PubMed Health⌕ Search

Biomedical subjects

M B Wheeler

Publications and source records attributed to M B Wheeler.

At least 73 records · Page 4Linked to original sources
PubMed1996

Characterization of SNARE protein expression in beta cell lines and pancreatic islets.

Pancreatic beta cells and cell lines were used in the present study to test the hypothesis that the molecular mechanisms controlling exocytosis from neuronal cells may be used by the beta cell to regulate insulin secretion. Using specific antisera raised against an array of synaptic proteins (SNAREs) implicated in the control of synaptic vesicle fusion and exocytosis, we have identified the expression of several SNAREs in the islet beta cell lines, beta TC6-f7 and HIT-T15, as well as in pancreatic islets. The v-SNARE vesicle-associated membrane protein (VAMP)-2 but not VAMP-1 immunoreactive proteins were detected in beta TC6-f7 and HIT-T15 cells and pancreatic islets. In these islet-derived cell lines, this 18-kDa protein comigrated with rat brain synaptic vesicle VAMP-2, which was cleaved by Tetanus toxin (TeTx). Immunofluorescence confocal microscopy and electron microscopy localized the VAMP-2 to the cytoplasmic side of insulin containing secretory granule membrane. In streptolysin O permeabilized HIT-T15 cells, TeTx inhibited Ca2+-evoked insulin release by 83 +/- 4.3%, which correlated well to the cleavage of VAMP-2. The beta cell lines were also shown to express a second vesicle (v)-SNARE, cellubrevin. The proposed neuronal target (t)-membrane SNAREs, SNAP-25, and syntaxin isoforms 1-4 were also detected by Western blotting. The beta cell 25-kDa SNAP-25 protein and syntaxin isoforms 1-3 were specifically cleaved by botulinum A and C toxins, respectively, as observed with the brain isoforms. These potential t-SNARES were localized by immunofluorescence microscopy primarily to the plasma membrane in beta cell lines as well as in islet beta cells. To determine the specific identity of the immunoreactive syntaxin-2 and -3 isoforms and to explore the possibility that these beta cells express the putative Ca2+-sensing molecule synaptotagmin III, RT-PCR was performed on the beta cell lines. These studies confirmed that betaTC6-F7 cells express syntaxin-2 isoforms, 2 and 2', but not 2'' and express syntaxin-3. They further demonstrate the expression of synaptotagmin III. DNA sequence analysis revealed that rat and mouse beta cell syntaxins 2, 2' and synaptotagmin III are highly conserved at the nucleotide and predicted amino acid levels (95-98%). The presence of VAMP-2, nSec/Munc-18, SNAP-25 and syntaxin family of proteins, along with synaptotagmin III in the islet cells and in beta cell lines provide evidence that neurons and beta cells share similar molecular mechanisms for Ca2+-regulated exocytosis. The inhibition of Ca2+-evoked insulin secretion by the proteolytic cleavage of HIT-T15 cell VAMP-2 supports the hypothesis that these proteins play an integral role in the control of insulin exocytosis.

Animals↗
PubMed1996

The third cytoplasmic domain of the GLP-1[7-36 amide] receptor is required for coupling to the adenylyl cyclase system.

