Regulation of intestine-specific spatiotemporal expression by the rat lactase promoter

Pilot study of correlation of selected genetic factors with cribra orbitalia in individuals from a medieval population from Slovakia

OBJECTIVE

The aim of this study is to investigate the potential genetic etiology of cribra orbitalia noted on human skeletal remains.

MATERIALS

We obtained and analyzed ancient DNA of 43 individuals with cribra orbitalia. The analyzed set represented medieval individuals from two cemeteries in western Slovakia, Castle Devín (11th-12th century AD) and Cífer-Pác (8th-9th century AD).

METHODS

We performed a sequence analysis of 5 variants in 3 genes associated with anemia (HBB, G6PD, PKLR), which are the most common pathogenic variants in present day of European populations, and one variant MCM6:c.1917 + 326 C>T (rs4988235) associated with lactose intolerance.

RESULTS

DNA variants associated with anemia were not found in the samples. The allele frequency of MCM6:c.1917 + 326 C was 0.875. This frequency is higher but not statistically significant in individuals displaying cribra orbitalia compared to individuals without the lesion.

SIGNIFICANCE

This study seeks to expand our knowledge of the etiology of cribra orbitalia by exploring the potential association between the lesion and the presence of alleles linked to hereditary anemias and lactose intolerance.

LIMITATIONS

A relatively small set of individuals were analyzed, so an unequivocal conclusion cannot be drawn. Hence, although it is unlikely, a genetic form of anemia caused by rare variants cannot be ruled out.

SUGGESTIONS FOR FURTHER RESEARCH

Genetic research based on larger sample sizes and in more diverse geographical regions.

Genetics of Lactose Intolerance: An Updated Review and Online Interactive World Maps of Phenotype and Genotype Frequencies

In humans the ability to digest milk lactose is conferred by a β-galactosidase enzyme called lactase-phlorizin hydrolase (LPH). While in some humans (approximately two-thirds of humankind) the levels of this enzyme decline drastically after the weaning phase (a trait known as lactase non-persistence (LNP)), some other individuals are capable of maintaining high levels of LPH lifelong (lactase persistence (LP)), thus being able to digest milk during adulthood. Both lactase phenotypes in humans present a complex genetic basis and have been widely investigated during the last decades. The distribution of lactase phenotypes and their associated single nucleotide polymorphisms (SNPs) across human populations has also been extensively studied, though not recently reviewed. All available information has always been presented in the form of static world maps or large dimension tables, so that it would benefit from the newly available visualization tools, such as interactive world maps. Taking all this into consideration, the aims of the present review were: (1) to gather and summarize all available information on LNP and LP genetic mechanisms and evolutionary adaptation theories, and (2) to create online interactive world maps, including all LP phenotype and genotype frequency data reported to date. As a result, we have created two online interactive resources, which constitute an upgrade over previously published static world maps, and allow users a personalized data exploration, while at the same time accessing complete reports by population or ethnicity.

Mouse fetal intestinal organoids: new model to study epithelial maturation from suckling to weaning

During the suckling-to-weaning transition, the intestinal epithelium matures, allowing digestion of solid food. Transplantation experiments with rodent fetal epithelium into subcutaneous tissue of adult animals suggest that this transition is intrinsically programmed and occurs in the absence of dietary or hormonal signals. Here, we show that organoids derived from mouse primary fetal intestinal epithelial cells express markers of late fetal and neonatal development. In a stable culture medium, these fetal epithelium-derived organoids lose all markers of neonatal epithelium and start expressing hallmarks of adult epithelium in a time frame that mirrors epithelial maturation in vivo In vitro postnatal development of the fetal-derived organoids accelerates by dexamethasone, a drug used to accelerate intestinal maturation in vivo Together, our data show that organoids derived from fetal epithelium undergo suckling-to-weaning transition, that the speed of maturation can be modulated, and that fetal organoids can be used to model the molecular mechanisms of postnatal epithelial maturation.

Single-nucleotide polymorphisms and activity analysis of the promoter and enhancer of the pig lactase gene

Lactose intolerance in northern Europeans is strongly associated with a single-nucleotide polymorphism (SNP) located 14 kb upstream of the human lactase gene: -13,910 C/T. We examined whether SNPs in the 5' flanking region of the pig lactase gene are similar to those in the human gene and whether these polymorphisms play a functional role in regulating pig lactase gene expression. The 5' flanking region of the lactase gene from several different breeds of pigs was cloned and analyzed for gene regulatory activity of a luciferase reporter gene. One SNP was found in the enhancer region (-797 G/A) and two were found in the promoter region (-308G/C and -301 A/G). The promoter C-308,G-301(Pro-CG) strongly promotes the expression of the lactase gene, but the promoter G-308,A-301(Pro-GA) does not. The enhancer A-797(Enh-A) genotype for Pro-GA can significantly enhance promoter activity, but has an inhibitory effect on Pro-CG. The Enhancer G-797(Enh-G) has a significant inhibitory effect on both promoters. In conclusion, the order of effectiveness on the pig lactase gene is Enh-A+Pro-GA>Enh-A/G+Pro-CG>Enh-G+Pro-GA.

