A 20-nucleotide element in the intestinal fatty acid binding protein gene modulates its cell lineage-specific, differentiation-dependent, and cephalocaudal patterns of expression in transgenic mice

Molecular regulation of both dietary vitamin A and fatty acid absorption and metabolism associated with larval morphogenesis of Senegalese sole (Solea senegalensis)

The present study aimed to deepen the understanding of molecular mechanisms governing the absorption and metabolism of some nutrients, growth and development in larvae of Senegalese sole (Solea senegalensis) fed with Artemia enriched with Easy Selco (ES, INVE) or Aquagrow Gold (AGG, ABN), which mainly differed in their vitamin A (VA) content and fatty acid composition. The expression profile of genes involved in VA metabolism (crbp2, rbp, crabp1), lipid transport (i-fabp, l-fabp), nuclear receptors for VA and fatty acids (rarα1, rxrα, pparβ), growth (igf1, igf2 and their receptor igf1r) and development (bgp) was analyzed at 22, 30 and 38 days post hatching. The main results suggested that the amount of VA absorbed by larvae is controlled at the intestinal level by crbp2 in both groups, preventing excessive accumulation of this vitamin in the target tissues. The stable expression of i-fabp in the ES group with age could cause an excessive fat accumulation in the intestine inducing, in turn, the steatosis found in the liver and vascular system of these specimens. In liver, the regulation of rbp and fabp expression reflected the status of the physiological functions demanding VA and lipids. The findings revealed that dietary composition induced different strategies for VA and lipid absorption and metabolism affecting, in turn, larval development, growth and health.

Transcriptional regulation of the intestinal luminal Na⁺ and Cl⁻ transporters

The epithelial apical membrane Na+/H+ exchangers [NHE (sodium hydrogen exchanger)2 and NHE3] and Cl-/HCO3- exchangers [DRA (down-regulated in adenoma) and PAT-1 (putative anion transporter 1)] are key luminal membrane transporters involved in electroneutral NaCl absorption in the mammalian intestine. During the last decade, there has been a surge of studies focusing on the short-term regulation of these electrolyte transporters, particularly for NHE3 regulation. However, the long-term regulation of the electrolyte transporters, involving transcriptional mechanisms and transcription factors that govern their basal regulation or dysregulation in diseased states, has only now started to unfold with the cloning and characterization of their gene promoters. The present review provides a detailed analysis of the core promoters of NHE2, NHE3, DRA and PAT-1 and outlines the transcription factors involved in their basal regulation as well as in response to both physiological (butyrate, protein kinases and probiotics) and pathophysiological (cytokines and high levels of serotonin) stimuli. The information available on the transcriptional regulation of the recently identified NHE8 isoform is also highlighted. Therefore the present review bridges a gap in our knowledge of the transcriptional mechanisms underlying the alterations in the gene expression of intestinal epithelial luminal membrane Na+ and Cl- transporters involved in electroneutral NaCl absorption. An understanding of the mechanisms of the modulation of gene expression of these transporters is important for a better assessment of the pathophysiology of diarrhoea associated with inflammatory and infectious diseases and may aid in designing better management protocols.

Molecular cloning and promoter analysis of downregulated in adenoma (DRA)

Downregulated in adenoma (DRA), also referred to as SLC26A3, is an intestinal anion transporter essential for intestinal chloride absorption. Mutations in DRA result in congenital chloride diarrhea. DRA expression has been shown to be induced by differentiation and to be modulated by cytokines. However, mechanisms of DRA gene transcription and its tissue-specific targeting have not yet been investigated. In this study, we cloned a 3,765-bp promoter fragment of human DRA gene and characterized its activity in human colonic LS174T and Caco-2 human colon cell lines. Primer extension identified a single transcriptional initiation site that was identical in both colon cancer cell lines and normal colon. Although hepatic nuclear factor HNF-4 is involved in the basal activity of DRA promoter, sodium butyrate induces its activity in LS174T cells via the binding of Yin Yang 1 (YY1) and GATA transcription factors to their respective cis-elements in promoter region. We also demonstrated a reduction in DRA promoter activity in Caco-2 cells by IFN-gamma, suggesting that regulation of DRA promoter by IFN-gamma may contribute to the pathophysiology of intestinal inflammation. Furthermore, we showed that the DRA promoter fragment is sufficient to drive human growth hormone transgene expression specifically in villus epithelial cells of the small intestine and in differentiated upper crypt and surface epithelial cells of the colon. Our studies provide evidence for the involvement of HNF-4, YY1, and GATA transcription factors in DRA expression in intestinal differentiated epithelial cells.

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.

Intestinal apolipoprotein A-IV gene transcription is controlled by two hormone-responsive elements: a role for hepatic nuclear factor-4 isoforms

In the small intestine, the expression of the apolipoprotein (apo) C-III and A-IV genes is restricted to the enterocytes of the villi. We have previously shown that, in transgenic mice, specific expression of the human apo C-III requires a hormone-responsive element (HRE) located in the distal region of the human apoA-IV promoter. This HRE binds the hepatic nuclear factors (HNF)-4alpha and gamma. Here, intraduodenal injections in mice and infections of human enterocytic Caco-2/TC7 cells with an adenovirus expressing a dominant-negative form of HNF-4alpha repress the expression of the apoA-IV gene, demonstrating that HNF-4 controls the apoA-IV gene expression in enterocytes. We show that HNF-4alpha and gamma functionally interact with a second HRE present in the proximal region of the human apoA-IV promoter. New sets of transgenic mice expressing mutated forms of the promoter, combined with the human apo C-III enhancer, demonstrate that, whereas a single HRE is sufficient to reproduce the physiological cephalo-caudal gradient of apoA-IV gene expression, both HREs are required for expression that is restricted to villi. The combination of multiple HREs may specifically recruit regulatory complexes associating HNF-4 and either coactivators in villi or corepressors in crypts.

