using isozyme-specific probes revealed that aldolase A and C are expressed in complementary cell types. With the exception of cerebellar Purkinje cells, aldolase A mRNA is found in neurons; aldolase C message is detected in astrocytes, some cells of the pia mater, and Purkinje cells. We isolated aldolase C genomic clones that span the entire protein coding region from 1.5 kb 5' to the transcription start site to 0.5 kb 3' to the end of the last exon. The bacterial gene, lacZ, was inserted in two different locations and the constructs tested in transgenic mice. When the protein coding sequences were replaced with lacZ, three of five transgenic lines expressed beta-galactosidase only in cells of the pia mater; one line also expressed in astrocyte-like cells. When lacZ was inserted into the final exon (and all structural gene sequences were retained) transgene expression was observed in astrocytes in all regions of the central nervous system as well as in pial cells. Thus, with the exception of Purkinje cell expression, the behavior of the full-length transgene mimics the endogenous aldolase C gene. The results with the shorter transgene suggest that additional enhancer elements exist within the intragenic sequences. The absence of Purkinje cell staining suggests that the cis elements required for this expression must be located outside of the sequences used in this study.

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.

Negative regulation of the mouse aldolase A gene. A cell cycle-dependent DNA binding activity functions as a silencer of gene transcription

The expression of aldolase A L-type mRNA is increased in growth-arrested mouse NIH3T3 cells and remarkably down-regulated in actively proliferating cells. Treatment of proliferating cells with cycloheximide abolished the down-regulation of L-type mRNA expression, thus indicating that a protein factor acts as repressor in proliferating cells. Transient transfection experiments in NIH3T3 cells showed that a negative regulatory cis-element (NRE) is involved in the modulation of the transcriptional activity of the distal L promoter. The repressor, which is a protein of approximately 97 kDa, binds the murine aldolase A NRE, revealing a much more intense DNA-protein complex in proliferating NIH3T3 cells than in serum-deprived cells. Mutations in the negative regulatory cis-element showed that the GA-rich motif is required for protein binding and silencer function. We conclude that the expression of L-type mRNA is modulated by the interaction between a cell cycle-dependent DNA-binding protein and the murine aldolase A NRE.

Structure of aldolase A (muscle-type) cDNA and its regulated expression in oocytes, embryos and adult tissues of Xenopus laevis

We obtained cDNA (XALDA; 1466 bp) for Xenopus laevis aldolase A gene (muscle-type), whose amino acid sequence had 88% similarity to those of mammalian aldolase A genes. XALDA mRNA occurred abundantly in skeletal muscle and at low levels also in other adult tissues, and such mRNA distribution was reflected in zymograms. In oocytes XALDA mRNA occurred at a relatively high level from stage I, and the mRNA level peaked at stage II, then decreased in later stages. XALDA mRNA in the full-grown oocyte was inherited as maternal mRNA throughout maturation and fertilization until midblastula stage, but its level became very low during gastrula and early neurula stages, and then increased greatly in later stages. While maternal XALDA mRNA was distributed uniformly in early embryos, mRNA zygotically expressed after late neurula stage occurred mainly in somites. In blastula animal caps XALDA mRNA occurred at a low level, but the expression was greatly enhanced by activin treatment. Thus, in Xenopus laevis aldolase A gene is actively transcribed in earlier phase of oogenesis, inherited as maternal mRNA in early embryos in a cell-type nonspecific way, then in later phases of embryogenesis, it is strongly expressed in somites with its concomitant ubiquitous expression at low levels in almost all the other cell types.

Identification of the human aldolase A gene as the first induced target for the TR2 orphan receptor, a member of the steroid hormone receptor superfamily

The human TR2 orphan receptor (TR2) is a member of the steroid/thyroid hormone receptor superfamily that regulates the transcription of complex gene networks and subsequently controls diverse aspects of growth, development, and differentiation. In the present study, we have found that the TR2 is one of the M1 site (nucleotide numbers 2017-2034, 5'-AAAAGGGCAGGGGTCATT-3') binding proteins of the muscle-specific pM promoter in the human aldolase A gene. Electrophoretic mobility shift assay (EMSA) showed a specific binding with high affinity (dissociation constant = 4.6 nM) between the TR2 and the M1 element. Circular permutation assay revealed a localized DNA flexibility induced by the TR2 binding, and the bend angle was estimated to be 73 +/- 2 degrees. Furthermore, a dual-luciferase reporter gene assay demonstrated that the TR2 may enhance the expression of luciferase activities via the wild-type M1 site but not the mutant M1 element in human QM7 muscle myoblasts. In conclusion, our data represent the first case of demonstrating that the TR2 may serve as a transcriptional inducer in muscle-specific aldolase A gene expression.

