Biomedical subjects

A L Schroeder

Publications and source records attributed to A L Schroeder.

At least 19 recordsLinked to original sources

PubMed2006

Use of bovine somatotropin for increased skeletal and lean tissue growth of Holstein steers.

One hundred-sixty Holstein growing-finishing steers (initial BW of 185 kg) were blocked by BW to determine the effectiveness of long-term bovine somatotropin (bST) administration on lean, skeletal, and carcass measurements. Steers were randomly allocated to 4 treatments (10 steers/treatment) within a block (n = 4 blocks). Treatments were control, no bST (C-C); bST from d 0 to 182 (bST-C); bST from d 183 to slaughter (C-bST); and bST from d 0 to slaughter (bST-bST). Steers received a s.c. injection of placebo or bST at 14-d intervals. Doses were 320 mg of bST/injection from d 0 to 112 and 640 mg of bST/injection from d 113 to slaughter. The last treatment was administered 31 d before slaughter. Steers received a 14% CP (DM basis) diet from d 0 to 182 and 11.5% CP from d 183 to slaughter that consisted of dry, whole-shelled corn and a pelleted protein-mineral supplement. Steers were slaughtered when BW per block averaged 615 kg (d 325, 353, 367, and 381 for the 4 blocks, respectively). Thirty steers were removed from the study because of poor performance with respect to their pen mates, illness, lameness, death, incomplete castration, and incorrect treatment. Serum IGF-I concentrations increased 151% (P < 0.01) from d 7 through 35 in bST-treated steers compared with control steers. During the first 182 d, bST-C and bST-bST steers were heavier (P < 0.01) and had greater (P < 0.01) ADG, G:F, hip height, and hip height gain compared with C-C and C-bST steers. From d 183 to slaughter, C-bST steers had reduced (P < 0.05) daily DMI and greater G:F than bST-C steers. At final slaughter, C-bST and bST-bST steers had greater (P < 0.05) hip height than C-C steers. Noncarcass weight was increased and dressing percent reduced (P < 0.05) in C-bST and bST-bST steers compared with C-C steers. Quality grade was least (P < 0.05) in bST-bST carcasses compared with C-C, whereas bST-C and C-bST carcasses were intermediate. At final slaughter, steers receiving bST had greater (P < 0.05) carcass protein and water composition and lower (P < 0.05) carcass lipid and lipid accretion than C-C steers. Bovine somatotropin was effective in reducing carcass fat and increasing edible lean. Administering bST to young, lightweight steers increased skeletal growth and noncarcass weight without an increase in total carcass weight, but decreased carcass quality.

Animals↗

PubMed2006

Effects of ractopamine supplementation on behavior of British, Continental, and Brahman crossbred steers during routine handling.

Equal numbers of British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 420) were used to examine the effects of ractopamine supplementation and biological type on behavior during routine handling. Steers were blocked by BW within type and allocated to pens, resulting in 2 pens (10 cattle per pen) representing each block x type subclass. Pens within each block x type subclass then were randomly assigned to ractopamine supplementation treatments (0 or 200 mg.steer(-1).d(-1)), which were administered during the final 28 d of the finishing period. At the time final BW were obtained (28 d after treatment initiation), a single, trained observer, blinded with respect to treatment designations, recorded subjective scores to characterize behavior of each animal. Scores included entry force score (degree of force required to load the animal into the chute); entry speed score (walk, trot, run); chute behavior score (calm, restless shifting, moderate struggling); and exit speed score (walk, trot, run). Ractopamine supplementation had no effect on entry force score, chute behavior score, or exit speed score; however, cattle supplemented with ractopamine entered the chute more rapidly than did control cattle. Biological cattle type was a significant source of variation in entry force score and exit speed score. Continental crossbreds required greater (P < 0.05) force to enter the squeeze chute than did Brahman crossbred or British steers. In addition, Continental crossbred and Brahman crossbred steers left the processing chute with the greatest speed, whereas British steers exited the processing chute most slowly. Biological cattle type did not affect scores for entry speed or behavior during restraint in the chute. No adverse effects of ractopamine supplementation on cattle behavior were observed in this study.

