The mouse intestinal fatty acid binding protein gene: nucleotide sequence, pattern of developmental and regional expression, and proposed structure of its protein product

Fatty acid binding protein as a new age biomarker

Small lipid-binding proteins known as fatty acid-binding proteins (FABPs) are extensively expressed in cells having elevated levels of fatty acid (FA) metabolism. There are ten known FABPs in mammals that exhibit expression patterns specific to tissues and tertiary structures that are substantially preserved. FABPs were first investigated as FA transport proteins inside cells. Subsequent research has shown that they are involved in signalling within their expression cells and in metabolism of lipid, directly and through the control of expression of gene. Additionally, there is evidence that they might be released and influence circulatory function. It has been observed that some tissues and organs linked to inflammatory, metabolic illnesses and also infectious disease have markedly elevated expression levels of FABPs. Thus, in addition to previously identified markers, FABPs represent a promising new biomarker that require additional investigation to optimise illness detection and prognosis techniques.

Pathogenic Impact of Fatty Acid-Binding Proteins in Parkinson's Disease-Potential Biomarkers and Therapeutic Targets

Parkinson's disease is a neurodegenerative condition characterized by motor dysfunction resulting from the degeneration of dopamine-producing neurons in the midbrain. This dopamine deficiency gives rise to a spectrum of movement-related symptoms, including tremors, rigidity, and bradykinesia. While the precise etiology of Parkinson's disease remains elusive, genetic mutations, protein aggregation, inflammatory processes, and oxidative stress are believed to contribute to its development. In this context, fatty acid-binding proteins (FABPs) in the central nervous system, FABP3, FABP5, and FABP7, impact α-synuclein aggregation, neurotoxicity, and neuroinflammation. These FABPs accumulate in mitochondria during neurodegeneration, disrupting their membrane potential and homeostasis. In particular, FABP3, abundant in nigrostriatal dopaminergic neurons, is responsible for α-synuclein propagation into neurons and intracellular accumulation, affecting the loss of mesencephalic tyrosine hydroxylase protein, a rate-limiting enzyme of dopamine biosynthesis. This review summarizes the characteristics of FABP family proteins and delves into the pathogenic significance of FABPs in the pathogenesis of Parkinson's disease. Furthermore, it examines potential novel therapeutic targets and early diagnostic biomarkers for Parkinson's disease and related neurodegenerative disorders.

Role of fatty acid binding proteins (FABPs) in cancer development and progression

Fatty acid binding proteins (FABPs) are small, water soluble proteins that bind long chain fatty acids and other biologically active ligands to facilitate intracellular localization. Twelve FABP family members have been identified to date, with 10 isoforms expressed in humans. Functionally, FABPs are important in fatty acid metabolism and transport, with distinct family members having the capacity to influence gene transcription. Expression of FABPs is usually cell/tissue specific to one predominant FABP family member. Dysregulation of FABP expression can occur through genetic mutation and/or environmental-lifestyle influences. In addition to intracellular function, exogenous, circulating FABP expression can occur and is associated with specific disease states such as insulin resistance. A role for FABPs is increasingly being reported in tumor biology with elevated exogenous FABP expression being associated with tumor progression and invasiveness. However, a less clear role has been appreciated for dysregulated FABP expression during cell transformation and early expansion.

Preferential gene expression and epigenetic memory of induced pluripotent stem cells derived from mouse pancreas

Induced pluripotent stem cells (iPSCs) have been established from various somatic cell types. Accumulating evidence suggests that iPSCs from different cell sources have distinct molecular and functional properties. Here, we establish iPSC derived from mouse pancreas (Panc-iPSC) and compared their properties with those of iPSC derived from tail-tip fibroblast (TTF-iPSC). The metabolic profile differs between Panc-iPSC and TTF-iPSC, indicating distinct cell properties in these iPSCs. Expression of Pdx1, a marker of pancreas differentiation, is increased through formation of embryoid body (EB) in Panc-iPSC, but the level is similar to that in TTF-iPSC. In contrast, EBs derived from Panc-iPSC express liver-specific albumin (Alb) and alpha-fetoprotein (Afp) genes much more strongly than those from TTF-iPSC. Epigenetic analysis shows a different histone modification pattern between Panc-iPSC and TTF-iPSC. Promoter regions of Alb and Afp genes in Panc-iPSC are suggested to have a more open chromatin structure than those in TTF-iPSC, which also is seen in primary cultured pancreatic cells. Our data suggest that Panc-iPSC possesses distinct differentiation capacity from that of TTF-PSC, which may be influenced by epigenetic memory.

Wnt and Notch signals guide embryonic stem cell differentiation into the intestinal lineages

The studies of differentiation of mouse or human embryonic stem cells (hESCs) into specific cell types of the intestinal cells would provide insights to the understanding of intestinal development and ultimately yield cells for the use in future regenerative medicine. Here, using an in vitro differentiation procedure of pluripotent stem cells into definitive endoderm (DE), inductive signal pathways' guiding differentiation into intestinal cells was investigated. We found that activation of Wnt/β-catenin and inhibition of Notch signaling pathways, by simultaneous application of 6-bromoindirubin-3'-oxime (BIO), a glycogen synthase kinase-3β inhibitor, and N-[(3,5-Difluorophenyl)acetyl]-L-alanyl-2-phenylglycine-1,1-dimethylethyl ester (DAPT), a known γ-secretase inhibitor, efficiently induced intestinal differentiation of ESCs cultured on feeder cell. BIO and DAPT patterned the DE at graded concentrations. Upon prolonged culture on feeder cells, all four intestinal differentiated cell types, the absorptive enterocytes and three types of secretory cells (goblet cells, enteroendocrine cells, and Paneth cells), were efficiently differentiated from mouse and hESC-derived intestinal epithelium cells. Further investigation revealed that in the mouse ESCs, fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) signaling act synergistically with BIO and DAPT to potentiate differentiation into the intestinal epithelium. However, in hESCs, FGF signaling inhibited, and BMP signaling did not affect differentiation into the intestinal epithelium. We concluded that Wnt and Notch signaling function to pattern the anterior-posterior axis of the DE and control intestinal differentiation.

