Search PubMed⌕ Search

Biomedical subjects

C B Stewart

Publications and source records attributed to C B Stewart.

At least 19 recordsLinked to original sources
PubMed2006

Effect of crabgrass (Digitaria ciliaris) hay harvest interval on forage quality and performance of growing calves fed mixed diets.

Twelve 0.81-ha crabgrass (Digitaria ciliaris [Retz.] Koel.) hay fields were harvested at 21, 35, and 49 d of regrowth (average phonological growth stage of 30, 51, and 56, respectively). Increased harvest interval exhibited a linear decrease (P < 0.01) in CP (14.1, 13.7, and 10.6% of DM, respectively) and increase (P < 0.01) in NDF (65.3, 70.6, and 70.2% of DM, respectively) and ADF (35.7, 38.9, and 42.7% of DM, respectively). Hays were incorporated into 3 diets that contained 20% (DM basis) crabgrass hay, ground corn (33%), and soybean hulls (32%). Diets contained 14.4, 14.4, and 13.6% CP; 1.83, 1.72, and 1.81 Mcal of NE(m)/kg; and 1.21, 1.10, and 1.17 Mcal of NE(g)/kg; respectively. Diets were fed to beef calves in 12 pens at a rate of 2.3% (DM basis) of BW in 1 experiment (n = 120, initial BW 210 +/- 4.4 kg) and ad libitum in another experiment (n = 60, initial BW 207 +/- 4.4 kg). To measure passage rate of the hay and concentrate portions of the diets, 12 heifer calves (BW = 145 +/- 4.5 kg) were individually fed at 2.3% of BW for 14 d and dosed with Dy-labeled soybean hulls and Yb-labeled hay. In situ DM digestibility of the hays and diets were determined using 3 ruminally cannulated steers (BW = 584 +/- 10.4 kg). Harvest interval did not affect (P > or = 0.11) ADG of limit-fed calves during the diet acclimation or growing phases (average 0.32 and 0.80 kg, respectively) or ADG of calves fed ad libitum (average 1.21 kg). Dry matter intake of calves fed ad libitum averaged 7.9 kg/d (3.28% of BW) and was not affected (P > or = 0.22) by harvest interval. Gain:feed was not affected (P > or = 0.20) by harvest interval (0.13 and 0.15 for limit-fed and ad libitum-fed calves, respectively). Increased harvest interval linearly increased (P < 0.01) ruminal retention time of the hay and tended (P = 0.06) to linearly increase ruminal retention time of the concentrate portions of the diet. Harvest interval linearly decreased (P < or = 0.05) the extent of degradability and effective degradability of DM and NDF of hays, but DM disappearance of the total diet did not differ (P > or = 0.35). In the conditions of this study, increasing harvest interval of crabgrass hay from 21 to 49 d had no deleterious impact on animal performance or efficiency of gain when fed to growing calves in a high-concentrate mixture.

Animal Feed↗
PubMed2000

Xenopus laevis peripherin (XIF3) is expressed in radial glia and proliferating neural epithelial cells as well as in neurons.

Neuronal intermediate filament (nIF) proteins form the most abundant component of the axonal cytoskeleton. Thus, understanding their function and the regulation of their expression is essential for comprehending how axonal structure is regulated. Although most vertebrate nIF proteins are classified as type IV intermediate filament (IF) proteins, additional nIF proteins exist in frogs (Xenopus laevis), cyprinid fishes, and mammals (called XIF3, plasticin, and peripherin, respectively) that are classified as type III. Expression of a type III nIF protein is correlated strongly with the earliest phases of axonal outgrowth in fishes but less so in mammals. To understand better how the correlation between type III nIF protein expression and early phases of axonal outgrowth has changed during evolution, the authors examined XIF3 expression in Xenopus laevis. In Xenopus, the association between XIF3 expression and early axonal outgrowth was especially strong. For example, during early axonal development, XIF3 expression preceded and was more abundant and widespread than that of any of the type IV nIF proteins. As axons matured, neuronal expression of XIF3 gradually became more restricted while that of type IV nIF proteins increased. These results support the idea that type III nIF proteins play a special role during early phases of axonal outgrowth. In addition to finding XIF3 in neurons, the authors also unexpectedly found it in regions of the central nervous system that contain proliferating cells and radial glia. As a framework for interpreting variations in nIF expression in different vertebrate species, the authors built phylogenetic trees to clarify relationships among vertebrate nIF proteins. These trees supported the classification of XIF3, plasticin, and peripherin as orthologs (products of the same genetic locus, evolving separately only since the species lineages diverged). Thus, XIF3, plasticin, and peripherin probably should be referred to as Xenopus, fish, and mammalian peripherin, respectively. This finding argues that differences in expression of these three proteins in frogs, fishes, and mammals are the result of regulatory changes to the peripherin ancestral gene along each lineage. The expression of a peripherin ortholog in Xenopus glia may represent either an adaptation that arose since the divergence of Xenopus from mammals or, alternatively, a feature retained from an ancestral IF protein that was expressed originally both in neurons and in glia.

