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J I Gordon

Publications and source records attributed to J I Gordon.

At least 109 records · Page 6Linked to original sources
PubMed1994

Genetic analysis of the role of Saccharomyces cerevisiae acyl-CoA synthetase genes in regulating protein N-myristoylation.

NMT1 is an essential Saccharomyces cerevisiae gene which encodes myristoyl-CoA:protein N-myristoyltransferase (Nmt1p). Nmt1p transfers myristate (C14:0), from myristoyl-CoA to the amino-terminal Gly residue of several essential cellular proteins. Little information is available about how myristoyl-CoA metabolism is regulated in eukaryotic cells. We have isolated and characterized three unlinked Fatty Acid Activation genes from S. cerevisiae, FAA1, FAA2, and FAA3. In vitro biochemical assays reveal that the myristoyl-CoA synthetase activity of purified Faa2p is approximately equal to that of Faa1p, and two orders of magnitude greater than that of Faa3p. Analysis of NMT1 strains containing faa1, faa2, and/or faa3 null alleles indicates that Faa1p, Faa2p, and Faa3p are not essential for vegetative growth when de novo acyl-CoA synthesis by fatty acid synthetase (Fas) is active. S. cerevisiae strains containing nmt1-181 exhibit temperature-sensitive growth arrest and myristic acid auxotrophy due to the reduced affinity of its mutant protein product (nmtGly451-->Asp) for myristoyl-CoA. Comparison of the growth characteristics of isogenic NMT1 and nmt1-181 strains with all possible combinations of faa1, faa2, and faa3 null alleles, in the presence or absence of an active Fas complex, indicates that (i) Faa1p is responsible for activation of imported fatty acids to their CoA derivatives; (ii) Faa2p and Faa3p are able to access endogenous but not imported fatty acid substrates; (iii) nmt181p requires myristoyl-CoA production from both Fas and Faas for cells to remain viable at nonpermissive temperatures; (iv) Faa2p is unique among the three Faas in its ability, when overproduced, to partially rescue growth of a nmt1-181 strain at nonpermissive temperatures on yeast/peptone/dextrose (YPD) media without C14:0 supplementation; (v) acyl-CoAs produced by Faa1p, Faa2p, or Faa3p are not specifically targeted for beta-oxidation; and (vi) the ability of NMT1, faa1 delta, faa2 delta, faa3 delta strains to remain viable in the absence of an active Fas complex on YPD plus C14:0, or on media that contains fatty acids as the sole carbon source, suggests that S. cerevisiae contains other acyl-CoA synthetases which can activate imported fatty acids.

Acyltransferases↗
PubMed1994

Biochemical studies of three Saccharomyces cerevisiae acyl-CoA synthetases, Faa1p, Faa2p, and Faa3p.

The efficiency and specificity of protein N-myristoylation appear to be influenced by the availability of myristoyl-CoA and other potential acyl-CoA substrates of myristoyl-CoA:protein N-myristoyltransferase. Recent studies have revealed that Saccharomyces cerevisiae contains at least three acyl-CoA synthetase genes (FAA for fatty acid activation). We have expressed Faa1p, Faa2p, and Faa3p in a strain of Escherichia coli that lacks its own endogenous acyl-CoA synthetase (FadD). Each S. cerevisiae acyl-CoA synthetase contained a carboxyl-terminal His tag so that it could be purified to homogeneity in a single step using nickel chelate affinity chromatography. In vitro assays of C3:0-C24:0 fatty acids indicate that Faa1p prefers C12:0-C16:0, with myristic and pentadecanoic acid (C15:0) having the highest activities. Faa2p can accommodate a wider range of acyl chain lengths: C9:0-C13:0 are preferred and have equivalent activities, although C7:0-C17:0 fatty acids are tolerated as substrates with no greater than a 2-fold variation in specific activity. The myristoyl-CoA synthetase activities of Faa1p and Faa2p are 2 orders of magnitude greater than that of Faa3p in vitro. Faa3p has a preference for C16 and C18 fatty acids with a cis-double bond at C-9-C-10. The temperature optimum for Faa1p is 30 degrees C, while Faa2p and Faa3p have the greatest activities at 25 degrees C. These in vitro observations were confirmed using two in vivo assays: (i) measurement of the ability of each S. cerevisiae acyl-CoA synthetase to direct the incorporation of exogenously derived tritiated myristate, palmitate, or oleate into cellular phospholipids produced in a fadD- strain of E. coli during exponential growth at 24 or 37 degrees C and (ii) measurement of the incorporation of [3H]myristate into a yeast N-myristoylprotein coexpressed with Nmt1p and Faa1p, Faa2p, or Faa3p in the fadD- strain.