Defining suitable reference genes for RT-qPCR analysis on intestinal epithelial cells

The study of the mammalian intestinal epithelium concerns several aspects of cellular and molecular biology. In fact, most of these studies aim to define molecular components or mechanisms related with the control of stemness and the balance between cell proliferation and differentiation in physiopathological conditions. It is worth mentioning that real-time quantitative reverse transcription-polymerase chain reaction (RT-qPCR) approaches are commonly used, but only a few studies are available regarding suitable reference genes to normalize gene expression data. The present study was designed to validate potential reference genes in freshly isolated proliferating or differentiated epithelial cells from the mouse intestine. We also extended our analysis to the IEC6 intestinal epithelial cells, as a promising model to study intestinal physiopathology in vitro. The stability of six potential reference genes (Hprt1, Ppia, Gapdh, Rplp0, Ppib, and Vil1) has been tested both in epithelial cells isolated from the mouse intestine and in the IEC6 cell line. The software programs-geNorm and Normfinder-were used to obtain an estimation of the expression stability of each gene and, by comparing the results, to identify the most suitable genes for RT-qPCR data normalization. These multiple approaches allowed us to select different suitable reference genes for the correct quantification of mRNAs depending on the differentiated or proliferative nature of the cells.

Comparative evolutionary genomics of medaka and three-spined stickleback fabp2a and fabp2b genes with fabp2 of zebrafish

Here we describe the evolutionary relationship of the duplicated intestinal fatty acid binding protein genes fabp2a and fabp2b from medaka and three-spined stickleback by comparing them to the well-studied fabp2 gene from zebrafish. The duplicated fabp2 genes from medaka and three-spined stickleback consist of four exons separated by three introns, which code for a polypeptide of 132 amino acids. Fabp2a and Fabp2b of medaka and three-spined stickleback share highest sequence identity with zebrafish Fabp2. All Fabp2/FABP2 sequences from vertebrates form a distinct clade in a neighbor-joining phylogenetic tree with a robust 100% bootstrap value, which indicates that the medaka and three-spined stickleback fabp2a and fabp2b are orthologs of zebrafish fabp2. The syntenic genes of fabp2a and fabp2b from medaka and three-spined stickleback were shown to be conserved with the syntenic genes of fabp2/FABP2 from zebrafish and human, evidence that the duplicated fabp2 genes from medaka and three-spined stickleback most likely arose from the teleost-specific whole-genome duplication. The tissue-specific distribution of medaka and three-spined stickleback fabp2a and fabp2b transcripts, and zebrafish fabp2 transcripts, assayed by RT-qPCR suggests the acquisition of new function(s) by the medaka fabp2a, and the distinct evolution of fabp2b compared with fabp2a in the medaka and three-spined stickleback genomes.

A system to enrich for primitive streak-derivatives, definitive endoderm and mesoderm, from pluripotent cells in culture

Two lineages of endoderm develop during mammalian embryogenesis, the primitive endoderm in the pre-implantation blastocyst and the definitive endoderm at gastrulation. This complexity of endoderm cell populations is mirrored during pluripotent cell differentiation in vitro and has hindered the identification and purification of the definitive endoderm for use as a substrate for further differentiation. The aggregation and differentiation of early primitive ectoderm-like (EPL) cells, resulting in the formation of EPL-cell derived embryoid bodies (EPLEBs), is a model of gastrulation that progresses through the sequential formation of primitive streak-like intermediates to nascent mesoderm and more differentiated mesoderm populations. EPL cell-derived EBs have been further analysed for the formation of definitive endoderm by detailed morphological studies, gene expression and a protein uptake assay. In comparison to embryoid bodies derived from ES cells, which form primitive and definitive endoderm, the endoderm compartment of embryoid bodies formed from EPL cells was comprised almost exclusively of definitive endoderm. Definitive endoderm was defined as a population of squamous cells that expressed Sox17, CXCR4 and Trh, which formed without the prior formation of primitive endoderm and was unable to endocytose horseradish peroxidase from the medium. Definitive endoderm formed in EPLEBs provides a substrate for further differentiation into specific endoderm lineages; these lineages can be used as research tools for understanding the mechanisms controlling lineage establishment and the nature of the transient intermediates formed. The similarity between mouse EPL cells and human ES cells suggests EPLEBs can be used as a model system for the development of technologies to enrich for the formation of human ES cell-derived definitive endoderm in the future.

The human fatty acid-binding protein family: evolutionary divergences and functions

Fatty acid-binding proteins (FABPs) are members of the intracellular lipid-binding protein (iLBP) family and are involved in reversibly binding intracellular hydrophobic ligands and trafficking them throughout cellular compartments, including the peroxisomes, mitochondria, endoplasmic reticulum and nucleus. FABPs are small, structurally conserved cytosolic proteins consisting of a water-filled, interior-binding pocket surrounded by ten anti-parallel beta sheets, forming a beta barrel. At the superior surface, two alpha-helices cap the pocket and are thought to regulate binding. FABPs have broad specificity, including the ability to bind long-chain (C16-C20) fatty acids, eicosanoids, bile salts and peroxisome proliferators. FABPs demonstrate strong evolutionary conservation and are present in a spectrum of species including Drosophila melanogaster, Caenorhabditis elegans, mouse and human. The human genome consists of nine putatively functional protein-coding FABP genes. The most recently identified family member, FABP12, has been less studied.

Genomic organization of Atlantic salmon (Salmo salar) fatty acid binding protein (fabp2) genes reveals independent loss of duplicate loci in teleosts

Gene and genome duplications are considered to be driving forces of evolution. The relatively recent genome duplication in the common ancestor of salmonids makes this group of fish an excellent system for studying the re-diploidization process and the fates of duplicate genes. We characterized the structure and genome organization of the intestinal fatty acid binding protein (fabp2) genes in Atlantic salmon as a means of understanding the evolutionary fates of members of this protein family in teleosts. A survey of EST databases identified three unique salmonid fabp2 transcripts (fabp2aI, fabp2aII and fabp2b) compared to one transcript in zebrafish. We screened the CHORI-214 Atlantic salmon BAC library and identified BACs containing each of the three fabp2 genes. Physical mapping, genetic mapping and fluorescence in situ hybridization of Atlantic salmon chromosomes revealed that Atlantic salmon fabp2aI, fabp2aII and fabp2b correspond to separate genetic loci that reside on different chromosomes. Comparative genomic analyses indicated that these genes are related to one another by two genome duplications and a gene loss. The first genome duplication occurred in the common ancestor of all teleosts, giving rise to fabp2a and fabp2b, and the second in the common ancestor of salmonids, producing fabp2aI, fabp2aII, fabp2bI and fabp2bII. A subsequent loss of fabp2bI or fabp2bII gave the complement of fabp2 genes seen in Atlantic salmon today. There is also evidence for independent losses of fabp2b genes in zebrafish and tetraodon. Although there is no evidence for partitioning of tissue expression of fabp2 genes (i.e., sub-functionalization) in Atlantic salmon, the pattern of amino acid substitutions in Atlantic salmon and rainbow trout fabp2aI and fabp2aII suggests that neo-functionalization is occurring.