Nutrition, population growth and disease: a short history of lactose

Food and nutrition have played a crucial role in biological evolution. Lactation in mammals was one key invention. A central role in milk is played by lactose, otherwise an exotic sugar in nature. Lactose digestion needs the induction of specialized gut enzymes. This enzyme is shut off in a precisely timed developmental step leading to lactose malabsorption promoting weaning in the young and ovulation in the mother. The lactose-lactase system could thus regulate optimal birth spacing in land mammals. The domestication of cattle promoted milk as a food item also for adult nutrition. This was only possible by two further key inventions: the concomitant domestication of lactic acid bacteria which ferment the non-digestible lactose to the easily absorbed lactic acid and the mutation to lactase persistence (LP) in adults from dairy societies. This mutation represents one of the strongest selected loci of the human genome. Since no crucial nutritional selective advantage is conferred by LP, its dominance might be the result of indirect effects like the spread of cattle pathogens into humans. Lactase is also temporarily lost in rotavirus and Escherichia coli childhood diarrhoea and persistent diarrhoea is consequently best treated with lactose-free diets.

The human lactase persistence-associated SNP -13910*T enables in vivo functional persistence of lactase promoter-reporter transgene expression

Lactase is the intestinal enzyme responsible for digestion of the milk sugar lactose. Lactase gene expression declines dramatically upon weaning in mammals and during early childhood in humans (lactase nonpersistence). In various ethnic groups, however, lactase persists in high levels throughout adulthood (lactase persistence). Genetic association studies have identified that lactase persistence in northern Europeans is strongly associated with a single nucleotide polymorphism (SNP) located 14 kb upstream of the lactase gene: -13910*C/T. To determine whether the -13910*T SNP can function in vivo to mediate lactase persistence, we generated transgenic mice harboring human DNA fragments with the -13910*T SNP or the ancestral -13910*C SNP cloned upstream of a 2-kb rat lactase gene promoter in a luciferase reporter construct. We previously reported that the 2-kb rat lactase promoter directs a post-weaning decline of luciferase transgene expression similar to that of the endogenous lactase gene. In the present study, the post-weaning decline directed by the rat lactase promoter is impeded by addition of the -13910*T SNP human DNA fragment, but not by addition of the -13910*C ancestral SNP fragment. Persistence of transgene expression associated with the -13910*T SNP represents the first in vivo data in support of a functional role for the -13910*T SNP in mediating the human lactase persistence phenotype.

Characterization of expression in mice of a transgene containing 3.3 kb of the human lactase-phlorizin hydrolase (LPH) 5' flanking sequence

BACKGROUND AND AIM

The regulation of human intestinal lactase-phlorizin hydrolase remains incompletely understood. One kb of pig and 2 kb of rat 5'-flanking sequence controls correct tissue, cell, topographic, and villus LCT expression. To gain insight into human LCT expression, transgenic mouse lines were generated from 3.3 kb of human LPH 5' flanking sequence from a lactase persistent individual fused to a human growth hormone (hGH) reporter bounded by an insulator.

METHODS

Four lines were identified in which reporter expression was specifically detectable in the intestine and no other organ, two of which demonstrated hGH expression specific to small and large intestine. Quantitative RT-PCR was carried out on proximal to distal segments of small intestine at fetal days 16.5 and 18.5 and at birth, postnatal days 7 and 28 in line 22.

RESULTS

In fetal intestine, hGH expression demonstrated a proximal to distal gradient similar to that in native intestine. There was no significant difference between hGH expression levels at 7 and 28 days in segment 3, the midpoint of the small intestine, where expression of endogenous lactase is maximal at 7 days and declines significantly by 28 days. Distal small intestine displayed high levels of hGH expression in enteroendocrine cells, which were shown to be a subset of the PYY cells.

CONCLUSIONS

Thus, a 3.3-kb LPH 5' flanking sequence construct from a lactase persistent individual is able to maintain postnatal expression in transgenic mice post weaning.

Pdx1 inactivation restricted to the intestinal epithelium in mice alters duodenal gene expression in enterocytes and enteroendocrine cells

Null mutant mice lacking the transcription factor pancreatic and duodenal homeobox 1 (Pdx1) are apancreatic and survive only a few days after birth. The role of Pdx1 in regulating intestinal gene expression has therefore yet to be determined in viable mice with normal pancreatic development. We hypothesized that conditional inactivation of Pdx1 restricted to the intestinal epithelium would alter intestinal gene expression and cell differentiation. Pdx1(flox/flox);VilCre mice with intestine-specific Pdx1 inactivation were generated by crossing a transgenic mouse strain expressing Cre recombinase, driven by a mouse villin 1 gene promoter fragment, with a mutant mouse strain homozygous for loxP site-flanked Pdx1. Pdx1 protein is undetectable in all epithelial cells in the intestinal epithelium of Pdx1(flox/flox);VilCre mice. Goblet cell number and mRNA abundance for mucin 3 and mucin 13 genes in the proximal small intestine are comparable between Pdx1(flox/flox);VilCre and control mice. Similarly, Paneth cell number and expression of Paneth cell-related genes Defa1, Defcr-rs1, and Mmp7 in the proximal small intestine remain statistically unchanged by Pdx1 inactivation. Although the number of enteroendocrine cells expressing chromogranin A/B, gastric inhibitory polypeptide (Gip), or somatostatin (Sst) is unaffected in the Pdx1(flox/flox);VilCre mice, mRNA abundance for Gip and Sst is significantly reduced in the proximal small intestine. Conditional Pdx1 inactivation attenuates intestinal alkaline phosphatase (IAP) activity in the duodenal epithelium, consistent with an average 91% decrease in expression of the mouse enterocyte IAP gene, alkaline phosphatase 3 (a novel Pdx1 target candidate), in the proximal small intestine following Pdx1 inactivation. We conclude that Pdx1 is necessary for patterning appropriate gene expression in enterocytes and enteroendocrine cells of the proximal small intestine.

