The cloning, genetic mapping, and expression of the constitutive sucrose synthase locus of maize

Two differentially expressed genes encode isoenzymes of sucrose synthase in Zea mays. A clone of the shrunken 1 (Sh1) locus, the structural gene for the major endosperm form of sucrose synthase, was used to isolate a genomic clone of constitutive sucrose synthase (Css), the structural gene for the isoenzyme expressed in embryo and other tissues. The Css clone was positively identified by RNA blot analysis of RNA from wild type and a sh1 deletion stock and by analysis of the in vitro translation product of hybrid-selected mRNA. Southern blot analysis of DNA from monosomic plants derived from an r-x1 stock, coupled with restriction fragment length polymorphism mapping, placed the Css gene 32 map units from Sh1 on chromosome 9. In seedling tissues, Css mRNA is present at higher levels than Sh1 mRNA. Expression of both Sh1 and Css in root tissue is enhanced by anaerobic conditions, although Css is induced to a lesser extent than is Sh1. Thus, Css appears to be expressed constitutively, whereas Sh1 is expressed at high levels only in response to specific developmental and environmental stimuli.

Maize VP1 complements Arabidopsis abi3 and confers a novel ABA/auxin interaction in roots

The maize Vp1 gene and abi3 gene of Arabidopsis are believed to be orthologs based on similarities of the mutant phenotypes and amino acid sequence conservation. Here we show that expression of VP1 driven by the 35S promoter can partially complement abi3-6, a deletion mutant allele of abi3. The visible phenotype of seed produced from VP1 expression in the abi3 mutant background is nearly indistinguishable from wild type. VP1 fully restores abscisic acid (ABA) sensitivity of abi3 during seed germination and suppresses the early flowering phenotype of abi3. The temporal regulation of C1-beta-glucuronidase (GUS) and chlorophyll a/b binding protein (cab3)-GUS reporter genes in developing seeds of 35S-VP1 lines were similar to wild type. On the other hand, two qualitative differences are observed between the 35S-VP1 line and wild type. The levels of CRC and C1-GUS expression are markedly lower in the seeds of 35S-VP1 lines than in wild type suggesting incomplete complementation of gene activation functions. Similar to ectopic expression of ABI3 (Parcy et al., 1994), ectopic expression of VP1 in vegetative tissue enhances ABA inhibition of root growth. In addition, 35S-VP1 confers strong ABA inducible expression of the normally seed-specific cruciferin C (CRC) gene in leaves. In contrast, ectopic ABA induction of C1-GUS is restricted to a localized region of the root elongation zone. The ABA-dependent C1-GUS expression expanded to a broader area in the root tissues treated with exogenous application of auxin. Interestingly, auxin-induced lateral root formation is completely suppressed by ABA in 35S-VP1 plants but not in wild type. These results indicate VP1 mediates a novel interaction between ABA and auxin signaling that results in developmental arrest and altered patterns of gene expression.

Localization and targeting of the VP14 epoxy-carotenoid dioxygenase to chloroplast membranes

Abscisic acid (ABA) is a key regulator of seed dormancy and plant responses to environmental challenges. ABA is synthesized via an oxidative cleavage of 9-cis epoxy-carotenoids, the first committed and key regulatory step in the ABA biosynthetic pathway. Vp14 of maize encodes an epoxy-carotenoid dioxygenase that is soluble when expressed in E. coli. An important goal has been to determine how the soluble VP14 protein is targeted to epoxy-carotenoid substrates that are located in the thylakoid and envelope membranes of chloroplasts and other plastids. Using an in vitro chloroplast import assay, we have shown that VP14 is imported into chloroplasts with cleavage of a short stroma-targeting domain. The mature VP14 exists in two forms, one which is soluble in stroma and the other bound to thylakoid membranes. Analysis of a series of truncated VP14 mutants mapped the membrane targeting signal to the 160 amino acid N-terminal sequence. A putative amphipathic alpha-helix within this region is essential, but not sufficient, for the membrane targeting. Either deletion of or insertion of helix breaking residues into this region abolished the membrane binding, whereas a chimeric protein carrying just the amphipathic region fused with bacterial glutathione S-transferase failed to associate with the thylakoid membrane. The membrane-bound VP14 was partially resistant to chaotropic washes such as 0.1 M Na2CO3 (pH 11.5) and 6 M urea. Unlabelled recombinant VP14 inhibited the tight binding of imported VP14, suggesting that VP14 is associated with specific components of the thylakoid membrane.

LY393615, a novel neuronal Ca(2+) and Na(+) channel blocker with neuroprotective effects in models of in vitro and in vivo cerebral ischemia

In the present studies we have examined the effects of a new calcium channel blocker, LY393615 ((N-Butyl-[5,5-bis-(4-fluorophenyl)tetrahydrofuran-2-yl]methylamine hydrochloride, NCC1048) in a model of hypoxia-hypoglycaemia in vitro and in a gerbil model of global and in two rat models of focal cerebral ischaemia in vivo. Results indicated that LY393615 protected against hypoxia-hypoglycaemic insults in brain slices and also provided significant protection against ischaemia-induced hippocampal damage in gerbil global cerebral ischaemia when dosed at 10, 12.5 (P<0.05) or 15 mg/kg i.p. (P<0.01) 30 min before and 2 h 30 min after occlusion. The compound penetrated the brain well after a 15 mg/kg i.p. dose and had a half-life of 2.5 h. In further studies LY393615 was protective 1 h post-occlusion when administered at 15 mg/kg i.p. followed by 2 doses of 5 mg/kg i.p. 2 and 3 h later. LY393615 dosed at 15 mg/kg i.p. followed by 2 further doses of 5 mg/kg i.p. (2 and 3 h later) also produced a significant reduction in the infarct volume following Endothelin-1 (Et-1) middle cerebral artery occlusion in the rat when administration was initiated immediately (P<0.01) or 1 h (P<0.05) after occlusion. The compound was also evaluated in the intraluminal monofilament model of focal ischaemia. The animals had the middle cerebral artery occluded for 2 h, and 15 min after reperfusion LY393615 was administered at 15 mg/kg i.p. followed by 2 mg/kg/h i.v. infusion for 6 h. There was no reduction in infarct volume using this dosing protocol. In conclusion, in the present studies we have reported that a novel calcium channel blocker, LY393615, with good bioavailability protects against neuronal damage caused by hypoxia-hypoglycaemia in vitro and both global and focal cerebral ischaemia in vivo. The compound is neuroprotective when administered post-occlusion and may therefore be a useful anti-ischaemic agent.