Fibroblast growth factor receptor-3 regulates Paneth cell lineage allocation and accrual of epithelial stem cells during murine intestinal development

Fibroblast growth factor receptor 3 (FGFR-3) is expressed in the lower crypt epithelium, where stem cells of the intestine reside. The role of FGFR-3 signaling in regulating features of intestinal morphogenesis was examined in FGFR-3-null (FGFR-3(-/-)) mice. FGFR-3(-/-) mice had only about half the number of intestinal crypts and a marked decrease in the number of functional clonogenic stem cells, as assessed by an in vivo microcolony-forming assay, compared with wild-type littermates. A marked deficit in allocation of progenitor cells to Paneth cell differentiation was noted, although all the principal epithelial lineages were represented in FGFR-3(-/-) mice. The total cellular content and nuclear localization of beta-catenin protein were reduced in FGFR-3(-/-) mice, as was expression of cyclin D1 and matrix metalloproteinase-7, major downstream targets of beta-catenin/T cell factor-4 (Tcf-4) signaling. Activation of FGFR-3 in Caco-2 cells, an intestinal epithelial cell line, abrogated the fall in beta-catenin/Tcf-4 signaling activity that is normally observed in these cells as cultures become progressively more confluent. These findings are consistent with the hypothesis that, during intestinal development, FGFR-3 signaling regulates crypt epithelial stem cell expansion and crypt morphogenesis, as well as Paneth cell lineage specification, through beta-catenin/Tcf-4-dependent and -independent pathways.

Molecular cloning and tissue-specific expression of intestinal-type fatty acid binding protein in porcine

The intestinal fatty acid-binding protein (I-FABP) shows binding specificity for long-chain fatty acids and is proposed to be involved in the uptake of dietary fatty acids and their intracellular transport. In this study, the full-length cDNA of I-FABP was cloned from pig intestine by homology cloning approach combined with 3' and 5' RACE. Sequence analysis and bioinformatics study showed that this cDNA contained 614 nucleotides, with a 399 bp open reading frame (ORF) flanked by a 43 bp 5' UTR and a 172 bp 3' UTR. The encoded 132 amino acids of pig I-FABP with a molecular weight of approximately 15 kDa shared a high sequence identity of 68%-85% with those of other species. In addition, the phylogenetical analysis also indicated that the pig I-FABP was in the same branch with those of other species. The tissue-specific expression of pig I-FABP was measured by Northern hybridization and semi-quantitative RT-PCR. The results demonstrated that pig I-FABP mRNA was extensively present in various tissues, but I-FABP transcript of approximately 620 bp was more abundant in intestine than in other tissues.

Establishment and characterization of monoclonal and polyclonal antibodies against human intestinal fatty acid-binding protein (I-FABP) using synthetic regional peptides and recombinant I-FABP

We have succeeded in raising highly specific anti-human intestinal fatty acid-binding protein (I-FABP) monoclonal antibodies by immunizing animals with three synthetic regional peptides, i.e., the amino terminal (RP-1: N-acetylated 1-19-cysteine), middle portion (RP-2: cysteinyl-91-107) and carboxylic terminal (RP-3: cysteinyl-121-131) regions of human I-FABP, and the whole I-FABP molecule as antigens. We also raised a polyclonal antibody by immunizing with a recombinant (r) I-FABP. To ascertain the specificity of these antibodies for human I-FABP, the immunological reactivity of each was examined by a binding assay using rI-FABP, partially purified native I-FABP and related proteins such as liver-type (L)-FABP, heart-type (H)-FABP, as well as the regional peptides as reactants, and by Western blot analysis. In addition, the expression and distribution of I-FABP in the human gastrointestinal tract were investigated by an immunohistochemical technique using a carboxylic terminal region-specific monoclonal antibody, 8F9, and a polyclonal antibody, DN-R2. Our results indicated that both the monoclonal and polyclonal antibodies established in this study were highly specific for I-FABP, but not for L-FABP and H-FABP. Especially, the monoclonal antibodies raised against the regional peptides, showed regional specificity for the I-FABP molecule. Immunoreactivity of I-FABP was demonstrated in the mucosal epithelium of the jejunum and ileum by immunohistochemical staining, and the immunoreactivity was based on the presence of the whole I-FABP molecule but not the presence of any precursors or degradation products containing a carboxylic terminal fragment. It is concluded that some of these monoclonal and polyclonal antibodies, such as 8F9, 4205, and DN-R2, will be suitable for use in research on the immunochemistry and clinical chemistry of I-FABP because those antibodies can recognize both types of native and denatured I-FABP. In order to detect I-FABP in blood samples, it is essential to use this type of antibody, reactive to native type of I-FABP. It is anticipated that, in the near future, such a method for measuring I-FABP will be developed as a useful tool for diagnosing intestinal ischemia by using some of these antibodies.

Regulated Nodal signaling promotes differentiation of the definitive endoderm and mesoderm from ES cells

Nodal signaling induces the formation of the endoderm and mesoderm during gastrulation. Nodal expression persists until the definitive endoderm progenitor has completely formed, and disappears thereafter. A tightly regulated Nodal expression system is essential for the differentiation of embryonic stem (ES) cells into distinct tissue lineages. On this basis, we established an ES cell differentiation system with the tetracycline-regulated expression of Nodal. The upregulated Nodal signaling pathway and its downstream transcriptional targets induced the specification of ES cells into definitive endoderm and mesoderm derivatives, and the subsequent downregulation of Nodal signaling promoted further maturation of the gut tube both in vitro and in vivo. Sustained expression of the Nodal gene inhibited the maturation of the definitive endoderm owing to persistent Oct3 and/or Oct4 expression and teratoma formation. Furthermore, quantitative single cell analysis by flow cytometry using CXCR4, VEGFR2 and PDGFR-α indicated that this protocol for definitive endoderm and mesoderm differentiation is superior to any other available protocol. Our findings also indicated that the Nodal or Nodal-related molecules secreted from Nodal-expressing ES cells could cause genetically unmanipulated ES cells to induce the expression of the Nodal signaling pathway and its downstream targets, which consequently leads to the differentiation of the ES cells into definitive endoderm and mesoderm. Our differentiation system, using tightly regulated Nodal expression, enabled us to investigate the mechanism of ES cell differentiation into definitive endoderm or mesoderm derivatives. Our findings also demonstrate that Nodal-expressing ES cells might be a source of highly active proteins that could be used for developing endoderm or mesoderm tissues in regenerative medicine.