Lactose digestion and the evolutionary genetics of lactase persistence

It has been known for some 40 years that lactase production persists into adult life in some people but not in others. However, the mechanism and evolutionary significance of this variation have proved more elusive, and continue to excite the interest of investigators from different disciplines. This genetically determined trait differs in frequency worldwide and is due to cis-acting polymorphism of regulation of lactase gene expression. A single nucleotide polymorphism located 13.9 kb upstream from the lactase gene (C-13910 > T) was proposed to be the cause, and the -13910*T allele, which is widespread in Europe was found to be located on a very extended haplotype of 500 kb or more. The long region of haplotype conservation reflects a recent origin, and this, together with high frequencies, is evidence of positive selection, but also means that -13910*T might be an associated marker, rather than being causal of lactase persistence itself. Doubt about function was increased when it was shown that the original SNP did not account for lactase persistence in most African populations. However, the recent discovery that there are several other SNPs associated with lactase persistence in close proximity (within 100 bp), and that they all reside in a piece of sequence that has enhancer function in vitro, does suggest that they may each be functional, and their occurrence on different haplotype backgrounds shows that several independent mutations led to lactase persistence. Here we provide access to a database of worldwide distributions of lactase persistence and of the C-13910*T allele, as well as reviewing lactase molecular and population genetics and the role of selection in determining present day distributions of the lactase persistence phenotype.

Lactose and lactase--who is lactose intolerant and why?

Lactase-phlorizin hydrolase (LPH) is expressed only in the small intestine and is confined to absorptive enterocytes on the villi with a tightly controlled pattern of expression along the proximal to distal and crypt-villus axes of the intestine. LPH expression is regulated mainly at the level of lactase (LCT) gene transcription that directs 2 phenotypes: a decline in LCT activity (LCT nonpersistence) in mid-childhood in the majority of the world's population, and maintenance of the lactase levels found in infancy (LCT persistence) in people of northern European extraction and scattered populations elsewhere. The molecular mechanisms that regulate these phenotypes are not completely understood. A population genetic association of lactase persistence with 2 single nucleotide polymorphisms in the distal 5'-flanking region of LCT (-13.9T and -22A) has been confirmed in northern Europeans, but this fails to explain lactase persistence found in some African groups. Any hypothesis for the control of lactase expression must reconcile the presence of high levels of activity in early life in all humans and the characteristic loss of activity found subsequently in many but not all people.

Bioluminescence imaging to monitor bladder cancer cell adhesion in vivo: a new approach to optimize a syngeneic, orthotopic, murine bladder cancer model

OBJECTIVE

To improve the orthotopic murine bladder cancer model by using bioluminescent (BL) MB49 tumour cells for noninvasive in vivo monitoring of tumour growth and to examine the efficacy of integrin receptor-blocking oligopeptides on preventing tumour cell adhesion in this improved bladder cancer model.

MATERIALS AND METHODS

The capacity of oligopeptide combinations to interfere with tumour cell adhesion was assessed in vivo in a syngeneic, orthotopic, murine bladder cancer model. Tumour outgrowth was monitored noninvasively by bioluminescence imaging (BLI) after administration of luciferase-expressing MB49(LUC) bladder cancer cells. The presence of tumour cells was verified histologically and immunohistochemically on paraffin wax-embedded sections of excised bladders.

RESULTS

Anti-adhesive oligopeptides effectively inhibited tumour outgrowth. BLI detected tumour cells at an early stage when there were no clinical signs of cancer in any of the mice. The technique has high sensitivity in detecting tumour cell implantation, but is less reliable in assessing tumour volume in advanced-stage disease due to light attenuation in large tumours.

CONCLUSIONS

Peptides targeting adhesion molecules prevent attachment of bladder cancer cells to the injured bladder wall. BLI is a sensitive method for detecting luminescent bladder cancer cells in an orthotopic mouse model.

Gata4 and Hnf1alpha are partially required for the expression of specific intestinal genes during development

The terminal differentiation phases of intestinal development in mice occur during cytodifferentiation and the weaning transition. Lactase-phlorizin hydrolase (LPH), liver fatty acid binding protein (Fabp1), and sucrase-isomaltase (SI) are well-characterized markers of these transitions. With the use of gene inactivation models in mature mouse jejunum, we have previously shown that a member of the zinc finger transcription factor family (Gata4) and hepatocyte nuclear factor-1alpha (Hnf1alpha) are each indispensable for LPH and Fabp1 gene expression but are both dispensable for SI gene expression. In the present study, we used these models to test the hypothesis that Gata4 and Hnf1alpha regulate LPH, Fabp1, and SI gene expression during development, specifically focusing on cytodifferentiation and the weaning transition. Inactivation of Gata4 had no effect on LPH gene expression during either cytodifferentiation or suckling, whereas inactivation of Hnf1alpha resulted in a 50% reduction in LPH gene expression during these same time intervals. Inactivation of Gata4 or Hnf1alpha had a partial effect ( approximately 50% reduction) on Fabp1 gene expression during cytodifferentiation and suckling but no effect on SI gene expression at any time during development. Throughout the suckling period, we found a surprising and dramatic reduction in Gata4 and Hnf1alpha protein in the nuclei of absorptive enterocytes of the jejunum despite high levels of their mRNAs. Finally, we show that neither Gata4 nor Hnf1alpha mediates the glucocorticoid-induced precocious maturation of the intestine but rather are downstream targets of this process. Together, these data demonstrate that specific intestinal genes have differential requirements for Gata4 and Hnf1alpha that are dependent on the developmental time frame in which they are expressed.