Age Factors↗
PubMed1997

Episodic adaptive evolution of primate lysozymes.

Although the darwinian concept of adaptation was established nearly a century ago, it has been difficult to demonstrate rigorously that the amino-acid differences between homologous proteins from different species have adaptive significance. There are currently two major types of sequence tests for positive darwinian selection on proteins from different species: sequence convergence, and neutral rate violation (reviewed in ref. 1). Lysozymes from the stomachs of cows and langur monkeys, two mammalian species displaying fermentation in the foregut, are an example of amino-acid sequence convergence among homologous proteins. Here we combine tests of neutral rate violation with reconstruction of ancestral sequences to document an episode of positive selection on the lineage leading to the common ancestor of the foregut-fermenting colobine monkeys. This analysis also detected a previously unsuspected adaptive episode on the lineage leading to the common ancestor of the modern hominoid lysozymes. Both adaptive episodes were followed by episodes of negative selection. Thus this approach can detect adaptive and purifying episodes, and localize them to specific lineages during protein evolution.

Adaptation, Physiological↗
PubMed1996

A quick, direct method that can differentiate expressed mitochondrial genes from their nuclear pseudogenes.

Direct sequencing of mitochondrial DNA (mtDNA) following amplification using the polymerase chain reaction (PCR) has found widespread use in population genetic and phylogenetic research over the past few years. Recently, nuclear copies of mitochondrial genes have been reported in diverse eukaryotic species, often confounding such research (reviewed in [2,3]). Under certain circumstances, nuclear pseudogenes can be amplified more efficiently than the intended mtDNA target, even when using as template mtDNA that has been purified by gradient centrifugation. If the transfer of the gene copy to the nucleus happened recently, it can be difficult-if not impossible-to identify the legitimate mitochondrial sequence. Here, we present a simple method that can identify expressed mitochondrial genes, using the cytochrome b gene of the particularly problematical proboscis monkey as an example. Because mtDNA is transcribed and processed into polyadenylated mRNAs reverse transcription coupled to PCR can be used to amplify the expressed mitochondrial version. This method produced an unambiguous sequence for the proboscis monkey mitochondrial cytochrome b gene; in contrast, traditional DNA-based PCR methods produced ambiguous sequence, because many nuclear pseudogenes were present. Phylogenetic analysis of the cytochrome b gene suggests that the proboscis monkey groups with the Asian langurs, rather than forming a sister taxon to all Asian and African colobines as was previously suggested. Reverse transcriptase-coupled PCR should be applicable to many other cases of nuclear transfer of mtDNA, including those involving ribosomal genes.

Animals↗
PubMed1995

Insertions and duplications of mtDNA in the nuclear genomes of Old World monkeys and hominoids.

Using oligonucleotide primers designed to match conserved regions of mammalian mitochondrial DNA (mtDNA), we have amplified and sequenced two divergent cytochrome b nuclear pseudogenes from orangutan cellular DNA. Evolutionary analysis suggests that a nuclear transfer occurred about 30 million years ago on the lineage leading to the catarrhines (Old World monkeys and hominoids), and involved a long (at least 3 kilobases), probably damaged, piece of mtDNA. After this transfer, the pseudogene duplicated, giving rise to the two copies that are probably present in all hominoids, including humans. More recent transfers involving the entire cytochrome b gene have also occurred in the Old World monkeys. Such nuclear copies of mtDNA can confound phylogenetic and population genetic studies, and be an insidious source of DNA contamination of 'ancient' and forensic DNA. Indeed, contamination with these anciently transferred human pseudogenes is almost certainly the source of the cytochrome b sequences recently reported from 'dinosaur bone DNA'.

Animals↗
PubMed1994

Molecular evolution. Dissolving the barriers.

The crystal structure of lysin, a protein involved in abalone fertilization, together with evolutionary sequence analysis, provides clues to lysin's non-enzymatic mode of action and possible role in speciation.

Amino Acid Sequence↗
PubMed1994

Aloe vera, hydrocortisone, and sterol influence on wound tensile strength and anti-inflammation.

Aloe vera at doses of 100 and 300 mg/kg daily for 4 days blocked the wound healing suppression of hydrocortisone acetate up to 100% using the wound tensile strength assay. This response was because of the growth factors present in A. vera masking the wound healing inhibitors such as sterols and certain amino acids. The sterols showed good anti-inflammatory activity (-36%) in reducing the croton oil-induced ear swelling. This activity displayed a dose-response relationship.

Aloe↗
PubMed1993

Multiple cDNA sequences of bovine tracheal lysozyme.