ARL 17477, a selective nitric oxide synthase inhibitor, with neuroprotective effects in animal models of global and focal cerebral ischaemia

In the present studies, we have evaluated the effects of N-[4-(2-¿[(3-Chlorophenyl)methyl]amino¿ethyl)phenyl]-2-thiophenecarbo ximidamide dihydrochloride (ARL 17477) on recombinant human neuronal NOS (nNOS) and endothelial NOS (eNOS). We then carried out pharmacokinetic studies and measured cortical nitric oxide synthase (NOS) inhibition to determine that the compound crossed the blood brain barrier. Finally, the compound was evaluated in a model of global ischaemia in the gerbil and two models of transient focal ischaemia in the rat. The IC(50) values for ARL 17477 on human recombinant human nNOS and eNOS were 1 and 17 microM, respectively. ARL 17477 (50 mg/kg i.p.) produced a significant reduction in the ischaemia-induced hippocampal damage following global ischaemia when administered immediately post-occlusion, but failed to protect when administration was delayed until 30 min post-occlusion. In the endothelin-1 model of focal ischaemia, ARL 17477 (1 mg/kg i.v.) significantly attenuated the infarct volume when administered at either 0, 1 or 2 h post-endothelin-1 (P<0.05). In the intraluminal suture model, ARL 17477 at both 1 and 3 mg/kg i.v. failed to reduce the infarct volume measured at 1, 3 or 7 days post-occlusion. These results demonstrate that ARL 17477 protects against global ischaemia in gerbils and provides some reduction in infarct volume following transient middle cerebral artery occlusion in rats, indicating that nNOS inhibition may be a useful treatment of ischaemic conditions.

Signaling from the embryo conditions Vp1-mediated repression of alpha-amylase genes in the aleurone of developing maize seeds

The VP1 transcription factor functions as both a repressor and an activator of gene expression in the developing aleurone. Vp1 activation of the anthocyanin pathway exhibits strict cell autonomy in aleurone. In contrast, Vp1-mediated repression of hydrolase genes in aleurone cells during seed development is determined by a combination of cell autonomous and cell non-autonomous signals. To analyze signaling between the embryo and aleurone during seed development, a T-B3La chromosome translocation was used to create seed that has non-concordant embryo and endosperm genotypes. We show that de-repression of an Amy-GUS reporter gene in developing vp1 mutant aleurone cells strongly depends on the presence of a viviparous embryo. Genetic ablation of the developing embryo in vp1 mutant and Vp1 seeds through the introduction of an early embryo mutation caused a similar enhancement of Amy-GUS expression in the aleurone, suggesting that the quiescent embryo present in normal seed is a critical source of inhibitory signals. Analysis of an ABA deficient vp1 vp5 double mutant indicates that ABA synthesized in the embyro interacts additively with Vp1 to prevent precocious induction of alpha-amylase genes in the aleurone of the developing seed. A lack of ABA synthesis, however, does not account for the strongly synergistic interaction between a viviparous vp1 embryo and mutant aleurone suggesting that a quiescent embyro is a source of other inhibitory signals.

Characterization of the ABA-deficient tomato mutant notabilis and its relationship with maize Vp14

The notabilis (not) mutant of tomato has a wilty phenotype due to a deficiency in the levels of the plant hormone abscisic acid (ABA). The mutant appears to have a defect in a key control step in ABA biosynthesis--the oxidative cleavage of a 9-cis xanthophyll precursor to form the C15 intermediate, xanthoxin. A maize mutant, viviparous 14 (vp14) was recently obtained by transposon mutagenesis. This maize genetic lesion also affects the oxidative cleavage step in ABA synthesis. Degenerate primers for PCR, based on the VP14 predicted amino acid sequence, have been used to provide probes for screening a wilt-related tomato cDNA library. A full-length cDNA clone was identified which is specific to the not gene locus. The ORFs of the tomato cDNA and maize Vp14 are very similar, apart from parts of their N-terminal sequences. The not mutation has been characterized at the DNA level. A specific A/T base pair deletion of the coding sequence has resulted in a frameshift mutation, indicating that not is a null mutant. This observation is discussed in connection with the relatively mild phenotype exhibited by not mutant homozygotes.

MDL 101,002, a free radical spin trap, is efficacious in permanent and transient focal ischemia models

The present work describes the neuroprotective effects of the free radical spin trap, MDL 101,002, in models of permanent and transient focal ischemia. Permanent focal ischemia was carried out by occlusion of the distal segment of the middle cerebral artery (MCA) and CCA's in Spontaneously Hypertensive (SH) and Wistar rats. Transient focal ischemia was undertaken by occluding the origin of the MCA for 180 min by the intraluminar monofilament method in Wistar rats. With permanent distal MCA occlusion in SH rats, 100 mg/kg i.v. at 30 min post-ischemia resulted in a significant 40% reduction in infarct volume. Similarly, a 75 mg/kg bolus + 45 mg/kg-h dose of MDL 101,002 given i.v. at 5 min post-ischemia resulted in a 90% or 60% decrease in infarct volume in the mixed permanent/transient distal MCA model with Wistar rats using 120 or 180 min of CCA occlusion, respectively. When full reperfusion was established, after 180 min of occlusion in the proximal MCA model, a dose of 40 mg/kg + infusion and 75 mg/kg + infusion resulted in a significant 50% and 70% decrease in ischemic damage, respectively. MDL 101,002 is clearly an effective neuroprotective agent in all models examined. This work would suggest that this novel cyclic nitrone spin trap affords effective neuroprotection and is useful for the treatment of ischemic stroke.