Base Sequence↗
PubMed1994

Isothermal titration calorimetric studies of Saccharomyces cerevisiae myristoyl-CoA:protein N-myristoyltransferase. Determinants of binding energy and catalytic discrimination among acyl-CoA and peptide ligands.

Saccharomyces cerevisiae myristoyl-CoA:protein N-myristoyltransferase (Nmt1p) is an essential, monomeric enzyme that catalyzes the transfer of myristate from CoA to the amino-terminal Gly residue of cellular proteins. Product inhibition studies indicate that Nmt1p has an ordered Bi Bi reaction mechanism with myristoyl-CoA binding to the apo-enzyme to form a high affinity binary complex followed by binding of peptide with subsequent release of CoA and then the myristoylpeptide product. We have used isothermal titration calorimetry to quantify the effects of varying acyl chain length and removing the 3'-phosphate group of CoA on the energetics of interaction between Nmt1p and acyl-CoA ligands. Myristoyl-CoA binds to apo-Nmt1p with an affinity of 15 nM, corresponding to a binding free energy of -10.9 kcal/mol. This free energy is composed of a large favorable enthalpy of -24 kcal/mol and a large unfavorable entropic term. This large negative delta H degrees is consistent with a conformational change in the enzyme upon ligation, allowing synthesis of a functional peptide binding site. Binding of palmitoyl-CoA and lauroyl-CoA is driven by an exothermic enthalpy change which is much smaller than the corresponding parameter for myristoyl-CoA binding. The large differences in binding enthalpy and entropy (delta delta H degrees and T delta delta S degrees = 8-9 kcal/mol) demonstrate that the "off-length" acyl-CoAs bind to Nmt1p in a significantly different energetic fashion from myristoyl-CoA, even though the enzyme does not have a great deal of specificity among these ligands in terms of binding free energy (delta delta G degrees < or = 1 kcal/mol). The effect of removing the CoA 3'-phosphate group from myristoyl-CoA is similar to the effect of a two-carbon change in acyl chain length: i.e. an enthalpy dominated reduction in binding affinity. However, kinetic studies reveal that removing the 3'-phosphate from myristoyl-CoA has little effect on Nmt1p's catalytic efficiency, indicating that the 3'-phosphate group contributes binding free energy but little catalytic destabilization. The greater delta delta G degrees, with smaller delta delta H degrees and delta delta S degrees components, produced by removing the 3'-phosphate compared to increasing chain length suggests that it is not primarily the interactions of the 3'-phosphate which are disrupted when palmitoyl-CoA is substituted for myristoyl-CoA. No detectable interactions were noted between apo-Nmt1p and the substrate peptide, GAAPSKIV-NH2, providing additional support for the preferred ordered reaction mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

Acyl Coenzyme A↗
PubMed1994

The substrate specificity of Saccharomyces cerevisiae myristoyl-CoA: protein N-myristoyltransferase. Polar probes of the enzyme's myristoyl-CoA recognition site.

Saccharomyces cerevisiae myristoyl-CoA:protein N-myristoyltransferase (Nmt1p) is a monomeric enzyme that is essential for vegetative growth. Nmt1p catalyzes the co-translational transfer of myristate from CoA to the amino-terminal Gly of cellular proteins in an ordered Bi Bi reaction mechanism that initially involves binding of myristoyl-CoA to the apoenzyme. Forty one fatty acid analogs were synthesized to define features in the acyl chain of myristoyl-CoA which are important determinants of its recognition by Nmt1p's acyl-CoA binding site as well as to help us deduce the structure of the binding site itself. These analogs included dicarboxylic acids, omega-nitrocarboxylic acids, analogs equivalent in length to C13:0-C15:0 which contain electronegative halogens at their omega-termini, hydroxytetradecanoic acids with hydrogen replaced by OH from C3 to C13, and azidophenyl-containing fatty acids with the linear azide unit attached either meta or para to phenyl and with variations in the length of their methylene chains. These compounds were converted to their CoA derivatives using Pseudomonas acyl-CoA synthetase and then surveyed as substrates for purified Nmt1p in an in vitro assay system that included an octapeptide derived from residues 1-8 of the human immunodeficiency virus Pr55gag polyprotein precursor. The results suggest that the myristoyl-CoA binding site contains a conical-shaped "receptor" that interacts with the omega-terminus of the bound acyl chain of acyl-CoAs. The acuteness of this cone determines the enzyme's capacity to accommodate steric bulk at the omega-terminus as well as Nmt1p's sensitivity to the distance between the eclipsed C5-C6 bond of a bound acyl chain and its omega-terminus. The activity profile of the various analog-CoAs also indicates that the enzyme's myristoyl-CoA binding site can accommodate fatty acid analogs with marked increases in polarity at their omega-terminus (compared to C14:0) as long as their chain length is equivalent to that of myristate.