Adrenergic beta-Agonists↗

PubMed2000

A Neurospora double-strand-break repair gene, mus-11, encodes a RAD52 homologue and is inducible by mutagens.

We isolated a Neurospora crassa cDNA that encodes a Rad52 homologue (ncRAD52) by PCR, using degenerate primers. RFLP mapping demonstrated that the cloned gene is located close to the ro-4 locus on the right arm of linkage group V (LGVR). In a second experiment, we used sib selection to identify a cosmid clone containing the mus-11 gene in a N. crassa genomic library. Fine-scale mapping of the mus-11 mutant showed the gene order on LGVR near ro-4 to be: ad-7 - (9.5 mu) - pab-2 (7.8 mu) - mus-11 - (3.7 mu) - inv. The nucleotide sequence of the mus-11 gene matched that of the ncRAD52 cDNA. Thus, the mus-11 gene encodes the Rad52 homologue. The deduced amino acid sequence of the MUS11 protein shows 32.0% and 27.5% overall identity to the Schizosaccharomyces pombe Rad22 protein and the human hRad52 protein, respectively, and a higher level of identity (55-66%) within the conserved N-terminal region (141 residues). The MUS11 protein shows homology to Rad52 from budding yeast only within the N-terminal region (53.2% identity over 141 amino acids) which is conserved among Rad52 homologues. Yeast two-hybrid analysis reveals that the MUS11 protein binds to both the MEI-3 protein, a Rad51 homologue, and to itself in vivo. An ncRAD52 mutant obtained by the RIPping procedure showed the same sensitivity as the original mus-11 mutant to the following mutagens and chemicals: UV light, 4NQO (4-nitroquinoline 1-oxide), MMS (methyl methanesulfonate), EMS (ethyl methanesulfonate), MNNG (N-methyl-N'-nitro-N-nitrosoguanidine), TBHP (tert-butyl hydroperoxide), HU (hydroxyurea) and histidine. Unlike the RAD52 transcript in Saccharomyces cerevisiae, the mus-11 transcript could not be detected in mycelium under normal growth conditions, but expression of the gene was induced by UV irradiation or treatment with MMS.

Amino Acid Sequence↗

PubMed1999

The effects of ionizing radiation on DNA synthesis in eukaryotic cells.

PURPOSE: To review observations of the effects of ionizing radiation on DNA synthesis in eukaryotes. CONTENT: Available information broadly falls into two categories: descriptions of the phenomenon, including dose response data and analysis; and, more recently, investigations utilizing genetic approaches. The down-regulation of DNA replication in the presence of radiation-induced DNA damage appears to be an active cellular response, termed the S-phase damage-sensing (SDS) checkpoint control (Larner et al. 1997). Observations on a variety of eukaryotes, including man, suggest that the regulatory controls involved are highly conserved and may additionally function in G1 and G2 checkpoint controls. Budding yeast, fission yeast and human homologues are identified. CONCLUSIONS: The SDS checkpoint control appears to be comprised of a complex of checkpoint proteins that respond to the stalled replication complex. The replication complex is thought to signal down-regulation of the mitotic kinase, ensuring that the cell does not enter mitosis while S phase is delayed. Concomitantly, the checkpoint complex is believed to transmit a signal via two key checkpoint proteins (Rad3 and Cds1 in the fission yeast), in order to arrest further DNA synthesis initiation.

Animals↗

PubMed1994

Superoxide dismutase (sod-1) null mutants of Neurospora crassa: oxidative stress sensitivity, spontaneous mutation rate and response to mutagens.

