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Biomedical subjects

R L Fischer

Publications and source records attributed to R L Fischer.

At least 19 recordsLinked to original sources
PubMed2003

Growth, carcass traits, and plasma amino acid concentrations of gilts fed low-protein diets supplemented with amino acids including histidine, isoleucine, and valine.

Three experiments were conducted to determine the fifth-limiting amino acid for growing pigs in an 11% CP, corn-soybean meal diet. In each experiment, 36 gilts (initial weight 19.5, 21.9, and 21.0 kg, respectively) were penned individually and fed one of six diets in a randomized block design for 35 d. Diets containing 16, 12, and 11% CP were fed in each experiment. All 12 and 11% CP diets were supplemented with lysine, tryptophan, threonine, and methionine to provide the same total concentrations as those in the 16% CP diet. In Exp. 1, the 11% CP diet was supplemented with isoleucine, valine, or isoleucine + valine to concentrations equal to those in the 16% CP diet. In Exp. 2, the 11% CP diet was supplemented with histidine, histidine + valine, or histidine + isoleucine + valine. In Exp. 3, the 11% CP diet was supplemented with valine, histidine + valine, or isoleucine + valine. Gilts were allowed free access to feed and water. In all experiments, ADG and feed efficiency (G/F) were reduced (P < or = 0.07) as dietary protein was reduced. Supplementation of isoleucine alone further reduced (P < 0.05) ADG, ADFI, G/F, and fat-free lean gain. In contrast, supplementation of valine alone resulted in numerical increases in ADG and ADFI in two experiments, although the differences were not significant (P > 0.05). Supplementation with histidine and valine together resulted in growth performance equal to or greater than that of pigs fed the 12% CP diet, but less than that of pigs fed the 16% CP diet. Supplementation of isoleucine and valine together resulted in better growth performance (P < 0.05) than supplementation of either amino acid alone. In two experiments (Exp. 1 and 3), supplementation of the 11% CP diet with isoleucine and valine together resulted in ADG that were not significantly different (P > 0.05) from those of pigs fed the 16% CP diet. Supplementation of all three amino acids (Exp. 2) did not improve performance over supplementations with histidine and valine. Plasma urea concentrations were reduced (P < 0.05) as dietary protein was lowered from 16 to 12%. Additions of crystalline amino acids did not affect plasma urea levels. Plasma amino acid concentrations reflected the dietary additions of crystalline amino acids, but did not assist in the identification of the sequence of limiting amino acids. These data suggest that valine is the fifth-limiting amino acid and that either histidine or isoleucine is the sixth-limiting amino acid in an 11% CP diet.

Amino Acids, Essential↗
PubMed2002

Stability of green fluorescent protein using luminescence spectroscopy: is GFP applicable to field analysis of contaminants?

Green fluorescent protein (GFP) was first isolated in the early 1970s for experimental use from coelenterates or the Pacific jellyfish. Aequorea victoria (Morin and Hastings, 1971). GFP has since become a favored biomarker in the photophysical analysis of molecular and cell biology because of its strong intrinsic visible fluorescence and the feasibility of fusing it to other proteins without affecting their normal functions (Creemers et al., 2000). Here we report using Bacillus subtilis expressing GFP to evaluate the influence of different environmental pH conditions on GFP fluorescence. Emission acquisitions were configured to excite at 471 nm and detect at an emission from 490 to 650 nm at 1-nm increments. Fluorescence intensity was significantly better at pH 7 (4.2 x 105 cps; P-value < 0.01) than at acid or alkaline conditions. GFP is a good biomarker for environments near netural conditions: however, GFP may be unsuitable where soils or waters are below or above pH 7 because of loss in fluorescence intensity. Alternative fluorescent markers and delivery systems must be examined in different environments to optimize responses from bioreporter molecules.

Bacillus subtilis↗
PubMed2002

Nitrogen metabolism and growth performance of gilts fed standard corn-soybean meal diets or low-crude protein, amino acid-supplemented diets.