Truncated forms of glucagon-like peptide-1 (tGLP-1) are potent endogenous stimuli of insulin secretion from pancreatic beta cells and have powerful antidiabetogenic effects. In the present study we sought to determine the precise regions of the tGLP-1 receptor (R) that are required for its efficient coupling to the adenylyl cyclase (AC) system since it is well established that cAMP is the primary second messenger activated by tGLP-1. The predicted third intracellular loop (IC3) of the rat tGLP-1R was systemically scanned using a mutagenic based strategy. The resulting receptor mutants were expressed in COS-7 cells and examined for cAMP formation in response to tGLP-1 stimulation (10nM) and [125I] tGLP-1(7-36) amide binding. A single block deletion (IC3-1) within the N-terminal region of IC3 (K334-L335-K336) resulted in a dramatic reduction in the cAMP response to tGLP-1 (7.1 +/- 1.4% of the wild type (wt) tGLP-1R response, n = 3, p < or = 0.01), while displaying comparable levels of expression, (expressed as the %Bmax of the wt-tGLP-1R (101 +/- 13%, n = 3, p > or = 0.05). This receptor mutation was further analyzed by stable expression in CHO-K1 cells. In agreement with the COS model, IC3-1 displayed comparable levels of receptor expression (97 +/- 16% Bmax of wt tGLP-1R, n = 3, p > or = 0.05) and affinity for tGLP-1(Kd of 460 +/- 15pM vs. 450 +/- 12pM wt tGLP-1R, n = 3, p > or = 0.05), but was unable to effectively stimulate cAMP production (7.7 +/- 0.4% of wt tGLP-1R, n = 3, p < or = 0.01) in response to tGLP-1 (10nM), No other mutation examined within the IC3 domain displayed a lack of correlation between binding activity and cAMP accumulation. Further analysis of the K334-L335-K336 sequence by substitution analysis revealed that a K334 to A substitution was the only modification to result in a striking attenuation of the cAMP response (28 +/- 1.9% of wt tGLP-1, n = 3, p < or = 0.01). These results strongly suggest that within the IC3 domain the N-terminal KLK sequence or a portion thereof (specifically K-334) is required for the efficient coupling of the tGLP-1 receptor to the AC system.

Adenylyl Cyclases↗
PubMed1996

Timing of induced ovulation in C.B-17/Icr-scid/scid and B6SJLF1 mice.

The time of induced ovulation after superovulation was evaluated in 3- to 8-week-old C.B-17/Icr-scid/scid and B6SJLF1 mice. Mice received intraperitoneal injections of 5 IU of equine chorionic gonadotropin (CG) followed by 5 IU of human (h) CG 48 h apart. Hormones were administered at 1700. Mice were kept on a 14-h light cycle, with lights off at 1900. Nine mice of each strain were sacrificed (3 mice x 3 replicates) at 8, 10, 12, 14, and 16 h after hCG injection. Ovaries and oviducts from each mouse were removed and placed in M-2 collection medium in one well of a 9-well Pyrex culture plate. The oviducts were flushed with M-2 medium, and the number of oocytes from each mouse was counted under a binocular Nikon dissecting microscope. Both mouse strains began ovulating at 8 h after hCG administration. Ovum counts peaked at 12 h in B6SJLF1 mice and at 16 h in C.B-17/Icr-scid/scid mice. A statistically significant strain difference between mean oocytes collected was detected at 10 and 12 h. For both time points, differences were at the 1% level of significance. There was no difference in the mean number of oocytes collected at 14 and 16 h. The mean number of ovulated oocytes increased markedly between 10 to 12 h after hCG in B6SJLF1 mice. The number of ovulated oocytes also increased in C.B-17/Icr-scid/scid mice, although more gradually. These results suggest that the timing of ovulation may be more tightly controlled in superovulated B6SJLF1 than in C.B-17/Icr-scid/scid mice. Superovulated C.B-17/Icr-scid/scid mice finish ovulation 2 to 4 h later than do B6SJLF1 mice. Therefore the best time to harvest pronuclear embryos should be 14 to 16 h after hCG administration in C.B-17/Icr-scid/scid mice and 12 h after hCG in B6SJLF1 mice. To optimize fertilization, mating should occur within 3 h of ovulation and should be planned from 11 to 17 h after hCG for C.B-17/Icr-scid/scid mice and 9 to 15 h after hCG in B6SJLF1 mice. Because male and female pronuclei form 4 to 7 and 6 to 9 h respectively after insemination, the most pronuclear stage embryos should be obtained by collecting them 20 to 21 h after hCG in C.B-17/Icr-scid/scid mice and 18 to 19 h in B6SJLF1 mice.