Enzymatic superoxide-dismutase activity is believed to be important in defense against the toxic effects of superoxide. Although superoxide dismutases are among the best studied proteins, numerous questions remain concerning the specific biological roles of the various superoxide-dismutase types. In part, this is because the proposed damaging effects of superoxide are manifold, ranging from inactivation of certain metabolic enzymes to DNA damage. Studies with superoxide-deficient mutants have proven valuable, but surprisingly few such studies have been reported. We have constructed and characterized Neurospora crassa mutants that are null for sod-1, the gene that encodes copper-zinc superoxide dismutase. Mutant strains are sensitive to paraquat and elevated oxygen concentrations, and they exhibit an increased spontaneous mutation rate. They appear to have near wild-type sensitive to near- and far-UV, heat shock and gamma-irradiation. Unlike the equivalent Saccharomyces cerevisiae mutant and the sodA sodB double mutant of Escherichia coli, they do not exhibit aerobic auxotrophy. These results are discussed in the context of an attempt to identify consensus phenotypes among superoxide dismutase-deficient mutants. N. crassa sod-1 null mutant strains were also employed in genetic and subcellular fractionation studies. Results support the hypothesis that a single gene (sod-1), located between Fsr-12 and leu-3 on linkage group I, is responsible for most or all CuZn superoxide dismutase activity in this organism.

Fungal Proteins↗

PubMed1991

mei-2, a mutagen-sensitive mutant of Neurospora defective in chromosome pairing and meiotic recombination.

A Neurospora crassa mutation, mei-2, affecting meiosis and mutagen sensitivity, was characterized for its effect on meiotic recombination and chromosome pairing. Results from homozygous mei-2 crosses involving distant markers on the same chromosome demonstrated a drastic reduction in meiotic recombination. However, mitotic recombination continued to occur. Cytological observations indicated that pairing of homologous chromosomes in zygotene was greatly reduced or absent, resulting in aberrant segregation at anaphase I and often at subsequent divisions as well. The few mature ascospores produced were frequently disomic for one or more chromosomes.

Chromosomes, Fungal↗

PubMed1989

Deoxyribonucleoside triphosphate pools in mutagen sensitive mutants of Neurospora crassa.

Deoxyribonucleoside triphosphate (dNTP) levels were measured in wild type Neurospora and nine mutagen-sensitive mutants, at nine different genes. Eight of these mutants are sensitive to hydroxyurea and histidine and show chromosomal instability, a phenotype which could result from altered levels of dNTPs. Two patterns were seen. Five of the mutants had altered ratios of dNTPs, with relatively high levels of dATP and dGTP and low levels of dCTP, but changes in the dTTP/dCTP ratio did not correlate with changes in spontaneous mutation levels. During exponential growth all but two of the mutants had small but consistent increases in dNTP pools compared to wild type. DNA content per microgram dry hyphae was altered in several mutants but these changes showed no correlation with the dNTP pool alterations.

DNA, Fungal↗

PubMed1988

Damage-resistant DNA synthesis in eukaryotes.

The molecular basis of sensitivity of ionizing radiation and other damaging agents is not clearly defined in eukaryotes. While a large number of mutants have been described only a few have been demonstrated to have a defect in the repair of damage to DNA. An interesting characteristic of a sub-group of these mutants, in different species extending throughout the phylogenetic scale, is the presence of damage-resistant DNA synthesis. This phenomenon is observed in cells from individuals with the genetic disorder ataxia telangiectasia, in HeLa cells treated with fluorodeoxyuridine prior to UV irradiation, in mutants of the fungus Neurospora crassa, the slime mould Dictyostelium discoideum, the fruit fly Drosophila melanogaster and possibly in the "wasted" mouse mutant. In the case of ataxia telangiectasia sensitivity is only observed to ionizing radiation or radiomimetic chemicals whereas sensitivity to a wider spectrum of mutagens is reported for the lower eukaryotic mutants. In all cases a reduced inhibition of DNA synthesis is obtained after exposure to an agent to which the cell type is hypersensitive. It is unclear how damage-resistant DNA synthesis contributes to increased sensitivity in these cells, but is unlikely to be the major mechanism predisposing to radiation-induced cell death. The description of a derivative of an ataxia telangiectasia cell line with normal sensitivity to radiation but still maintaining resistant DNA synthesis partially uncouples radioresistant DNA synthesis and radiosensitivity. This paper is designed to review the phenomenon of damage-resistant DNA synthesis in a number of mutants.