Two experiments were conducted to determine the CP concentration below which N retention and growth performance are reduced when low-protein, amino acid-supplemented, corn-soybean meal diets are fed. In a N balance trial (Exp. 1), 12 gilts (initial weight 41 kg) were fitted with urinary catheters and fed six different diets during three 7-d periods in an incomplete block design. The diets were: 1) 18% CP; 2) 14% CP + AA, 3) 16% CP; 4) 12% CP + AA; 5) 14% CP; and 6) 10% CP + AA. Amino acids (lysine, threonine, tryptophan, and methionine) were supplemented such that the concentrations in the low-protein diets were equal to those in their standard (4% CP higher) counterparts. Nitrogen retention (g/d) decreased (P < 0.01) as CP decreased, in both standard (27.10, 24.53, and 20.99) and low-protein (21.51, 19.18, and 15.83) diets, but was lower (P < 0.01) in low-protein diets. There were no differences among treatments (P > 0.05) in biological value (68.2% standard vs 71.0% low-protein). In a growth performance trial (Exp. 2), 36 gilts (initial weight 19.5 kg) were penned individually and fed one of six diets for 35 d in a randomized complete block design. Dietary treatments were a 16% CP standard diet and low-protein diets formulated to contain 15, 14, 13, 12, and 11% CP supplemented with crystalline lysine, tryptophan, threonine, and methionine to equal the total concentrations in the standard diet. Protein concentration affected (P < or = 0.05) ADG, ADFI, feed efficiency, fat-free lean gain, longissimus muscle area, plasma urea, and plasma concentrations of most essential AA. For most of these traits, the major difference was poor performance of pigs fed the 11% CP diet. Thus, in Exp. 1, at AA concentrations from deficient to excess, low-protein, amino acid-supplemented diets failed to produce the same N retention as the equivalent corn-soybean meal diets. However in Exp. 2, the same performance was obtained with 16, 15, 14, 13, and 12% CP. Based on these data, we suggest that N balance is more sensitive than growth to amino acid adequacy andthat other AA (e.g., isoleucine and valine) may limit growth performance when the protein concentration is reduced by more than four percentage units.

Amino Acids↗
PubMed2001

Polycomb repression of flowering during early plant development.

All plants flower late in their life cycle. For example, in Arabidopsis, the shoot undergoes a transition and produces reproductive flowers after the adult phase of vegetative growth. Much is known about genetic and environmental processes that control flowering time in mature plants. However, little is understood about the mechanisms that prevent plants from flowering much earlier during embryo and seedling development. Arabidopsis embryonic flower (emf1 and emf2) mutants flower soon after germination, suggesting that a floral repression mechanism is established in wild-type plants that prevents flowering until maturity. Here, we show that polycomb group proteins play a central role in repressing flowering early in the plant life cycle. We found that mutations in the Fertilization Independent Endosperm (FIE) polycomb gene caused the seedling shoot to produce flower-like structures and organs. Flower-like structures were also generated from the hypocotyl and root, organs not associated with reproduction. Expression of floral induction and homeotic genes was derepressed in mutant embryos and seedlings. These results suggest that FIE-mediated polycomb complexes are an essential component of a floral repression mechanism established early during plant development.

Arabidopsis↗
PubMed2001

LEAFY COTYLEDON2 encodes a B3 domain transcription factor that induces embryo development.

The Arabidopsis LEAFY COTYLEDON2 (LEC2) gene is a central embryonic regulator that serves critical roles both early and late during embryo development. LEC2 is required for the maintenance of suspensor morphology, specification of cotyledon identity, progression through the maturation phase, and suppression of premature germination. We cloned the LEC2 gene on the basis of its chromosomal position and showed that the predicted polypeptide contains a B3 domain, a DNA-binding motif unique to plants that is characteristic of several transcription factors. We showed that LEC2 RNA accumulates primarily during seed development, consistent with our finding that LEC2 shares greatest similarity with the B3 domain transcription factors that act primarily in developing seeds, VIVIPAROUS1/ABA INSENSITIVE3 and FUSCA3. Ectopic, postembryonic expression of LEC2 in transgenic plants induces the formation of somatic embryos and other organ-like structures and often confers embryonic characteristics to seedlings. Together, these results suggest that LEC2 is a transcriptional regulator that establishes a cellular environment sufficient to initiate embryo development.