Animals↗
PubMed1995

Gene-centromere mapping of bovine DYA, DRB3, and PRL using secondary oocytes and first polar bodies: evidence for four-strand double crossovers between DYA and DRB3.

A genetic map consisting of three loci anchored at the centromere of bovine chromosome 23 was constructed by genotyping secondary oocytes (SO) and first polar bodies (PB1) using a polymerase chain reaction (PCR)-based approach. Primary oocytes arrested in prophase of meiosis I were stimulated in vitro to resume division and extrude PB1. Sixty SO and their matched PB1 were collected from 14 cows by micro-manipulation, subjected to amplification of the whole genome by primer extension preamplification, and genotyped independently for the linked genes PRL, DRB3, and DYA by PCR-RFLP analysis. Single-locus analysis of gene-centromere recombination rates were theta cen-DYA = 0.042, theta cen-DRB3 = 0.113, and theta cen-PRL = 0.166. The most likely order is cen-DYA-DRB3-PRL. Analysis of typing data from 3 cows revealed three meiotic divisions consistent with "linkage phase exchange" between DYA and DRB3 or PRL. One of the three linkage phase exchanges was confirmed by complementary genotypes in a matched secondary oocyte-first polar body pair. Such linkage phase exchanges could result from four-strand double crossovers between homologous chromosomes. Because all four gametes produced by four-strand double crossovers will be recombinant, more frequent occurrence of such events in females may explain the sexual dimorphism in genetic maps. Alternatively, four-strand crossovers could represent a type of recombination hotspot between DYA and DRB3, suggesting a mechanism for the high recombination frequency (15%) between these two class II genes of the bovine major histocompatibility complex.

Animals↗
PubMed1995

Production of live offspring with predicted genotypes using PCR-RFLP analysis of polar bodies from mouse oocytes.

Accurate identification of genotypes in gametes and early embryos could facilitate the efficient production of offspring with desirable traits. This study demonstrates the feasibility of producing offspring with predictable genotypes from micromanipulated mouse oocytes. The Polymerase Chain Reaction (PCR) was used to amplify genes in the IA subregion of the major histocompatibility complex of the mouse. The validity of the approach was demonstrated in experiment 1 with IA haplotypes of unfertilized mouse ova amplified via PCR and distinguished by restriction fragment length polymorphism (RFLP) analysis. In experiment 2, fertilized oocytes were micromanipulated to remove the first and second polar bodies, which were then genotyped by validated PCR-RFLP procedures. Primary oocytes of heterozygous females contain two copies of each of the different alleles. Following meiosis I and II, the genotype of the ovum was predicted by subtracting the alleles observed in micromanipulated polar body samples. Sixty-two fertilized ova were micromanipulated and transferred to recipient females resulting in 27 live offspring (44%). The correct maternal contribution to the embryonic genotype was predicted in 19 of 27 (71%) offspring as confirmed by PCR-RFLP analysis of DNA from pup tails. Predicted genotypes of two pups were not confirmed (7%), whereas no prediction could be made in six cases (22%).

Animals↗
PubMed1995

Multilocus analysis for gene-centromere mapping using first polar bodies and secondary oocytes.

Polar body and oocyte typing is a new technique for gene-centromere mapping and for generating female linkage maps. A maximum likelihood approach is presented for ordering multiple markers relative to the centromere and for estimating recombination frequencies between markers and between the centromere and marker loci. Three marker-centromere orders are possible for each pair of markers: two orders when the centromere flanks the two markers and one order when the centromere is flanked by the two markers. For each possible order, the likelihood was expressed as a function of recombination frequencies for two adjacent intervals. LOD score for recombination frequency between markers or between the centromere and a marker locus was derived based on the likelihood for each gene-centromere order. The methods developed herein provide a general solution to the problem of multilocus gene-centromere mapping that involves all theoretical crossover possibilities, including four-strand double crossovers.