Functional conserved elements mediate intestinal-type fatty acid binding protein (I-FABP) expression in the gut epithelia of zebrafish larvae

Intestinal-type fatty acid binding protein (I-FABP) plays an important role in the intracellular binding and trafficking of long chain fatty acids in the intestine. The aim of this study, therefore, was to elucidate the regulation and spatiotemporal expression of the I-FABP gene during zebrafish larval development. We performed in vivo reporter-gene analysis in zebrafish by using a transient and transgenic approach. Green fluorescent protein-reporter analyses revealed that the proximal 192-bp region of the I-FABP promoter is sufficient to direct intestine-specific expression during zebrafish larval development. Functional dissection of a 41-bp region within this 192-bp promoter revealed that one C/EBP and two GATA-like binding sites, along with a novel 15-bp element within it are required for I-FABP gene expression in vivo. In addition, the six consensus sites (CCACATCAGCATGAA) in the 15-bp element are critical for I-FABP gene regulation in the zebrafish gut epithelia. Comparison analyses of the orthologous 15-bp element from mammalian I-FABP genes suggests that these mammalian elements are functionally equivalent to the zebrafish 15 element. These results provide the first in vivo evidence that these binding sites (C/EBP and GATA) and the novel 15-bp element contribute to intestine-specific gene expression and that they are functionally conserved across vertebrate evolution.

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.

Zebrafish intestinal fatty acid binding protein (I-FABP) gene promoter drives gut-specific expression in stable transgenic fish

Mammalian intestinal fatty acid-binding protein (I-FABP) is a small cytosolic protein and is thought to play a crucial role of intracellular fatty acid trafficking and metabolism in gut. To establish an in vivo system for investigating its tissue-specific regulation during zebrafish intestinal development, we isolated 5'-flanking sequences of the zebrafish L-FABP gene and used a transgenic strategy to generate gut-specific transgenic zebrafish with green/red fluorescent intestine. The 4.5-kb 5'-flanking sequence of zebrafish I-FABP gene was sufficient to direct fluorescent expression in intestinal tube, first observed in 3 dpf embryos and then continuously to the adult stage. This pattern of transgenic expression is consistent with the expression pattern of the endogenous gene. In all five transgenic lines 45-52% of the F2 inheritance rates were consistent with the ratio of Mendelian segregation. These fish can also provide a valuable resource of labeled adult intestinal cells for in vivo or in vitro studies. Finally, it is possible to establish an in vivo system using these fish for screening genes required for gut development. genesis 38:26-31, 2004.

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.

Dextran sulfate sodium-induced inflammation is enhanced by intestinal epithelial cell chemokine expression in mice

Dextran sulfate sodium (DSS) induces an inflammatory bowel disease-like colitis in animals. To determine the contribution of epithelium to inflammation in the intestine, we examined the effects of DSS in transgenic mice that specifically secrete macrophage inflammatory protein-2 (MIP-2) from the intestinal epithelium. We first confirmed the production of MIP-2 from intestinal epithelial cells by Western blots in transgenic mice. MIP-2 transgenic mice were therefore an appropriate model to examine the role of epithelial cell chemokines in an inflammatory state induced by DSS. We then examined the neutrophil migration into the intestine and the effect of DSS on this migration by myeloperoxidase staining. There was an increase of myeloperoxidase-positive neutrophils in the intestine from wild-type and transgenic mice after the DSS treatment. Furthermore, the increase of neutrophils under stimulation with DSS was confirmed quantitatively by measuring specific tissue myeloperoxidase activities. It was significantly greater in DSS-treated MIP-2 transgenic mice than in wild-type mice in both the small intestine and colon. These results suggest that the inflammatory effects of DSS on both small intestine and colon are enhanced by MIP-2 secreted by epithelial cells in the transgenic mice. In conclusion, intestinal epithelial cells can act in concert with other inflammatory stimuli in maintaining inflammation.

Cutting-edge technology: IV. Genomic engineering for studies of the gastrointestinal tract in mice

Advances in our understanding of the complex, dynamic interactions that exist among the gastrointestinal microflora, the epithelium of the gastrointestinal mucosae, and the immune system have been facilitated by powerful new genetic tools. Recent understanding that the gastrointestinal epithelium performs not only a barrier function but is also an active sensor of the microflora and an important intermediary in regulating and integrating cross-talk between it and cells of the innate and adaptive immune systems provides one of the most fertile and challenging areas for application of these technologies. The intestinal epithelium also represents an important model system for study of programs of cell lineage commitment and differentiation, given its continual and rapid regeneration throughout life and the regional differences in these programs that exist along the gastrocolonic and crypt-villous axes. This review will highlight current and emerging technologies that are available in the mouse model for identification and manipulation of genetic elements that regulate the normal and pathological physiology of the intestinal tissues in the post-genomic era.

Decreased expression of 14-3-3sigma in neuroendocrine tumors is independent of origin and malignant potential

We recently reported that 14-3-3sigma is frequently inactivated in small cell lung cancer (SCLC) and a part of large cell carcinomas. Subsequent studies revealed that the large cell carcinomas could be morphologically categorized as large cell neuroendocrine carcinomas (LCNEC). The present study therefore examines 14-3-3sigma expression in a spectrum of neuroendocrine lung tumors, which had varied p53 status, proliferative activity and clinical aggressiveness. The expression of 14-3-3sigma was decreased in all four categories of the spectrum, (5 out of 5 typical carcinoids, 2 out of 2 atypical carcinoids, 5 out of 7 LCNECs and 15 out of 18 SCLCs). In sharp contrast, the level of 14-3-3sigma expression in 75 non-small cell lung cancers (NSCLCs) was the same as that in normal lung tissue, with only one exception. The expression status of neuroendocrine tumors and NSCLCs was not affected by p53 status, but dense promoter hypermethylation of the 14-3-3sigma gene was specifically observed in neuroendocrine tumors, suggesting that methylation plays a regulatory role in 14-3-3sigma expression in vivo as well as in vitro. Furthermore, the expression was not only down-regulated in pulmonary neuroendocrine tumors, but also in neuroendocrine tumors arising from various other organs, through examination of 123 non-pulmonary tumors. Since various carcinogenic machineries are involved in the neuroendocrine tumors, a reduced expression of 14-3-3sigma might be required for the development of neuroendocrine tumors. Constitutive 14-3-3sigma expression was distributed exclusively in putative stem cells of the normal lung, namely the basal cells of the bronchus, and type II pneumocytes. Notably, 14-3-3sigma expression was up-regulated during the regeneration of type II pneumocytes, suggesting that 14-3-3sigma plays a biological role when a regenerative and/or differentiating drive is activated, facilitating exit from stem cells.