Acyl Coenzyme A↗
PubMed1994

Comparison of myristoyl-CoA:protein N-myristoyltransferases from three pathogenic fungi: Cryptococcus neoformans, Histoplasma capsulatum, and Candida albicans.

Myristoyl-CoA:protein N-myristoyltransferase (Nmt) transfers myristate from CoA to the N-terminal Gly residue of cellular proteins in an ordered reaction mechanism that first involves binding of myristoyl-CoA to the apoenzyme. The gene encoding Saccharomyces cerevisiae Nmt1p (NMT1) is essential for vegetative growth. Candida albicans, Cryptococcus neoformans var. neoformans, and Histoplasma capsulatum are the principal causes of systemic fungal infections in immunocompromised humans. Metabolic labeling studies indicate that they synthesize a small set of cellular N-myristoylproteins during exponential growth on rich media, the most prominent of which co-migrate with two essential functionally interchangeable S. cerevisiae N-myristoylproteins, ADP ribosylation factor-1 (Arf1p) and Arf2p. NMT and ARF genes have been recovered from C. neoformans and H. capsulatum using the polymerase chain reaction. They are single copy genes, interrupted by multiple introns. C. neoformans and H. capsulatum Nmts have approximately 50% amino acid sequence identity with the orthologous S. cerevisiae, C. albicans, and Homo sapiens N-myristoyltransferases, whereas C. neoformans and H. capsulatum Arfs are approximately 80% identical with C. albicans Arf and S. cerevisiae Arf1p and Arf2p. Functional studies of C. neoformans and C. albicans Nmts conducted in Escherichia coli reveal that (i) both efficiently acylate S. cerevisiae Arf2p; (ii) C. neoformans Arf is a substrate for C. neoformans Nmt; and (iii) substitution of an Asp for a Gly located 5 residues from the C terminus of these two enzymes causes marked temperature-dependent reductions in their catalytic efficiency, just as it does with S. cerevisiae and H. sapiens Nmts. Wild type C. neoformans, C. albicans, and H. sapiens NMTs can fully complement the lethal phenotype of a S. cerevisiae nmt1 null allele at 24 and 37 degrees C when the GAL1-10 promoter controlling their expression is induced by galactose. Only the C. albicans enzyme is able to do so when the promoter is repressed with glucose. This complementation profile likely arises, at least in part, from differences in the protein substrate specificities of the orthologous Nmts. A Gly-->Asp mutation in S. cerevisiae, C. neoformans, C. albicans, and H. sapiens Nmts produces temperature-sensitive growth arrest in isogenic S. cerevisiae strains with a nmt1 null allele. Growth of strains producing the mutant C. albicans or H. sapiens, but not the C. neoformans, enzyme can be rescued by myristate at the non-permissive temperature (37 degrees C) even in the presence of cerulenin, an inhibitor of fatty acid synthetase.(ABSTRACT TRUNCATED AT 400 WORDS)

Acyltransferases↗
PubMed1994

Differentiation and self-renewal in the mouse gastrointestinal epithelium.

The mouse gut epithelium represents a dynamic, geographically well organized, developmental system for examining self-renewal and differentiation. Reagents are now available for identifying the molecular mechanisms that regulate cell fate in the gut, the migration-associated differentiation programs of its component cell lineages, and its axial patterning. Considerable attention needs to be paid to two variables when studying gastrointestinal epithelial cell biology: space and time. This has necessitated the use of normal, chimeric, and transgenic animals as experimental models.