Rapamycin inhibits aldolase A expression during human lymphocyte activation

Rapamycin (RAPA) strongly inhibits lymphocyte activation and proliferation, but does not affect most of the activation-related gene expression at the mRNA level. In order to understand the mechanism of action of RAPA and to gain further insights in lymphocyte signalling which is impaired by RAPA, we screened for RAPA-sensitive genes using differential hybridization. The expression of human aldolase A gene was found to be inducible during T and B cell activation, and the induction was repressed by RAPA at both the mRNA and enzymatic levels. The other two important immunosuppressants, cyclosporin A and FK506, also inhibited the mitogen-induced upregulation. However, none of these three drugs inhibited the constitutive expression. There was no fluctuation of aldolase A expression during the cell cycle, and RAPA failed to block the first cell cycle after synchronization in Jurkat cells. However, the second cycle was hampered by RAPA, and this was correlated with the inhibition of aldolase A expression during this later stage. Since aldolase A is a key enzyme in glycolysis and lymphocytes mainly depend on glycolysis for energy supply, the data from this study suggest that aldolase A might be one of the downstream targets of RAPA. The inhibition of the enzyme upregulation might deprive the cells of additional supply of energy, and prevent the cells from entering an optimal status for proliferation.

The human mineralocorticoid receptor gene promoter: its structure and expression

The structure and expression of a clone containing the promoter region, all of exon 1, and part of the first intron of the human mineralocorticoid receptor (hMR) gene is presented. The clone has three sets of CAAT and TATA elements, one located at the very 5'-end of the clone, one located just 5'- to the start of transcription, and one set located in intron A, approximately 300 bp into the intron. The major start of transcription site by primer extension analysis and ribonuclease protection assays is located 26 bp downstream of a TATA-like box (TTTAA) and 90 and 143 bp downstream, respectively, of two CCAAT boxes. Putative cis-transcription factor binding sites are as follows: two potential AP1 sites, one potential AP2 site, two ATF/CREB sites, six potential GC boxes or SP1 sites, one potential perfect half-palindromic estrogen response element, and three potential PEA3 sites. Therefore, the hMR promoter region contains elements characteristic of both regulated genes and "housekeeping" genes. CAT assays of overlapping deletions of the promoter region demonstrated tissue-specific regulation in human neuroepithelioma (SK-N-MC-IXC) and non-neuronal, peripheral choriocarcinoma cell lines (JEG-3).

Expression and regulation of the dystrophin Purkinje promoter in human skeletal muscle, heart, and brain

Dystrophin mRNA transcripts from the P (Purkinje) promoter were shown to be differentially expressed in human skeletal muscle, heart, and brain. The expression pattern was characteristic of tissue type and developmental stage. Polymerase chain reaction (PCR) analysis of the P promoter transcripts in adult skeletal muscle and adult brain identified two alternatively spliced sequences, one that encodes a full-length dystrophin mRNA and a second that transcribes a termination codon 27 nucleotides (8 amino acids) after the ATG initiation site. Alternative splicing of this truncated coding transcript was developmentally regulated, and it was expressed as the major form in adult cortical brain and adult heart. The biological significance of this peptide remains unclear. The full-length transcript was the major form in fetal cortical brain and adult skeletal muscle. Ribonuclease protection assay demonstrated that as much as 20% of dystrophin transcription in normal adult skeletal muscle was derived from the full-length transcript from the P promoter. In contrast, adult heart did not express significant levels of P promoter derived transcripts. Thus, transcripts from the P promoter were found to be developmentally regulated in the brain, and its activity was differentially expressed in skeletal versus cardiac muscle tissues. These data show that the P promoter transcript displays a broader scope of expression, regulation, and complexity than previously appreciated.

