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R L Fischer

Publications and source records attributed to R L Fischer.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1999

Mutations in FIE, a WD polycomb group gene, allow endosperm development without fertilization.

A fundamental problem in biology is to understand how fertilization initiates reproductive development. Higher plant reproduction is unique because two fertilization events are required for sexual reproduction. First, a sperm must fuse with the egg to form an embryo. A second sperm must then fuse with the adjacent central cell nucleus that replicates to form an endosperm, which is the support tissue required for embryo and/or seedling development. Here, we report cloning of the Arabidopsis FERTILIZATION-INDEPENDENT ENDOSPERM (FIE) gene. The FIE protein is a homolog of the WD motif-containing Polycomb proteins from Drosophila and mammals. These proteins function as repressors of homeotic genes. A female gametophyte with a loss-of-function allele of fie undergoes replication of the central cell nucleus and initiates endosperm development without fertilization. These results suggest that the FIE Polycomb protein functions to suppress a critical aspect of early plant reproduction, namely, endosperm development, until fertilization occurs.

Alleles↗
PubMed1998

Arabidopsis LEAFY COTYLEDON1 is sufficient to induce embryo development in vegetative cells.

The Arabidopsis LEAFY COTYLEDON1 (LEC1) gene is required for the specification of cotyledon identity and the completion of embryo maturation. We isolated the LEC1 gene and showed that it functions at an early developmental stage to maintain embryonic cell fate. The LEC1 gene encodes a transcription factor homolog, the CCAAT box-binding factor HAP3 subunit. LEC1 RNA accumulates only during seed development in embryo cell types and in endosperm tissue. Ectopic postembryonic expression of the LEC1 gene in vegetative cells induces the expression of embryo-specific genes and initiates formation of embryo-like structures. Our results suggest that LEC1 is an important regulator of embryo development that activates the transcription of genes required for both embryo morphogenesis and cellular differentiation.

Amino Acid Sequence↗
PubMed1996

A mutation that allows endosperm development without fertilization.

The mechanisms that initiate reproductive development after fertilization are not understood. Reproduction in higher plants is unique because it is initiated by two fertilization events in the haploid female gametophyte. One sperm nucleus fertilizes the egg to form the embryo. A second sperm nucleus fertilizes the central cell to form the endosperm, a unique tissue that supports the growth of the embryo. Fertilization also activates maternal tissue differentiation, the ovule integuments form the seed coat, and the ovary forms the fruit. To investigate mechanisms that initiate reproductive development, a female-gametophytic mutation termed fie (fertilization-independent endosperm) has been isolated in Arabidopsis. The fie mutation specifically affects the central cell, allowing for replication of the central cell nucleus and endosperm development without fertilization. The fie mutation does not appear to affect the egg cell, suggesting that the processes that control the initiation of embryogenesis and endosperm development are different. FIE/fie seed coat and fruit undergo fertilization-independent differentiation, which shows that the fie female gametophyte is the source of signals that activates sporophytic fruit and seed coat development. The mutant fie allele is not transmitted by the female gametophyte. Inheritance of the mutant fie allele by the female gametophyte results in embryo abortion, even when the pollen bears the wild-type FIE allele. Thus, FIE carries out a novel, essential function for female reproductive development.

Journal Article↗
PubMed1996

Dietary and serum folate: their influence on the outcome of pregnancy.

We examined the influence of folate intake from diet and supplements b y 28 wk of gestation and third trimester circulating concentrations of serum folate on the outcome of pregnancy in women from Camden, NJ. Mean daily folate intake by week 28 included both dietary and supplemental folate obtained prospectively in 832 women. Circulating concentrations of serum folate as well as serum vitamin B-12 were assayed at 28 wk of gestation (+/- 2 wk) by radioimmunoassay. The outcomes of interest included preterm delivery (<37 wk) and infants with low birth weight (<2500 g). Mean folate intake was significantly correlated with circulating concentrations of serum folate (r=0.17, P<0.001). Women with a low mean daily folate intake (</-240 microgram/d) had an approximately twofold greater risk of preterm delivery and infant low birth weight after maternal characteristics, energy intake, and other correlated nutrients were controlled for. Lower concentrations of serum folate at week 28 were also associated with a greater risk of preterm delivery and low birth weight.