Amino Acid Sequence↗
PubMed2001

Etiology of third-trimester maternal hyperuricemia in nonpreeclamptic twin gestations.

OBJECTIVE: To determine whether the higher maternal serum uric acid levels observed in the third trimester of nonpreeclamptic twin gestations result from increased uric acid production or decreased renal excretion. METHODS: Thirty-four nonpreeclamptic subjects with twin gestations were analyzed, along with 34 singleton controls matched for age, ethnicity, prepregnancy weight, height, and gestational age. For each subject, a serum sample and 24-hour urine specimen were obtained in the third trimester. Serum and urine uric acid and creatinine levels were determined, as well as total 24-hour urine uric acid, uric acid clearance, creatinine clearance, fractional uric acid clearance, and net tubular uric acid absorption. RESULTS: The twin gestation group had significantly higher maternal serum uric acid levels (5.2 +/- 1.2 compared with 4.0 +/- 1.0 mg/dL, P <.001) and maternal serum creatinine levels (0.7 +/- 0.2 compared with 0.5 +/- 0.1 mg/dL, P <.001) than the paired singleton group. This was associated with greater 24-hour urine uric acid excretion (688.7 +/- 167.0 compared with 597.7 +/- 164.2 mg, P =.04) and 24-hour urine creatinine excretion (1268.4 +/- 249.9 compared with 1161.2 +/- 277.1 mg, P =.03) in the twin group. No differences were seen between the groups in uric acid clearance, creatinine clearance, fractional uric acid clearance, filtered uric acid load, or net uric acid absorption. CONCLUSION: The higher maternal serum uric acid levels observed in the third trimester of nonpreeclamptic twin gestations result in part from increased uric acid production, as reflected in the increased daily uric acid excretion.

Female↗
PubMed2001

The Arabidopsis embryo mutant schlepperless has a defect in the chaperonin-60alpha gene.

We identified a T-DNA-generated mutation in the chaperonin-60alpha gene of Arabidopsis that produces a defect in embryo development. The mutation, termed schlepperless (slp), causes retardation of embryo development before the heart stage, even though embryo morphology remains normal. Beyond the heart stage, the slp mutation results in defective embryos with highly reduced cotyledons. slp embryos exhibit a normal apical-basal pattern and radial tissue organization, but they are morphologically retarded. Even though slp embryos are competent to transcribe two late-maturation gene markers, this competence is acquired more slowly as compared with wild-type embryos. slp embryos also exhibit a defect in plastid development-they remain white during maturation in planta and in culture. Hence, the overall developmental phenotype of the slp mutant reflects a lesion in the chloroplast that affects embryo development. The slp phenotype highlights the importance of the chaperonin-60alpha protein for chloroplast development and subsequently for the proper development of the plant embryo and seedling.

Amino Acid Sequence↗
PubMed2001

Regional localization of suspensor mRNAs during early embryo development.

We investigated gene activity within the giant embryos of the scarlet runner bean (Phaseolus coccineus) to gain understanding of the processes by which the apical and basal cells become specified to follow different developmental pathways after division of the zygote. We identified two mRNAs, designated G564 and C541, that accumulate specifically within the suspensor of globular-stage embryos. G564 mRNA accumulates uniformly throughout the suspensor, whereas C541 mRNA accumulates to a higher level within the large basal cells of the suspensor that anchor the embryo to the surrounding seed tissue. Both G564 and C541 mRNAs begin to accumulate shortly after fertilization and are present within the two basal cells of embryos at the four-cell stage. In contrast, at the same stage, these mRNAs are not detectable within the two descendants of the apical cell. Nor are they detectable within cells of the embryo sac before fertilization, including the egg cell. We used a G564/beta-glucuronidase reporter gene to show that the G564 promoter is activated specifically within the basal region and suspensor of preglobular tobacco embryos. Analysis of the G564 promoter identified a sequence domain required for transcription within the suspensor that contains several copies of a conserved motif. These results show that derivatives of the apical and basal cells transcribe different genes as early as the four-cell stage of embryo development and suggest that the apical and basal cells are specified at the molecular level after division of the zygote.