Altered emotional behavioral responses in mice lacking brain-type fatty acid-binding protein gene

Brain-type fatty acid-binding protein (B-FABP) belongs to a family of intracellular lipid-binding proteins. B-FABP exhibits a binding affinity to long-chain fatty acids (FAs) whose effects on brain functions including development, emotion, learning and memory have been proposed. B-FABP is localized in the ventricular germinal cells in embryonic brain and astrocytes in developing and mature brain of rodents. In the present study we generated the mouse harboring a null mutation in the B-FABP gene and studied its phenotype. B-FABP mutant mice exhibited the enhanced anxiety and increased fear memory as well as the decreased content of docosahexaenoic acid (DHA) in their brain during the neonatal period without detection of any histological changes in the brain. In the adult brain, B-FABP was localized more numerously to the astrocytes in the amygdala and septal area than to those in the hippocampal area. Analysis of FA content in the amygdala of adult brain revealed that arachidonic and palmitic acids increased significantly in the mutant mice compared with wild-type. Furthermore, the response of N-methyl-d-aspartate receptor-mediated current to DHA in isolated neurons from B-FABP mutant brain was significantly decreased compared with that of wild-type, while no significant differences were detected in behavioral responses related to the spatial learning/memory or in the hippocampal long-term potentiation. These data indicate that B-FABP is crucially involved in the fear memory and anxiety through its binding with FAs and/or its own direct effects on pertinent metabolism/signaling of FAs.

The multigene family of fatty acid-binding proteins (FABPs): function, structure and polymorphism

Fatty acid-binding proteins (FABPs) are members of the superfamily of lipid-binding proteins (LBP). So far 9 different FABPs, with tissue-specific distribution, have been identified: L (liver), I (intestinal), H (muscle and heart), A (adipocyte), E (epidermal), Il (ileal), B (brain), M (myelin) and T (testis). The primary role of all the FABP family members is regulation of fatty acid uptake and intracellular transport. The structure of all FABPs is similar - the basic motif characterizing these proteins is beta-barrel, and a single ligand (e.g. a fatty acid, cholesterol, or retinoid) is bound in its internal water-filled cavity. Despite the wide variance in the protein sequence, the gene structure is identical. The FABP genes consist of 4 exons and 3 introns and a few of them are located in the same chromosomal region. For example, A-FABP, E-FABP and M-FABP create a gene cluster. Because of their physiological properties some FABP genes were tested in order to identify mutations altering lipid metabolism. Furthermore, the porcine A-FABP and H-FABP were studied as candidate genes with major effect on fatness traits.

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.

Characterization of equine intestinal fatty acid binding protein and its use in managing horses with colic

OBJECTIVE

To determine the nucleotide sequence of the equine intestinal fatty acid binding protein (I-FABP) gene, its expression in various regions of the gastrointestinal tract, and the use of measuring I-FABP in horses with colic. Animals-86 horses with colic.

PROCEDURE

The mRNA sequence for the I-FABP gene was obtained by use of a rapid amplification of complementary DNA ends technique. Comparative I-FABP gene expression was quantitated by use of a real-time reverse transcription-polymerase chain reaction assay. Amounts of I-FABP in abdominal fluid and plasma were measured by use of an ELISA kit. Association between I-FABP concentrations and clinical variables was performed by nonparametric analysis, and associations of these variables with intestinal ischemia were determined by the Spearman correlation test.

RESULTS

The nucleotide sequence had 87% identity with human I-FABP The I-FABP gene was highly expressed in the small intestinal mucosa but had low expression in the colon. High concentrations of I-FABP in abdominal fluid correlated with an increase in protein concentrations in peritoneal fluid and nonsurvival, whereas plasma I-FABP concentrations correlated with the necessity for abdominal surgery. Clinical variables associated with intestinal ischemia included the color and protein content of abdominal fluid and serum creatine kinase activity.

CONCLUSIONS AND CLINICAL RELEVANCE

Determination of I-FABP concentrations in abdominal fluid and plasma may be useful for predicting survival and the need for abdominal surgical intervention in horses with colic. Furthermore, serum creatine kinase activity and color and protein concentrations of abdominal fluid may be useful in the diagnosis of intestinal ischemia.

Sequence, linkage mapping and early developmental expression of the intestinal-type fatty acid-binding protein gene (fabp2) from zebrafish (Danio rerio)

The intestinal fatty acid-binding protein (I-FABP) shows binding specificity for long-chain fatty acids and is proposed to be involved in uptake of dietary fatty acids and their intracellular transport. We have determined the sequence of the gene encoding I-FABP in zebrafish. The zebrafish I-FABP gene contains four exons interrupted by three introns. Radiation hybrid mapping assigned the I-FABP gene to linkage group 1. A 924 bp sequence 5' upstream of the initiation codon in the I-FABP gene contained several putative cis-acting regulatory elements. In adult zebrafish, reverse transcription-polymerase chain reaction (RT-PCR) detected I-FABP mRNA in intestine, brain, liver, muscle and testis. Quantitative RT-PCR demonstrated that I-FABP mRNA was most abundant in intestine, followed by brain. I-FABP mRNA levels were very low in muscle, testis, heart, liver, skin and ovary. RT-PCR using total RNA extracted from zebrafish embryos detected I-FABP mRNA as early as 12 h post-fertilization. Whole-mount in situ hybridization to zebrafish embryos detected I-FABP mRNA in the yolk syncytial layer (YSL) at early somitogenesis. Later during embryonic development the I-FABP mRNA was detected in the intestinal bulb, liver and pancreas primordium. Expression in YSL, liver or pancreas has not been previously reported for fish or mammalian I-FABP genes and may be related to specific physiological differences between fishes and mammals.

Development of definitive endoderm from embryonic stem cells in culture

The cellular and molecular events regulating the induction and tissue-specific differentiation of endoderm are central to our understanding of the development and function of many organ systems. To define and characterize key components in this process, we have investigated the potential of embryonic stem (ES) cells to generate endoderm following their differentiation to embryoid bodies (EBs) in culture. We found that endoderm can be induced in EBs, either by limited exposure to serum or by culturing in the presence of activin A (activin) under serum-free conditions. By using an ES cell line with the green fluorescent protein (GFP) cDNA targeted to the brachyury locus, we demonstrate that endoderm develops from a brachyury(+) population that also displays mesoderm potential. Transplantation of cells generated from activin-induced brachyury(+) cells to the kidney capsule of recipient mice resulted in the development of endoderm-derived structures. These findings demonstrate that ES cells can generate endoderm in culture and, as such, establish this differentiation system as a unique murine model for studying the development and specification of this germ layer.

