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M B Wheeler

Publications and source records attributed to M B Wheeler.

At least 91 records · Page 5Linked to original sources
PubMed1994

Ligand-specificity of the rat GLP-I receptor recombinantly expressed in Chinese hamster ovary (CHO-) cells.

Glucagon-like peptide-I (GLP-I) is a potent incretin hormone and is considered as a new therapeutic tool in the treatment of diabetes mellitus. This study was designed to precisely characterize the binding behavior and activation of the recombinant GLP-I receptor against naturally occurring ligands of the glucagon/VIP/secretin peptide hormone family. CHO-cells were stably transfected with a plasmid containing a cDNA encoding for the rat GLP-I receptor. Northern blot analysis with this cDNA showed a single band of 2.7 kb in CHO cells, while in RINm5F cells, three bands of 2.7, 3.4, and 3.6 kb were specifically labelled. In receptor-binding studies 125I-GLP-I was displaced by GLP-I and weakly by PHI and oxyntomodulin but not by helodermin, helospectin I, helospectin II, secretin, VIP, and PACAP-38. Intracellular cAMP generation was stimulated by GLP-I, PHI, and oxyntomodulin. Helodermin, helospectin I, helospectin II, secretin, VIP, and PACAP-38 were not able to displace 125I-GLP-I from its receptor or to stimulate intracellular cAMP production. This data shows that the GLP-I receptor is characterized by a high ligand specificity.

Animals↗
PubMed1993

Age at puberty, ovulation rate, uterine length, prenatal survival and litter size in Chinese Meishan and Yorkshire females.

Studies on the ovulation rate, prenatal survival and litter size of Chinese Meishan pigs have given widely divergent results depending on the extent of inbreeding of the animals, their original genetic diversity, the age and parity, and the conditions of management. To obtain meaningful results, it is necessary to characterize the population under study. The following report characterizes populations of Meishan and Yorkshire of a widely diverse background. First farrowing data were collected on 21 Meishan and 20 Yorkshire gilts. Meishan gilts had 12.4 fully formed piglets and Yorkshire gilts had 7.4 fully formed piglets (P < 0.01). Meishan gilts averaged 1.86 mummified fetuses per litter vs 0.05 per Yorkshire litter (P < 0.01). Yorkshire piglets averaged 1.3 kg body weight at birth vs 0.9 kg for Meishan piglets (P < 0.01). At 47 days of second gestation, 19 Meishan and 12 Yorkshire sows averaged 22.7 and 16.3 corpora lutea (CL), respectively (P < 0.01). Uterine length and number of fetuses were not different (P > 0.40) in the two breeds. Daily estrous detection of 50 Meishan and 34 Yorkshire gilts began at 60 and 120 days of age, respectively. Meishan gilts reached sexual maturity at 95 days of age, which was 105 days earlier than Yorkshire gilts (P < 0.01). Meishan gilts were in estrus nearly 1 day longer than Yorkshire gilts at first, second and third estrus (P < 0.05). No differences in cycle length between breeds were detected for the first or second estrous cycle (P > 0.60). Nineteen Meishan gilts were slaughtered at 51 days of gestation and their reproductive tracts were recovered. The mean number of dissected CL (17.0), number of fetuses (13.1), total uterine length (396 cm), spacing per fetus (29.9 cm), allantoic (124.9 ml) and amniotic (32.2 ml) volumes, crown-rump length (82.8 mm), weight (35.4 g), sex, and direction of each fetus were determined. Chinese Meishan gilts reached puberty much earlier and were in estrus longer than Yorkshire gilts and Meishan sows had more CL than Yorkshire sows.

Journal Article↗
PubMed1993

Animal production--a longstanding biotechnological success.

Biotechnology has been practiced in one form or another under many banners since the beginning of the domestication of animal species. Many of the previously used tools of animal breeding have played and will continue to play an important role in the selection and propagation of desirable and economically important characteristics in livestock. From this viewpoint, animal production practices have been a long-standing biotechnological success. We now produce more animal products with fewer animals than was imagined even 10 y ago. These animal products are produced more efficiently and with less competition with humans for high-quality cereal grains. However, improvements are still needed in product composition and production efficiency, especially in growth, disease resistance, and reproduction. The attainment of such improvements will depend heavily on our ability to quantify desirable traits, to identify markers linked to gene(s) responsible for those traits, to select or redesign populations of superior individuals, and to propagate those animals.

Animals↗
PubMed1993

The role of the free cytosolic calcium level in beta-cell signal transduction by gastric inhibitory polypeptide and glucagon-like peptide I(7-37).