Base Sequence↗
PubMed2001

Dietary manipulation to reduce aerial ammonia concentrations in nursery pig facilities.

Two 4-wk trials (preliminary study) and three 5-wk trials (major study) were conducted to determine the effects of adding Yucca schidigera extract or anhydrous calcium chloride to nursery diets on the growth performance of nursery pigs and aerial ammonia concentration. The pigs were weaned between 13 and 15 d of age and had an initial BW of 3 to 6 kg. In each trial, pigs were allotted to three identical pig nursery rooms that were environmentally regulated. There were three diets (one diet per room): 1) control, containing 23% CP; 2) control plus 125 ppm of Yucca schidigera extract; and 3) control plus 1.95% anhydrous calcium chloride. Growth performance was recorded weekly. Aerial ammonia concentration was measured daily using aspiration detector tubes and during the last week of each trial using diffusion tubes. Manure samples were collected twice a week during the experimental period to determine ammonia and N concentrations and pH. Plasma urea concentration was determined in blood samples collected from the pigs at the end of each trial. Data were analyzed using split-plot and Latin square designs for the preliminary and major studies, respectively. Feed intake was similar among pigs fed all three diets. There were no differences in ADG and ADG/ADFI (G/F) between pigs fed the control diet and pigs fed the yucca extract diet (P > or = 0.41). In all trials, pigs fed the calcium chloride diet had lower ADG and G/F than pigs fed the other two diets (P < 0.05). In the preliminary study, aerial ammonia tended to be greater in the rooms in which pigs were fed the control diet than in the rooms with pigs fed the yucca extract diet (P = 0.08) and the calcium chloride diet (P = 0.11). In the major study, aerial ammonia increased weekly (diet x week; P < 0.001) in all rooms. In the 4th wk, ammonia concentrations were greater (P < 0.001) in the rooms in which pigs were fed the control diet than in the rooms in which the other two diets were fed. Dietary treatment had no effect on plasma urea concentration (P > or = 0.10), manure ammonia and N concentrations (P > or = 0.50), and manure pH (P > or = 0.78). Although aerial ammonia concentrations were relatively low, the addition of Yucca schidigera extract or calcium chloride to the diet of nursery pigs reduced ammonia concentrations in the nursery rooms.

Air Pollutants↗
PubMed2001

Are maternal and sonographic factors associated with the detection of a fetal echogenic cardiac focus?

OBJECTIVE: To evaluate the influence of maternal weight and the orientation of the fetal 4-chamber heart view on the detection of a fetal echogenic cardiac focus. METHODS: In this nested case-control study, 103 women undergoing anatomic surveys at 15 to 22 weeks between January 1, 1997, and June 15, 1999, were identified as having an echogenic cardiac focus via our computerized database. A control group was selected from among the same group of patients. Data were collected from the sonography reports, prenatal records, and sonographic images of 4-chamber heart views; maternal characteristics and sonographic details were recorded, including the orientation of the 4-chamber view (apical, basilar, and right and left lateral). RESULTS: Gravidas in the echogenic cardiac focus group were more likely to be of lower weight (68.0 +/- 14.4 versus 72.9 +/- 18.3 kg; P = .04), of lower body mass index (25.5 +/- 5.3 versus 27.3 +/- 6.2 kg/m2; P = .03), of younger age (24.4 +/- 6.5 versus 26.9 +/- 6.9 years; P = .01), and African American or Asian (37.9% versus 27.2% and 9.7% versus 2%; P = .01). Cases were scanned at earlier gestational ages (18.9 +/- 1.6 versus 19.5 +/- 1.7 weeks; P = .01). The focus group was more likely to have had an apical view of the fetal heart taken (80.8% versus 51.4%; P = .0001). Controls were more likely to have had a right lateral view taken (44.6% versus 20.8%; P = .002). No significant difference was found between groups in terms of any other maternal or sonographic variable studied. CONCLUSIONS: The echogenic cardiac focus group was more likely to have a lower body mass index and to be scanned with the apical fetal heart view. The orientation of the fetal 4-chamber heart view exerted the most statistically significant influence on detection rates for the echogenic cardiac focus, implying that the more technically facile the sonographic study, the more likely an echogenic cardiac focus will be found.