Expression analyses of zebrafishtransferrin,ifabp, andelastaseB mRNAs as differentiation markers for the three major endodermal organs: Liver, intestine, and exocrine pancreas

In the present work, three zebrafish cDNA clones encoding transferrin, intestinal fatty acid binding protein (IFABP), and elastaseB were cloned and their expression patterns in early zebrafish development were characterized as differentiation markers for the three major endoderm organs: liver, intestine, and exocrine pancreas. transferrin and ifabp mRNAs exhibit a biphasic expression pattern during early development. transferrin mRNAs were first expressed at approximately 7 hours postfertilization (hpf) in the yolk syncytial layer (YSL) and later in the liver rudiment (from approximately 48 hpf) and in the esophagus transiently (72-96 hpf). Ifabp mRNAs were initially expressed in the YSL at the ventral side during late epiboly (8-9 hpf), spread throughout the YSL of later stage embryos, and appeared in the intestine rudiment at approximately 36 hpf. In contrast to the transferrin and ifabp mRNAs, elastaseB mRNAs were not expressed in the yolk sac or YSL, and these transcripts were detected exclusively in the exocrine pancreas after approximately 56 hpf.

Fibroblast growth factor receptor-3 is expressed in undifferentiated intestinal epithelial cells during murine crypt morphogenesis

Prior studies have demonstrated that fibroblast growth factor receptor-3 (FGFR-3) regulates proliferation of undifferentiated intestinal epithelial cells in vitro. However, the function(s) of FGFR-3-mediated signaling during intestinal development and epithelial differentiation in vivo remain unknown. The goal of this study was to define the temporal, regional, and cell-specific patterns of FGFR-3 expression and its ligands during normal intestinal ontogeny and epithelial regeneration. Both the IIIb and IIIc isoforms of FGFR-3 mRNA, which result from differential splicing of the FGFR-3 primary transcript, were detected in mouse small intestine as early as embryonic day 16. FGFR-3 levels peaked in the small intestine from 7 to 21 days after birth and decreased thereafter to reach the low levels observed in adult mice. FGFR-3 IIIb and IIIc mRNA levels were highest in the duodenum and proximal jejunum with lower levels of both seen in the distal jejunum, ileum, and colon. FGFR-3 was expressed in a subset of proliferating undifferentiated crypt epithelial cells located in the intervillous epithelium and in the lower half of nascently forming crypts but not in differentiated epithelial cell types. FGFR-3 IIIb was the dominant isoform expressed in both small intestinal and colonic crypts. Expression of FGF1, FGF2, and FGF9, known ligands of FGFR-3, paralleled patterns of FGFR-3 expression during gut development. These data suggest that signaling through FGFR-3 plays a role in regulating morphogenic events involved in formation of intestinal crypts and/or the fate of epithelial stem cells.

Analysis of tissue-specific and PPARalpha-dependent induction of FABP gene expression in the mouse liver by an in vivo DNA electroporation method

Peroxisome proliferator (PPAR)alpha ligand Wy14,643 induces liver-fatty acid binding protein (FABP) spontaneously and heart-FABP gradually, but not intestine-FABP mRNA expression in the mouse liver. These strict regulations have not been reproduced in cultured cell systems. We applied a DNA electroporation method to directly introduce reporter gene constructs into the livers of mice. This system reproduced the in vivo responses of the above three FABP gene promoters to the PPARalpha ligand but not that of a promoter containing the typical three PPAR binding sites in tandem. Deletion and mutation analyses of the mouse L-FABP gene suggested that, in addition to the binding site for PPARalpha, a far upstream sequence is required for PPAR-dependent transactivation in the liver. In contrast to the cultured cell systems, our in vivo DNA electroporation method showed that PPARalpha binding to the promoter is necessary but not sufficient for PPARalpha ligand-dependent transcriptional activation of the L-FABP gene in vivo.

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.

Direct lineage tracing reveals the ontogeny of pancreatic cell fates during mouse embryogenesis

Lineage tracing follows the progeny of labeled cells through development. This technique identifies precursors of mature cell types in vivo and describes the cell fate restriction steps they undergo in temporal order. In the mouse pancreas, direct cell lineage tracing reveals that Pdx1- expressing progenitors in the early embryo give rise to all pancreatic cells. The progenitors for the mature pancreatic ducts separate from the endocrine/exocrine tissues before E12.5. Expression of Ngn3 and pancreatic polypeptide marks endocrine cell lineages during early embryogenesis, and these cells behave as transient progenitors rather than stem cells. In adults, Ngn3 is expressed within the endocrine islets, and the NGN3+ cells seem to contribute to pancreatic islet renewal. These results indicate the stage at which each progenitor population is restricted to a particular fate and provide markers for isolating progenitors to study their growth, differentiation, and the genes necessary for their development.

Cellular retinol-binding protein type II (CRBPII) in adult zebrafish (Danio rerio). cDNA sequence, tissue-specific expression and gene linkage analysis

We have determined the nucleotide sequence of a zebrafish cDNA clone that codes for a cellular retinol-binding protein type II (CRBPII). Radiation hybrid mapping revealed that the zebrafish and human CRBPII genes are located in syntenic groups. In situ hybridization and emulsion autoradiography localized the CRBPII mRNA to the intestine and the liver of adult zebrafish. CRBPII and intestinal fatty acid binding protein (I-FABP) mRNA was colocalized to the same regions along the anterior-posterior gradient of the zebrafish intestine. Similarly, CRBPII and I-FABP mRNA are colocalized in mammalian and chicken intestine. CRBPII mRNA, but not I-FABP mRNA, was detected in adult zebrafish liver which is in contrast to mammals where liver CRBPII mRNA levels are high during development but rapidly decrease to very low or undetectable levels following birth. CRBPII and I-FABP gene expression appears therefore to be co-ordinately regulated in the zebrafish intestine as has been suggested for mammals and chicken, but CRBPII gene expression is markedly different in the liver of adult zebrafish compared to the livers of mammals. As such, retinol metabolism in zebrafish may differ from that of mammals and require continued production of CRBPII in adult liver. The primary sequence of the coding regions of fish and mammalian CRBPII genes, their relative chromosomal location in syntenic groups and possibly portions of the control regions involved in regulation of CRBPII gene expression in the intestine appear therefore to have been conserved for more than 400 million years.