Adolescent↗
PubMed1996

The AINTEGUMENTA gene of Arabidopsis required for ovule and female gametophyte development is related to the floral homeotic gene APETALA2.

Ovules play a central role in plant reproduction, generating the female gametophyte within sporophytic integuments. When fertilized, the integuments differentiate into the seed coat and support the development of the embryo and endosperm. Mutations in the AINTEGUMENTA (ANT) locus of Arabidopsis have a profound effect on ovule development. Strong ant mutants have ovules that fail to form integuments or a female gametophyte. Flower development is also altered, with a random reduction of organs in the outer three whorls. In addition, organs present in the outer three floral whorls often have abnormal morphology. Ovules from a weak ant mutant contain both inner and outer integuments but generally fail to produce a functional female gametophyte. We isolated the ANT gene by using a mutation derived by T-DNA insertional mutagenesis. ANT is a member of a gene family that includes the floral homeotic gene APETALA2 (AP2). Like AP2, ANT contains two AP2 domains homologous with the DNA binding domain of ethylene response element binding proteins. ANT is expressed most highly in developing flowers but is also expressed in vegetative tissue. Taken together, these results suggest that ANT is a transcription factor that plays a critical role in regulating ovule and female gametophyte development.

Amino Acid Sequence↗
PubMed1995

The BELL1 gene encodes a homeodomain protein involved in pattern formation in the Arabidopsis ovule primordium.

Ovule development in Arabidopsis involves the formation of three morphologically defined proximal-distal pattern elements. Integuments arise from the central pattern element. Analysis of Bell 1 (Bel 1) mutant ovules indicated that BEL1 was required for integument development. Cloning of the BEL1 locus reveals that it encodes a homeodomain transcription factor. Prior to integument initiation, BEL1 RNA localizes to the central domain, providing molecular evidence for a central pattern element. Therefore, proximal-distal patterning of the ovule involves the regulated expression of the BEL1 gene that controls integument morphogenesis. A model for BEL1 function is evaluated with regard to new data showing the expression pattern of the floral homeotic gene AGAMOUS (AG) early in wild-type and BEL1 ovule development.

AGAMOUS Protein, Arabidopsis↗
PubMed1995

Maternal serum uric acid levels in twin gestations.

OBJECTIVE: To establish normative values of serum uric acid levels in women with twin gestations and to compare maternal serum uric acid levels of twins and singletons, stratified by the presence or absence of preeclampsia. METHODS: Sixty-seven normotensive and 16 preeclamptic women with twin gestations, who had no underlying chronic hypertension or renal insufficiency, had serum uric acid levels measured on admission to the labor and delivery unit. These levels were compared with those of 83 normotensive and 10 preeclamptic singleton gravidas admitted to the same unit. A receiver operating characteristic (ROC) curve was used to determine the optimal maternal serum uric acid cutoff value for twin gestations and to compare this value with that of singleton gestations. RESULTS: Women with non-preeclamptic twin pregnancies had significantly higher mean (+/- standard deviation) serum uric acid concentration than women with non-preeclamptic singleton pregnancies (5.4 +/- 1.6 versus 4.7 +/- 1.2 mg/dL, respectively, P = .001). Gravidas with twin gestations complicated by preeclampsia had significantly higher serum uric acid levels than their preeclamptic singleton counterparts (7.7 +/- 1.3 versus 5.9 +/- 1.1 mg/dL, respectively, P = .001). Using a ROC curve, we determined that a maternal serum uric acid level of 6.5 mg/dL appeared to be the optimal cutoff for identifying preeclampsia in twin gestations, with a sensitivity of 94% and specificity of 78%. CONCLUSION: With or without preeclampsia, women carrying twins have significantly higher serum uric acid levels than their singleton counterparts, which suggests a need for separate normative values for twin gestations. We propose that a serum uric acid level of 6.5 mg/dL or greater be used to identify those women with twin gestations who are at higher risk for preeclampsia.

Adolescent↗
PubMed1995

Fetal growth and the etiology of preterm delivery.