The principal role of lysozyme is to prevent bacterial invasion at body surfaces. We are interested in how lysozyme is regulated at the surface of the respiratory tract, where the serous gland cell is regarded as the primary cellular source of this enzyme. Since the cow genome contains at least 10 lysozyme-like genes, our objective was to determine which of them are expressed in the cow tracheal gland serous cell. By screening tracheal cDNA libraries with a probe constructed from the cDNA encoding stomach lysozyme 2, we obtained 3 lysozyme cDNAs: 5a (1023 base pairs (bp)), 7a (1060 bp), and 14d (1249 bp). cDNA 7a corresponds to a previously reported gene (showing sequence identity to the stomach 2 lysozyme gene), whereas cDNAs 5a and 14d correspond to lysozyme genes not previously reported. Northern blot analysis of cow tracheal RNA showed lysozyme mRNAs of three distinct lengths. Based on hybridization with probes specific for each cDNA, we determined that the longest transcript corresponded to cDNA 5a, the shortest to 7a, and the intermediate-length transcript to 14d. Cultured cow tracheal gland serous cell RNA, reverse transcribed and amplified by the polymerase chain reaction with primers common to all three cDNAs, yielded a product that hybridized to oligonucleotide probes specific for all three cDNAs but most strongly to that for 5a. These results indicate that multiple lysozyme mRNAs are expressed in the cow trachea and that the lysozyme encoded by cDNA 5a is the major form expressed in the tracheal gland serous cell. This serous cell lysozyme is predicted to differ importantly in structure from both 7a and 14d lysozymes, with an arginine:lysine ratio almost 10-fold higher. The sequence differences may underlie functional differences, including variable resistance to proteolysis and variable affinity for large polyanions (e.g. mucins) found in the respiratory tract lumen.

Amino Acid Sequence↗
PubMed1993

The powers and pitfalls of parsimony.

Parsimony analysis is a powerful tool for the study of biological evolution. It is used to construct phylogenetic trees, to evaluate alternative hypotheses objectively, and to study evolutionary pattern and process. Yet, as comparative data sets expand, the pitfalls of parsimony analysis are catching experts and novices alike.

Animals↗
PubMed1992

Human skin mast cell carboxypeptidase: functional characterization, cDNA cloning, and genealogy.

We functionally characterized human skin mast cell carboxypeptidase A (MC-CPA), and explored its evolutionary relationship to other carboxypeptidases to understand further the structural basis for the substrate preferences of this enzyme. Purified human skin MC-CPA displayed more activity than did bovine pancreatic carboxypeptidase A (CPA) against carboxyl-terminal leucine residues, about equal activity with phenylalanine and tyrosine residues, and no activity with tryptophan or alanine. To correlate kinetic data with structure, we isolated and sequenced a cDNA encoding MC-CPA from human skin, and directly sequenced 30% of the purified protein. These sequences agreed with that of human lung MC-CPA, and further support the evidence for a single MC-CPA gene in humans. Four amino acid replacements, resulting in a net positive change in non-hydrogen atoms in the S1' subsite of MC-CPA, were associated with less alteration in substrate specificity, relative to bovine CPA, than might be expected from studies using rat CPA1 and CPA2. We noted two consensus N-linked glycosylation sites in human MC-CPA that are not found in rat and mouse MC-CPA, or in bovine CPA; that at least one of these sites is glycosylated in vivo was verified by N-glycosidase F treatment, lentil lectin binding, and Concanavalin A-Sepharose chromatography. Evolutionary trees constructed from the known carboxypeptidase sequences suggested that MC-CPA most likely evolved from a carboxypeptidase B-like enzyme, independent of the pancreatic CPA. Thus, in the carboxypeptidase gene family, MC-CPA displays a unique genealogy and several amino acid replacements in its S1' binding pocket that result in substrate specificity quite similar to bovine CPA.

Amino Acid Sequence↗
PubMed1991

Structural evolution of an enzyme specificity. The structure of rat carboxypeptidase A2 at 1.9-A resolution.

The structure of rat carboxypeptidase A2 (CPA2), which has a unique specificity for tryptophan-containing COOH-terminal peptides, has been determined in an unliganded state at 1.9-A resolution and refined to a crystallographic R-factor of 18.3%. Comparison of the structure of CPA2 with that of bovine carboxypeptidase A (referred to here as CPA1) reveals that the specificity of the former for larger amino acids probably arises from two amino acid replacements within the binding cavity (Thr268----Ala and Leu203----Met), coupled with differences in the positions of conserved residues in a surface loop on one face of the specificity pocket. The position of the reactive-site surface loop may be affected also by a disulfide bridge between Cys210 and Cys244. In this unliganded form of the enzyme, Tyr248 takes up a position interior to the specificity pocket and is distinct from that observed in bovine CPA1. The structural differences between CPA1 and CPA2 correlate strongly with crystallographically determined temperature factors and thus appear to be largest where the enzyme is flexible.

Amino Acid Sequence↗
PubMed1989

Episodic evolution in the stomach lysozymes of ruminants.

By sequencing lysozymes c from deer and pig stomachs and comparing them to the known amino acid sequences of other lysozymes c, it was possible to examine the rate of sequence change during and after the period in which this enzyme acquired a new function. Evolutionary tree analysis suggests that the rate went up while lysozyme was being recruited to function as a digestive enzyme in the stomach of early ruminants. Later, presumably after lysozyme was well adapted for functioning in the new environment, which contains acid, pepsin, and fermentation products, the rate of amino acid replacement became subnormal.

Adaptation, Physiological↗