Animals↗
PubMed1995

DNA sequence of the porcine alpha-lactalbumin 5' flanking region and single-base polymorphisms within this region.

The 5' flanking region of the alpha-lactalbumin (alpha-LA) gene was sequenced for the Duroc, Yorkshire and Meishan breeds of swine to identify potential sequence variants within this regulatory region of the porcine alpha-LA gene. The sequenced region of the gene encompasses 391bp5' of the translation start site to 11bp3' of the translation start site. Within this sequence of the porcine alpha-LA gene two single-base pair differences were detected. One variant occurs at position -178 and the other at position -235 from the translation start site. Each of the variations can be detected by a restriction fragment length polymorphism within a polymerase chain reaction amplified product. The polymorphisms at the -178 and -235 positions appear to be genetically linked in the animals that have been analysed.

Animals↗
PubMed1995

Functional expression of the rat pancreatic islet glucose-dependent insulinotropic polypeptide receptor: ligand binding and intracellular signaling properties.

Incretins are endogenous peptides released from the gastrointestinal tract into the circulation during a meal that potentiate glucose-stimulated insulin secretion. At present, there are two established incretins: glucose-dependent insulinotropic polypeptide (GIP) and the truncated glucagon-like peptides (tGLPs), which are now being investigated for use in the treatment of diabetes mellitus. In the present study we cloned a rat islet GIP receptor complementary DNA (GIP-R1) to answer several important questions regarding the ligand-binding and intracellular signaling properties of the GP receptor. GIP-R1, when expressed transiently in monkey kidney (COS-7) or stably in Chinese hamster ovary (CHO-K1) cells, demonstrated comparable high affinity binding for either synthetic porcine (sp) GIP or synthetic human (sh) GIP. The IC50 values for displacement of [125I]spGIP in CHO-K1 cells were 2.6 +/- 0.8 and 3.1 +/- 0.9 nM for two different preparations of shGIP, and 3.7 +/- 1.5 and 3.6 +/- 0.4 nM for two preparations of spGIP. Saturation isotherms obtained with both intact cells and membranes gave monophasic binding curves with apparent Kd values of 204 +/- 17 and 334 +/- 94 pM, respectively. Cells expressed 12-15 x 10(3) receptors/cell. In COS-7 cells, spGIP and shGIP also exhibited similar IC50 values (7.6 +/- 1.2 and 8.9 +/- 1.8 nM, respectively). The receptor in CHO-K1 cells bound GIP-(1-30) with lower affinity (IC50 = 39 +/- 17 nM), whereas the fragments GIP-(19-30), GIP-(18-28), and GIP-(21-26) showed no apparent binding. The specificity of the receptor was further examined using several structurally related peptides. Surprisingly, exendin-(9-39) [Ex-(9-39)], a GLP-1 receptor antagonist, and Ex-4-(1-39), a GLP-1 receptor agonist, demonstrated some affinity for the GIP receptor, with 39% and 21% displacement of [125I]spGIP, respectively, at 1 microM. Other members of the secretin/vasoactive intestinal peptide family of peptides tested showed no interaction. GIP-R1 receptor binding correlated with activation of the adenylyl cyclase system, whereby spGIP and shGIP evoked concentration-dependent increases in cAMP accumulation with EC50 values of 8.7 +/- 1.5 x 10(-10)M and 8.1 +/- 1.6 x 10(-10)M for spGIP and shGIP, respectively. Increases in cAMP in the presence of 10 nM spGIP were not dependent on the ambient glucose concentration, with 22- and 18-fold increases in cAMP accumulation at 0.1 and 5.5 mM glucose, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Maintenance of bovine oocytes in prophase of meiosis I by high [cAMP]i.