Fast-muscle-specific DNA-protein interactions occurring in vivo at the human aldolase A M promoter are necessary for correct promoter activity in transgenic mice

The human aldolase A tissue-specific M promoter (pM) has served as a model system for identifying pathways that lead to fast-muscle-specialized expression. The current study has delimited the sequences necessary and sufficient for fast-muscle-specific expression in transgenic mice to a short 209-bp fragment extending from bp -164 to +45 relative to the pM transcription start site. Genomic footprinting methods showed that in this proximal region, the same elements that bind muscle nuclear proteins in vitro are involved in DNA-protein interactions in intact muscle nuclei of transgenic mice. Furthermore, these experiments provided the first evidence that different DNA-binding activities exist between slow and fast muscles in vivo. Fast-muscle-specific interactions occur at an element named M1 and at a muscle-specific DNase I-hypersensitive site that was previously detected by in vitro methods. The formation of the muscle-specific DNase I-hypersensitive site reflects binding of proteins to a close element, named M2, which contains a binding site for nuclear factors of the NF1 family. Mutational analysis performed with transgenic mice confirmed the importance of the M1 element for high-level fast-muscle-specific pM activity and suggested that the M2/NF1 element is differently required for correct pM expression in distinct fast muscles. In addition, two other protein binding sites, the MEF3 motif and the USF site, seem to act as stage-specific activators and/or as participants in the establishment of an active chromatin configuration at pM.

NOR-2 (neuron-derived orphan receptor), a brain zinc finger protein, is highly induced during liver regeneration

Zinc-finger proteins are involved in several cellular processes. Some of these proteins are implicated in the primary cellular response in regenerating liver and mitogen-stimulated cells. Using a rat cDNA brain library, we have isolated a clone designated NOR-2, encoding a protein containing two zinc-finger motifs and whose expression is highly induced during G0/G1 transition. We analysed the expression of NOR-2 mRNAs during early growth in regenerating liver and in both insulin-stimulated H4-II cells and pheochromocytoma-derived cell line PC12 treated by NGF. In these systems, there is an early, rapid and transient accumulation of NOR-2 mRNAs. The induction of NOR-2 mRNAs does not require de novo protein synthesis, since it is not prevented by cycloheximide treatment. Mobility shift assays show that NOR-2 protein binds to NBRE, a target sequence for r-NGFI-B family. Structurally, NOR-2 is closely related to the recently identified NOR-1 factor. Therefore, like NOR-1, NOR-2 belongs to the r-NGFI-B sub-family of nuclear receptors superfamily.

The plastid aldolase gene from Chlamydomonas reinhardtii: intron/exon organization, evolution, and promoter structure

Genomic clones encoding the plastidic fructose-1,6-bisphosphate aldolase of Chlamydomonas reinhardtii were isolated and sequenced. The gene contains three introns which are located within the coding sequence for the mature protein. No introns are located within or near the sequence encoding the transit-peptide, in contrast to the genes for plastidic aldolases of higher plants. Neither the number nor the positions of the three introns of the C. reinhardtii aldolase gene are conserved in the plastidic or cytosolic aldolase genes of higher plants and animals. The 5' border sequences of introns in the aldolase gene of C. reinhardtii exhibit the conserved plant consensus sequence. The 3' acceptor splice sites for introns 1 and 3 show much less similarity to the eukaryotic consensus sequences than do those of intron 2. The plastidic aldolase gene has two tandemly repeated CAAT box motifs in the promoter region. Genomic Southern blots indicate that the gene is encoded by a single locus in the C. reinhardtii genome.

Characterization of the proximal promoter of the human histone H2A.Z gene

Histone H2A.Z is a distinct and evolutionarily conserved member of the histone H2A family whose synthesis, in contrast to that of most other histone species, is not dependent on DNA replication. The gene for H2A.Z lacks the signals involved in the 3' processing of replication-linked histone mRNA species and contains introns as well as polyadenylation signals. The H2A.Z gene proximal promoter, a 200-bp region upstream of the transcription start site that provides maximal activity in CAT reporter studies, contains three CCAAT and two GGGCGG elements as well as a consensus TATA element. In vitro DNase I footprint analysis of this region indicated that the central CCAAT and the distal GGGCGG elements were protected by factors present in HeLa nuclear extract. Site-directed mutations of selected promoter elements were generated in the H2A.Z gene promoter region of a CAT reporter construct by a novel one-step PCR procedure. Of the elements examined, the central CCAAT element was found to be the most important determinant of promoter activity; its disruption decreased CAT reporter activity by 65%. Disruption of the proximal CCAAT or the distal GGGCGG elements led to decreases in activity of 40%, while disruption of any of the other examined led to smaller decreases. Gel-mobility shift analysis showed that the three CCAAT elements had overlapping but not identical binding specificities for nuclear factors. The two GGGCGG elements both were found to bind transcription factor Sp1, but the distal element bound Sp1 with higher affinity. The findings show that the central and proximal CCAAT elements and the distal GGGCGG element appear to be the major determinants of the transcriptional activity of the H2A.Z gene.