Temporal dependent neuroprotection with propentofylline (HWA 285) in a temporary focal ischemia model

Propentofylline (HWA 285, 3-methyl-1-(5-oxo-hexyl)-7-propylxanthine) is an adenosine uptake and phosphodiesterase inhibitor that has been shown to be neuroprotective in both global and permanent focal ischemia animal models. However, to date, the efficacy of propentofylline has never been examined in an animal model of temporary focal ischemia or the 'therapeutic window' systematically examined in a focal ischemia model. The present experiments were designed to investigate these. Temporary (3 h) middle cerebral artery occlusion was accomplished by the monofilament method. Infarct volumes were determined at 24 h from 2,3,5-triphenyltetrazolieum chloride (TTC) stained coronal slices. Animals were dosed with vehicle or propentofylline at 3 mg/kg bolus and/or a 6 mg/kg per h infusion (24 h infusion) at 30 min, 1 h or 3 h post ischemia onset. Physiological monitoring on a subset of animals indicated no changes in mean arterial pressure, blood gases, blood pH, and glucose levels with either ischemia or drug treatment. Propentofylline treatment resulted in a statistically significant decrease in infarct volume when an infusion dose of 6 mg/kg per h was initiated at 30 min or when a bolus of 3 mg/kg plus an infusion dose was initiated at 1 h but not 3 h post ischemia. Therefore, propentofylline is neuroprotective in a model of temporary focal ischemia. This suggests that combination therapy with propentofylline might lead to clinical improvement beyond that which would occur with thrombolytics alone. The apparent short window of opportunity for effective dosing is consistent with the proposed mechanism of action for propentofylline.

Six-hour window of opportunity for calpain inhibition in focal cerebral ischemia in rats

BACKGROUND AND PURPOSE

Stroke patients often experience a significant temporal delay between the onset of ischemia and the time to initiation of therapy. Thus, there is a need for neuroprotectants with a long therapeutic window of opportunity. The efficacy of a potent, central nervous system-penetrating calpain inhibitor (MDL 28,170) was evaluated in a temporary model of focal cerebral ischemia to determine the window of opportunity for intracellular protease inhibition.

METHODS

An ex vivo brain protease inhibition assay established pharmacodynamic dosing parameters for MDL 28,170. Middle cerebral artery (MCA) occlusion was accomplished by advancing a monofilament through the internal carotid artery to the origin of the MCA. Postmortem infarct volumes were determined by quantitative image analysis of triphenyltetrazolium-stained brain sections.

RESULTS

Maximal inhibition of brain protease activity was observed 30 minutes after injection of MDL 28,170 with an estimated pharmacodynamic half-life of 2 hours. MDL 28,170 caused a dose-dependent reduction in infarct volume when administered 30 minutes after MCA occlusion. A window of opportunity study was conducted to determine the maximal delay between the onset of ischemia and the initiation of efficacious therapy. MDL 28,170 reduced infarct volume when therapy was delayed for 0.5, 3, 4, and 6 hours after the initiation of ischemia. The protective effect of MDL 28,170 was lost after an 8-hour delay.

CONCLUSIONS

These data indicate that the therapeutic window of opportunity for calpain inhibition is at least 6 hours in a reversible focal cerebral ischemia model. This protection is observed despite the lethal hypoxic and excitotoxic challenge, suggesting that calpain activation may be an obligatory, downstream event in the ischemic cell death cascade.

The quiescent/colorless alleles of viviparous1 show that the conserved B3 domain of VP1 is not essential for ABA-regulated gene expression in the seed

A series of vp1 alleles distinguish at least two classes of maturation-related genes that are regulated by the VP1 factor and abscisic acid (ABA). The intermediate vp1-c821708 and vp1-McW alleles have quiescent (non-viviparous) anthocyanin-deficient phenotypes while maintaining significant levels of maturation-specific gene expression in the developing embryo. However, expression of the C1 regulatory gene of the anthocyanin pathway is not detected in these mutants. Reduced steady-state levels of structurally altered VP1 proteins are detected in quiescent mutant embryos. The VP1-McW protein sequence lacks the highly conserved region encoded by exons 3-5 of the Vp1 gene. A sensitive RT-PCR assay was used to rule out significant amounts of intact transcripts in the vp1-McW mutant that could account for the quiescent phenotype. In transient expression assays, the VP1-McW protein and other mutants with a truncated B3 domain of VP1 retained a strong capacity to synergistically enhance ABA-regulation of the Em-GUS reporter gene; whereas transactivation of both Em-GUS and C1-sh-GUS genes in the absence of hormone was strongly inhibited. These results indicate that the largest conserved region in VP1 homologs (B3) is critical for gene activation at low or insignificant ABA dosages; whereas the N-terminal domain provides a key interface with ABA signaling pathways in the developing seed.