OBJECTIVE: To confirm that preterm delivery is associated with fetal growth restriction (FGR), and to determine if the various etiologies of preterm delivery are associated with the same degree and type of FGR. METHODS: Two hundred ninety young, primarily minority gravidas who had routine initial ultrasound examinations also had subsequent ultrasound examinations at 32 weeks' gestation. Fetal growth characteristics were compared between preterm (less than 37 weeks' gestation) and term deliveries, and among preterm deliveries with medical or obstetric indications, premature rupture of membranes (PROM), and spontaneous preterm labor. RESULTS: Forty-six infants (15.9%) were born preterm. At 32 weeks' gestation, all fetuses later delivered preterm were already smaller than fetuses later delivered at term (P < .05) for all dimensions: head circumference (HC), abdominal circumference (AC), biparietal diameter (BPD), and femur length (FL). However, after stratifying by cause of preterm delivery for those fetuses later delivered for medical or obstetric indications, we found that only AC was decreased (P < .01) and that the HC-AC ratio was elevated (asymmetric FGR). Neonates delivered after unsuccessfully treated PROM or preterm labor were symmetrically smaller in all characteristics (HC, AC, BPD, and FL). CONCLUSION: By 32 weeks' gestation, fetuses later delivered preterm are already significantly smaller than fetuses later delivered at term. However, when stratified by the etiology of preterm delivery, infants delivered preterm for medical or obstetric indications had asymmetric growth patterns, which suggests a growth failure late in pregnancy. Infants delivered preterm after PROM or after failed or no tocolysis for spontaneous preterm labor were proportionately smaller, implying an overall slowing of growth that may originate early in pregnancy and possibly demonstrate a more chronic stress.

Adult↗
PubMed1994

Maternal growth during pregnancy and the competition for nutrients.

The influence of maternal growth in knee height during pregnancy on birth weight, gestation, and maternal body composition was examined in 318 teenagers (144 growing, 174 nongrowing) and 276 mature women from the Camden Study. Body-composition differences associated with maternal growth did not arise until after 28 wk gestation, when growing gravidas continued to accrue fat, had larger gestational gains, and retained more of their gestational weight gain postpartum. Nevertheless, still-growing young mothers had infants with lower birth weight, particularly when the mother continued to accrue higher amounts of fat on the arm or back (subscapular site) late in gestation. Thus, despite an apparently sufficient weight gain and the accumulation of abundant stores during pregnancy, young still-growing women appeared not to mobilize fat reserves late in pregnancy to enhance fetal growth, apparently reserving them instead for their own continued development.

Adipose Tissue↗
PubMed1994

Changes in maternal upper arm fat stores are predictors of variation in infant birth weight.

The relationship between changes in maternal subcutaneous fat and infant birth weight was studied in 608 low income women. A loss of upper arm fat area (> 6.4 cm2), measured from 28 wk gestation to 4-6 wk postpartum, was associated with greater birth weight (+144 g, P < 0.01). However, when pregravid weight was low (< 25th percentile for age), a loss of upper arm fat area was associated with a birth weight lower by more than 300 g than that for women with higher pregravid weights who also lost fat, indicating that maternal stores among those with low weight may have been relatively depleted. Continued gains in upper arm fat area (> 5 cm2) from 28 wk gestation to the postpartum period was also associated with a lower birth weight (-123 g, P < 0.02). The mothers who gained upper arm fat late in pregnancy or continued to accrue fat in the postpartum period had the largest gestational weight gains, bore infants who were smaller, and retained the most weight postpartum. Thus, change in upper arm fat is a significant predictor of variation in infant birth weight.

Adipose Tissue↗
PubMed1993

Identification of an ethylene-responsive region in the promoter of a fruit ripening gene.