The effects of high intracellular cAMP concentrations ([cAMP]i) on germinal vesicle maintenance of bovine cumulus-oocyte complexes were investigated, using 8-bromo-3',5'-cAMP (8-Br-cAMP) or an invasive adenylate cyclase from Bordetella pertussis to increase the [cAMP]i. The effects of interactions of these agents with macromolecular supplements in culture medium (fetal calf serum, FCS; polyvinylpyrrolidone, PVP; BSA), and different methods of processing complexes before culture, on subsequent germinal vesicle maintenance by invasive adenylate cyclase were studied. While 8-Br-cAMP was unable to maintain germinal vesicle arrest in the majority of oocytes for 20 h (36% with FCS, 24% with BSA, 18% with PVP), it maintained germinal vesicle arrest in a high proportion of cumulus-enclosed oocytes when BSA or PVP was used (37% with FCS, 52% with BSA, 53% with PVP). The difference in frequency of germinal vesicle maintenance between macromolecular supplements was not related to [cAMP]i when assayed after culture for 2 h with invasive adenylate cyclase. Complexes processed in whole follicular fluid were not maintained in meiotic arrest (26%) when cultured with invasive adenylate cyclase and PVP. Complexes processed in follicular fluid with 3-isobutyl 1-methylxanthine (IBMX) plus invasive adenylate cyclase were arrested at the germinal vesicle stage at high frequencies (65%), while those processed in IBMX or IBMX plus 8-Br-cAMP-supplemented follicular fluid had intermediate (43% and 49%, respectively) frequencies of intact germinal vesicles. Oocyte complexes processed in follicular fluid supplemented with IBMX and invasive adenylate cyclase formed morulae and blastocysts (27.2%), as did oocytes processed in follicular fluid alone (26%). Phosphoprotein profiles showed that control oocytes and 8-Br-cAMP-treated oocytes share a profile that is different from that of oocytes treated with invasive adenylate cyclase. These results show that increased [cAMP]i reversibly maintains bovine oocytes in meiotic arrest for an extended period without the occurrence of the post-translational protein modifications observed during meiotic resumption or transient arrest.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Maintenance of meiotic arrest by increasing [cAMP]i may have physiological relevance in bovine oocytes.

Invasive adenylate cyclase (iAC) reversibly inhibits spontaneous maturation of cumulus-enclosed bovine oocytes by increasing the intracellular concentration of cAMP, [cAMP]i. In this study, physiological aspects of maintaining meiotic arrest in bovine oocytes by iAC were investigated. The maintenance of germinal vesicle arrest by iAC in both cumulus-enclosed and denuded bovine oocytes was concentration dependent (r2 = 0.857). Denuded bovine oocytes were more sensitive to maintenance of meiotic arrest by iAC then were cumulus-enclosed oocytes. At the highest concentration, 70% of the cumulus-enclosed and 90% of the denuded bovine oocytes were maintained in meiotic arrest. The iAC increased [cAMP]i in both intact cumulus-oocyte complexes and enclosed oocytes in a concentration-dependent manner (r2 = 0.795). Cumulus-enclosed oocytes maintained in meiotic arrest by iAC retained developmental competence when subsequently cultured in iAC-free medium and then fertilized. The [cAMP]i in bovine complexes decreased precipitously upon release from follicles and remained low for the next 125 min. However, the [cAMP]i of the enclosed oocytes did not change. Bovine oocytes commit to undergo meiosis in a progressive manner. Approximately 10% of the oocytes were already committed when aspirated. This proportion increased to 40% at 2 h and 70% at 5 h. Use of two inhibitors of cAMP-dependent protein kinase A provided further evidence that cAMP functions in mediating meiotic arrest in bovine oocytes. Bovine oocytes, therefore, are sensitive to different cAMP concentrations, and are developmentally competent after iAC-induced arrest, and complexes containing oocytes exhibit a decrease in [cAMP]i before spontaneous maturation. These results suggest that maintenance of meiotic arrest by iAC is accomplished through modulation of cellular machinery, and regulation of oocyte maturation by [cAMP]i may be physiologically relevant.