Restriction of apolipoprotein A-IV gene expression to the intestine villus depends on a hormone-responsive element and parallels differential expression of the hepatic nuclear factor 4alpha and gamma isoforms

The apoA-I/C-III/A-IV gene cluster, like most intestine-specific genes, displays a specific pattern of expression along the intestinal cephalocaudal and crypt-to-villus axes. We have shown that this specific pattern of expression requires the distal apoA-IV promoter and the apoC-III enhancer. Using a new set of transgenic mice, we demonstrate here that the restriction of apoA-IV gene transcription to villus enterocytes requires a hormone-responsive element (HRE) located within the apoA-IV distal promoter. We showed, using nuclear extracts from villus or crypt epithelial cells, that this HRE bound the transcription factor hepatic nuclear factor 4 (HNF-4). We also found that the HNF-4gamma isoform was produced only in the villus, whereas the HNF-4alpha isoform was produced along the entire length of the crypt-to-villus axis. Our results demonstrate that the HRE of the distal apoA-IV promoter is responsible for the restriction of gene expression to villus epithelial cells and that this HRE binds HNF-4 isoforms. The in vivo observation of parallel gradients for apoA-IV and HNF-4gamma gene expression raises questions concerning whether this transcription factor plays a specific role in the control of enterocyte differentiation.

Distinct epithelial responses in experimental colitis: implications for ion uptake and mucosal protection

In the present study, we aimed to investigate enterocyte- and goblet cell-specific functions during the different phases of acute colitis induced with dextran sulfate sodium (DSS). Rats were treated with DSS for 7 days, followed by a 7-day recovery period. Colonic tissue was excised on days 2 (onset of disease), 7 (active disease), and 14 (regenerative phase). Enterocyte functions were studied by the expression of carbonic anhydrases (CAs), sodium/hydrogen exchangers (NHEs) and intestinal fatty acid-binding protein (iFABP) and by alkaline phosphatase (AP) activity. The expression and secretion of the mucin Muc2 and trefoil factor family peptide-3 (TFF3) were used as parameters for goblet cell function. DSS induced a downregulation of the CAs, NHEs, and iFABP in some normal-appearing surface enterocytes and in most of the flattened-surface enterocytes during disease onset and active disease. During the regenerative phase most enterocytes expressed these genes again. Quantitative analysis revealed a significant decrease in CAs, NHEs, and iFABP expression levels during onset and active disease. During the regenerative phase, the expression levels of the CAs were restored, whereas the expression levels of the NHEs and iFABP remained decreased. In contrast, enterocyte-specific AP activity was maintained in normal and flattened enterocytes during DSS-induced colitis. Goblet cells continued to express MUC2 and TFF3 during and after DSS treatment. Moreover, Muc2 and TFF3 expression and secretion levels were maintained or even increased during each of the DSS-induced disease phases. In conclusion, DSS-induced colitis was associated with decreased expression of CAs, NHEs, and iFABP. The loss of these genes possibly accounts for some of the pathology seen in colitis. The maintenance or upregulation of Muc2 and TFF3 synthesis and secretion levels implies that goblet cells at least maintain their epithelial defense and repair capacity during acute inflammation induced by DSS.

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

Lactase gene transcription is spatially restricted to the proximal and middle small intestine of the developing mouse. To identify regions of the lactase gene involved in mediating the spatiotemporal expression pattern, transgenic mice harboring 0.8-, 1.3-, and 2.0-kb fragments of the 5'-flanking region cloned upstream of a firefly-luciferase reporter were generated. Transgene expression was assessed noninvasively in living mice using a sensitive low light imaging system. Two independent, 1.3- and 2.0-kb, lactase promoter-reporter transgenic lines expressed appropriate high levels of luciferase activity in the small intestine (300-3,000 relative light units/microg) with maximal expression in the middle segments. Post-weaned 30-day transgenic offspring also demonstrated an appropriate 4-fold maturational decline in luciferase expression in the small intestine. The pattern of the 2.0-kb promoter transgene mRNA abundance most closely mimicked that of the endogenous lactase gene with respect to spatiotemporal restriction. In contrast, a 0.8-kb promoter-reporter construct expressed low level luciferase activity (<25 relative light units/microg) in multiple organs and throughout the gastrointestinal tract in transgenic mice. Thus, a distinct 5'-region of the lactase promoter directs intestine-specific expression in the small intestine of transgenic mice, and regulatory sequences have been localized to a 1.2-kb region upstream of the lactase transcription start site. In addition, we have demonstrated that in vivo bioluminescence imaging can be utilized for assessment of intestinal expression patterns of a luciferase reporter gene driven by lactase promoter regions in transgenic mice.

MIP-2 secreted by epithelial cells increases neutrophil and lymphocyte recruitment in the mouse intestine

BACKGROUND

Invasion of the intestinal mucosa by leucocytes is a characteristic of intestinal inflammation but the role of the epithelium in orchestrating this recruitment has not been examined in vivo. Cultured intestinal epithelial cells secrete a wide variety of chemokines, often in response to agents present in the intestinal lumen. Macrophage inflammatory protein 2 (MIP-2) is a chemokine that attracts neutrophils, and its secretion from intestinal epithelial cells is enhanced by inflammatory stimuli such as interleukin 1beta. We hypothesised that the production of MIP-2 by epithelial cells would increase leucocyte migration into the intestine.