Combined magnetic resonance and bioluminescence imaging of live mice

We perform combined magnetic resonance and bioluminescence imaging of live mice for the purpose of improving the accuracy of bioluminescence tomography. The imaging is performed on three live nude mice in which tritium-powered light sources are surgically implanted. High-resolution magnetic resonance images and multispectral, multiview bioluminescence images are acquired in the same session. An anatomical model is constructed by segmenting the magnetic resonance images for all major tissues. The model is subsequently registered with nonlinear transformations to the 3-D light exittance (exiting intensity) surface map generated from the luminescence images. A Monte Carlo algorithm, along with a set of tissue optical properties obtained from in vivo measurements, is used to solve the forward problem. The measured and simulated light exittance images are found to differ by a factor of up to 2. The greatest cause of this moderate discrepancy is traced to the small errors in source positioning, and to a lesser extent to the optical properties used for the tissues. Discarding the anatomy and using a homogeneous model leads to a marginally worse agreement between the simulated and measured data.

Illuminating cellular physiology: recent developments

Bioluminescent methods are gaining more and more attention among scientists due to their sensitivity, selectivity and simplicity; coupled with the fact that the bioluminescence can be monitored both in vitro and in vivo. Since the discovery of bioluminescence in the 19th century, enzymes involved in the bioluminescent process have been isolated and cloned. The bioluminescent reactions in several different organisms have also been fully characterized and used as reporters in a wide variety of biochemical assays. From the 1990s it became clear that bioluminescence can be detected and quantified directly from inside a living cell. This gave rise to numerous possibilities for the in vivo monitoring of intracellular processes non-invasively using bioluminescent molecules as reporters. This review describes recent developments in the area of bioluminescent imaging for cell biology. Newly developed imaging methods allow transcriptional/translational regulation, signal transduction, protein-protein interaction, oncogenic transformation, cell and protein trafficking, and target drug action to be monitored in vivo in real-time with high temporal and spatial resolution; thus providing researchers with priceless information on cellular functions. Advantages and limitations of these novel bioluminescent methods are discussed and possible future developments identified.

Lactase gene promoter fragments mediate differential spatial and temporal expression patterns in transgenic mice

Lactase gene expression is spatiotemporally regulated during mammalian gut development. We hypothesize that distinct DNA control regions specify appropriate spatial and temporal patterning of lactase gene expression. In order to define regions of the lactase promoter involved in mediating intestine-specific and spatiotemporal restricted expression, transgenic mice harboring 100 bp, 1.3- and 2.0- kb fragments of the 5' flanking region of the rat lactase gene cloned upstream of a luciferase reporter were characterized. The 100-bp lactase promoter-reporter transgenic mouse line expressed maximal luciferase activity in the intestine with a posterior shift in spatial restriction and ectopic expression in the stomach and lung. The temporal pattern of expression mediated by the 1.3-kb promoter?reporter transgene increases with postnatal maturation in contrast with the postnatal decline mediated by the 2.0-kb promoter-reporter transgene and the endogenous lactase gene. The differential transgene expression patterns mediated by the lactase promoter fragments suggests that intestine-specific spatial and temporal control elements reside in distinct regions of the DNA sequences upstream of the lactase gene transcription start-site.

Expression of firefly luciferase in Candida albicans and its use in the selection of stable transformants

The infectious yeast Candida albicans is a model organism for understanding the mechanisms of fungal pathogenicity. We describe the functional expression of the firefly luciferase gene, a reporter commonly used to tag genes in many other cellular systems. Due to a non-standard codon usage by this yeast, the CUG codons were first mutated to UUG to allow functional expression. When integrated into the chromosome of C. albicans with a strong constitutive promoter, cells bioluminesce when provided with luciferin substrate in their media. When fused to the inducible promoter from the HWP1 gene, expression and bioluminescence was only detected in cultures conditioning hyphal growth. We further used the luciferase gene as a selection to isolate transformed cell lines from clinical isolates of C. albicans, using a high-density screening strategy that purifies transformed colonies by virtue of light emission. This strategy requires no drug or auxotrophic selectable marker, and we were thus able to generate stable transformants of clinical isolates that are identical to the parental strain in all aspects tested, other than their bioluminescence. The firefly luciferase gene can, therefore, be used as a sensitive reporter to analyze gene function both in laboratory and clinical isolates of this medically important yeast.