Noncoordinate changes in the steady-state mRNA expressed from aldolase A and aldolase C genes during differentiation of chicken myoblasts

In chickens, as in all vertebrates, tissue-specific expression of aldolase isozymes A, B, and C is developmentally coordinated. These developmental transitions in aldolase expression have been studied most extensively by charting enzyme activity during normal and abnormal development of specific vertebrate tissues. Indeed, aldolase expression has been a key marker for normal differentiation and for retrodifferentiation during carcinogenesis. Aldolase expression during chicken myoblast differentiation offers a model for investigating the regulatory mechanisms of these developmental transitions at the level of gene expression. For these studies, cDNAs encoding the most isozyme-specific regions of both chicken aldolase A and C were cloned. The chicken aldolase A cDNA represents the first report of this sequence. Aldolase steady-state mRNA expression was measured during chicken myoblast differentiation in primary cultures using RNase protection assays with cRNA probes generated from these aldolase cDNA clones. Steady-state mRNA for aldolase C, the predominant embryonic aldolase isozyme in chickens, did not significantly change throughout myoblast differentiation. In contrast, expression of steady-state mRNA for aldolase A, the only aldolase isozyme found in adult-skeletal muscle, was not detected until after myoblast fusion was approximately 50% completed. Aldolase A expression gradually increased throughout myoblast differentiation until approximately 48 h after fusion was completed when there was a dramatic increase. These results are contrasted with those of Turner et al. (1974) [Dev Biol 37:63-89] that showed a coordinated switch in isozyme activities between the embryonic aldolase C and the muscle-specific aldolase A. This discordant expression indicates that the aldolase A and C genes may employ different regulatory mechanisms during myoblast differentiation.

Fast-muscle-specific expression of human aldolase A transgenes

The expression of the human aldolase A gene is controlled by three alternative promoters. In transgenic mice, pN and pH are active in all tissues whereas pM is activated specifically in adult muscles composed mainly of fast, glycolytic fibers. To detect potential regulatory regions involved in the fast-muscle-specific activation of pM, we analyzed DNase I hypersensitivity in a 4.3-kbp fragment from the 5' end of the human aldolase A gene. Five hypersensitive sites were located near the transcription initiation site of each promoter in those transgenic-mouse tissues in which the corresponding promoter was active. Only one muscle-specific hypersensitive site was detected, mapping near pM. To functionally delimit the elements required for muscle-specific activity of pM, we performed a deletion analysis of the aldolase A 5' region in transgenic mice. Our results show that a 280-bp fragment containing 235 bp of pM proximal upstream sequences together with the noncoding M exon is sufficient for tissue-specific expression of pM. When a putative MEF-2-binding site residing in this proximal pM region is mutated, pM is still active and no change in its tissue specificity is detected. Furthermore, we observed a modulation of pM activity by elements lying further upstream and downstream from pM. Interestingly, pM was expressed in a tissue-specific way in all transgenic mice in which the 280-bp region was present (32 lines and six founder animals). This observation led us to suggest that the proximal pM region contains elements that are able to override to some extent the effects of the surrounding chromatin.

Fast-muscle-specific expression of human aldolase A transgenes

The expression of the human aldolase A gene is controlled by three alternative promoters. In transgenic mice, pN and pH are active in all tissues whereas pM is activated specifically in adult muscles composed mainly of fast, glycolytic fibers. To detect potential regulatory regions involved in the fast-muscle-specific activation of pM, we analyzed DNase I hypersensitivity in a 4.3-kbp fragment from the 5' end of the human aldolase A gene. Five hypersensitive sites were located near the transcription initiation site of each promoter in those transgenic-mouse tissues in which the corresponding promoter was active. Only one muscle-specific hypersensitive site was detected, mapping near pM. To functionally delimit the elements required for muscle-specific activity of pM, we performed a deletion analysis of the aldolase A 5' region in transgenic mice. Our results show that a 280-bp fragment containing 235 bp of pM proximal upstream sequences together with the noncoding M exon is sufficient for tissue-specific expression of pM. When a putative MEF-2-binding site residing in this proximal pM region is mutated, pM is still active and no change in its tissue specificity is detected. Furthermore, we observed a modulation of pM activity by elements lying further upstream and downstream from pM. Interestingly, pM was expressed in a tissue-specific way in all transgenic mice in which the 280-bp region was present (32 lines and six founder animals). This observation led us to suggest that the proximal pM region contains elements that are able to override to some extent the effects of the surrounding chromatin.