AIM

To study the effects of a chemokine secreted from intestinal epithelial cells in vivo.

METHODS

MIP-2 was expressed in the mouse intestinal epithelium using an epithelial cell specific promoter from the gene encoding the intestinal fatty acid binding protein. The intestines of these transgenic mice were then analysed.

RESULTS

Epithelial cells from transgenic mice expressed MIP-2 but wild-type mice did not. Neutrophil recruitment, examined by myeloperoxidase (MPO) staining and total MPO activity per unit weight of intestine, was significantly increased in transgenic mice in both the small intestine and proximal colon, and this was blocked by anti-MIP-2 antibody treatment. Both intraepithelial and lamina propria lymphocytes were also increased in transgenic mice. They showed chemotactic activity to MIP-2 in the Boyden chambers and expressed MIP-2 receptor (CXCR-2) mRNA confirmed by reverse transcription-polymerase chain reaction.

CONCLUSION

These experiments are the first to show a functional role for epithelial chemokines in vivo and reveal an unexpected role for the neutrophil chemokine MIP-2 in controlling mucosal lymphocyte migration.

Nucleotide sequence of a cDNA clone coding for an intestinal-type fatty acid binding protein and its tissue-specific expression in zebrafish (Danio rerio)

We have cloned a cDNA from zebrafish (Danio rerio) that contains an open-reading frame of 132 amino acids coding for a fatty acid binding protein (FABP) of approximately 15 kDa. Multiple sequence alignment revealed extensive amino acid identity between this zebrafish FABP and intestinal-like FABPs (I-FABP) from other species. The zebrafish I-FABP cDNA hybridized to single restriction fragments of total zebrafish genomic DNA digested with the restriction endonucleases PstI Bg/II or EcoRI suggesting that a single copy of the I-FABP gene is present in the zebrafish genome. An oligonucleotide probe complementary to the zebrafish I-FABP mRNA hybridized to an mRNA of approximately 800 bases in Northern blot analysis. In situ hybridization revealed that the I-FABP mRNA was expressed exclusively in the intestine of the adult zebrafish.

The T3(b) gene promoter directs intestinal epithelial cell-specific expression in transgenic mice

Although a few promoters that direct intestinal epithelial cell-specific expression in transgenic animals have been reported, they are not necessarily appropriate for transgenic studies in terms of activity and tissue specificity. Here, we examined the tissue specificity of transgene expression directed by the 2.8-kb promoter region of the T3(b) gene, which encodes one of the non-classical major histocompatibility complex class I molecules. The transgene was expressed exclusively in the epithelial cells of the small and large intestines at high levels. The results indicate that the T3(b) promoter is useful for directing transgene expression specifically in intestinal epithelial cells.

Factors involved in the duodenal expression of the human calbindin-D9k gene

Calbindin-D9k is expressed in the cytoplasm of intestinal cells, where it is critical for dietary calcium absorption. Two striking aspects of the expression of this gene are its vitamin-D dependency and regional differences in expression, with high levels only in duodenum. We report studies of the human calbindin-D9k promoter. Differences between the reported sequences of the human calbindin-D9k promoter were first clarified before undertaking a functional analysis of this sequence. Studies of the rat gene have indicated that several transcription factors, including the caudal-related homeobox factor (CDX-2), hepatic nuclear factor-4 and CCAAT-enhancer-binding protein alpha (C/EBPalpha), could interact with elements in the promoter. Although these elements are conserved in the human gene, we show here that their intestinal distribution makes them unlikely to be critical positive factors. The calbindin-D9k gene contains multiple potential binding sites for homeobox transcription factors; one of these, known as IPF-1 or PDX-1, co-localizes in the intestine with calbindin-D9k. We show in gel-shift assays that the sequence within a putative vitamin-D-response element in the human calbindin-D9k promoter can bind expressed IPF-1/PDX-1 protein, although we cannot confirm binding of the vitamin-D-receptor protein. CDX-2 binds to the region around the TATA box, as in the rat gene, and may act as a negative factor in the distal intestine. Transfection studies in Caco-2 and MCF-7 cells with heterologous reporter vectors containing up to 1303 bp of the gene showed that this functioned as a weak promoter and indicated the presence of suppressor sequences, but did not show vitamin-D responsiveness. This indicates that other elements are also needed for the control of human calbindin-D9k expression.

Regulation of alpha1-antitrypsin gene expression in human intestinal epithelial cell line caco-2 by HNF-1alpha and HNF-4

There is still relatively limited information about mechanisms of gene expression in enterocytes and mechanisms by which gene expression is regulated during enterocyte differentiation. Using the human intestinal epithelial cell line Caco-2, which spontaneously differentiates from a cryptlike to a villouslike enterocyte, we have previously shown that there is a marked increase in transcription of the well-characterized alpha1-antitrypsin (alpha1-AT) gene during enterocyte differentiation. In this study we examined the possibility of identifying the cis-acting elements and trans-acting DNA-binding proteins responsible for expression of the alpha1-AT gene in Caco-2 cells during differentiation. Footprint analysis and electrophoretic mobility shift assays showed that hepatocyte nuclear factor-1alpha (HNF-1alpha), HNF-1beta, and HNF-4 from nuclear extracts of Caco-2 cells specifically bound to two regions in the proximal promoter of the alpha1-AT gene. Cotransfection studies showed that HNF-1alpha and HNF-4 had a synergistic effect on alpha1-AT gene expression. RNA blot analysis showed that HNF-1alpha and HNF-4 mRNA levels and electrophoretic mobility shift assays showed that HNF-1alpha binding activity increase coordinately with alpha1-AT mRNA levels during differentiation of Caco-2 cells. Finally, overexpression of antisense ribozymes for HNF-1alpha in Caco-2 cells resulted in a selective decrease in endogenous alpha1-AT gene expression. Together, these results provide evidence that HNF-1alpha and HNF-4 play a role in the mechanism by which the alpha1-AT gene is upregulated during enterocyte differentiation in the model Caco-2 cell system.