Genetic control of abscisic acid biosynthesis in maize

Abscisic acid (ABA), an apocarotenoid synthesized from cleavage of carotenoids, regulates seed maturation and stress responses in plants. The viviparous seed mutants of maize identify genes involved in synthesis and perception of ABA. Two alleles of a new mutant, viviparous14 (vp14), were identified by transposon mutagenesis. Mutant embryos had normal sensitivity to ABA, and detached leaves of mutant seedlings showed markedly higher rates of water loss than those of wild type. The ABA content of developing mutant embryos was 70% lower than that of wild type, indicating a defect in ABA biosynthesis. vp14 embryos were not deficient in epoxy-carotenoids, and extracts of vp14 embryos efficiently converted the carotenoid cleavage product, xanthoxin, to ABA, suggesting a lesion in the cleavage reaction. vp14 was cloned by transposon tagging. The VP14 protein sequence is similar to bacterial lignostilbene dioxygenases (LSD). LSD catalyzes a double-bond cleavage reaction that is closely analogous to the carotenoid cleavage reaction of ABA biosynthesis. Southern blots indicated a family of four to six related genes in maize. The Vp14 mRNA is expressed in embryos and roots and is strongly induced in leaves by water stress. A family of Vp14-related genes evidently controls the first committed step of ABA biosynthesis. These genes are likely to play a key role in the developmental and environmental control of ABA synthesis in plants.

The selectivity of MDL 74,721 in models of neurogenic versus vascular components of migraine

MDL 74,721 (R)-2-(N1,N1-dipropylamino)-8-methylaminosulfonylmethyl-1,2,3,4-te trahydronaphthalene, a sulfonamidotetralin, has been found to exhibit a 10,000-fold greater potency in neurogenic versus vascular models of migraine. Sumatriptan, a relatively pure 5-HT1D/5-HT1B receptor agonist, also showed higher potency versus neurogenic inflammation. However, for sumatriptan the potency difference (100-fold) in the two pathophysiological models was less pronounced than seen for MDL 74,721. The affinity profile of MDL 74,721 at 5-HT1 receptor subtypes may in part explain its ability to differentiate these two physiological responses. MDL 74,721 demonstrated nanomolar affinity for 5-HT1A (12.7 +/- 0.3 nM) and 5-HT1D (41.3 +/- 10.9 nM) but considerably lower affinity for 5-HT1B receptors (> 1000 nM). Serotonin-like activity was seen in in vitro functional assays including inhibition of forskolin-stimulated cAMP accumulation in human 5-HT1D receptor-transfected fibroblasts or eliciting vasoconstriction in isolated human pial arteries. The intrinsic activity (relative to 5 - HT[E(Amax)]) and affinity (pD2) for the human cerebrovascular 5-HT receptors were: 5-HT (100%, 7.51 +/- 0.09), sumatriptan (94%, 6.85 +/- 0.1) and MDL 74,721 (66%, 5.70 +/- 0.23). In anaesthetised cats, treatment with MDL 74,721 resulted in a dose-related reduction in the percentage of carotid flow going through the arteriovenous anastomoses to the lungs, with an ED50 of 0.3 mg/kg i.v., the same as sumatriptan. However, in the guinea-pig neurogenic model, MDL 74,721 inhibited plasma protein extravasation with an ED50 of 0.023 microg/kg compared to 2.5 microg/kg for sumatriptan. MDL 74,721 was also effective in this model (in rats) after oral administration. In conclusion, MDL 74,721 demonstrates a preclinical profile consistent with anti-migraine efficacy. Its marked preference for inhibiting neurogenic inflammation makes this compound a useful tool for assessing the relative contribution of this pathophysiological mechanism to the human disease state.

Specific oxidative cleavage of carotenoids by VP14 of maize

The plant growth regulator abscisic acid (ABA) is formed by the oxidative cleavage of an epoxy-carotenoid. The synthesis of other apocarotenoids, such as vitamin A in animals, may occur by a similar mechanism. In ABA biosynthesis, oxidative cleavage is the first committed reaction and is believed to be the key regulatory step. A new ABA-deficient mutant of maize has been identified and the corresponding gene, Vp14, has been cloned. The recombinant VP14 protein catalyzes the cleavage of 9-cis-epoxy-carotenoids to form C25 apo-aldehydes and xanthoxin, a precursor of ABA in higher plants.

The conserved B3 domain of VIVIPAROUS1 has a cooperative DNA binding activity

The biochemical activities that underlie the genetically defined activator and repressor functions of the VIVIPAROUS1 (VP1) protein have resisted in vitro analysis. Here, we show that a glutathione S-transferase (GST) fusion protein, including only the highly conserved B3 domain of VP1, has a highly cooperative, sequence-specific DNA binding activity. GST fusion proteins that include larger regions of the VP1 protein have very low activity, indicating that removal of the flanking protein sequences is necessary to elicit DNA binding in vitro. DNA competition and DNase I footprinting analyses show that B3 binds specifically to the Sph element involved in VP1 activation of the C1 gene, whereas binding to the G-box-type VP1-responsive element is of low affinity and is nonspecific. Footprint analysis of the C1 promoter revealed that sequences flanking the core TCCATGCAT motif of Sph also contribute to the recognition of the Sph element in its native context. The salient features of the in vitro GST-B3 DNA interaction are in good agreement with the protein and DNA sequence requirements defined by the functional analyses of VP1 and VP1-responsive elements in maize cells.

CRINKLY4: A TNFR-like receptor kinase involved in maize epidermal differentiation

The maize crinkly4 (cr4) mutation affects leaf epidermis differentiation such that cell size and morphology are altered, and surface functions are compromised, allowing graft-like fusions between organs. In the seed, loss of cr4 inhibits aleurone formation in a pattern that reflects the normal progression of differentiation over the developing endosperm surface. The cr4 gene was isolated by transposon tagging and found to encode a putative receptor kinase. The extracellular domain contains a cysteine-rich region similar to the ligand binding domain in mammalian tumor necrosis factor receptors (TNFRs) and seven copies of a previously unknown 39-amino acid repeat. The results suggest a role for cr4 in a differentiation signal.