Spatio-temporal patterns of intestine-specific transcription factor expression during postnatal mouse gut development

The small intestine matures from a primitive tube into morphologically and functionally distinct regions during gut development. Maximal expression of the genes encoding the digestive enzymes lactase-phlorizin hydrolase and sucrase-isomaltase is spatially restricted to distinct segments along the anterior-posterior axis of the small intestine and is temporally regulated during postnatal maturation. Transcription factors capable of interacting with the intestinal lactase and sucrase gene promoters are candidate regulators of spatio-temporal patterning during gut development and maturation. We aimed to quantitatively examine and compare the relative expression levels of a set of intestine-specific transcription factors along the anterior-posterior gut axis during postnatal maturation. Our analysis was focused on the transcription factors capable of regulating the intestinal lactase and sucrase-isomaltase genes. A real-time PCR protocol was used to quantitatively examine and compare spatially and temporally the relative transcript abundance levels for intestine-specific factors during postnatal intestinal maturation. Distinct spatial expressions patterns were detected along the length of the small intestine for PDX-1, Cdx-2, GATA-4, GATA-5, GATA-6, HNF-1alpha, HNF-1beta and CDP transcription factor genes. There is a general decline in transcript abundance for the factor genes during postnatal maturation. Defining the spatio-temporal expression patterns for intestine-specific transcription factor genes contributes to investigation of the roles that factor gradients play in mediating gut development and differentiation.

T-13910 DNA variant associated with lactase persistence interacts with Oct-1 and stimulates lactase promoter activity in vitro

Two phenotypes exist in the human population with regard to expression of lactase in adults. Lactase non-persistence (adult-type hypolactasia and lactose intolerance) is characterized by a decline in the expression of lactase-phlorizin hydrolase (LPH) after weaning. In contrast, lactase-persistent individuals have a high LPH throughout their lifespan. Lactase persistence and non-persistence are associated with a T/C polymorphism at position -13,910 upstream the lactase gene. A nuclear factor binds more strongly to the T-13,910 variant associated with lactase persistence than the C-13,910 variant associated with lactase non-persistence. Oct-1 and glyceraldehyde-3-phosphate dehydrogenase were co-purified by DNA affinity purification using the sequence of the T-13,910 variant. Supershift analyses show that Oct-1 binds directly to the T-13,910 variant, and we suggest that GAPDH is co-purified due to interactions with Oct-1. Expression of Oct-1 stimulates reporter gene expression from the T and the C-13,910 variant/LPH promoter constructs only when it is co-expressed with HNF1alpha. Binding sites for other intestinal transcription factors (GATA-6, HNF4alpha, Fox and Cdx-2) were identified in the region of the -13,910 T/C polymorphism. Three of these sites are required for the enhancer activity of the -13,910 region. The data suggest that the binding of Oct-1 to the T-13,910 variant directs increased lactase promoter activity and this might provide an explanation for the lactase persistence phenotype in the human population.

Adult-type hypolactasia and regulation of lactase expression

A common genetically determined polymorphism in the human population leads to two distinct phenotypes in adults, lactase persistence and adult-type hypolactasia (lactase non-persistence). All healthy newborn children express high levels of lactase and are able to digest large quantities of lactose, the main carbohydrate in milk. Individuals with adult-type hypolactasia lose their lactase expression before adulthood and consequently often become lactose intolerant with associated digestive problems (e.g. diarrhoea). In contrast, lactase persistent individuals have a lifelong lactase expression and are able to digest lactose as adults. Lactase persistence can be regarded as the mutant phenotype since other mammals down-regulate their lactase expression after weaning (the postweaning decline). This phenomenon does not occur in lactase persistent individuals. The regulation of lactase expression is mainly transcriptional and it is well established that adult-type hypolactasia is inherited in an autosomal recessive manner, whereas persistence is dominant. The recent findings of single nucleotide polymorphisms associated with lactase persistence have made it possible to study the potential mechanisms underlying adult-type hypolactasia. This work has led to the identification of gene-regulatory sequences located far from the lactase gene (LCT). The present review describes the recent advances in the understanding of the regulation of lactase expression and the possible mechanisms behind adult-type hypolactasia.

Genetic variation and lactose intolerance: detection methods and clinical implications

The maturational decline in lactase activity renders most of the world's adult human population intolerant of excessive consumption of milk and other dairy products. In conditions of primary or secondary lactase deficiency, the lactose sugars in milk pass through the gastrointestinal tract undigested or are partially digested by enzymes produced by intestinal bacterial flora to yield short chain fatty acids, hydrogen, carbon dioxide, and methane. The undigested lactose molecules and products of bacterial digestion can result in symptoms of lactose intolerance, diarrhea, gas bloat, flatulence, and abdominal pain. Diagnosis of lactose intolerance is often made on clinical grounds and response to an empiric trail of dietary lactose avoidance. Biochemical methods for assessing lactose malabsorption in the form of the lactose breath hydrogen test and direct lactase enzyme activity performed on small intestinal tissue biopsy samples may also be utilized. In some adults, however, high levels of lactase activity persist into adulthood. This hereditary persistence of lactase is common primarily in people of northern European descent and is attributed to inheritance of an autosomal-dominant mutation that prevents the maturational decline in lactase expression. Recent reports have identified genetic polymorphisms that are closely associated with lactase persistence and nonpersistence phenotypes. The identification of genetic variants associated with lactase persistence or nonpersistence allows for molecular detection of the genetic predisposition towards adult-onset hypolactasia by DNA sequencing or restriction fragment length polymorphism analysis. The role for such genetic detection in clinical practice seems limited to ruling out adult-onset hypolactasia as a cause of intolerance symptoms but remains to be fully defined. Attention should be paid to appropriate interpretation of genetic detection in order to avoid potentially harmful reduction in dairy intake or misdiagnosis of secondary lactase deficiency.