Animals↗

PubMed1988

A new mutagen-sensitive mutant in Neurospora, mus-16.

A new gene, mus-16, is determined by the nitrogen mustard-sensitive Neurospora mutant of Baker, Parish and Curtis (1984) which is defective in the removal of DNA-DNA and DNA-protein crosslinks. This gene is on the left arm of linkage group V between caf-1 and lys-1. The mus-16(JMB) mutant is sensitive to the alkylating agents methyl methanesulfonate (MMS) [dose reduction factor (drf) 8-10 X], N-methyl-N'-nitro-N-nitrosoguanidine (drf 5-6 X), the amino acid histidine and the drug hydroxyurea. It is not sensitive to ultraviolet-light, gamma-irradiation, or mitomycin C (MMC). It shows normal spontaneous mutation rates but increased induction of mutation by MMS. Homozygous crosses are barren, showing no signs of sporulation. Mitotic spontaneous chromosome instability is increased. The mus-16 mutation is similar to several non-excision repair-defective mutants in Neurospora. Some of these may be defective in repair of alkylation damage. The MMC data supports earlier data that in fungi MMC is incapable of forming DNA-DNA crosslinks.

Chromosome Deletion↗

PubMed1988

Growth, carcass composition and plasma melatonin in postpubertal beef heifers fed melatonin.

Two experiments were conducted to determine if feeding melatonin alters plasma concentrations of melatonin, growth and carcass composition of postpubertal beef heifers exposed to 16 h light (L):8 h dark (D). In Exp. 1, 16 heifers were blocked by initial body weight (318 +/- 5.6 kg). Four heifers were killed before starting the melatonin treatment to obtain initial carcass composition. Six heifers received vehicle (95% ethanol) and six were fed melatonin (4 mg/100 kg body weight) daily for 58 d at 1330 to coincide with the middle of the 16-h light period. On d 59 heifers were slaughtered. Melatonin feeding increased the percentage of fat in rib (P less than .05) and longissimus muscle (LD; P less than .10) and carcass fat accretion 28% (P less than .09) but reduced the percentage of protein 8% in rib (P less than .05) and carcass protein accretion 30% (P less than .09). Other measures in the carcass and body weight gain were not affected (P greater than .10) by feeding melatonin. Plasma concentrations of melatonin increased (P less than .01) from 10 to 140 pg/ml within 30 min of feeding melatonin. In Exp. 2, 24 heifers were blocked by initial body weight (348 +/- 13.7 kg). Eight heifers were killed initially, eight received vehicle and eight were fed melatonin for 63 d as described in Exp. 1. Melatonin did not influence (P greater than .10) body weight gain or any measure in the carcass; however, these heifers were fatter (40.1%) than those in Exp. 1 (30.9%) at the beginning of the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Measurement of protein turnover in skeletal muscle strips.

Isolated porcine and bovine muscle strips were incubated in Krebs Ringer bicarbonate buffer to determine in vitro protein synthesis (PS) and protein degradation (PD) rates to validate the in vitro system for use with livestock species. The addition of 5X plasma concentrations of amino acids to the medium stimulated PS 30%. Addition of 3.5 mM leucine to a leucine-deficient buffer supplemented with amino acids decreased PD 37% and stimulated PS 24%. The addition of .1 U/ml insulin reduced PD 28% and increased PS 30%. Protein degradation was elevated in longitudinally split rat soleus and extensor digitorum longus muscles compared to their contralateral intact muscles. Muscle strips must be removed within 15 min of exsanguination because PD rates become greatly elevated thereafter. ATP concentrations declined during incubation, but the addition of ATP or creatine had no effect on either PD or PS. Neither PD nor PS was affected by the addition of transferrin, fetuin, ascorbate, dexamethasone or indomethacin to the incubation medium. However, muscle strips were sensitive to the addition of triiodothyronine (T3), PD was increased up to 75% as T3 concentration was increased, and PS rates doubled compared to controls. Serum from mature barrows or gilts had no effect on protein turnover, but the addition of 10% and 15% serum from boars increased both PD and PS. With fasted pigs a continual decline in PS occurred over 5 d, whereas PD was elevated at 3 d and then declined to rates comparable to the fed state after 5 d. These data suggest that the in vitro system has application for assessing relative changes that occur in vivo following nutritional, physiological and endocrinological manipulation.