Localization and interaction of the cis-acting elements for abscisic acid, VIVIPAROUS1, and light activation of the C1 gene of maize

The C1 regulatory gene of the maize anthocyanin pathway is regulated by a combination of developmental and environmental signals that include the Viviparous1 (Vp1) gene, abscisic acid (ABA), and light. Using protoplast electroporation and particle bombardment assays, we have defined c/s-acting elements that are necessary and sufficient for the activation of C1 by ABA, VP1, and light, respectively. The sequence from positions -142 to -132 (CGTCCATGCAT) is essential for VP1 activation, whereas a larger overlapping element from -147 to -132 (CGTGTCGTCCATGCAT) is necessary and sufficient for activation by ABA. A separate light (blue and red)-responsive c/s element is located between positions -116 and -59. Light interacts synergistically with the ABA and VP1 responses in transient expression assays, suggesting that combinatorial interaction between modules plays a role in integrating these signals in the developing seed.

A Similar Dichotomy of Sugar Modulation and Developmental Expression Affects Both Paths of Sucrose Metabolism: Evidence from a Maize Invertase Gene Family

Invertase and sucrose synthase catalyze the two known paths for the first step in carbon use by sucrose-importing plant cells. The hypothesis that sugar-modulated expression of these genes could provide a means of import adjustment was initially suggested based on data from sucrose synthases alone; however, this hypothesis remained largely conjectural without critical evidence for invertases. Toward this end, a family of maize invertases was cloned and characterized. Here, we show that invertases are indeed sugar modulated and, surprisingly, like the sucrose synthase genes, fall into two classes with contrasting sugar responses. In both families, one class of genes is upregulated by increasing carbohydrate supply (Sucrose synthase1 [Sus1] and Invertase2 [Ivr2]), whereas a second class in the same family is repressed by sugars and upregulated by depletion of this resource (Shrunken1 [Sh1] and Invertase1 [Ivr1]). The two classes also display differential expression during development, with sugar-enhanced genes (Sus1 and Ivr2) expressed in many importing organs and sugar-repressed, starvation-tolerant genes (Sh1 and Ivr1) upregulated primarily during reproductive development. Both the Ivr1 and Ivr2 invertase mRNAs are abundant in root tips, very young kernels, silk, anthers, and pollen, where a close relationship is evident between changes in message abundance and soluble invertase activity. During development, patterns of expression shift as assimilate partitioning changes from elongating silks to newly fertilized kernels. Together, the data support a model for integrating expression of genes differentially responsive to carbohydrate availability (i.e., feast and famine conditions) with developmental signals. The demonstration that similar regulatory patterns occur in both paths of sucrose metabolism indicates a potential to influence profoundly the adjustment of carbon resource allocation.

Transcription factor veracity: is GBF3 responsible for ABA-regulated expression of Arabidopsis Adh?

Assignment of particular transcription factors to specific roles in promoter elements can be problematic, especially in systems such as the G-box, where multiple factors of overlapping specificity exist. In the Arabidopsis alcohol dehydrogenase (Adh) promoter, the G-box regulates expression in response to cold and dehydration, presumably through the action of abscisic acid (ABA), and is bound by a nuclear protein complex in vivo during expression in cell cultures. In this report, we test the conventional wisdom of biochemical approaches used to identify DNA binding proteins and assess their specific interactions by using the G-box and a nearby half G-box element of the Arabidopsis Adh promoter as a model system. Typical in vitro assays demonstrated specific interaction of G-box factor 3 (GBF3) with both the G-box and the half G-box element. Dimethyl sulfate footprint analysis confirmed that the in vitro binding signature of GBF3 essentially matches the footprint signature detected in vivo at the G-box. Because RNA gel blot data indicated that GBF3 is itself induced by ABA, we might have concluded that GBF3 is indeed the GBF responsible in cell cultures for binding to the Adh G-box and is therefore responsible for ABA-regulated expression of Adh. Potential limitations of this conclusion are exposed by the fact that other GBFs bind the G-box with the same signature as GBF3, and subtle differences between in vivo and in vitro footprint signatures indicate that factors other than or in addition to GBF3 interact with the half G-box element.

Preclinical characterization of the potential of the putative atypical antipsychotic MDL 100,907 as a potent 5-HT2A antagonist with a favorable CNS safety profile

In preclinical studies, [R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl]-4- piperidinemethanol] [formula: see text] (MDL 100,907), a putative atypical antipsychotic, was characterized in vitro as a potent and selective ligand for the serotonin2A (5-HT2A) receptor and was evaluated in vitro and in vivo as a potent 5-HT2A receptor antagonist. Furthermore, MDL 100,907's potential CNS safety profile and selectivity as a potential antipsychotic agent were evaluated and compared with benchmark compounds. MDL 100,907 demonstrated low nanomolar or subnanomolar binding in vitro at the 5-HT2A receptor and showed a > 100-fold separation from all other receptors measured. MDL 100,907 had subnanomolar potency as a 5-HT2A antagonist in vitro in reversing 5-HT-stimulated inositol phosphate accumulation in NIH 3T3 cells transfected with the rat 5-HT2A receptor. In vivo, MDL 100,907 potently inhibited 5-methoxy-N, N-dimethyltryptamine-induced head twitches in mice or 5-hydroxytryptophan-induced head twitches in rats. In vivo functional tests in mice revealed a > 500-fold separation between doses that produced 5-HT2A antagonism and doses that produced alpha 1-adrenergic or striatal D2 antagonism. Using inhibition of D-amphetamine-stimulated locomotion in mice as a measure of potential antipsychotic efficacy, MDL 100,907 showed a superior CNS safety index relative to the reference compounds, haloperidol, clozapine, risperidone, ritanserin, and amperozide, in each of five tests for side effect potential, including measures of ataxia, general depressant effects, alpha 1-adrenergic antagonism, striatal D2 receptor antagonism, and muscle relaxation. MDL 100,907 did not antagonize apomorphine-induced stereotypes in rats, suggesting that it potentially lacks extrapyramidal side effect liability. MDL 100,907 showed selectivity as a potential antipsychotic in that it lacked consistent activity in selected rodent models of anticonvulsant, antidepressant, analgesic, or anxiolytic activity. In summary, these preclinical data indicate that MDL 100,907 is a potent and selective ligand at the 5-HT2A receptor. MDL 100,907's potent 5-HT2A antagonist activity might account for its activity in preclinical models of antipsychotic potential. Ongoing clinical evaluation with MDL 100,907 will test the hypothesis that 5-HT2A receptor antagonism is sufficient for antipsychotic activity in humans.