Altered water barrier function in epidermal-type fatty acid binding protein-deficient mice

We have generated mutant mice for epidermal-type fatty acid binding protein by the gene targeting technique and examined the phenotype in detail. Despite a lack in the expression of epidermal-type fatty acid binding protein mRNA and its protein in the skin and other tissues of the mutant mice, the animals appeared normal in gross and histologic examination. Northern blot analysis of other fatty acid binding proteins revealed a distinct elevated gene expression of heart-type fatty acid binding protein in the skin of the homozygous mice. In analyses of the skin, no differences were observed in contents of major fatty acids, electron microscopic appearance as well as inflammatory responses in ear skin between the mutant and wild-type mice. Basal transepidermal water loss of homozygous mice was lower than that of the wild mice. When acetone was applied to the skin for disruption of the water permeability barrier, recovery in transepidermal water loss was delayed, although maximum transepidermal water loss upon acetone treatment was similar between homozygous and wild-type mice in terms of size and time course. The molecular mechanism by which epidermal-type fatty acid binding protein contributes to the water barrier function of the skin remains to be elucidated.

PYY-mediated fatty acid induced intestinal differentiation

An essential process for fatty acid digestion, absorption and assimilation is the constant replacement of mature intestinal epithelial cells by differentiating stem cells. Free fatty acids (FFA) and PYY may act in concert to alter mucosal cell differentiation through the cytoskeletal-extracellular matrix interactions. PYY induced expression of tetraspanins and intestinal fatty acid binding protein (I-FABP) may be part of a mechanism whereby FFA modulate expression of differentiation dependent proteins in the mucosa. This modulation provides a means for FFA to act as signal molecules in the feedback regulation of their own assimilation.

Transgenic mouse model of intestine-specific mucosal injury and repair

Most studies of injury and repair to mucosal tissue have used nonspecific mediators to induce injury. Damage to the mucosal epithelium resulting from chemical or radiation treatment associated with cancer therapy may fall into this category of injury. When such treatments are applied, it is generally not possible to predict or control the extent of possible injury. This fact makes analysis of inductive and reparative processes difficult. In addition, the role of the immune system in the etiology and subsequent healing of mucosal tissue following cancer therapy with or without bone marrow transplantation remains unclear. To study tissue- and antigen-specific immune damage of intestinal mucosal tissue, we generated transgenic mice that express a nominal antigen exclusively in intestinal epithelial cells. The transfer of antigen-specific CD8 T cells with concomitant virus infection resulted in the destruction of intestinal epithelial cells and disease. The destructive phase in some cases was followed by complete recovery and tolerance induction. This model will provide a system that can be regulated for analysis of the mediators of mucosa-specific tissue damage and repair.

Thyroid hormone-induced expression of sonic hedgehog correlates with adult epithelial development during remodeling of the Xenopus stomach and intestine

Sonic hedgehog (Shh) was isolated from the Xenopus laevis intestine as an early thyroid hormone (TH) response gene. To investigate possible roles of TH-upregulated expression of Shh during metamorphosis, we raised a polyclonal antibody against Xenopus Shh and immunohistochemically examined the relationship between Shh expression and the larval-to-adult intestinal remodeling at the cellular level. Our results indicate that the epithelial-specific expression of Shh in the intestine spatiotemporally correlates well with active proliferation and/or initial differentiation of the secondary (adult) epithelial primordia that originate from stem cells, but not with apoptosis of the primary (larval) epithelium. Given the similar transformations of the stomach during metamorphosis, we also analyzed Shh expression in this organ and found similar correlations in the stomach, although the position of the adult epithelial primordia and their final differentiation in the stomach are different from those in the intestine. Furthermore, we show here that Shh expression is organ-autonomously induced by TH and its correlation with the adult epithelial development is reproduced in vitro in both the intestine and the stomach. More importantly, addition of recombinant Shh protein to the culture medium results in developmental anomalies of both organs. However, differentiation of the adult epithelium is more severely inhibited by exogenous Shh in the intestine than in the stomach. These results suggest that TH-upregulated expression of Shh plays important roles in the postembryonic gastrointestinal remodeling, but its roles are at least partially different between the intestine and the stomach.

EGF regulates early embryonic mouse gut development in chemically defined organ culture

The profound intestinal epithelial defects in the newborn epidermal growth factor receptor (EGFR) knockout mouse suggests that EGFR signaling plays important roles in embryonic gut development. Herein, we further elucidated the function of EGFR signaling on early embryonic gut development by comparing the effects of 1-10 ng/mL of exogenous epidermal growth factor (EGF) or 10-25 microM of the tyrphostin 3,4,5 trihydroxybenzene malononitrile, a specific inhibitor of EGFR tyrosine kinase, on intact E12 Swiss-Webster mouse midgut grown in chemically defined organ culture using Fitton-Jackson BGJb medium for 4 or 6 d. Intestinal development during culture was assayed by morphometry, histology, reverse transcription/competitive PCR for villin and intestinal fatty acid binding protein mRNA, and immunohistochemistry for epithelial proliferative markers. During organ culture, control specimens grew in length, developed smooth muscle, simple columnar epithelial and goblet cell phenotypes, showed early villus formation in the proximal intestine, and increased expression of villin and intestinal fatty acid binding protein mRNA. EGF failed to significantly alter small intestinal lengthening, whereas EGF 10 ng/mL inhibited colonic length growth. Tyrphostin 25 microM resulted in regional losses of stromal and smooth muscle cells in the small intestine and absent colonic goblet cells. In controls, cellular proliferation initially occurred throughout the small intestinal epithelium but became increasingly localized to the intervillus crypt regions. This sequestration of epithelial proliferation into crypts was much more apparent in EGF-treated versus tyrphostin-treated specimens. EGFR activation, therefore, appears to accelerate the maturation rate of goblet cells and the differential crypt/villus proliferation pattern in early embryonic mouse gut.

Differential effects of PPARalpha activators on induction of ectopic expression of tissue-specific fatty acid binding protein genes in the mouse liver

The effect of a potent peroxisome proliferator-activated receptor (PPAR) alpha activator Wy14,643 on tissue-specific expression of fatty acid binding (FABP) genes was studied. Wy14,643 immediately induced liver-, intestine- and FABP but not PPARgamma-regulated adipose-FABP (or aP2) mRNAs in respective mouse tissues. Moreover, it gradually induced ectopic expression of heart- and adipose-FABP mRNAs to significant levels in the liver. However, ectopic expression was not induced in the liver of PPARalpha-null mouse, indicating an obligatory role of the receptor in the modulated expression. Among the four PPARalpha activators examined, only Wy14,643 induced ectopical expression of heart-FABP in the liver. Thus, tissue-specificity of the FABP gene expression is not absolute and, with a potent activator, can be distorted by PPARalpha.