Using the glucose-responsive hamster beta-cell line (hamster insulin tumor cells), we examined the cellular mechanisms by which gastric inhibitory polypeptide (GIP) and glucagon-like peptide I(7-37) (GLP-I) potentiate glucose-stimulated insulin secretion. Glucose alone increased insulin secretion and increased the free cytosolic calcium levels ([Ca2+]i) without altering cAMP content. When added to glucose-stimulated cells, GIP and GLP-I increased cAMP levels and further increased insulin secretion. At 4 mM but not 0.4 mM glucose, both peptides triggered a dose-dependent rise in [Ca2+]i with ED50s of 0.4 and 0.2 nM for GIP and GLP-I, respectively. The increase in [Ca2+]i was blocked by either chelation of extracellular Ca2+ with EGTA or nimodipine, the voltage-dependent Ca2+ channel blocker. Nimodipine also inhibited the potentiation of glucose-stimulated insulin secretion by GIP and GLP-I without inhibition of the stimulatory effect of these two peptides on cAMP accumulation. Neither peptide altered phosphoinositide metabolism, further underlining that the mobilization of intracellular Ca2+ from endoplasmic reticulum is not involved in the GIP and GLP-I signal transduction pathways. This study establishes that GIP and GLP-I potentiate glucose-stimulated insulin secretion by increasing extracellular Ca2+ influx through voltage-dependent Ca2+ channels.

Animals↗
PubMed1993

Functional expression of the rat glucagon-like peptide-I receptor, evidence for coupling to both adenylyl cyclase and phospholipase-C.

In man, glucagon-like peptide-I-(7-37) [GLP-I-(7-37)] is the most potent endogenous insulin-stimulating hormone. Although GLP-I-(7-37)-stimulated insulin secretion from the beta-cell is associated with an increase in cAMP accumulation, little is known about the signal transduction pathways used by this peptide. Using a cDNA encoding a high affinity rat GLP-I-(7-37) receptor [Kd = 4.1 nM for GLP-I-(7-37); Kd = 1 microM for GLP-I-(1-36) amide] expressed in a monkey kidney cell line (COS-7), we have demonstrated that the receptor is not only coupled to adenylyl cyclase, but is associated with an increase in the free cytosolic calcium level ([Ca2+]i). GLP-I-(7-37) increased both cAMP and [Ca2+]i in a dose-dependent manner and with equal potency (ED50 = 2.0 nM). The major source of the increased [Ca2+]i was found to be through the release of intracellular pools of Ca2+ associated with an increase in phosphoinositol turnover. Northern blot hybridization studies demonstrated that the GLP-I-(7-37) receptor gene was expressed in relatively high abundance in pancreatic islets and lung, but was also expressed at lower levels in the brain, liver, kidney, and skeletal muscle. This study establishes that a single GLP-I receptor species can mediate the effects of GLP-I-(7-37) through multiple G-protein-coupled signaling pathways, including the adenylyl cyclase system, phospholipase-C, and changes in [Ca2+]i.

Adenylyl Cyclases↗
PubMed1993

Cloning and functional expression of the human glucagon-like peptide-1 (GLP-1) receptor.

Truncated forms of glucagon-like peptide-1 are the most potent endogenous stimuli of insulin secretion and have powerful antidiabetogenic effects. To determine the structure and coupling mechanisms of the human GLP-1 receptor we have isolated two pancreatic islet cDNAs, encoding the 463 amino acid receptor and differing mainly in their 3' untranslated regions. The deduced amino acid sequence is 90% homologous with the rat GLP-1 receptor. Northern blot analysis shows expression of a single 2.7 kb transcript in pancreatic tissue. When expressed in COS-7 cells the recombinant receptor conferred specific, high affinity GLP-1(7-37) binding. GLP-1(7-37) increased intracellular cAMP in a concentration dependent manner and caused an increase in the free cytosolic calcium ([Ca2+]i) from an intracellular pool, characteristic of phospholipase C (PLC) activation. Thus, like the structurally related glucagon and parathyroid hormone receptors, the human GLP-1 receptor can activate multiple intracellular signaling pathways including adenylyl cyclase and PLC. Knowledge of the GLP-1 receptor structure will facilitate the development of receptor agonists and elucidation of the important role of GLP-1 in normal physiology and disease states.

Amino Acid Sequence↗
PubMed1993

Effects of porcine somatotropin on growth and carcass composition of Meishan and Yorkshire barrows.