Gametophyte genetics in Zea mays L.: dominance of a restoration-of-fertility allele (Rf3) in diploid pollen

In Zea mays L. plants carrying the S-type of sterility-inducing cytoplasm, male fertility is determined by a gametophytic, nuclear restoration-of-fertility gene. Haploid pollen carrying the fertility-restoring allele (historically designated Rf3) is starch-filled and functional, whereas pollen carrying the nonrestoring allele (historically designated rf3) is shrunken and nonfunctional. Because restoration of fertility occurs in haploid tissue, the dominance relationship of restoring and nonrestoring alleles is unknown. We have tested the dominance relationship of the restoring and nonrestoring alleles at the rf3 locus in diploid pollen. The meiotic mutant elongate was used to generate tetraploid plants carrying both Rf3 and rf3 alleles in the S cytoplasm. These plants shed predominantly starch-filled pollen, consistent with dominance of the restoring allele. Restriction fragment length polymorphisms linked to the rf3 locus demonstrated cotransmission of rf3 and Rf3 alleles through heterozygous diploid pollen, providing conclusive genetic evidence that the restoring allele is the dominant or functional form of this restoration-of-fertility gene. We suggest that other S-cytoplasm restorers result from loss-of-function mutations and propose analysis of unreduced gametes as a test of this model.

Integrated control of seed maturation and germination programs by activator and repressor functions of Viviparous-1 of maize

The Viviparous-1 (VP1) transcriptional activator of maize is required for abscisic acid induction of maturation-specific genes late in seed development leading to acquisition of desiccation tolerance and arrest in embryo growth. Here, we show that VP1 also inhibits induction of the germination-specific alpha-amylase genes in aleurone cells of the developing seed and thereby appears to be involved in preventing precocious hydrolyzation of storage compounds accumulating in the endosperm. In developing seeds of the somatically instable vp1-m2 mutant, hydrolase activity was derepressed specifically in endosperm sectors underlying vp1 mutant aleurone. A barley alpha-amylase promoter-GUS reporter construct (Amy-GUS) was induced in developing vp1 mutant aleurone cells but not in wild-type aleurone cells. Moreover, transient expression of recombinant VP1 and vp1 mutant aleurone cells strongly inhibited expression of Amy-GUS and thus effectively complemented this aspect of the mutant phenotype. VP1 specifically repressed induction of Amy-GUS by the hormone gibberellic acid in aleurone of germinating barley seeds. Deletion of the acidic transcriptional activation domain of VP1 did not affect the inhibitory activity, indicating that VP1 has a discrete repressor function. Hence, physically combining activator and repressor functions in one protein may provide a mechanism to integrate the control of two normally consecutive developmental programs, seed maturation and seed germination.

Overlap of Viviparous1 (VP1) and abscisic acid response elements in the Em promoter: G-box elements are sufficient but not necessary for VP1 transactivation

The relationship between promoter sequences that mediate Viviparous1 (VP1) transactivation and regulation by abscisic acid (ABA) in the wheat Em promoter was investigated using deletion analysis and directed mutagenesis. The Em1a G-box is strongly coupled to VP1 transactivation as well as to ABA regulation; however, the Em promoter includes additional components that can support VP1 transactivation without ABA responsiveness or synergism. Oligonucleotide tetramers of several G-box sequences, including Em1a, Em1b, and the dyad G-box element from the UV light-regulated parsley chalcone synthase gene, were sufficient to confer VP1 transactivation and the synergistic interaction with ABA to the -45 cauliflower mosaic virus 35S core promoter. These data suggest that VP1 can activate transcription through at least two classes of cis-acting sequences, including the G-box elements and the Sph regulatory motif found in the C1 promoter. The contrasting roles of these motifs in the Em and C1 promoters suggest a basis for the differential regulation of the corresponding genes by VP1.

Structural features of the maize sus1 gene and protein

Genomic clones, cDNA clones, and protein of the maize (Zea mays L.) Suc synthase1 (sus1) gene were isolated and sequenced. Termini (5' and 3') of the transcribed unit were identified. The SUS1 protein was purified from tissue culture cells as a phosphorylated protein. The overall structure of sus1 is virtually identical with that of the paralogous gene, shrunken1 (sh1); however, the last intron of sh1 is missing in sus1. This intron bears much sequence similarity with the adjacent exon, suggesting that the intron arose from an internal duplication. Although the placement of the other 14 introns is identical in both genes, the introns exhibit markedly greater differences in size and sequence relative to that shown by the exons. An explanation for the differential rate of divergence of exons and introns is selection pressure for gene function. Additionally, comparisons of coding regions of plant sucrose synthases show that sh1-like and sus1-like genes can be found in all monocots so far analyzed. These latter observations point to an important role played by both genes in this group of plants.

Xanthines with C8 chiral substituents as potent and selective adenosine A1 antagonists

Several 8-substituted 1,3-dipropylxanthines were synthesized, and their receptor binding affinities at adenosine A1 and A2 receptors were measured. When enantiomeric pairs of compounds were examined, the R enantiomers were significantly more potent than the corresponding S enantiomers. The most potent compound at the A1 receptor was (R)-3,7-dihydro-8-(1-methyl-2-phenylethyl)-1,3-dipropyl-1H-purine-2,6-di one (5a; MDL 102,503), whose Ki value at the A1 receptor was 6.9 nM. However, a more selective compound was (R)-3,7-dihydro-8-(1-phenylpropyl)-1,3-dipropyl-1H-purine-2,6-dione (5d; MDL 102,234), which had a Ki value of 23.2 nM at the A1 receptor and an A2/A1 ratio of 153.