Animals↗
PubMed1994

The mouse ileal lipid-binding protein gene: a model for studying axial patterning during gut morphogenesis.

Normal, chimeric-transgenic, and transgenic mice have been used to study the axial patterns of ileal lipid-binding protein gene (Ilbp) expression during and after completion of gut morphogenesis. Ilbp is initially activated in enterocytes in bidirectional wave that expands proximally in the ileum and distally to the colon during late gestation and the first postnatal week. This activation occurs at the same time that a wave of cytodifferentiation of the gut endoderm is completing its unidirectional journey from duodenum to colon. The subsequent contraction of Ilbp's expression domain, followed by its reexpansion from the distal to proximal ileum, coincides with a critical period in gut morphogenesis (postnatal days 7-28) when its proliferative units (crypts) form, establish their final stem cell hierarchy, and then multiply through fission. The wave of reactivation is characterized by changing patterns of Ilbp expression: (a) at the proximal most boundary of the wave, villi contain a mixed population of scattered ileal lipid-binding protein (ILBP)-positive and ILBP-negative enterocytes derived from the same monoclonal crypt; (b) somewhat more distally, villi contain vertical coherent stripes of wholly ILBP-positive enterocytes derived from monoclonal crypts and adjacent, wholly ILBP-negative stripes of enterocytes emanating from other monoclonal crypts; and (c) more distally, all the enterocytes on a villus support Ilbp expression. Functional mapping studies of Ilbp's promoter in transgenic mice indicate that nucleotides -145 to +48 contain cis-acting elements sufficient to produce an appropriately directed distal-to-proximal wave of Ilbp activation in the ileum, to maintain an appropriate axial distribution of monophenotypic wholly reporter-positive villi in the distal portion of the ileum, as well as striped and speckled villi in the proximal portion of its expression domain, and to correctly support reporter production in villus-associated ileal enterocytes. Nucleotides -417 to -146 of Ilbp contain a "temporal" suppressor that delays initial ileal activation of the gene until the second postnatal week. Nucleotides -913 to -418 contain a temporal suppressor that further delays initial activation of the gene until the third to fourth postnatal week, a spatial suppressor that prohibits gene expression in the proximal quarter of the ileum and in the proximal colon, and a cell lineage suppressor that prohibits expression in goblet cells during the first two postnatal weeks.

Amino Acid Sequence↗
PubMed1994

Saccharomyces cerevisiae contains four fatty acid activation (FAA) genes: an assessment of their role in regulating protein N-myristoylation and cellular lipid metabolism.

Saccharomyces cerevisiae has been used as a model for studying the regulation of protein N-myristoylation. MyristoylCoA:protein N-myristoyl-transferase (Nmt1p), is essential for vegetative growth and uses myristoylCoA as its substrate. MyristoylCoA is produced by the fatty acid synthetase (Fas) complex and by cellular acylCoA synthetases. We have recently isolated three unlinked Fatty Acid Activation (FAA) genes encoding long chain acylCoA synthetases and have now recovered a fourth by genetic complementation. When Fas is active and NMT1 cells are grown on media containing a fermentable carbon source, none of the FAA genes is required for vegetative growth. When Fas is inactivated by a specific inhibitor (cerulenin), NMT1 cells are not viable unless the media is supplemented with long chain fatty acids. Supplementation of cellular myristoylCoA pools through activation of imported myristate (C14:0) is predominantly a function of Faa1p, although Faa4p contributes to this process. Cells with nmt181p need larger pools of myristoylCoA because of the mutant enzyme's reduced affinity for this substrate. Faa1p and Faa4p are required for maintaining the viability of nmt1-181 strains even when Fas is active. Overexpression of Faa2p can rescue nmt1-181 cells due to activation of an endogenous pool of C14:0. This pool appears to be derived in part from membrane phospholipids since overexpression of Plb1p, a nonessential lysophospholipase/phospholipase B, suppresses the temperature-sensitive growth arrest and C14:0 auxotrophy produced by nmt1-181. None of the four known FAAs is exclusively responsible for targeting imported fatty acids to peroxisomal beta-oxidation pathways. Introduction of a peroxisomal assembly mutation, pas1 delta, into isogenic NMT1 and nmt1-181 strains with wild type FAA alleles revealed that when Fas is inhibited, peroxisomes contribute to myristoylCoA pools used by Nmt1p. When Fas is active, a fraction of cellular myristoylCoA is targeted to peroxisomes. A NMT1 strain with deletions of all four FAAs is still viable at 30 degrees C on media containing myristate, palmitate, or oleate as the sole carbon source--indicating that S. cerevisiae contains at least one other FAA which directs fatty acids to beta-oxidation pathways.