Regulatory sequences of the mouse villin gene that efficiently drive transgenic expression in immature and differentiated epithelial cells of small and large intestines

Villin is an early marker of epithelial cells from the digestive and urogenital tracts. Indeed villin is expressed in the stem cells and the proliferative cells of the intestinal crypts. To investigate the underlying molecular mechanisms and particularly those responsible for the restricted tissue specificity, a large genomic region of the mouse villin gene has been analyzed. A 9-kilobase (kb) regulatory region of the mouse villin gene (harboring 3.5 kb upstream the transcription start site and 5.5 kb of the first intron) was able to promote transcription of the LacZ reporter gene in the small and large intestines of transgenic mice, in a transmissible manner, and thus efficiently directed subsequent beta-galactosidase expression in epithelial cells along the entire crypt-villus axis. In the kidney, the transgene was also expressed in the epithelial cells of the proximal tubules but is likely sensitive to the site of integration. A construct lacking the first intron restricted beta-galactosidase expression to the small intestine. Thus, the 9-kb genomic region contains the necessary cis-acting elements to recapitulate the tissue-specific expression pattern of the endogenous villin gene. Hence, these regulatory sequences can be used to target heterologous genes in immature and differentiated epithelial cells of the small and/or large intestinal mucosa.

Development of the human gastrointestinal tract: twenty years of progress

A combination of approaches has begun to elucidate the mechanisms of gastrointestinal development. This review describes progress over the last 20 years in understanding human gastrointestinal development, including data from both human and experimental animal studies that address molecular mechanisms. Rapid progress is being made in the identification of genes regulating gastrointestinal development. Genes directing initial formation of the endoderm as well as organ-specific patterning are beginning to be identified. Signaling pathways regulating the overall right-left asymmetry of the gastrointestinal tract and epithelial-mesenchymal interactions are being clarified. In searching for extrinsic developmental regulators, numerous candidate trophic factors have been proposed, but compelling evidence remains elusive. A critical gene that initiates pancreas development has been identified, as well as a number of genes regulating liver, stomach, and intestinal development. Mutations in genes affecting neural crest cell migration have been shown to give rise to Hirschsprung's disease. Considerable progress has been achieved in understanding specific phenomena, such as the transcription factors regulating expression of sucrase-isomaltase and fatty acid-binding protein. The challenge for the future is to integrate these data into a more complete understanding of the physiology of gastrointestinal development.

The -700/-310 fragment of the apolipoprotein A-IV gene combined with the -890/-500 apolipoprotein C-III enhancer is sufficient to direct a pattern of gene expression similar to that for the endogenous apolipoprotein A-IV gene

Spatial gene expression in the intestine is mediated by specific regulatory sequences. The three genes of the apoA-I/C-III/A-IV cluster are expressed in the intestine following cephalocaudal and crypt-to-villus axes. Previous studies have shown that the -780/-520 enhancer region of the apoC-III gene directs the expression of the apoA-I gene in both small intestinal villi and crypts, implying that other unidentified elements are necessary for a normal intestinal pattern of apoA-I gene expression. In this study, we have characterized transgenic mice expressing the chloramphenicol acetyltransferase gene under the control of different regions of the apoC-III and apoA-IV promoters. We found that the -890/+24 apoC-III promoter directed the expression of the reporter gene in crypts and villi and did not follow a cephalocaudal gradient of expression. In contrast, the -700/+10 apoA-IV promoter linked to the -500/-890 apoC-III enhancer directed the expression of the reporter gene in enterocytes with a pattern of expression similar to that of the endogenous apoA-IV gene. Furthermore, linkage of the -700/-310 apoA-IV distal promoter region to the -890/+24 apoC-III promoter was sufficient to restore the appropriate pattern of intestinal expression of the reporter gene. These findings demonstrate that the -700/-310 distal region of the apoA-IV promoter contains regulatory elements that, in combination with proximal promoter elements and the -500/-890 enhancer, are necessary and sufficient to restrict apoC-III and apoA-IV gene expression to villus enterocytes of the small intestine along the cephalocaudal axis.

Anterior-posterior patterning within the Caenorhabditis elegans endoderm

The endoderm of higher organisms is extensively patterned along the anterior/posterior axis. Although the endoderm (gut or E lineage) of the nematode Caenorhabditis elegans appears to be a simple uniform tube, cells in the anterior gut show several molecular and anatomical differences from cells in the posterior gut. In particular, the gut esterase ges-1 gene, which is normally expressed in all cells of the endoderm, is expressed only in the anterior-most gut cells when certain sequences in the ges-1 promoter are deleted. Using such a deleted ges-1 transgene as a biochemical marker of differentiation, we have investigated the basis of anterior-posterior gut patterning in C. elegans. Although homeotic genes are involved in endoderm patterning in other organisms, we show that anterior gut markers are expressed normally in C. elegans embryos lacking genes of the homeotic cluster. Although signalling from the mesoderm is involved in endoderm patterning in other organisms, we show that ablation of all non-gut blastomeres from the C. elegans embryo does not affect anterior gut marker expression; furthermore, ectopic guts produced by genetic transformation express anterior gut markers generally in the expected location and in the expected number of cells. We conclude that anterior gut fate requires no specific cell-cell contact but rather is produced autonomously within the E lineage. Cytochalasin D blocking experiments fully support this conclusion. Finally, the HMG protein POP-1, a downstream component of the Wnt signalling pathway, has recently been shown to be important in many anterior/posterior fate decisions during C. elegans embryogenesis (Lin, R., Hill, R. J. and Priess, J. R. (1998) Cell 92, 229–239). When RNA-mediated interference is used to eliminate pop-1 function from the embryo, gut is still produced but anterior gut marker expression is abolished. We suggest that the C. elegans endoderm is patterned by elements of the Wnt/pop-1 signalling pathway acting autonomously within the E lineage.