Effects of porcine somatotropin (pST) on growth and carcass characteristics of Meishan (Ms) and Yorkshire (Y) barrows given 3 mg of pST or saline daily were determined for two end points. First, 26 Ms and 26 Y barrows were treated from 119 d of age until the Y barrows reached 108 kg. Second, another 18 Ms barrows were treated to 108 kg BW. Age- and weight-matched treatments were analyzed. Results for both groups indicated pST effects (P < .05) for feed conversion (+) and intake (-), dressing percentage (-), percentage of carcass fat (-) and protein and water (+), leaf fat (-), backfat (BF) thickness (-), longissimus muscle area (LMA; +), skin thickness (+), muscle firmness and marbling scores (-), organ weights (+), belly (-), clear plate (-), ham (+), and total boneless cuts (BC; +). Somatotropin effects were also present for loin (-) and boneless Boston butt (BBB; +) in the age-matched group and for ADG (+), carcass weight (-), loin (-), jowl (-), and tenderloin (+) in the weight-matched group. Breed effects (P < .05), in favor of Y barrows, in both treatments existed for ADG (+) and feed intake (+), carcass weight (+), dressing percentage (+), LMA (+), skin thickness (-), muscle color and firmness scores (-), muscling score (+), all wholesale cuts (WC; +) except clear plate (age-matched), all trimmed cuts (TC; +) except picnic shoulder (weight-matched), and all BC (+). Breed effects, in favor of Y barrows, were also determined for carcass length (+), percentage of carcass ash (-), leaf fat (+), average BF thickness (+), and heart (-) and liver (-) weights in age-matched animals and percentage of carcass fat (-), protein (+), water (+), leaf fat (-), 10th rib, average, and P2 BF thicknesses (-), marbling score (-), femur length (-), and liver weights (+) in weight-matched animals. A higher response to pST (P < .05) was determined in Ms barrows than in Y barrows for percentage of carcass protein (+), liver (+), and heart (+) in the age-matched treatment and 10th rib BF thickness (-) and heart weight (+) in the weight-matched treatment. Yorkshire barrows treated with pST had more improved values for color score (+; age-matched) and BBB (+; weight-matched).

Adipose Tissue↗
PubMed1992

Identification of a transcriptional enhancer important for enteroendocrine and pancreatic islet cell-specific expression of the secretin gene.

It is well established that the gene encoding the hormone secretin is expressed in a specific enteroendocrine cell, the S cell. We now show that the secretin gene is transiently expressed in insulin-producing B cells of the developing pancreatic islets in addition to the intestine. Furthermore, secretin is produced by most established islet cell lines. In order to identify and characterize the regulatory elements within the secretin gene that control tissue-specific expression, we have introduced secretin reporter gene constructions into the secretin-producing HIT and STC-1 cell lines as well as the nonexpressing INR1-G9 glucagonoma line. Analysis of deletion mutants revealed that sequences between 174 and 53 bp upstream from the transcriptional start site are required for maximal expression in secretin-producing cells. This positive element functioned independently of position and orientation. Further deletions into the enhancer resulted in a stepwise loss of transcriptional activity, suggesting the presence of several discrete control elements. The sequence CAGCTG within the secretin enhancer closely resembles that of the core of the B-cell-specific enhancer in the insulin gene. Point mutations introduced into this putative element led to greater than 85% reduction in transcriptional activity. Gel mobility shift assays suggested that a factor in B cells closely related or identical to proteins that bind to the insulin enhancer interacts with the CAGCTG motif in the secretin gene.

Animals↗
PubMed1992

Cloning of a novel alpha 1-subunit of the voltage-dependent calcium channel from the beta-cell.

To study the molecular regulation of voltage-dependent Ca2+ channels (VDCCs) in the beta-cell, we have cloned a cDNA for the alpha 1-subunit from a hamster insulin-secreting cell line (HIT-T15). The cDNA (HCa3a) encodes a 1610-amino acid protein with four repeating membrane domains and an overall structure characteristic of other alpha 1-subunits. Although the cDNA shows a high degree of sequence homology (97%) with a rat brain alpha 1-subunit (RB alpha 1), the C-terminal 15 amino acids of HCa3a share no similarity with any cloned alpha 1 protein. High stringency Northern blot analysis revealed a single transcript of approximately 8.6 kilobases in HIT cells and hamster pancreas. A similarly sized species was detected in hamster brain, heart, and skeletal muscle. Using polymerase chain reaction and a primer set unique to HCa3a, this alpha 1 isoform was found to be expressed in islet cell lines derived from rat, mouse, and hamster. The HIT cell alpha 1-subunit is also expressed in discrete regions of the rat central nervous system, including the cortex, cerebellum, hypothalamus, and brain stem. The expression of two alpha 1 isoforms (HCa3a and cardiac) in the HIT cell underscores the possible complexity of VDCCs in the regulation of beta-cell signal transduction. With its widespread tissue distribution, HCa3a does not conform to the current classification system used for L-type VDCCs; this suggests that an alternative system of classification is required.