Complex regulation of the lactase-phlorizin hydrolase promoter by GATA-4

Lactase-phlorizin hydrolase (LPH), a marker of intestinal differentiation, is expressed in absorptive enterocytes on small intestinal villi in a tightly regulated pattern along the proximal-distal axis. The LPH promoter contains binding sites that mediate activation by members of the GATA-4, -5, and -6 subfamily, but little is known about their individual contribution to LPH regulation in vivo. Here, we show that GATA-4 is the principal GATA factor from adult mouse intestinal epithelial cells that binds to the mouse LPH promoter, and its expression is highly correlated with that of LPH mRNA in jejunum and ileum. GATA-4 cooperates with hepatocyte nuclear factor (HNF)-1alpha to synergistically activate the LPH promoter by a mechanism identical to that previously characterized for GATA-5/HNF-1alpha, requiring physical association between GATA-4 and HNF-1alpha and intact HNF-1 binding sites on the LPH promoter. GATA-4 also activates the LPH promoter independently of HNF-1alpha, in contrast to GATA-5, which is unable to activate the LPH promoter in the absence of HNF-1alpha. GATA-4-specific activation requires intact GATA binding sites on the LPH promoter and was mapped by domain-swapping experiments to the zinc finger and basic regions. However, the difference in the capacity between GATA-4 and GATA-5 to activate the LPH promoter was not due to a difference in affinity for binding to GATA binding sites on the LPH promoter. These data indicate that GATA-4 is a key regulator of LPH gene expression that may function through an evolutionarily conserved mechanism involving cooperativity with an HNF-1alpha and/or a GATA-specific pathway independent of HNF-1alpha.

Transcriptional regulation of the lactase-phlorizin hydrolase promoter by PDX-1

Lactase-phlorizin hydrolase gene expression is spatially restricted along the anterior-posterior gut axis. Lactase gene transcription is maximal in the distal duodenum and jejunum in adult mammals and is barely detectable in the proximal duodenum. By contrast, pancreatic duodenal homeobox-1 (PDX-1) protein is expressed maximally in the proximal duodenum. This study aimed to determine the role of PDX-1 in regulating lactase gene promoter activity in intestinal epithelial cells. Caco-2 cells were cotransfected with lactase promoter-reporter constructs in the presence of a PDX-1 expression vector and assayed for luciferase activity. PDX-1 cotransfection results in repression of lactase promoter activity. Sequence analysis of the lactase promoter revealed a putative PDX-1 DNA binding site in the proximal 100-bp lactase gene promoter. EMSAs demonstrated that PDX-1 can interact with the lactase promoter binding site but not with a site in which the core PDX-1 binding sequence TAAT is mutated. Site-directed mutagenesis of the PDX-1 core binding site in the lactase promoter-reporter construct suggests that PDX-1 can function independently of DNA binding to its consensus binding site. Stable overexpression of PDX-1 results in repression of the endogenous human lactase gene in differentiated Caco-2 cells. Given the contrasting spatial expression pattern, PDX-1 may function to specify the anterior boundary of lactase expression in the small intestine and is thus a candidate regulator of anterior spatial restriction in the gut.

Regulatory regions in the rat lactase-phlorizin hydrolase gene that control cell-specific expression

OBJECTIVES

Lactase-phlorizin hydrolase (LPH) is an enterocyte-specific gene whose expression has been well-characterized, not only developmentally but also along the crypt-villus axis and along the length of the small bowel. Previous studies from the authors' laboratory have demonstrated that 2 kb of the 5'-flanking region of the rat LPH gene control the correct tissue, cell, and crypt-villus expression in transgenic animals.

METHODS

To examine further the regulation conferred by this region, protein-DNA interactions were studied using DNase I footprint analyses in LPH-expressing and nonexpressing cell lines. Functional delineation of this 5'-flanking sequence was performed using deletion analysis in transient transfection assays.

RESULTS

Studies revealed a generally positive activity between -74 and -37 bp, a cell-specific negative region between -210 and -95 bp, and additional elements further toward the 5'-terminus that conferred a highly cell-specific response in reporter activity. Computer analysis of distal regions encompassing identified footprints revealed potential binding sites for various intestinal transcription factors. Co-transfection and electromobility shift assay experiments indicated binding of HNF3beta at three sites relevant to LPH expression.

CONCLUSIONS

The data demonstrate that the cell specificity of LPH gene expression depends upon both positive and negative interactions among elements in the first 2 kb of the LPH 5'-flanking region.

A dual function fusion protein of Herpes simplex virus type 1 thymidine kinase and firefly luciferase for noninvasive in vivo imaging of gene therapy in malignant glioma

Background

Suicide gene therapy employing the prodrug activating system Herpes simplex virus type 1 thymidine kinase (HSV-TK)/ ganciclovir (GCV) has proven to be effective in killing experimental brain tumors. In contrast, glioma patients treated with HSV-TK/ GCV did not show significant treatment benefit, most likely due to insufficient transgene delivery to tumor cells. Therefore, this study aimed at developing a strategy for real-time noninvasive in vivo monitoring of the activity of a therapeutic gene in brain tumor cells.