Creating and maintaining the gastrointestinal ecosystem: what we know and need to know from gnotobiology

Studying the cross talk between nonpathogenic organisms and their mammalian hosts represents an experimental challenge because these interactions are typically subtle and the microbial societies that associate with mammalian hosts are very complex and dynamic. A large, functionally stable, climax community of microbes is maintained in the murine and human gastrointestinal tracts. This open ecosystem exhibits not only regional differences in the composition of its microbiota but also regional differences in the differentiation programs of its epithelial cells and in the spatial distribution of its component immune cells. A key experimental strategy for determining whether "nonpathogenic" microorganisms actively create their own regional habitats in this ecosystem is to define cellular function in germ-free animals and then evaluate the effects of adding single or several microbial species. This review focuses on how gnotobiotics-the study of germ-free animals-has been and needs to be used to examine how the gastrointestinal ecosystem is created and maintained. Areas discussed include the generation of simplified ecosystems by using genetically manipulatable microbes and hosts to determine whether components of the microbiota actively regulate epithelial differentiation to create niches for themselves and for other organisms; the ways in which gnotobiology can help reveal collaborative interactions among the microbiota, epithelium, and mucosal immune system; and the ways in which gnotobiology is and will be useful for identifying host and microbial factors that define the continuum between nonpathogenic and pathogenic. A series of tests of microbial contributions to several pathologic states, using germ-free and ex-germ-free mice, are proposed.

Intestinal expression of the calbindin-D9K gene in transgenic mice. Requirement for a Cdx2-binding site in a distal activator region

The calbindin-D9K gene encodes a vitamin D-induced calcium-binding protein that is expressed as a marker of small intestine differentiation. We have shown that 4580 base pairs of its 5' DNA regulatory region can target reporter transgene expression in the intestine and cause this transgene to respond like the endogenous gene to vitamin D active metabolite and that the homeoprotein Cdx2 is bound to the TATA box in the intestine. We now show that the 4580 base pairs construct confers a differentiated pattern of reporter transgene expression in the intestine and that cooperation between the proximal promoter and a distal element located in an opened chromatin structure is responsible for the intestinal expression and vitamin D responsiveness of the transgene. Gel shift and footprinting assays using duodenal nuclear extracts indicate that this distal element contains a Cdx2-binding site. Finally, a mutation in this distal Cdx2-binding site dramatically decreases intestinal expression in transgenic mice. This report, using an in vivo approach, demonstrates the crucial role of Cdx2 for the transcription of an intestinal gene.

Distinct functions are implicated for the GATA-4, -5, and -6 transcription factors in the regulation of intestine epithelial cell differentiation

Based on conserved expression patterns, three members of the GATA family of transcriptional regulatory proteins, GATA-4, -5, and -6, are thought to be involved in the regulation of cardiogenesis and gut development. Functions for these factors are known in the heart, but relatively little is understood regarding their possible roles in the regulation of gut-specific gene expression. In this study, we analyze the expression and function of GATA-4, -5, and -6 using three separate but complementary vertebrate systems, and the results support a function for these proteins in regulating the terminal-differentiation program of intestinal epithelial cells. We show that xGATA-4, -5, and -6 can stimulate directly activity of the promoter for the intestinal fatty acid-binding protein (xIFABP) gene, which is a marker for differentiated enterocytes. This is the first direct demonstration of a target for GATA factors in the vertebrate intestinal epithelium. Transactivation by xGATA-4, -5, and -6 is mediated at least in part by a defined proximal IFABP promoter element. The expression patterns for cGATA-4, -5, and -6 are markedly distinct along the proximal-distal villus axis. Transcript levels for cGATA-4 increase along the axis toward the villus tip; likewise, cGATA-5 transcripts are largely restricted to the distal tip containing differentiated cells. In contrast, the pattern of cGATA-6 transcripts is complementary to cGATA-5, with highest levels detected in the region of proliferating progenitor cells. Undifferentiated and proliferating human HT-29 cells express hGATA-6 but not hGATA-4 or hGATA-5. Upon stimulation to differentiate, the transcript levels for hGATA-5 increase, and this occurs prior to increased transcription of the terminal differentiation marker intestinal alkaline phosphatase. At the same time, hGATA-6 steady-state transcript levels decline appreciably. All of the data are consistent with evolutionarily conserved but distinct roles for these factors in regulating the differentiation program of intestinal epithelium. Based on this data, we suggest that GATA-6 might function primarily within the proliferating progenitor population, while GATA-4 and GATA-5 function during differentiation to activate terminal-differentiation genes including IFABP.

Advances in nutrition and gastroenterology: summary of the 1997 A.S.P.E.N. Research Workshop

BACKGROUND

The 1997 A.S.P.E.N. Research Workshop was held at the annual meeting in San Francisco, on January 26, 1997. The workshop focused on advances in clinical and basic research involving the interface between nutrient and luminal gastroenterology.

METHODS

Presentations on the genetic regulation of gastrointestinal development, the molecular biology of small intestinal adaptation, the effect of nutrition support on intestinal mucosal mass, the relationship between nutrition and gastrointestinal motility, nutrient absorption, and gastrointestinal tract substrate metabolism were made by the preeminent leaders in the field.

RESULTS

The investigators presented an insightful analysis of each topic by reviewing data from their own laboratories and the published literature.

CONCLUSIONS

This workshop underscored the important interactions between nutrition and luminal gastroenterology at the basic science, metabolic/physiologic, and clinical levels. The integration of presentations from the different disciplines provided a unique interaction of information and ideas to advance our understanding of nutrition and gastrointestinal tract.