Animals↗

PubMed1987

Gamma-ray-sensitive mutants of Neurospora crassa with characteristics analogous to ataxia telangiectasia cell lines.

Well characterized gamma-ray sensitive mutants of the fungus Neurospora crassa have been screened for characteristics analogous to those of cell lines derived from humans with the genetic disease, ataxia telangiectasia (AT). Two Neurospora mutants, uvs-6 and mus-9, show the AT cell line characteristics of gamma-ray and bleomycin sensitivity, and little or no repression of DNA synthesis following treatment with these agents. Normal human or Neurospora cells show an extensive biphasic DNA synthesis repression (to 50% of control) and when DNA synthesis is analyzed by alkaline sucrose gradient centrifugation, repression of DNA synthesis by low doses of gamma-radiation occurs primarily in low molecular weight (MW) DNA pieces in both organisms. In AT cells and the uvs-6 mutant, no repression in synthesis of low or higher MW DNA is seen at low doses, while the mus-9 mutant shows little repression of high MW DNA, but an intermediate level of low MW DNA synthesis. Both mutants have been shown previously to have an increased level of spontaneous chromosome instability as do AT lines. The uvs-6 and mus-9 mutations are known to be due to two different genes in two different epistatic groups. These results demonstrate that AT-like cellular characteristics can arise from defects in at least two and probably any of several genes, and that lower eukaryotes such as Neurospora can provide an inexpensive and useful model for AT while avoiding the problems inherent in using transformed cell lines.

Ataxia Telangiectasia↗

PubMed1986

Chromosome instability in mutagen sensitive mutants of Neurospora.

Four mutagen sensitive mutants of Neurospora (mus-7, mus-9, mus-11, and mei-2) are shown to increase mitotic chromosome instability in the duplication test developed by Newmeyer. Three other mutagen-sensitive mutants (upr-1, mus-8, and mus-10) do not increase chromosome instability. Previously three mutagen-sensitive mutants (uvs-3, uvs-6, and mei-3) were also shown to increase chromosome instability. The growth of all seven mutants that increase chromosome instability, is shown here to be more sensitive to hydroxyurea than that of wild type. Hydroxyurea, a compound which inhibits the enzyme ribonucleotide diphosphate reductase, is also shown to increase chromosome instability in the absence of any mutagen-sensitive mutation. These seven mutations are known to represent seven different genes in two epistasis groups. They have been shown previously to have four other properties in common: meiotic defects and sensitivity to gamma-rays, methyl methane sulfonate and the amino acid histidine. Their shared properties lead to the prediction here that all have reduced or altered deoxyribonucleotide pools.

Cell Division↗

PubMed1983

Release of high molecular weight DNA from Neurospora crassa using enzymic digestions.

Methods are described that allow extraction of high molecular weight DNA from germinated conidia of Neurospora crassa. By labelling DNA with ribonucleosides, early conidia were shown to be active in DNA synthesis. These cells when treated with the enzyme Zymolyase became fragile and could be readily lysed with ionic detergents to release high molecular weight DNA. The DNA extracted from Zymolyase treated cells on to alkaline sucrose gradients sedimented as a heterogeneous species of up to 150 x 10(6) molecular weight. A minor DNA species (presumably mitochondrial) of 20 x 10(6) molecular weight comprised 2-7% of the total. The identity of the DNA was confirmed by sensitivity to DNAase, the diphenylamine assay and TLC. Sedimentation patterns were unaffected by protease digestions and no anomalous high speed rotor effects were evident. Isopycnic gradients suggested that the DNA released was uncomplexed with either protein or carbohydrates. Sepharose chromatography of extracted, RNAase-treated Zymolyase lysate resulted in clearly separate high molecular weight DNA and RNA-protein elution profiles. UV light preferentially inhibited nuclear DNA synthesis and drastically reduced the size and amount of nascent DNA being synthesized in the excision defective uvs-2 mutant. Sites in parental DNA sensitive to Micrococcus luteus UV endonuclease were measured in cells made permeable with Triton X-100.