Methods

The HSV-TK gene was fused to the firefly luciferase (Luc) gene and the fusion construct HSV-TK-Luc was expressed in U87MG human malignant glioma cells. Nude mice with subcutaneous gliomas stably expressing HSV-TK-Luc were subjected to GCV treatment and tumor response to therapy was monitored in vivo by serial bioluminescence imaging. Bioluminescent signals over time were compared with tumor volumes determined by caliper.

Results

Transient and stable expression of the HSV-TK-Luc fusion protein in U87MG glioma cells demonstrated close correlation of both enzyme activities. Serial optical imaging of tumor bearing mice detected in all cases GCV induced death of tumor cells expressing the fusion protein and proved that bioluminescence can be reliably used for repetitive and noninvasive quantification of HSV-TK/ GCV mediated cell kill in vivo.

Conclusion

This approach may represent a valuable tool for the in vivo evaluation of gene therapy strategies for treatment of malignant disease.

Characterization of the rat intestinal Fc receptor (FcRn) promoter: transcriptional regulation of FcRn gene by the Sp family of transcription factors

The regulatory elements that control the transcriptional regulation of the intestinal Fc receptor (FcRn) have not been elucidated. The objective of this study was to characterize the core promoter region of the rat FcRn gene. Chimeric clones that contained various regions of the promoter located upstream of the luciferase reporter were transiently transfected into either IEC-6 or Caco-2 cell lines and nuclear extracts were used to perform DNase I footprint and DNA binding assays (EMSA). Transfection of chimeric upstream nested deletions-luciferase reporter clones into either of these cell lines supported robust reporter activity and identified the location of the minimal promoter at -157/+135. DNase I footprint analysis revealed two complexes located within the gene's core promoter region, and site-directed mutagenesis identified two regions that were critical to maintain basal expression. EMSA identified the presence of five Sp elements within the immediate promoter region that are capable of binding members of the Sp family of proteins. Among the five Sp elements, one element appears to not bind Sp1, Sp2, or Sp3 while influencing the interaction of Sp proteins with an adjacent Sp site. Overexpression of either Sp1 or Sp3 augments activity of the minimal promoter in Sp-deficient Drosophila SL2 cells. In summary, we report on the characterization of the rat FcRn minimal promoter, including the characterization of five Sp elements within this region that interact with members of the Sp family of transcriptional factors and drive promoter activity in intestinal cell lines.

The EZC-Prostate Model: Noninvasive Prostate Imaging in Living Mice

Recently, progress in the development of prostate-specific promoters and high resolution imaging techniques has made real-time monitoring of transgenic expression possible, opening a vista of potentially important in vivo models of prostate disease. Herein, we describe a novel prostate reporter model, called the EZC-prostate model that permits both ex vivo and in vivo imaging of the prostate using a sensitive charge-coupled device. Firefly luciferase and enhanced green fluorescent protein were targeted to the prostate epithelium using the composite human kallikrein 2 (hK2)-based promoter, hK2-E3/P. In EZC-prostate mice, the ventral and dorsal/lateral prostate lobes were brilliant green under fluorescence microscopy, with expression localized to the secretory epithelium. In contrast, enhanced green fluorescent protein was undetectable in the anterior lobes of prostate, seminal vesicles, testes, liver, lung, and brain. The kinetics of luciferase activity in intact and castrated living mice monitored with the IVIS charge-coupled device-based imaging system confirmed that firefly luciferase expression was largely prostate restricted, increased with age up to 24 wk, and was androgen dependent. Decreases in reporter expression after 24 wk may reflect well known, age-related decreases in androgen signaling with age in humans. Ex vivo imaging of microdissected animals further confirmed that the luminescence detected in living mice emanated predominately from the prostate, with minor signals originating from the testes and cecum. These data demonstrate that the hK2-E3/P promoter directs strong prostate-specific expression in a transgenic mouse model. Multigenic models, generated by crosses with various hyperplastic and neoplastic prostate disease models, could potentially provide powerful new tools in longitudinal monitoring of changes in prostate size, androgen signaling, metastases, or response to novel therapies without sacrificing large cohorts of animals.

Genetics of lactase persistence and lactose intolerance

The enzyme lactase that is located in the villus enterocytes of the small intestine is responsible for digestion of lactose in milk. Lactase activity is high and vital during infancy, but in most mammals, including most humans, lactase activity declines after the weaning phase. In other healthy humans, lactase activity persists at a high level throughout adult life, enabling them to digest lactose as adults. This dominantly inherited genetic trait is known as lactase persistence. The distribution of these different lactase phenotypes in human populations is highly variable and is controlled by a polymorphic element cis-acting to the lactase gene. A putative causal nucleotide change has been identified and occurs on the background of a very extended haplotype that is frequent in Northern Europeans, where lactase persistence is frequent. This single nucleotide polymorphism is located 14 kb upstream from the start of transcription of lactase in an intron of the adjacent gene MCM6. This change does not, however, explain all the variation in lactase expression.