Anteroposterior gradient of epithelial transformation during amphibian intestinal remodeling: immunohistochemical detection of intestinal fatty acid-binding protein

To determine whether the remodeling of the well-organized intestinal epithelium during amphibian metamorphosis is regionally regulated along the anteroposterior axis of the intestine, we raised a polyclonal antibody against the Xenopus laevis intestinal fatty acid-binding protein (IFABP), which is known to be specifically expressed in intestinal absorptive cells, and examined immunohistochemically the differentiation, proliferation, and apoptosis of the epithelial cells throughout X. laevis small intestine. During pre- and prometamorphosis, IFABP-immunoreactive (ir) epithelial cells were localized only in the anterior half of the larval intestine. At the beginning of metamorphic climax, apoptotic cells detected by nick end-labeling (TUNEL) suddenly increased in number in the entire larval epithelium, concurrently with the appearance of adult epithelial primordia. Subsequently, the adult primordia in the anterior part of the intestine developed more rapidly by active cell proliferation than those in the posterior part, and replaced the larval epithelial cells earlier than those in the posterior part. IFABP-ir cells in the adult epithelium were first detectable at the tips of newly formed folds in the proximal part of the intestine. Thereafter, IFABP expression gradually progressed both in the anteroposterior direction and in the crest-trough direction of the folds. These results suggest that developmental processes of the adult epithelium in the X. laevis intestine are regionally regulated along the anteroposterior axis of the intestine, which is maintained throughout metamorphosis, and along the trough-crest axis of the epithelial folds, which is newly established during metamorphosis. Furthermore, the regional differences in IFABP expression along the anteroposterior axis of the intestine were reproduced in organ cultures in vitro. In addition, IFABP expression was first down-regulated and then reactivated in vitro when the anterior part, but not the posterior part, of the larval intestine was treated with thyroid hormone (TH) for extended periods. Therefore, it seems that, in addition to TH, an endogenous factor(s) localized in the intestine itself with an anteroposterior gradient participates in the development of the adult epithelium during amphibian metamorphosis.

Examining the role of Paneth cells in the small intestine by lineage ablation in transgenic mice

The Paneth cell lineage is one of four epithelial lineages derived from the adult mouse small intestine's multipotent stem cell. Mature Paneth cells secrete antimicrobial peptides (cryptdins), growth factors, as well as two gene products, a secreted phospholipase A2 and matrilysin, that has been implicated as modifiers of adenoma formation in mice containing a mutation in the tumor suppressor Apc. Immature Paneth cells are located just above and below the cell layer, in intestinal crypts, that has been proposed to contain the multipotent stem cell. Paneth cells differentiate during a downward migration to the crypt base. The location and direction of Paneth cell migration, their high density and long residency time at the crypt base, and the nature of their secreted gene products, suggest that they may influence the structure and/or function of the stem cell niche. Paneth cell ablation can therefore be viewed as an experimental manipulation of the cellular microenvironment that purportedly contains the stem cell and its immediate descendants. Two types of ablation experiments were performed in transgenic mice. Nucleotides -6500 to +34 of the mouse cryptdin-2 gene (CR2) were used to express an attenuated diphtheria toxin A fragment. Light and electron microscopic immunohistochemical analyses of several pedigrees of postnatal day 28 to 180 animals established that ablation of Paneth cells is accompanied by an increase in the proportion of undifferentiated crypt base columnar cells. These cells normally co-exist with Paneth cells. The ablation does not produce a detectable effect on the proliferation or terminal differentiation programs of the other three lineages or on host-microbial interactions. The last conclusion is based on the ability of crypts to remain free of microbes detectable by Gram and Warthin-Starry stains and by retention of the normal crypt-villus distribution of components of the diffuse gut-associated lymphoid tissue. CR2-directed expression of simian virus 40 large T antigen also results in a loss of mature Paneth cells but produces a marked amplification of crypt cells having a morphology intermediate between Paneth and granule goblet cells. EM immunohistochemical analyses suggest that intermediate cells can differentiate to mature goblet cells but not to Paneth cells, as they migrate up the crypt-villus axis. Our findings suggest that (i) stemness in the crypt is not defined by instructive interactions involving the Paneth cell; (ii) expressing a Paneth cell fate may require that precursors migrate to the crypt base; (iii) antimicrobial factors produced by Paneth cells are not required to prevent colonization of small intestinal crypts; and (iv) this lineage does not function to maintain the asymmetric crypt-villus distribution of components of the diffuse gut-associated lymphoid tissue.

Bi-transgenic mice reveal that K-rasVal12 augments a p53-independent apoptosis when small intestinal villus enterocytes reenter the cell cycle

Studies in cell culture systems have indicated that oncogenic forms of Ras can affect apoptosis. Activating mutations of Ras occur in approximately 30% of all human tumors and 50% of colorectal carcinomas. Since these mutations appear at early or intermediate stages in multistep journeys to neoplasia, an effect on apoptosis may help determine whether initiated cells progress towards a more neoplastic state. We have tested the effects of K-rasVal12 on apoptosis in transgenic mice. A lineage-specific promoter was used to direct expression of human K-rasVal12, with or without wild-type (wt) or mutant SV-40 T antigens (TAg), in postmitotic villus enterocytes, the principal cell type of the small intestinal epithelium. Enterocytes can be induced to reenter the cell cycle by TAgWt. Reentry is dependent upon the ability of TAg to bind pRB and is associated with a p53-independent apoptosis. Analyses of K-rasVal12 x TAgWt bi-transgenic animals indicated that K-rasVal12 can enhance this apoptosis threefold but only in cycling cells; increased apoptosis does not occur when K-rasVal12 is expressed alone or with a TAg containing Glu107,108two head right arrow Lys107, 108 substitutions that block its ability to bind pRB. Analysis of bi-transgenic K-rasVal12 x TAgWt mice homozygous for wild-type or null p53 alleles established that the enhancement of apoptosis occurs through a p53-independent mechanism, is not attributable to augmented proliferation or to an increase in abortive cell cycle reentry (compared to TAgWt mice), and is not associated with detectable changes in the crypt-villus patterns of expression of apoptotic regulators (Bcl-2, Bcl-xL, Bak, and Bax) or mediators of epithelial cell-matrix interactions and survival (e.g., alpha5beta1 integrin and its ligand, fibronectin). Coexpression of K-rasVal12 and TAgWt produces dysplasia. The K-rasVal12-augmented apoptosis is unrelated to this dysplasia; enhanced apoptosis is also observed in cycling nondysplastic enterocytes that produce K-rasVal12 and a TAg with a COOH-terminal truncation. The dysplastic epithelium of K-rasVal12 x TAgWt mice does not develop neoplasms. Our results are consistent with this finding: (a) When expressed in initiated enterocytes with a proliferative abnormality, K-rasVal12 facilitates progression to a dysplastic phenotype; (b) by diminishing cell survival on the villus, the oncoprotein may impede further progression; and (c) additional mutations may be needed to suppress this proapoptotic response to K-rasVal12.