Identification of a novel first exon in the human dystrophin gene and of a new promoter located more than 500 kb upstream of the nearest known promoter

The dystrophin gene, which is mutated in patients with Duchenne and Becker muscular dystrophies, is the largest known human gene. Five alternative promoters have been characterized until now. Here we show that a novel dystrophin isoform with a different first exon can be produced through transcription initiation at a previously unidentified alternative promoter. The case study presented is that of a patient with Duchenne muscular dystrophy who had a deletion extending from the 5' end of the dystrophin gene to exon 2, including all promoters previously mapped in the 5' part of the gene. Transcripts from lymphoblastoid cells were found to contain sequences corresponding to exon 3, indicating the presence of new promoter upstream of this exon. The nucleotide sequence of amplified cDNA corresponding to the 5' end of the new transcript indicated that the 5' end of exon 3 was extended by 9 codons, only the last (most 3') of which codes for methionine. The genomic nucleotide sequence upstream from the new exon, as determined using inverse polymerase chain reaction, revealed the presence of sequences similar to a TATA box, an octamer motif and an MEF-2 element. The identified promoter/exon did not map to intron 2, as might have been expected, but to a position more than 500 kb upstream of the most 5' of the previously identified promoters, thereby adding 500 kb to the dystrophin gene. The sequence of part of the new promoter region is very similar to that of certain medium reiteration frequency repetitive sequences. These findings may help us understand the molecular evolution of the dystrophin gene.

Cloning of a brain-type aldolase cDNA and changes in its mRNA level during oogenesis and early embryogenesis in Xenopus laevis

A full length cDNA clone (cXALD3) for Xenopus laevis aldolase mRNA, which exists abundantly in oocytes, was isolated from Xenopus laevis ovary cDNA library, and its nucleotide sequence was determined. The cDNA was 1.8 kb in length and encoded 363 amino acids. From the deduced amino acid sequence and the Northern blot analysis of the RNAs from several adult tissues, this clone was concluded to be a brain-type aldolase gene. The XALD3 mRNA level per egg or embryo was high during early oogenesis, but was markedly reduced during late oogenesis and was maintained at low level during early embryogenesis until it started to increase at the late neurula stage. The mRNA was also detected in testis. The characteristic change in the temporal pattern of expression and the distribution of XALD3 mRNA among different tissues suggest a possibility that brain type aldolase may play some important roles in gametogenesis and in neurulation.

Cis-acting elements in the promoter region of the human aldolase C gene

We investigated the cis-acting sequences involved in the expression of the human aldolase C gene by transient transfections into human neuroblastoma cells (SKNBE). We demonstrate that 420 bp of the 5'-flanking DNA direct at high efficiency the transcription of the CAT reporter gene. A deletion between -420 bp and -164 bp causes a 60% decrease of CAT activity. Gel shift and DNase I footprinting analyses revealed four protected elements: A, B, C and D. Competition analyses indicate that Sp1 or factors sharing a similar sequence specificity bind to elements A and B, but not to elements C and D. Sequence analysis shows a half palindromic ERE motif (GGTCA), in elements B and D. Region D binds a transactivating factor which appears also essential to stabilize the initiation complex.

Six mRNAs with different 5' ends are encoded by a single gamma-glutamyltransferase gene in mouse

The 5' region of the mouse gamma-glutamyltransferase (gamma GT; EC 2.3.2.2) gene has been cloned and analyzed. This analysis, combined with sequence information obtained from gamma GT cDNA clones, indicates that in mouse a single gamma GT gene codes for six different mRNAs that differ in their 5' sequences. Analysis of steady-state levels of gamma GT RNA reveals different expression patterns for these RNAs in different organs. The six different 5' sequences are widely separated within a 10-kb region and three of them show 75-86% identify with the three known rat gamma GT cDNAs. Although the heterogeneity of the 5' ends of gamma GT RNAs may be explained in part by alternative splicing, it is likely that multiple promoters are involved in their generation.