Apparent regional differences in 5-HT1A binding may reflect [3H]8-OH-DPAT labeling of serotonin uptake sites

The binding of [3H]8-OH-DPAT and [3H]paroxetine to 5-HT1A and 5-HT uptake sites (respectively) was examined in membranes prepared from bovine dorsal raphe and hippocampus. KD and Bmax values for [3H]8-OH-DPAT binding were indistinguishable in dorsal raphe nucleus and hippocampus. Competition studies with MDL 73,005EF, a selective 5-HT1A ligand, revealed a high and a low affinity site in the dorsal raphe, but only the high affinity component in hippocampal membranes. The low affinity component in the dorsal raphe was reduced in the presence of fluoxetine; saturation isotherms with [3H]paroxetine indicated a 5-fold greater concentration of 5-HT uptake sites in this region. The results are discussed in the context of earlier reports of regional differences in the pharmacology of 5-HT1A receptors and the selectivity of [3H]8-OH-DPAT binding.

The Viviparous-1 gene and abscisic acid activate the C1 regulatory gene for anthocyanin biosynthesis during seed maturation in maize

The Viviparous-1 (Vp1) gene is required for expression of the C1 regulatory gene of the anthocyanin pathway in the developing maize seed. We show that VP1 overexpression and the hormone, abscisic acid (ABA), activate a reporter gene driven by the C1 promoter in maize protoplasts. Cis-acting sequences essential for these responses were localized. Mutation of a conserved sequence in the C1 promoter abolishes both ABA regulation and VP1 trans-activation. An adjacent 5-bp deletion blocks ABA regulation but not VP1 trans-activation. The latter mutant reconstructs the promoter of c1-p, an allele that is expressed during seed germination but not during seed maturation. We suggest that VP1 activates C1 specifically during maturation by interacting with one or more ABA-regulated transcription factors.

Sugar Levels Modulate Differential Expression of Maize Sucrose Synthase Genes

The two genes encoding sucrose synthase in maize (Sh1 and Sus1) show markedly different responses to changes in tissue carbohydrate status. This enzyme is widely regarded as pivotal to sucrose partitioning, import, and/or metabolism by developing plant organs. Excised maize root tips were incubated for varying periods in different sugars and a range of concentrations. The Sh1 mRNA was maximally expressed under conditions of limited carbohydrate supply (~0.2% glucose). In contrast, Sus1 transcript levels were low or nondetectable under sugar-depleted conditions and peaked at 10-fold greater glucose concentrations (2.0%). Responses to other metabolizable sugars were similar, but L-glucose and elevation of osmolarity with mannitol had little effect. Plentiful sugar supplies thus increased expression of Sus1, whereas reduced sugar availability enhanced Sh1. At the protein level, shifts in abundance of subunits encoded by Sh1 and Sus1 were much less pronounced but corresponded to changes in respective mRNA levels. Although total enzyme activity did not show net change, cellular localization of sucrose synthase protein was markedly altered. In intact roots, sucrose synthase was most prevalent in the stele and apex. In contrast, sugar depletion favored accumulation in peripheral cells, whereas high sugar levels resulted in elevated expression in all cell types. The differential response of the two sucrose synthase genes to sugars provides a potential mechanism for altering the pattern of enzyme distribution in response to changing carbohydrate status and also for adjusting the sucrose-metabolizing capacity of importing cells relative to levels of available photosynthetic products.

Organ-specific invertase deficiency in the primary root of an inbred maize line

An organ-specific invertase deficiency affecting only the primary root system is described in the Oh 43 inbred maize (Zea mays). Invertases (acid and neutral/soluble and insoluble) were assayed in various tissues of hybrid (NK 508) and inbred (Oh 43, W 22) maize lines to determine the basis for an early report that Oh 43 root tips were unable to grow on sucrose agar (27). Substantial acid invertase activity (7.3 to 16.1 micromoles of glucose per milligram of protein per hour) was evident in extracts of all tissues tested except the primary root system of Oh 43. This deficiency was also evident in lateral roots arising from the primary root. In contrast, morphologically identical lateral roots from the adventitious root system had normal invertase levels. These results suggest that ontogenetic origin of root tissues is an important determinant of invertase expression in maize. Adventitious roots (including the seminals) arise above the scutellar node and are, therefore, of shoot origin. The Oh 43 deficiency also demonstrated that invertase activity was not essential for maize root growth. Sucrose synthase was active in extracts from all root apices and theoretically provided the only available avenue for sucrose degradation in primary root tips of Oh 43. The deficiency described here will provide a useful avenue of investigation into the expression and significance of root invertase.

The Viviparous-1 developmental gene of maize encodes a novel transcriptional activator

The Viviparous-1 (Vp1) gene of maize is specifically required for expression of the maturation program in seed development. We show that Vp1 encodes a 73,335 dalton protein with no detectable homology to known proteins. An acidic transcriptional activation sequence was identified by fusion to the GAL4 DNA-binding domain. Expression of VP1 in maize protoplasts resulted in strong activation (greater than 130-fold) of a reporter gene fused to the promoter of a presumptive target gene. The acidic domain in VP1 was essential for transactivation and could be functionally replaced by the activator sequence of the herpes simplex virus VP16 protein. Our results indicate that VP1 is a novel transcription factor possibly involved in potentiation of a seed-specific hormone response.