Centrifugation, Density Gradient↗

PubMed1983

Mutagen sensitivity of Neurospora meiotic mutants.

The Neurospora meiotic mutants, mei-1, mei-2, mei-3, and mei-4 were tested for cross sensitivity to mutagens. Mei-2 and mei-3 are sensitive to MMS, gamma-irradiation and histidine. Mei-2 is not sensitive to ultraviolet (UV) at 20 degrees C. Tests with recombinants with crossovers to either side of mei-2 or mei-3 show that these traits are the pleiotropic properties of a single gene which also determines meiotic behavior. The mei-2 gene maps to the right of al-3 on linkage group V. It is not allelic to mus-11. Upon backcrossing, the originally dominant meiotic effect of mei-2 becomes recessive to partially dominant. The histidine sensitivity is recessive.

Alleles↗

PubMed1982

Postreplication repair in Neurospora crassa.

Changes in the molecular weight of nascent DNA made after ultraviolet (UV) irradiation have been studied in the excision-defective Neurospora mutant uvs-2 using isotopic pulse labeling, alkaline gradient centrifugation and alkaline filter elution. Both the size of nascent DNA and the rate of incorporation of label into DNA was reduced by UV light in a dose dependent manner. However, this DNA repair mutant did recover the ability to synthesize control-like high molecular weight DNA 3 hours after UV treatment, although the rate of DNA synthesis remained depressed after the temporary block to elongation (or ligation) had been overcome. Photoreactivation partially eliminated the depression of DNA synthesis rate and UV light killing of cells, providing strong evidence that the effects on DNA synthesis and killing were caused by pyrimidine cyclobutane dimers. The caffeine inhibition repair studies performed were difficult to quantitate but did suggest either partial inhibition of a single repair pathway or alternate postreplication DNA repair pathways in Neurospora. No enhancement in killing was detected after UV irradiation when cells were grown on caffeine containing plates.

Caffeine↗

PubMed1982

The role of pyrimidine dimers in postreplication repair in Neurospora.

Using the Micrococcus luteus dimer specific endonuclease assay of Wilkins (1973), and photoreactivation we have examined the induction and fate of ultraviolet induced pyrimidine dimers in the excision defective strain, uvs-2, of Neurospora crassa. Dimer induction was fluence dependent from 0 to 800 ergs/mm2 UV. An interdimer distance of 19.6 x 10(6) DNA molecular weight was found after a fluence of 220 ergs/mm2. We confirm the earlier report that this mutant is completely excision defective (Worthy and Epler 1972). Photoreactivation (PR), which greatly enhanced survival (by 10 fold after 440 ergs/mm2 UV), reduced significantly (40-44%) the number of UV-endonuclease sensitive sites found in irradiated DNA. This treatment also alleviated immediately some of the temporary blocks to high molecular weight DNA synthesis (elongation or ligation) seen in irradiated cells. We have also attempted to elucidate the mechanism of cellular postreplication repair used to overcome the UV inhibition to DNA synthesis. It was determined that during postreplication repair, Neurospora does not use recombination to bypass dimers and that single stranded DNA gaps opposite dimers do not appear to be present during the time when DNA being synthesized is made only in short pieces.

DNA Repair↗

PubMed1980

Mutagen-sensitive mutants in Neurospora.

Initial work on the fungus Neurospora crassa has shown that a least two DNA-repair systems exist in this eukaryote: excision repair and a mutation-prone repair. The evidence suggests that there is also a third repair system. Recently, new mutagen-sensitive strains have been isolated in several laboratories, but they are not yet fully characterized. A hunt for cytoplasmically inherited UV sensitivity has failed to turn up any such mutants among 25 new UV-sensitive isolates.

DNA Repair↗