Amino Acid Sequence↗
PubMed1991

The secretin gene: evolutionary history, alternative splicing, and developmental regulation.

The gene encoding the hormone secretin has been isolated and structurally characterized. The transcriptional unit is divided into four exons spanning 813 nucleotides. Comparison of the rat secretin gene to the other members of the glucagon-secretin gene family reveals that similarities are restricted to the exons encoding the biologically active peptides. Analysis of RNA from porcine intestine indicates that at least two transcripts are generated from the porcine secretin gene as a result of differential splicing. The longer and more abundant transcript appears to be identical to a previously isolated cDNA, which encodes a precursor that includes a 72-amino acid C-terminal extension peptide. The shorter transcript does not contain the third exon and, as a result, encodes only 44 residues beyond the C terminus of secretin. The amino acid sequence deduced from the shorter transcript is identical to a precursor form of secretin recently isolated from porcine duodenum [Gafvelin, G., Jornvall, H. & Mutt, V. (1990) Proc. Natl. Acad. Sci. USA 87, 6781-6785]. Developmental studies reveal that both secretin mRNA and peptide levels in the intestine are highest just before birth, prior to the onset of gastric acid secretion and feeding. This observation implies that secretin biosynthesis in developing animals is controlled independently of the principal factors known to regulate secretin release in adult animals.

Amino Acid Sequence↗
PubMed1991

Isolation, characterization, and developmental expression of the rat peptide-YY gene.

In the present study we describe the isolation, structural characterization, and developmental expression of the gene encoding the intestinal hormone peptide-YY. Examination of the nucleotide sequence of the peptide-YY gene reveals that each of the four exons encodes a functional domain of its mRNA that is analogous to the corresponding exons of the genes encoding two closely related peptides neuropeptide-Y and pancreatic polypeptide. The highly conserved structural organization of the genes encoding this family of three peptides suggests that each gene arose from the duplication of a common ancestral gene. Developmental studies reveal that the peptide-YY gene exhibits a complex pattern of tissue-specific expression in the gastrointestinal tract. Unlike many gastrointestinal hormones, peptide-YY mRNA levels are highest before birth. The pancreas appears to be the major site of peptide-YY gene expression in the fetus, exceeding colonic expression by 7-fold. The abundance of peptide-YY mRNA in the pancreas declines rapidly after birth, in contrast to the colon, where mRNA levels are maintained throughout development into adulthood. Expression of the peptide-YY gene before birth antedates the presence of known enteral secretagogues for this hormone, suggesting alternate mechanisms that control its biosynthesis during development.

Amino Acid Sequence↗
PubMed1990

Secretin: structure of the precursor and tissue distribution of the mRNA.

Secretin is a 27-amino acid gastrointestinal hormone that stimulates the secretion of bicarbonate-rich pancreatic fluid. The unusually high number of serine, leucine, and arginine residues in secretin has precluded the use of oligonucleotides to screen cDNA libraries to isolate a secretin cDNA. In the present study, a short cDNA encoding porcine secretin was amplified from duodenal mucosal first-strand cDNA template by using 16,384- and 4096-fold degenerate primers in the DNA polymerase chain reaction. From the sequence of the amplified cDNA, an unambiguous oligonucleotide probe was designed to screen a cDNA library. Here we report the sequences of cDNAs encoding the porcine and rat secretin precursors. The predicted amino acid sequences reveal that each precursor consists of a signal peptide, an N-terminal peptide, secretin, and a 72-amino acid C-terminal peptide. Secretin has been highly conserved through evolution. Rat secretin differs from its porcine counterpart by a single glutamine-for-arginine substitution at position 14. In contrast, the amino acid sequences of the C-terminal peptides are only 39% conserved between the two species, suggesting that the C-terminal peptide does not have an essential physiologic function. RNA blot hybridizations reveal that the rat secretin gene is expressed throughout the small intestine. Although secretin immunoreactivity has been localized in the central nervous system by some laboratories, we are unable to detect secretin mRNA in tissues of the central nervous system by Northern blot hybridization.

Amino Acid Sequence↗