Adenylyl Cyclases↗
PubMed1995

Growth and body composition of Meishan and Yorkshire barrows and gilts.

Five barrows and five gilts of each of two breeds (Meishan [Ms] and Yorkshire [Y]) were slaughtered at birth and at 41, 71, 123, and 171 d of age and five gilts of each breed were slaughtered at 260 d of age. Major organ and visceral weights were obtained immediately postmortem (PM), whereas carcass characteristics, carcass composition, femur measurements, and two individual muscle weights were obtained 24 h PM. Linear and quadratic regression coefficients on age differed between the two breeds, in favor of Y barrows and gilts, for live weight, carcass weight, longissimus muscle area (LMA), liver, heart, spleen, and kidney weights, and femur cross-sectional, medullary, and cortical areas (P < .001), leaf fat weight, and percentage of body fat and protein. In contrast to somatic tissue, Ms gilts had uteri and ovaries that grew faster than those of Y gilts from birth to 260 d of age (P < .05), although the uterus and ovary weights were similar for both breeds by 260 d of age (P < .05). Regression coefficients differed (P < .05) between the two sexes for live, carcass, liver, lung and trachea, stomach and esophagus and leaf fat weights, dressing percentage, percentage of body protein, 10th rib backfat (TRBF) thickness (P < .001), and small intestine, kidney (P < .01), heart, and spleen weights (P < .05). Breed differences in regression coefficients differed between the two sexes for percentage of body protein and leaf fat weights (P < .05). Yorkshire pigs were larger, later-maturing pigs that grew faster from birth to 171 d of age. Yorkshire pigs slaughtered at 171 d of age had heavier total wholesale cut (WC), trimmed cut (TC), and boneless cut (BC) weights than did Ms pigs of the same age (P < .001).

Animals↗
PubMed1994

Cyclic AMP in ruminal and other anaerobic bacteria.

An examination of cAMP levels in predominant species of ruminal bacteria and other anaerobic bacteria was conducted. Cellular cAMP concentrations of glucose-grown cultures of Butyrivibrio fibrisolvens 49, Prevotella ruminicola D31d, Selenomonas ruminantium HD4 and D, Megasphaera elsdenii B159, Streptococcus bovis JB1, Bacteroides thetaiotaomicron 5482, and Clostridium acetobutylicum ATCC 824 were determined at various times during growth by a competitive binding radioimmunoassay procedure. The results were compared to those for Escherichia coli NRRL B3704. The levels of cAMP ranged from undetectable for B. thetaiotaomicron to approximately 15 pmol/mg cell protein for P. ruminicola D31d. Varying the growth substrate in a manner previously shown to elicit regulatory response did not alter the level of cAMP in these organisms. In general, cAMP concentrations present in these organisms were much lower than the 6-25 pmol/mg cell protein observed for E. coli. The levels of cAMP in P. ruminicola were consistently higher than levels in other anaerobes, particularly during the early exponential and stationary phases of growth. Based on these data it seems unlikely that cAMP is involved in regulation of substrate catabolism in the anaerobic bacteria examined except in P. ruminicola where it may have an unknown regulatory function.

Animals↗
PubMed1994

Comparison of the semen characteristics of Fengjing, Meishan and Yorkshire boars.