The intestinal fatty acid binding protein is not essential for dietary fat absorption in mice

The intestinal fatty acid binding protein (I-FABP) belongs to a family of 15 kDa clamshell-like proteins that are found in many different tissues. So far, nine types have been identified. Their primary structures are highly conserved between species but somewhat less so among the different types. The function of these proteins, many of which are highly expressed, is not well understood. Their ability to bind lipid ligands suggests a role in lipid metabolism, but direct evidence for this idea is still lacking. We tested the hypothesis that I-FABP serves an essential role in the assimilation of dietary fatty acids by disrupting its gene (Fabpi) in the mouse. We discovered that Fabpi-/- mice are viable, but they display alterations in body weight and are hyperinsulinemic. Male Fabpi-/- mice had elevated plasma triacylglycerols and weighed more regardless of the dietary fat content. In contrast, female Fabpi-/- mice gained less weight in response to a high-fat diet. The results clearly demonstrate that I-FABP is not essential for dietary fat absorption. We propose that I-FABP functions as a lipid-sensing component of energy homeostasis that alters body weight gain in a gender-specific fashion.

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

We have determined the nucleotide sequence for two cDNA clones coding for a fatty acid binding protein (FABP) from zebrafish (Danio rerio). Comparison of the sequence with GenBank entries revealed extensive amino acid identity between this zebrafish FABP and brain FABPs (B-FABP) from other species. The zebrafish B-FABP cDNA hybridized to single restriction fragments of total zebrafish genomic DNA digested with the restriction endonucleases BglII or EcoRI suggesting that a single copy of the B-FABP gene is present in the zebrafish genome. Northern blot analysis demonstrated that the zebrafish B-FABP mRNA is approximately 850 nucleotides in length. In situ hybridization revealed that the B-FABP mRNA was expressed in the periventricular gray zone of the optic tectum of the adult zebrafish brain.

cDNA sequence and tissue-specific expression of a basic liver-type fatty acid binding protein in adult zebrafish (Danio rerio)

We have determined the nucleotide sequence for a cDNA clone derived from zebrafish (Danio rerio) that codes for a fatty acid binding protein (FABP). Amino acid sequence similarity of the zebrafish FABP was highest to FABPs isolated from the livers of catfish, chicken, salamander and iguana. The open-reading frame of the zebrafish FABP cDNA codes for a protein of 14.0 kDa with a calculated isoelectric point of 8.8. The zebrafish liver-type FABP (L-FABP) cDNA hybridized to single restriction fragments of total zebrafish genomic DNA digested with the restriction endonucleases HaeIII or EcoRI suggesting that a single copy of the L-FABP gene is present in the zebrafish genome. Northern blot analysis demonstrated that the zebrafish L-FABP cDNA hybridized to a transcript of 700 nucleotides in total zebrafish RNA. In situ hybridization and emulsion autoradiography revealed that the L-FABP was expressed exclusively in the liver of the adult zebrafish. Based on amino acid sequence similarity, the isoelectric point and its tissue-specific pattern of expression, we conclude that this zebrafish FABP belongs to the basic liver-type FABPs only found, thus far, in non-mammalian vertebrates.

Expression of intestine-specific antigen reveals novel pathways of CD8 T cell tolerance induction

Reactivity to intestinal epithelium-specific antigen was studied by transgenic expression of cytosolic ovalbumin controlled by an enterocyte-specific promoter. Transferred OVA-specific CD8 cells (OT-I) preferentially expanded in mucosal lymphoid tissues and the epithelium but failed to cause tissue damage. In contrast, concomitant VSV-ova infection induced OT-I-mediated epithelial cell destruction that correlated with antigen density. OT-I cells retained in the epithelium exhibited high levels of lytic activity but were unable to produce cytokines. The mice were systemically tolerant to OVA since endogenous CD8 cells were nonresponsive to VSV-ova infection. Thus, intestinal antigen gained access to peripheral tissues via absorption from effete epithelial cells. This system demonstrated a requirement for inflammation to drive pathogenic autoreactivity against enterocytes and identified pathways of intestine-specific immunoregulation.

Early mouse endoderm is patterned by soluble factors from adjacent germ layers

Endoderm that forms the respiratory and digestive tracts is a sheet of approximately 500–1000 cells around the distal cup of an E7.5 mouse embryo. Within 2 days, endoderm folds into a primitive gut tube from which numerous organs will bud. To characterize the signals involved in the developmental specification of this early endoderm, we have employed an in vitro assay using germ layer explants and show that adjacent germ layers provide soluble, temporally specific signals that induce organ-specific gene expression in endoderm. Furthermore, we show that FGF4 expressed in primitive streak-mesoderm can induce the differentiation of endoderm in a concentration-dependent manner. We conclude that the differentiation of gastrulation-stage endoderm is directed by adjacent mesoderm and ectoderm, one of the earliest reported patterning events in formation of the vertebrate gut tube.

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.

Vertebrate endoderm development

Endoderm, one of the three principal germ layers, contributes to all organs of the alimentary tract. For simplicity, this review divides formation of endodermal organs into four fundamental steps: (a) formation of endoderm during gastrulation, (b) morphogenesis of a gut tube from a sheet of cells, (c) budding of organ domains from the tube, and (d) differentiation of organ-specific cell types within the growing buds. We discuss possible mechanisms that regulate how undifferentiated endoderm becomes specified into a myriad of cell types that populate the respiratory and gastrointestinal tracts.

Gut specific expression using mammalian promoters in transgenic Xenopus laevis

The recent development of transgenic methods for the frog Xenopus laevis provides the opportunity to study later developmental events, such as organogenesis, at the molecular level. Our studies have focused on the development of the tadpole gut, where tissue specific promoters have yet to be identified. We have used mammalian promoters, for the genes elastase, pancreatic duodenal homeobox-1, transthyretin, and intestinal fatty acid binding protein to drive green fluorescent protein expression in live tadpoles. All of these were shown to drive appropriate tissue specific expression, suggesting that the molecular mechanisms organising the gut are similar in amphibians and mammals. Furthermore, expression from the elastase promoter is initiated in the pancreatic buds before morphological definition becomes possible, making it a powerful tool for the study of pancreatic determination.