Acyl Coenzyme A↗
PubMed1994

Lectins are sensitive tools for defining the differentiation programs of mouse gut epithelial cell lineages.

We have used histochemical methods to survey the cellular patterns of binding of a panel of 45 lectins with well-defined carbohydrate specificities to sections prepared from various regions of the gastric-to-colonic axis of fetal, neonatal, and adult FVB/N mouse gut. The results suggest that lectins can be used as remarkably sensitive tools to describe the differentiation programs of gastric and intestinal epithelial cell lineages as a function of their position along the cephalocaudal axis of the gut and as a function of developmental stage. Studies of intestinal isografts and transgenic mice that express Simian virus-40 T antigen in enterocytes suggest that many of these cell lineage-specific and spatial patterns of glycoconjugate production can be established and maintained in the absence of exposure to luminal contents and in the presence of specific proliferative abnormalities. This lectin panel should be useful for operationally defining subpopulations of the principal gut epithelial cell lineages in normal strains of mice, for describing variations in gut epithelial cell differentiation programs in mutant and transgenic mice, and for recovering specific epithelial cell lineages or subpopulations.

Aging↗
PubMed1994

Use of isografts to study proliferation and differentiation programs of mouse stomach epithelia.

A new model system has been developed for studying the factors that regulate the proliferation and differentiation programs of the principal cell lineages present in the mouse stomach epithelium. When embryonic day 14 (E14) stomachs from C57Bl/6 mice are implanted under the subcutaneous fascia of young adult male CBY/B6 nude mouse recipients, they are rapidly vascularized and begin to grow at rates comparable to the intact stomach of a similarly aged animal. Single- and multilabel immunohistochemical studies, conducted in the intact stomach of E14 to postnatal day 42 (P42) C57Bl/6 mice and in P7, P14, P28, and P42 C57Bl/6 isografts, suggest that the apparently undifferentiated glandular epithelium of E14 stomach already has encoded positional information that permits it to establish regional differences in cell populations even in the absence of exposure to normal luminal contents. Regional differentiation is manifested by the establishment of distinct zones, each composed of gastric units with zone-specific cell lineages. This axial patterning evolves at a rate similar to that of the intact stomach, even though the E14 isograft is placed in the hormonal environment of an adult host and therefore cannot be programmed by normal developmental changes in endocrine status. Moreover, patterning is maintained in isografts despite continuous renewal of its epithelial cell lineages. Although isografts apparently possess autonomously functioning temporal and spatial programs, perturbations were noted in the proliferation and/or differentiation programs of certain lineages, e.g., the rate of accumulation of endocrine cell subpopulations is reduced in these grafts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Regional differences in glycoconjugates of intestinal M cells in mice: potential targets for mucosal vaccines.

We have used a panel of lectins and antibodies to describe the composition of complex carbohydrates associated with M cells in various regions of the intestinal tract of adult BALB/c mice. The fucose-specific lectin Ulex europaeus agglutinin type I (UEA I) is a marker of M cells in the small intestine and recognized M cells at an early stage of differentiation. Subpopulations of M cells in a single follicle-associated epithelium (FAE) could be distinguished by different fucose-specific probes. Certain lectins revealed that M cells have basal processes that extend into the underlying lymphoid tissue. Colonic and rectal M cells display glycosylation patterns distinct from M cells of Peyer's patches and are characterized by terminal galactose. UEA I selectively adhered to Peyer's patch M cells in mucosal explants and in ligated intestinal loops in vivo. The lectin was taken up into endocytic vesicles and transported to the intra-epithelial pocket and other domains of the basolateral membrane. Thus M cell-specific glycoconjugates could serve as "receptors" for targeting of lectin-antigen conjugates to the mucosal immune system.

Animals↗
PubMed1993

Escherichia coli-derived rat intestinal fatty acid binding protein with bound myristate at 1.5 A resolution and I-FABPArg106-->Gln with bound oleate at 1.74 A resolution.