Age Factors↗
PubMed2000

Plant organ size control: AINTEGUMENTA regulates growth and cell numbers during organogenesis.

The control of cell proliferation during organogenesis plays an important role in initiation, growth, and acquisition of the intrinsic size of organs in higher plants. To understand the developmental mechanism that controls intrinsic organ size by regulating the number and extent of cell division during organogenesis, we examined the function of the Arabidopsis regulatory gene AINTEGUMENATA (ANT). Previous observations revealed that ANT regulates cell division in integuments during ovule development and is necessary for floral organ growth. Here we show that ANT controls plant organ cell number and organ size throughout shoot development. Loss of ANT function reduces the size of all lateral shoot organs by decreasing cell number. Conversely, gain of ANT function, via ectopic expression of a 35S::ANT transgene, enlarges embryonic and all shoot organs without altering superficial morphology by increasing cell number in both Arabidopsis and tobacco plants. This hyperplasia results from an extended period of cell proliferation and organ growth. Furthermore, cells ectopically expressing ANT in fully differentiated organs exhibit neoplastic activity by producing calli and adventitious roots and shoots. Based on these results, we propose that ANT regulates cell proliferation and organ growth by maintaining the meristematic competence of cells during organogenesis.

Arabidopsis↗
PubMed2000

Alterations in CER6, a gene identical to CUT1, differentially affect long-chain lipid content on the surface of pollen and stems.

Very long chain lipids contribute to the hydrophobic cuticle on the surface of all land plants and are an essential component of the extracellular pollen coat in the Brassicaceae. Mutations in Arabidopsis CER genes eliminate very long chain lipids from the cuticle surface and, in some cases, from the pollen coat. In Arabidopsis, the loss of pollen coat lipids can disrupt interactions with the stigma, inhibiting pollen hydration and causing sterility. We have positionally cloned CER6 and demonstrate that a wild-type copy complements the cer6-2 defect. In addition, we have identified a fertile, intragenic suppressor, cer6-2R, that partially restores pollen coat lipids but does not rescue the stem wax defect, suggesting an intriguing difference in the requirements for CER6 activity on stems and the pollen coat. Importantly, analysis of this suppressor demonstrates that low amounts of very long chain lipids are sufficient for pollen hydration and germination. The predicted CER6 amino acid sequence resembles that of fatty acid-condensing enzymes, consistent with its role in the production of epicuticular and pollen coat lipids >28 carbons long. DNA sequence analysis revealed the nature of the cer6-1, cer6-2, and cer6-2R mutations, and segregation analysis showed that CER6 is identical to CUT1, a cDNA previously mapped to a different chromosome arm. Instead, we have determined that a new gene, CER60, with a high degree of nucleotide and amino acid similarity to CER6, resides at the original CUT1 locus.

Acyltransferases↗
PubMed2000

Hypomethylation promotes autonomous endosperm development and rescues postfertilization lethality in fie mutants.

In most flowering plants, fertilization is necessary for development of the central cell into endosperm, but in the fie-1 mutant of Arabidopsis, the central cell can proliferate autonomously. However, autonomous fie-1 endosperms do not develop completely: They have fewer nuclei than sexually produced endosperms, cellularization does not take place, and no clear distinction is seen between the different endosperm compartments. Here, we show that autonomous endosperm develop much further in hypomethylated than normally methylated fie-1 mutants, undergoing cellularization and regional specification to resemble endosperm in sexually produced wild-type seeds. Therefore, the combination of maternal hypomethylation and loss of FIE function enables formation of differentiated endosperm without fertilization. A maternal fie-1 mutation is also lethal to sexual seeds, even if the pollen donor is wild type. We report that sexual mutant fie-1 endosperms fail to cellularize and overproliferate, consistent with the hypothesis that embryo abortion may be due, at least in part, to a defect in endosperm development. Finally, we show that pollen from hypomethylated plants rescues fie-1 mutant seeds provided that it also donates a wild-type paternal FIE allele. These results are discussed in light of models for parent-of-origin effects on seed development.