Transcriptional regulation of pig lactase-phlorizin hydrolase: involvement of HNF-1 and FREACs

BACKGROUND & AIMS

One-kilobase sequence of the upstream fragment of the pig lactase-phlorizin hydrolase gene has been shown to control small intestinal-specific expression and postweaning decline of lactase-phlorizin hydrolase in transgenic mice. The aim of this study was to identify the regulatory DNA elements and transcription factors controlling lactase-phlorizin hydrolase expression.

METHODS

The activity of different lactase-phlorizin hydrolase promoter fragments was investigated by transfection experiments using Caco-2 cells. Electrophoretic mobility shift assays and supershift analyses were used to characterize the interaction between intestinal transcription factors and the identified regulatory elements.

RESULTS

Functional analysis revealed three previously undescribed regulatory regions in the lactase-phlorizin hydrolase promoter: a putative enhancer between -894 and -798 binding hepatocyte nuclear factor (HNF)-1 at position -894 to -880; a repressor-binding element between -278 to -264 to which an HNF-3-like factor is able to bind; and an element between -178 to -164 that binds an activating transcription factor.

CONCLUSIONS

Identification of three new regulatory regions and HNF-1 and HNF-3-like transcription factor as players in the regulation of lactase-phlorizin hydrolase gene transcription has an impact on the understanding of the molecular mechanisms behind age-dependent, tissue-specific, differentiation-dependent, and regional regulation of expression in the intestine.

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.

A concise promoter region of the heart fatty acid-binding protein gene dictates tissue-appropriate expression

The heart fatty acid-binding protein (HFABP) is a member of a family of binding proteins with distinct tissue distributions and diverse roles in fatty acid metabolism, trafficking, and signaling. Other members of this family have been shown to possess concise promoter regions that direct appropriate tissue-specific expression. The basis for the specific expression of the HFABP has not been previously evaluated, and the mechanisms governing expression of metabolic genes in the heart are not completely understood. We used transient and permanent transfections in ventricular myocytes, skeletal myocytes, and nonmyocytic cells to map regulatory elements in the HFABP promoter, and audited results in transgenic mice. Appropriate tissue-specific expression in cell culture and in transgenic mice was dictated by 1.2 kb of the 5'-flanking sequence of FABP3, the HFABP gene. Comparison of orthologous murine and human genomic sequences demonstrated multiple regions of near-identity within this promoter region, including a CArG-like element close to the TATA box. Binding and transactivation studies demonstrated that this element can function as an atypical myocyte enhancer-binding factor 2 site. Interactions with adjacent sites are likely to be necessary for fully appropriate, tissue-specific, developmental and metabolic regulation.

Expression of putative fatty acid transporter genes are regulated by peroxisome proliferator-activated receptor alpha and gamma activators in a tissue- and inducer-specific manner

Regulation of gene expression of three putative long-chain fatty acid transport proteins, fatty acid translocase (FAT), mitochondrial aspartate aminotransferase (mAspAT), and fatty acid transport protein (FATP), by drugs that activate peroxisome proliferator-activated receptor (PPAR) alpha and gamma were studied using normal and obese mice and rat hepatoma cells. FAT mRNA was induced in liver and intestine of normal mice and in hepatoma cells to various extents only by PPARalpha-activating drugs. FATP mRNA was similarly induced in liver, but to a lesser extent in intestine. The induction time course in the liver was slower for FAT and FATP mRNA than that of an mRNA encoding a peroxisomal enzyme. An obligatory role of PPARalpha in hepatic FAT and FATP induction was demonstrated, since an increase in these mRNAs was not observed in PPARalpha-null mice. Levels of mAspAT mRNA were higher in liver and intestine of mice treated with peroxisome proliferators, while levels in hepatoma cells were similar regardless of treatment. In white adipose tissue of KKAy obese mice, thiazolidinedione PPARgamma activators (pioglitazone and troglitazone) induced FAT and FATP more efficiently than the PPARalpha activator, clofibrate. This effect was absent in brown adipose tissue. Under the same conditions, levels of mAspAT mRNA did not change significantly in these tissues. In conclusion, tissue-specific expression of FAT and FATP genes involves both PPARalpha and -gamma. Our data suggest that among the three putative long-chain fatty acid transporters, FAT and FATP appear to have physiological roles. Thus, peroxisome proliferators not only influence the metabolism of intracellular fatty acids but also cellular uptake, which is likely to be an important regulatory step in lipid homeostasis.

Subepithelial fibroblast cell lines from different levels of gut axis display regional characteristics

The intestine is characterized by morphofunctional differences along the proximodistal axis. The aim of this study was to derive mesenchymal cell lines representative of the gut axis. We isolated and cloned rat intestinal subepithelial myofibroblasts raised from 8-day proximal jejunum, distal ileum, and proximal colon lamina propria. Two clonal cell lines from each level of the gut were characterized. They 1) express the specific markers vimentin, smooth muscle alpha-actin, and smooth muscle myosin heavy chain, revealed by immunofluorescence microscopy and 2) distinctly support endodermal cell growth in a coculture model, depending on their regional origin, and 3) the clones raised from the various proximodistal regions maintain the same pattern of morphogenetic and growth and/or differentiation factor gene expression as in vivo: hepatocyte growth and/or scatter factor and transforming growth factor-beta 1 mRNAs analyzed by RT-PCR were more abundant, in the colon and ileal clones and mucosal connective tissue, respectively. In addition, epimorphin mRNA studied by Northern blot was also the highest in one ileal clone, in which it was selectively upregulated by all-trans retinoic acid (RA) treatment. Epimorphin expression in isolated 8-day intestinal lamina propria was higher in the distal small intestine and proximal colon than in the proximal small intestine. In conclusion, we isolated and characterized homogeneous cell subtypes that can now be used to approach the molecular regulation of the epithelium-mesenchyme-dependent regional specificity along the gut.

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.

A large-scale in situ hybridization system using an equalized cDNA library

We have developed a large-scale in situ hybridization system in which all the procedures are carried out on a 96-well format: digoxigenin-labeled probes were synthesized from PCR-amplified templates, sections were mounted on 96-well plates, and hybridization and immunohistochemistry protocols were carried out in each well of the plates. This system in combination with equalized (normalized) cDNA library as the source for the probes enables us to identify the cellular distribution of many mRNAs in various tissues rapidly and efficiently. Thus, this system may be a novel cloning method of identify genes differentially expressed in many tissues. In addition, this system has a potential to be automated.

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.