Rat intestinal fatty acid binding protein (I-FABP) is a 131-residue protein composed of two short alpha-helices (alpha I and alpha II) and 10 anti-parallel beta-strands organized into two nearly orthogonal beta-sheets. The structure of crystalline I-FABP with bound tetradecanoate (myristate) has been refined to a resolution of 1.5 A and compared to the 1.2 A structure of apo-I-FABP, the 1.9 A structure of I-FABP:hexadecanoate (palmitate) and the 1.75 A structure of I-FABP:9Z-octadecanoate (oleate) to determine how this model fatty acid receptor accommodates changes in the length of its fatty acid ligand. Myristate is located in the interior of the protein. A highly ordered, electrostatic network containing 7 hydrogen (H)-bonds links the OE1 and OE2 atoms of myristate's carboxylate group, the indole nitrogen of Trp82, NH1, and NH2 of Arg106, NE2, and OE1 of Gln115, and 2 interior ordered waters. The hydrocarbon chain of the bound fatty acid is slightly bent. Its convex face lies in a crevice, forming van der Waals contacts with the side chains of several hydrophobic and aromatic residues. Its concave face is exposed to an array of 8 interior ordered waters whose positions are stabilized by H-bond interactions with other waters, H-bond interactions with the side chains of polar/ionizable residues, and van der Waals contacts with the surface of the fatty acid. Addition of 2 or 4 methylenes to myristate produces remarkably little change in the positions of I-FABP's main chain and side chain atoms and interior ordered waters. The principal alterations are in the conformation of a surface opening (portal) connecting external and internal solvent and in the position of the benzene side chain of Phe55. Changes in the conformation of the portal reflect movement of two of its components: the backbone of alpha II and a type I turn (Ala73, Asp74) connecting two beta-strands. The positions of the main chain atoms of Ala73 and Asp74 appear to be determined by their ability to form van der Waals contacts with the omega-terminus of the fatty acid. The side chain of Phe55 appears to function as an adjustable aromatic lid, located over the portal, whose position is dependent on an ability to form van der Waals contacts with a fatty acid's omega-terminus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Use of transgenic mice to study regulation of gene expression in the parietal cell lineage of gastric units.

The mechanisms that regulate cell lineage-specific and differentiation-dependent patterns of gene expression in the gastric units of the stomach are largely unknown. Transgenic mice were generated in order to identify cis-acting sequences that determine the zymogenic cell-specific pattern of expression of the mouse intrinsic factor (InF) gene and the parietal cell-specific pattern of expression of the mouse H+/K(+)-ATPase beta-subunit gene. Portions of the 5'-nontranscribed domains of each gene were linked to the human growth hormone (hGH) gene beginning at its nucleotide +3. RNA blot hybridization studies combined with multilabel immunocytochemical surveys using a panel of lineage-specific antibodies and lectins indicated that nucleotides -1035 to +24 of the mouse H+/K(+)-ATPase beta-subunit gene direct a pattern of reporter production which recapitulates the parietal cell-specific and developmental patterns of expression of the endogenous gene. Analysis of three mosaic founders containing H+/K(+)-ATPase beta-subunit-1035 to +24/hGH+3 revealed that they had monophenotypic gastric units: a given unit contained either a wholly hGH-positive or a wholly hGH-negative population of parietal cells. These latter findings provide very strong evidence that gastric units are monoclonal, i.e. they are supplied by stem cells having one genotype. Although some, but not all, parietal cells are apparently derived from the same committed progenitor as zymogenic cells, virtually all parietal cells in a given gastric unit, but none of its zymogenic cells, express InF-1029 to +55/hGH+3. This suggests that InF-1029 to +55 may contain cis-acting sequences which allow parietal cell expression in other species (e.g. humans) but lack additional elements which normally function in mice to suppress InF expression in this lineage. The absence of hGH in zymogenic cells also means that the transcriptional regulatory environments of parietal and zymogenic cells derived from the same precursor are distinguishable by InF-1029 to +55. H+/K(+)-ATPase beta-subunit-1035 to +24 and InF-1029 to +55 are the only two sequences reported to date that are able to direct foreign gene expression exclusively to a gastric epithelial cell lineage in transgenic mice. This ability to deliver gene products to parietal cells can now be exploited to identify factors that control their normal proliferation and differentiation programs and/or to specifically alter their biological properties.