Transcription of the E4 gene is controlled by an increase in ethylene concentration during tomato fruit ripening. To investigate the molecular basis for ethylene regulation, we have examined the E4 promoter to identify cis elements and trans-acting factors that are involved in E4 gene expression. In transgenic tomato plants a chimeric gene construct containing a 1.4-kilobase E4 promoter fused to a beta-glucuronidase reporter gene is rapidly induced by ethylene in ripening fruit. Deletion of E4 promoter sequences to 193 base pairs reduces the level of GUS activity but does not affect ethylene induction. Transient expression of E4 promoter-luciferase chimeric gene constructs containing various deletions, introduced into tomato fruit pericarp by particle bombardment, indicates that a positive ethylene-responsive region is localized between nucleotides -161 and -85 relative to the transcription start site. DNase I footprint analysis shows that a nuclear factor in unripe fruit interacts specifically with sequences in this element, from -142 to -110, which are required for the ethylene response. The DNase I footprint of this factor is reduced in ethylene-treated unripe fruit and undetectable in ripe fruit. Based on the correlation of a nuclear factor binding site with promoter sequences required for ethylene induction, we propose that this in vitro DNA-binding activity may represent a factor that is involved in ethylene-regulated E4 gene expression.

Base Sequence↗
PubMed1993

Low zinc intake during pregnancy: its association with preterm and very preterm delivery.

Zinc affects growth, development, and reproduction. However, the effect of poor maternal zinc nutriture, usually measured as plasma zinc, on poor pregnancy outcome has not been consistent. The influence of dietary zinc on pregnancy outcome was examined in a cohort of 818 pregnant girls and women from a poor urban community in Camden, New Jersey (1985-1990). Zinc intake in this sample was 11.1 mg/day, a level ascertained from averaged 24-hour dietary recalls during pregnancy. Gravidas with low zinc intake (< or = 6 mg/day, amounting to 40% of the recommended dietary allowance for pregnancy) had lower caloric intake and multivitamin usage as well as a higher incidence of inadequate weight gain during pregnancy and iron deficiency anemia at entry to prenatal care compared with those with higher intakes. A low zinc intake was associated with approximately a twofold increase in the risk of low birth weight (< 2,500 g) after controlling for calories and other confounding variables. The risk of preterm delivery (< 37 completed weeks) was also increased, particularly when rupture of the membranes preceded the onset of labor (adjusted odds ratio = 3.46, 95% confidence interval 1.04-11.47). A low intake of dietary zinc earlier in pregnancy was associated with a greater than threefold increase in the risk of very preterm delivery (< 33 completed weeks). In conjunction with iron deficiency anemia at entry to prenatal care, the adjusted odds ratio for very preterm delivery with low zinc intake was 5.44 (95% confidence interval 1.58-18.79). Among the urban poor, a marginal zinc intake during pregnancy may play an important role in the duration of gestation and is associated with increased risk of preterm and very preterm delivery.

Adolescent↗
PubMed1993

Positive and negative regulatory regions control the spatial distribution of polygalacturonase transcription in tomato fruit pericarp.

The tomato fruit consists of a thick, fleshy pericarp composed predominantly of highly vacuolated parenchymatous cells, which surrounds the seeds. During ripening, the activation of gene expression results in dramatic biochemical and physiological changes in the pericarp. The polygalacturonase (PG) gene, unlike many fruit ripening-induced genes, is not activated by the increase in ethylene hormone concentration associated with the onset of ripening. To investigate ethylene concentration-independent gene transcription in ripe tomato fruit, we analyzed the expression of chimeric PG promoter-beta-glucuronidase (GUS) reporter gene fusions in transgenic tomato plants. We determined that a 1.4-kb PG promoter directs ripening-regulated transcription in outer pericarp but not in inner pericarp cells, with a sharp boundary of PG promoter activity located midway through the pericarp. Promoter deletion analysis indicated that a minimum of three promoter regions influence the spatial regulation of PG transcription. A positive regulatory region from -231 to -134 promotes gene transcription in the outer pericarp of ripe fruit. A second positive regulatory region from -806 to -443 extends gene activity to the inner pericarp. However, a negative regulatory region from -1411 to -1150 inhibits gene transcription in the inner pericarp. DNase I footprint analysis showed that nuclear proteins in unripe and ripe fruit interact with DNA sequences within each of these three regulatory regions. Thus, temporal and spatial control of PG transcription is mediated by the interaction of negative and positive regulatory promoter elements, resulting in gene activity in the outer pericarp but not the inner pericarp of ripe tomato fruit. The expression pattern of PG suggests that, although they are morphologically similar, there is a fundamental difference between the parenchymatous cells within the inner and outer pericarp.

Base Sequence↗