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.

Autonomous activity of the alternate aldolase A muscle promoter is maintained by a sequestering mechanism

The mouse aldolase A gene contains two closely-spaced alternate promoter/first exons. The more distal of the two, the M promoter, is muscle-specific while the 3' promoter, the H promoter, is expressed constitutively. Various segments from these promoter regions were linked to a reporter gene and used to transfect the myogenic cell line C2C12 and the hepatoma cell line BWTG3. A muscle-specific enhancer, MEN1, responsible for 80% of promoter M activity and containing 4 consensus MyoD binding sites was localized between -2578 to -2723 of the M promoter. Another muscle-specific enhancer and a restrictive element, MEN2/MSE, were found in the interval -1100 to -350. The MSE restrictive element was found to prohibit inappropriate up-regulation of the M promoter by selectively sequestering it from H promoter elements in both myoblasts and myotubes. Among the H promoter elements was found an enhancer, HEN, situated between -533 and -200 which did not function in myotubes. These studies also show that H promoter elements can act synergistically with a non-specific element, MAE, located between -350 and -130 of the M cap site greatly stimulating M promoter transcription in all cell types when the MSE restrictive element was absent. Through the analysis of interactions between these elements and the aldolase A and HSV-TK promoters we showed that neither the enhancers nor the promoter proximal sequences by themselves contain adequate information to reproduce the native pattern of aldolase A promoter modulation. Rather, the sequestering of the M promoter by the MSE restrictive element and the relative positioning and context of promoters M and H appear critical to the regulated expression of aldolase A.

The proximal promoter of the aldolase A gene remains active during myogenesis in vitro and muscle development in vivo

The gene for aldolase A in mouse has been shown to be regulated by alternative promoters with attendant alternative first exons. The distal promoter/exon M functions only in muscle while the proximal promoter/exon H is active in early muscle development and in most other tissues. We have analyzed the developmental expression of M and H promoters in mouse throughout myogenesis both in vitro and in vivo. In C2C12 cells RNase protection assays revealed the M promoter is induced within 24 hr of the onset of myogenic differentiation, and both M- and H-specific mRNAs accumulate over 5 days in culture. Nuclear run-on transcription and in situ hybridization with an exon-specific probe demonstrate that the H promoter remains transcriptionally active even in differentiated myotubes. The in vitro results were then compared to similar RNase protection studies of M and H expression during muscle development in vivo. These data show a marked similarity between promoter activation and steady-state transcript accumulation in vivo and in vitro, but within a limited developmental time frame (E15 to 1 week postnatal). In situ hybridizations suggest that simultaneous transcription from both promoters may also occur early in muscle development. Furthermore, the M promoter shows no fiber-type restriction until 1 to 3 weeks postnatally, coincident with muscle maturation, while the H promoter remains transcriptionally active at all stages of development and in all fiber types.

Tissue-specific expression of multiple gamma-glutamyl transpeptidase mRNAs in rat epithelia

gamma-Glutamyl transpeptidase (GGT) is an enzyme that plays a key role in interorgan glutathione transport. Three mRNAs (mRNAI, mRNAII, and mRNAIII) are known to encode the GGT precursor; they are initiated on three separate promoters on the single GGT gene. In this work, we identified by Northern blot and RNase H analysis a new GGT mRNA (mRNAIV). This mRNA differs from the others in its 5'-noncoding sequence. This mRNA species is the predominant GGT mRNA expressed in HTC hepatoma cells and in the small intestine in which its level increases from the base to the apex of the microvillus. The analysis of the GGT gene expression pattern in kidney, mammary gland, small intestine, liver, preneoplastic liver, and HTC hepatoma cells reveals a strong tissue or cell specificity. The mRNAIII was found in all the tissues and cells; in contrast, the expression of mRNAI, mRNAII, and mRNAIV is limited in normal tissues to the kidney and to the small intestine, the two tissues that display the highest enzyme activity. The synthesis of these three mRNAs is linked to the development of the kidney proximal tubule and to the differentiation of the enterocyte. The tissue and cell specificity of the GGT gene expression is based upon the use of multiple promoters that are controlled independently by specific cell factors.