Amino Acid Sequence↗
PubMed1993

Chimeric-transgenic mice represent a powerful tool for studying how the proliferation and differentiation programs of intestinal epithelial cell lineages are regulated.

An in vivo system has been developed for examining the effects of wild-type or mutant proteins on cell fate determination in the mouse intestinal epithelium or on the proliferation and differentiation programs of its component epithelial lineages. This system takes advantage of the fact that at the conclusion of gut morphogenesis, each intestinal crypt is composed of a monoclonal population of cells descended from a single active multipotent stem cell, each villus is supplied by several monoclonal crypts, and the four principal cell types of the intestinal epithelium differentiate during a rapid, geographically well-organized migration along the crypt-to-villus axis. Embryonic stem (ES) cells (129/Sv origin) are initially transfected with recombinant DNAs consisting of a reporter of interest linked to transcriptional regulatory elements that control the cell lineage-specific, differentiation-dependent, and axial patterns of expression of fatty acid binding protein genes in the gut. Stably transfected ES cells are subsequently introduced into host C57BL/6 blastocysts to generate chimeric-transgenic mice. At the borders of ES cell-derived and host blastocyst-derived epithelium, intestinal villi are found that are supplied by both ES cell- and host blastocyst-derived crypts. These villi can be rapidly identified in fixed whole-mount preparations of intestine using the alpha-L-fucose-specific Ulex europaeus agglutinin type I (UEA-I) lectin. They appear striped because UEA-I recognizes a cell-surface carbohydrate polymorphism between the inbred strains used to generate the chimeric animals. The strength of this system derives from the fact that two gut epithelial populations can be compared and contrasted that occupy virtually identical positions along the crypt-to-villus and duodenal-to-colonic axes within the same animal and differ only by the presence or absence of a single gene product. The band of blastocyst-derived epithelium in these striped, polyclonal villi can be used as an internal control to assess the biological effect of the transfected gene product produced in the adjacent stripe of ES-derived cells. The system can be used for either gain-of-function or loss-of-function experiments.

Animals↗
PubMed1993

Cell lineage-specific and differentiation-dependent patterns of CCAAT/enhancer binding protein alpha expression in the gut epithelium of normal and transgenic mice.

The proliferation and differentiation programs of gut epithelial cells are expressed rapidly and perpetually along an anatomically well defined pathway. The mouse intestine thus provides an excellent in vivo model system to define the contributions of CCAAT enhancer binding protein alpha (C/EBP alpha) and related bZIP proteins to these processes. Immunocytochemical studies revealed that C/EBP alpha is produced in villus-associated enterocytes located in the duodenum and jejunum of adult mice. The protein is located in the cytoplasmic and nuclear compartments of these cells. C/EBP alpha is not detectable in proliferating and nonproliferating epithelial cells situated in small intestinal crypts nor is it evident in any gut epithelial cell lineage located in the ileum and colon. The related C/EBP beta and C/EBP delta proteins are not detectable by sensitive immunocytochemical methods in epithelial cells distributed along the duodenal-to-colonic axis. Developmental surveys indicate that C/EBP alpha is confined to postmitotic, villus-associated epithelial cells during conversion of the polyclonal intervillus epithelium to monoclonal crypts. Analyses of intestinal isografts reveal that these developmental stage-specific, lineage-specific, differentiation-dependent, and regional patterns of C/EBP alpha expression can be established and maintained in the absence of exposure to luminal contents. Transgenic mice containing nucleotides -1178 to +28 of the rat intestinal fatty acid binding protein gene (I-FABP-1178 to +28) linked to the simian virus 40 large tumor antigen (T antigen) gene express T antigen in villus-associated enterocytes. This results in reentry of enterocytes into the cell cycle and a silencing of C/EBP alpha expression without an apparent effect on the accumulation of several markers of this lineage's terminal differentiation program or on gut morphogenesis. These findings indicate that there is a relationship between expression of C/EBP alpha in enterocytes and their exit from the cell cycle and suggest that I-FABP-1178 to +28/simian virus 40 T antigen transgenic mice could provide a screening assay for examining the role of C/EBP alpha in regulating the activity of genes known to be transcribed during differentiation of this gut epithelial cell lineage.

Animals↗