Semen characteristics of Chinese Fengjing, CHinese Meishan and American Yorkshire boars were examined. Samples were collected from 24 boars: 6 Fengjing, 12 Meishan and 6 Yorkshire. Three semen characteristics and 6 biochemical evaluations of semen or seminal plasma were analyzed. The whole semen parameters measured were gelatinous (gel) and gel-free volume and progressive motility. Fengjing boars were higher in gel volume than Meishan (P < 0.05) but not Yorkshire boars (P > 0.25), while Yorkshire boars were higher than Meishan boars in gel volume (P < 0.10). The gel-free volume was higher in Yorkshire and Fengjing boars than Meishan boars (P < 0.10), but Fengjing gel-free volumes did not differ from Yorkshire gel-free volumes (P > 0.80). However, the only difference detected for progressive motility was between Fengjing and Meishan boars (78.5 vs 74.5%; P < 0.10). Sperm concentration was higher in Meishan than Yorkshire boars (P < 0.01) although these breeds did not differ from Fengjing boars (P > 0.18). The biochemical messurements made were fructose, galactose, inositol, total carbohydrate and total protein in seminal plasma and pH in gel-free semen. Fengjing boars had higher concentrations of galactose in seminal plasma than Meishan or Yorkshire boars (P < 0.05), while Meishan seminal plasma had higher galactose concentrations than Yorkshire seminal plasma (P < 0.10). Fructose, inositol and total carbohydrate concentrations were all higher in Fengjing and Meishan seminal plasma than Yorkshire seminal plasma (P < 0.05). Fengjing seminal plasma had higher levels of inositol than Meishan seminal plasma (769 vs 566 mg/100 ml; P < 0.10). Furthermore, Fengjing and Meishan semen had similar fructose and total carbohydrate concentrations (P > 0.80). The pH level and total protein concentration did not differ among the 3 breeds (P > 0.30). This study indicated that breed differences were detected for several seminal parameters, although no single breed had consistantly higher values for all the parameters measured.

Journal Article↗
PubMed1994

Stable expression of the rat GLP-I receptor in CHO cells: activation and binding characteristics utilizing GLP-I(7-36)-amide, oxyntomodulin, exendin-4, and exendin(9-39).

Glucagon-like peptide-I (GLP-I) is a potent insulinotropic peptide that mediates its actions at pancreatic B-cells via specific receptors. In the present study we stably expressed the rat B-cell GLP-I receptor in CHO cells and studied binding characteristics and receptor activation utilizing the naturally occurring receptor agonist GLP-I(7-36)-amide (GLP-I), the proglucagon-derived GLP-I-related peptide oxyntomodulin, the GLP-I receptor agonist exendin-4, and the specific antagonist exendin(9-39). The potencies to displace [125I]GLP-I from the receptor were GLP-I > exendin-4 > exendin(9-39) > oxyntomodulin, and to displace [125I]exendin-4 GLP-I = exendin-4 > exendin(9-39) > oxyntomodulin. cAMP production was stimulated equally by GLP-I and exendin-4. Oxyntomodulin was less potent to stimulate cAMP generation. Exendin(9-39) blocked the stimulatory action of GLP-I and exendin-4 on cAMP production, but not that of oxyntomodulin. This study shows that GLP-I and exendin-4 are potent agonists at the transfected rat B-cell GLP-I receptor whereas oxyntomodulin is only a weak GLP-I receptor agonist. Furthermore, exendin(9-39) is a potent GLP-I receptor antagonist. This peptide is a valuable tool to further study the physiological actions of GLP-I.

Animals↗
PubMed1994

Development and validation of swine embryonic stem cells: a review.

The establishment of embryonic cell lines from swine should be useful for studies of cell differentiation, developmental gene regulation and the production of transgenics. This paper summarizes the establishment of porcine (Sus scrofa) embryonic stem (ES) cell lines from preimplantation blastocysts and their ability to develop into normal chimaeras. ES cells can spontaneously differentiate into cystic embryoid bodies with ectodermal, endodermal, and mesodermal cell types. Further, culture of ES cells to confluence or induction of differentiation with retinoic acid or dimethylsulfoxide results in morphological differentiation into fibroblasts, adipocytes, and epithelial, neuronal, and muscle cells. These ES cells have a normal diploid complement of 38 chromosomes. Scanning electron microscopy of the ES cells reveals a rounded or polygonal, epithelial-like cell with numerous microvilli. The differentiation of these embryonic cell lines into several cell types indicates a pluripotent cell. Furthermore, chimaeric swine have been successfully produced using such ES cells.

Animals↗