Arabidopsis↗
PubMed2000

Mutations in the FIE and MEA genes that encode interacting polycomb proteins cause parent-of-origin effects on seed development by distinct mechanisms.

In flowering plants, two cells are fertilized in the haploid female gametophyte. Egg and sperm nuclei fuse to form the embryo. A second sperm nucleus fuses with the central cell nucleus, which replicates to generate the endosperm, a tissue that supports embryo development. The FERTILIZATION-INDEPENDENT ENDOSPERM (FIE) and MEDEA (MEA) genes encode WD and SET domain polycomb proteins, respectively. In the absence of fertilization, a female gametophyte with a loss-of-function fie or mea allele initiates endosperm development without fertilization. fie and mea mutations also cause parent-of-origin effects, in which the wild-type maternal allele is essential and the paternal allele is dispensable for seed viability. Here, we show that FIE and MEA polycomb proteins interact physically, suggesting that the molecular partnership of WD and SET domain polycomb proteins has been conserved during the evolution of flowering plants. The overlapping expression patterns of FIE and MEA are consistent with their suppression of gene transcription and endosperm development in the central cell as well as their control of seed development after fertilization. Although FIE and MEA interact, differences in maternal versus paternal patterns of expression, as well as the effect of a recessive mutation in the DECREASE IN DNA METHYLATION1 (DDM1) gene on mutant allele transmission, indicate that fie and mea mutations cause parent-of-origin effects on seed development by distinct mechanisms.

Arabidopsis↗
PubMed1999

Control of fertilization-independent endosperm development by the MEDEA polycomb gene in Arabidopsis.

Higher plant reproduction is unique because two cells are fertilized in the haploid female gametophyte. Egg and sperm nuclei fuse to form the embryo. A second sperm nucleus fuses with the central cell nucleus that replicates to generate the endosperm, a tissue that supports embryo development. To understand mechanisms that initiate reproduction, we isolated a mutation in Arabidopsis, f644, that allows for replication of the central cell and subsequent endosperm development without fertilization. When mutant f644 egg and central cells are fertilized by wild-type sperm, embryo development is inhibited, and endosperm is overproduced. By using a map-based strategy, we cloned and sequenced the F644 gene and showed that it encodes a SET-domain polycomb protein. Subsequently, we found that F644 is identical to MEDEA (MEA), a gene whose maternal-derived allele is required for embryogenesis [Grossniklaus, U., Vielle-Calzada, J.-P., Hoeppner, M. A. & Gagliano, W. B. (1998) Science 280, 446-450]. Together, these results reveal functions for plant polycomb proteins in the suppression of central cell proliferation and endosperm development. We discuss models to explain how polycomb proteins function to suppress endosperm and promote embryo development.

Arabidopsis↗
PubMed1999

Imprinting of the MEDEA polycomb gene in the Arabidopsis endosperm.

In flowering plants, two cells are fertilized in the haploid female gametophyte. Egg and sperm nuclei fuse to form the embryo. A second sperm nucleus fuses with the central cell nucleus that replicates to generate the endosperm, which is a tissue that supports embryo development. MEDEA (MEA) encodes an Arabidopsis SET domain Polycomb protein. Inheritance of a maternal loss-of-function mea allele results in embryo abortion and prolonged endosperm production, irrespective of the genotype of the paternal allele. Thus, only the maternal wild-type MEA allele is required for proper embryo and endosperm development. To understand the molecular mechanism responsible for the parent-of-origin effects of mea mutations on seed development, we compared the expression of maternal and paternal MEA alleles in the progeny of crosses between two Arabidopsis ecotypes. Only the maternal MEA mRNA was detected in the endosperm from seeds at the torpedo stage and later. By contrast, expression of both maternal and paternal MEA alleles was observed in the embryo from seeds at the torpedo stage and later, in seedling, leaf, stem, and root. Thus, MEA is an imprinted gene that displays parent-of-origin-dependent monoallelic expression specifically in the endosperm. These results suggest that the embryo abortion observed in mutant mea seeds is due, at least in part, to a defect in endosperm function. Silencing of the paternal MEA allele in the endosperm and the phenotype of mutant mea seeds supports the parental conflict theory for the evolution of imprinting in plants and mammals.

Alleles↗