A ubiquitous enhancer shared by two promoters in the human aldolase A gene

The human aldolase A gene is transcribed from three different promoters, which are all clustered within a 1.6 kbp DNA domain. Two of these, PN and PH, are ubiquitous and seem to be co-regulated in most tissues while the third one, PM, is specific to adult skeletal muscle. We investigated the sequences involved in the ubiquitous activity of the PN and PH promoters of the human aldolase A gene. Deletion analysis, performed by transient expression assays of chloramphenicol acetyltransferase reporter genes in human HepG2 hepatoma cells, indicated that PH activity results from the interaction of an upstream activating region with two distinct core promoters. The upstream activating region was able to stimulate transcription from the HSV tk promoter as efficiently as the SV40 enhancer in all cell types tested. It appears, therefore, to be a strong ubiquitous enhancer. DNAsel footprinting revealed protections covering sequences scattered along the enhancer, including Sp1 and AP1 motifs. Importantly, we found that this enhancer was also necessary to activity of the other ubiquitous promoter of the aldolase A gene, PN. These studies demonstrate that expression of the human aldolase A gene is mediated by a complex interplay of enhancer and promoter elements.

Temporal regulation of viral and cellular gene expression during human T-lymphotropic virus type I-mediated lymphocyte immortalization

An autocrine mechanism of proliferation may play a significant role in the leukemogenesis of adult T-cell leukemia, a mature T-cell malignancy caused by human T-lymphotropic virus type I (HTLV-I). To further delineate the role of HTLV-I and the interleukin 2 (IL2) system in the transformation process, human primary lymphocytes were infected by cocultivation with lethally X-irradiated MT2 cells in the presence or absence of human rIL2; the polymerase chain amplification reaction was used to examine quantitatively the expression of HTLV-I, IL2, and IL2R alpha mRNAs during early and late proliferation phases that displayed polyclonal (days 7 to 49) and oligoclonal (days 100 to 150) proviral integration, respectively. IL2 mRNA and IL2 activity were transiently expressed during the polyclonal phase but were undetectable at later time points. IL2R alpha mRNA expression remained at a constitutively high level throughout the examined time course. Viral transcripts were detectable at each time point. Expression of the tax-rex mRNA was inversely related to IL2 mRNA levels; it was low early in the polyclonal phase but increased 30-fold with the development of oligoclonality. In addition, paraformaldehyde-fixed HTLV-I-producing cells activated peripheral blood lymphocytes. These data suggest that HTLV-I activates human T lymphocytes. However, IL2 expression is transient, indicating a limited involvement of an IL2 autocrine growth loop in the transformation process. Lastly, another viral determinant, in addition to the trans activator tax, may be important in HTLV-I-induced T-cell proliferation.

Expression of the rat aldolase B gene: a liver-specific proximal promoter and an intronic activator

The nature and location of the cis-acting DNA sequences regulating expression of the rat aldolase B gene has been investigated. Two liver-specific DNAse I hypersensitive sites were detected, one located just upstream from the cap site, the second in the middle of the first, 4.8-kbp-long, intron. A fragment of 190 bp 5' to the cap site behaved as a tissue-specific but weak core promoter: it directed a detectable reporter gene expression in the Hep G2 cells and hepatocytes, but not in fibroblasts. The tissue-specific expression was stimulated at least 16 fold when constructs contained the entire first intron. The intronic activating sequences could be ascribed to an inner 2 kbp fragment in which the downstream liver-specific DNAse I hypersensitive site was located.

Regulation of the multiple promoters of the human aldolase A gene: response of its two ubiquitous promoters to agents promoting cell proliferation

The human aldolase A gene is transcribed from three distinct promoters, the two ubiquitous promoters PN and PH and the muscle specific promoter PM. In the present study, we investigate further aldolase A mRNA structure and expression. We demonstrate that the upstream N-type exon is, in fact, extremely heterogeneous. RNAse H mapping experiments permit quantification of relative abundance of N, M, and H type mRNAs and show that the level of transcripts containing the downstream H-type exon is at least 30 times higher than that of those containing N exon, in all tissues tested. Aldolase A level is up-regulated in proliferating cells. Here we show that both N and H type mRNAs, although barely detectable in normal liver, are highly expressed in human hepatomas biopsies. Furthermore, in human lymphocytes, N-type mRNA level is enhanced by serum treatment, while in cultured Hep G2 cells, both N-type and H-type mRNA levels are increased by serum and by the tumor promoting agent PMA. Using CAT constructs in transfection experiments, we demonstrate that the H exon plus its upstream region can function autonomously: the 420 base pairs upstream of the H exon are sufficient to confer to promoter PH an efficiency comparable that of the complete SV40 early promoter and enhancer in two cell lines.