Evidence for a role of the gut hormone PYY in the regulation of intestinal fatty acid-binding protein transcripts in differentiated subpopulations of intestinal epithelial cell hybrids

Peptide tyrosine tyrosine (PYY) is a gut hormone present in endocrine cells in the lower intestine that can be released by the presence of luminal free fatty acids (FFAs). The biological action of this peptide includes inhibition of gut motility and gastrointestinal and pancreatic secretions. Intestinal fatty acid-binding protein (I-FABP) binds FFA and may be involved in their cytosolic trafficking. Quantitative in situ hybridization on heterogeneous populations of small intestinal somatic cell hybrids selected for endogenous I-FABP expression (hBRIE 380i cells) demonstrated a 5-fold increase in I-FABP transcripts in response to PYY (within 6 h) that was confined to clusters of differentiated cells, whereas ribonuclease protection assays performed on heterogeneous populations of these cells showed no significant differences. High affinity PYY receptors, with an IC50 of 5-50 pM, were identified in both differentiated and nondifferentiated cell populations, as determined by competitive binding assays and autoradiography. In situ hybridization of rat ileal tissue also revealed differing patterns of mRNA expression for liver fatty acid-binding protein (L-FABP) and I-FABP. Only I-FABP mRNA was detected in the villus tips. This localization correlated with the expression pattern of I-FABP mRNA in the hBRIE 380i cells where changes in transcripts were observed only in differentiated cells that did not incorporate bromodeoxyuridine. The sustained expression of I-FABP transcripts in the villar tips suggests (unlike L-FABP) that older terminally differentiated cell populations of the mucosa can still be PYY responsive. These studies demonstrate that physiological concentrations of PYY can regulate I-FABP and place this peptide in a key position as part of a feedback system that determines the processing of cytosolic FFA in the enterocyte. In addition, these studies suggest a mechanism whereby luminal agents can modulate expression of proteins in terminally differentiated cells in the gastrointestinal mucosa.

Suppressor and activator functions mediated by a repeated heptad sequence in the liver fatty acid-binding protein gene (Fabpl). Effects on renal, small intestinal, and colonic epithelial cell gene expression in transgenic mice

A 35-nucleotide sequence in the liver fatty acid-binding protein gene (Fabpl) has been identified that interacts with nuclear proteins present in adult mouse liver, kidney, stomach, small intestine, and colon. The binding site consists of a direct heptad repeat (TTCTGNNTT) separated by five nucleotides. Both heptads are required for formation of stable complexes with nuclear proteins in gel mobility shift assays. The in vivo functions mediated by the repeats were determined by comparing the expression of four Fabpl/human growth hormone fusion genes in multiple pedigrees of adult transgenic mice. The transgenes contained (i) nucleotides -596 to +21 of Fabpl linked to the human growth hormone reporter, (ii) 4 additional copies of the 35-base pair element placed at nucleotide -596 of Fabpl, (iii) 4 additional copies of the sequence placed just upstream of its endogenous site at nucleotide -132, and (iv) a sequence identical to (iii) but with all heptad repeats mutated within each of the 4 additional copies of the 35-base pair element. Transgene expression was defined by RNA blot hybridizations and by light and electron microscopic immunohistochemistry. The heptad repeat functions to suppress expression in tubular epithelial cells of the proximal nephron, in hepatocytes, in the mucus-producing pit cells of the gastric epithelium, and in absorptive enterocytes located in the proximal small intestine. There is a gradient of escape from enterocytic suppression as one moves from the proximal to distal small intestine. This escape progresses to involve successively less differentiated cells located closer and closer to the stem cell zone in crypts of Lieberkühn. The heptad repeat activates gene expression in the colonic epithelium so that all proliferating and nonproliferating cells in colonic crypts distributed from the cecum to the rectum support transgene expression. The heptad has no obvious sequence similarities to known transcription factor binding sites, suggesting that mediators of its in vivo activities are likely to be novel. One candidate factor is a 90-kDa protein identified in Southwestern blots. The 90-kDa protein also binds to an element in the matrix metalloproteinase-2 gene that functions as an enhancer in renal cells, shares sequence homology with the heptad, and generates similar-sized complexes in gel mobility shift assays as the Fabpl repeat. The heptad repeat represents a target for identifying transcription factors that regulate gene expression between gut and renal epithelia and that also regulate the differentiation program of the intestine's principal epithelial lineage as a function of its location along the duodenal-colonic axis. Finally, the Fabpl regulatory elements described in this report should be useful for delivering a variety of gene products throughout the colonic epithelium of transgenic mice.

Intestinal epithelial cell differentiation: new insights from mice, flies and nematodes

Decisions commonly made during development that affect proliferation, cell fate specification, differentiation, migration, and death are made repeatedly in the mouse small intestinal epithelium throughout adulthood. The results of these decisions are a stratification of proliferation, differentiation, and death along the mouse small intestine's crypt/villus axis. Recent genetic studies in Caenorhabditis elegans and Drosophila melanogaster have identified factors involved in determining cell fate and differentiation in gut endoderm. The stem cell hierarchy of the adult mouse intestinal epithelium makes it ideally suited for using chimeric animals to examine the functions of homologs of these lower eukaryotic (and other) proteins.