An upstream polymorphism associated with lactase persistence has increased enhancer activity

BACKGROUND & AIMS

Intestinal lactase activity declines during childhood in some humans. This phenotypic polymorphism of lactase persistence or nonpersistence into adult life has been shown in a recent study to be 100% associated with a T/C nucleotide polymorphism at position -13910 and approximately 97% with an A/G nucleotide polymorphism at position -22018. The aim of this study was to investigate the role of these nucleotide polymorphisms for lactase-phlorizin hydrolase (LPH) gene expression.

METHODS

The -13910 and -22018 regions were cloned from lactase-persistent and -nonpersistent individuals, and the regions were analyzed for gene regulatory activity of a luciferase reporter gene by transfection experiments using the intestinal cell line Caco-2. Electrophoretic mobility shift assays (EMSAs) were used to investigate protein/DNA interactions with the -13910 sequence.

RESULTS

We show that the -13910 region contains a strong enhancer. The -13910 regions from both lactase persistent (-13910T variant) and lactase nonpersistent (-13910C variant) have enhancer activity. However, the -13910T variant enhances the LPH promoter approximately 4 times more than the -13910C variant when analyzed in differentiated Caco-2 cells. A nuclear factor from both an intestinal and a nonintestinal extract binds strongly to the -13910T variant whereas the binding to the -13910C variant is much weaker.

CONCLUSIONS

The discovery of a functional difference between the 2 alleles at position -13910 supports the notion that the molecular difference between lactase persistence and nonpersistence is caused by the mutation at position -13910.

Evaluation of effector cell fate and function by in vivo bioluminescence imaging

The effector functions of immune cells have typically been examined using assays that require sampling of tissues or cells to reveal specific aspects of an immune response (e.g., antigen-specificity, cytokine expression or killing of target cells). The outcome of an immune response in vivo, however, is not solely determined by a single effector function of a specific cell population, but is the result of numerous cellular and molecular interactions that occur in the complex environment of intact organ systems. These interactions influence survival, migration, and activation, as well as final effector function of a given population of cells. Efforts to reveal the cellular and molecular basis of biological processes have resulted in a number of technologies that combine molecular biology and imaging sciences that are collectively termed as Molecular Imaging. This emerging field has developed to reveal functional aspects of cells, genes, and proteins in real time in living animals and humans and embraces multiple modalities, including established clinical imaging methods such as magnetic resonance imaging, single photon emission computed tomography, and positron emission tomography, as well as novel methodologies specifically designed for research animals. Here, we highlight one of the newer modalities, in vivo bioluminescence imaging, as a method for evaluating effector T cell proliferation, migration, and function in model systems of malignant and non-malignant diseases.

An enhancer activates the pig lactase phlorizin hydrolase promoter in intestinal cells

Lactase phlorizin hydrolase is a small intestinal-specific brush border protein commonly used as a specific marker of differentiated enterocytes. A number of transcription factors involved in the enterocyte-specific expression of lactase phlorizin hydrolase have been identified. An upstream regulatory region, which we have named the "LPH enhancer", located at position -894 to -798 in the porcine lactase phlorizin hydrolase gene, is necessary for high differentiation-dependent LPH expression in intestinal cells. The LPH enhancer was studied by mutation analysis, transfection experiments and electrophoretical mobility shift assays. The LPH enhancer is active in intestinal cells (Caco-2) and not in non-intestinal cells (HeLa). The LPH enhancer is only able to enhance expression when it is located in front of an intestinal-specific promoter such as the lactase phlorizin hydrolase promoter or the sucrase-isomaltase promoter. In front of an SV40-derived promoter the LPH enhancer has no stimulatory effect. In addition to the lack of promoter-promiscuity, the LPH enhancer is not a classical enhancer in the sense that it is not orientation-independent and it cannot function when located 3' of a reporter gene. The LPH enhancer contains at least three cis-elements (at -894 to -880, -880 to -875 and -833 to -814) with functional importance for the LPH enhancer activity.

Physical interaction between GATA-5 and hepatocyte nuclear factor-1alpha results in synergistic activation of the human lactase-phlorizin hydrolase promoter

GATA-4, -5, and -6 zinc finger and hepatocyte nuclear factor-1alpha (HNF-1alpha) homeodomain transcription factors are expressed in the intestinal epithelium and synergistically activate the promoter of intestinal genes. Here, we demonstrate that GATA-5 and HNF-1alpha physically associate both in vivo and in vitro and that this interaction is necessary for cooperative activation of the lactase-phlorizin hydrolase promoter. Furthermore, physical association is mediated by the C-terminal zinc finger of GATA factors and the homeodomain of HNF-1alpha. Deletion of HNF-1alpha activation domains or interruption of HNF-1-binding sites in the lactase-phlorizin hydrolase promoter resulted in a complete loss of cooperativity, whereas deletion of GATA-5 activation domains or interruption of GATA-binding sites resulted in a reduction, but not an elimination, of cooperativity. We hypothesize that GATA/HNF-1alpha cooperativity is mediated by HNF-1alpha through its activation domains, which are oriented for high levels of activation through binding to DNA and physical association with GATA factors. These data suggest a paradigm whereby intestine-specific gene expression is regulated by unique interactions among tissue-restricted transcription factors coexpressed in the intestine. Parallel mechanisms in other tissues as well as in Drosophila suggest that zinc finger/homeodomain interactions are an efficient pathway of cooperative activation of gene transcription that has been conserved throughout evolution.