An additional promoter functions in the human aldolase A gene, but not in rat

The aldolase A gene was isolated from a human DNA library, mapped and sequenced. This gene comprises 12 exons and spans 6.5 kb. From the genomic DNA sequence and from the previous sequence analysis of the cDNA, it was revealed that the first exon L1 and the second exon encode the 5' non-coding sequence of mRNA L1, while the third and forth exons (corresponding to exons M and L2) encode different mRNA, mRNA M and L2, respectively; the following eight exons (exons 5-12) are shared commonly by all the mRNA species. These results indicate that the mRNA species are generated from a single aldolase A gene from one of exons L1, M or L2, in addition to exons 5-12, and also that the usage of a leader exon is similar but clearly distinct from that of rat aldolase A gene which we analyzed [Joh, K., Arai, Y., Mukai, T. & Hori, K. (1986) J. Mol. Biol. 190, 401-410]. By comparing the promoter regions in the human and rat aldolase A genes, we found similar sequences in the rat genome corresponding to those of the human L1, M and L2 promoter. We could not, however, detect any transcripts starting from sequences corresponding to the human L1 promoter in the rat genome, although the products corresponding to human M and L2 were detected. Thus, we conclude that the L1 promoter was either acquired by the human genome or deleted from the rat genome after human and rat diverged during evolution.

Tissue specificity in expression and alternative RNA splicing of human phosphofructokinase-M and -L genes

Mode of the expression of phosphofructokinase (PFK) -M and -L genes was examined in various human tissues including muscle, placenta, liver, kidney, pancreas, stomach and reticulocytes. The gross level of mRNA expression of PFK-M and -L genes was estimated by Northern analysis. Polymerase chain reaction was used to detect mRNA expressed at low levels in these tissues. Tissue-specific expression of alternatively spliced PFK-M gene transcripts was also determined by polymerase chain reaction. The results indicated that alternative splicing of PFK-M gene transcripts was controlled in a tissue-specific manner.

Recent progress in the molecular genetic analysis of erythroenzymopathy

During the relatively recent period in which normal genes for most red cell enzymes have been isolated, the techniques of molecular biology have been applied to the studies of erythroenzymopathy. Single nucleotide substitutions have been identified in aldolase, triosephosphate isomerase, glucose 6-phosphate dehydrogenase, and adenylate kinase variants by the cloning and nucleotide sequence of the patients' genes. Up to now, all of the enzyme-deficient variants which have been investigated have been caused by point mutations. An exception is a hemolytic anemia secondary to increased adenosine deaminase (ADA) activity. Red cell ADA activity increases on the order of a hundred-fold in affected individuals. The basic abnormality appears to result from overproduction of structurally normal enzyme due to abnormal transcriptional or translational efficiency.

Quantitative estimation of minor mRNAs by cDNA-polymerase chain reaction. Application to dystrophin mRNA in cultured myogenic and brain cells

Amplification of the mRNA polymerase chain reaction is a very sensitive technique to detect low-abundance transcripts. We describe in this paper conditions necessary to make this technique quantitative. Quantification is performed in the exponential phase of the amplification process and the results are standardized with respect to those obtained with an exogenous mRNA which is co-reverse-transcribed and co-amplified in the same reaction as the analyzed transcripts. The primers are chosen in different exons to distinguish the amplification of mRNA fragments from the amplification of contaminating DNA. Analysis of the kinetics of amplification and parameters influencing this kinetics shows that: (a) in the exponential phase of amplification, the amount of amplified fragments is proportional to the initial amount of transcripts; (b) in a certain range of length fragment, the yield of amplification is inversely proportional to the length of the amplified fragments. Using this method we have demonstrated that the dystrophin gene is already activated at the myoblastic stage. A quantitative estimation of the transcript showed that the expression of this gene increases strongly in the course of in vitro myogenesis. In primary culture of mouse brain cells, the dystrophin gene was found to be more expressed in neuronal than in glial cells.