Guanine nucleotides are competitive inhibitors of N-methyl-D-aspartate at its receptor site both in vitro and in vivo

Guanine nucleotides were shown to alter N-methyl-d-aspartate (NMDA) receptor-effector coupling by competitive antagonism at the glutamate binding site, rather than via interaction with an intracellularly located GTP-binding protein. Thus, in contrast to known G-protein linked receptors, micromolar concentrations of guanine nucleotides and their analogs decreased both agonist [( 3H]glutamate) and antagonist [( 3H]-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid binding to the NMDA receptor complex. The most potent compound, the GDP analog guanosine-5'-O-(2-thiodiphosphate) (GDP beta S), was studied in detail. GDP beta S exhibited almost 200-fold selectivity for the glutamate recognition site vs. the strychnine-insensitive glycine binding site. IC50 values were 2.7 +/- 1.4 and 484 +/- 97 microM, respectively. GDP beta S also inhibited N-[1-(2-thienyl)cyclohexyl-3H]piperidine binding (IC50 was 28.0 +/- 3.7 microM) in an NMDA-reversible fashion. [3H]-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid saturation binding studies revealed an increase in Kd from 263 +/- 49 (control) to 552 +/- 134 nM (8 microM GDP beta S) without any change in maximum binding (4.94 +/- 0.34 and 5.19 +/- 0.58 pmol/mg of protein, respectively). GDP beta S was also a competitive inhibitor of the following NMDA-stimulated responses: elevation of cyclic GMP in neonatal rat cerebellar slices, release of preloaded [3H]norepinephrine from superfused rat hippocampal slices and elevation of cytosolic calcium concentration in fura-2-loaded cultured rat forebrain neurons. IC50 values were 78.4, 53.4 and 1.6 microM, respectively. Finally, GDP beta S resembled known NMDA receptor antagonists in its ability to block NMDA receptor-induced seizures after i.c.v. administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular Analysis of viviparous-1: An Abscisic Acid-Insensitive Mutant of Maize

The viviparous-1 (vp1) gene in maize controls multiple developmental responses associated with the maturation phase of seed formation. Most notably, mutant embryos have reduced sensitivity to the hormone abscisic acid, resulting in precocious germination, and blocked anthocyanin synthesis in aleurone and embryo tissues. The Vp1 locus was cloned by transposon tagging, using the Robertson's Mutator element present in the vp1-mum1 mutant allele. Detection of DNA rearrangements in several spontaneous and transposable element-induced mutant vp1 alleles, including a partial deletion of the locus, confirmed the identity of the clone. The Vp1 gene encodes a 2500-nucleotide mRNA that is expressed specifically in embryo and endosperm tissues of the developing seed. This transcript is absent in seed tissues of vp1 mutant stocks. Expression of C1, a regulatory gene for the anthocyanin pathway, is selectively blocked at the mRNA level in vp1 mutant seed tissues, indicating the Vp1 may control the anthocyanin pathway by regulating C1. We suggest that the Vp1 gene product functions to potentiate multiple signal transduction pathways in specific seed tissues.

Molecular Analysis of viviparous-1: An Abscisic Acid-Insensitive Mutant of Maize

The viviparous-1 (vp1) gene in maize controls multiple developmental responses associated with the maturation phase of seed formation. Most notably, mutant embryos have reduced sensitivity to the hormone abscisic acid, resulting in precocious germination, and blocked anthocyanin synthesis in aleurone and embryo tissues. The Vp1 locus was cloned by transposon tagging, using the Robertson's Mutator element present in the vp1-mum1 mutant allele. Detection of DNA rearrangements in several spontaneous and transposable element-induced mutant vp1 alleles, including a partial deletion of the locus, confirmed the identity of the clone. The Vp1 gene encodes a 2500-nucleotide mRNA that is expressed specifically in embryo and endosperm tissues of the developing seed. This transcript is absent in seed tissues of vp1 mutant stocks. Expression of C1, a regulatory gene for the anthocyanin pathway, is selectively blocked at the mRNA level in vp1 mutant seed tissues, indicating the Vp1 may control the anthocyanin pathway by regulating C1. We suggest that the Vp1 gene product functions to potentiate multiple signal transduction pathways in specific seed tissues.

A low dose of xylamine produces sustained and selective decreases in rat brain norepinephrine without evidence of neuronal degeneration

The effects of a chronic partial depletion of rat cortical NE by a single dose of xylamine (20 mg/kg i.p.) on pre- and postsynaptic noradrenergic functionality were studied 4 hr, 14, 21 and 35 days after treatment. This dose of xylamine resulted in a 40 to 50% selective decrease in cortical levels of NE and the major metabolites of NE, 3,4-dihydroxyphenylethyleneglycol and 3-methoxy-4-hydroxyphenylethyleneglycol and, when measured after 35 days, [3H]desipramine binding and dopamine-beta-hydroxylase activity were at control levels, which would indicate that the NE nerve terminals in the cortex were intact. The 21- or 35-day deficit of NE did not affect alpha-1, alpha-2, beta, dopamine2, 5-hydroxytryptamine, or gamma-aminobutyric acidB receptor densities, or the beta receptor mediated adenylate cyclase activity. In addition, desipramine (10 mg/kg i.p.) administration for 14 days (days 20 through 34) was able to down-regulate beta receptor number (16% decrease) and reduce NE-stimulated adenylate cyclase activity (22% decrease), indicating that postsynaptic plasticity was still maintained. Affective disorders do not appear to be associated with a substantial (or readily measurable) decrease in brain NE concentrations and there is no consistent evidence of an altered beta receptor responsiveness. Thus, partial depletion of NE with xylamine might represent a biochemical model reflecting the involvement of NE in depression which could be used to investigate more sensitive markers of altered noradrenergic function.

Partial purification of a nucleoside triphosphatase from the inner membrane of the chloroplast envelope of pea

A Mg2+-NTPase has been partially purified from the inner membrane of the pea chloroplast envelope. Isolated envelope membranes were solubilized with Triton X-100 and fractionated by DEAE-Sephadex chromatography, followed by ultrafiltration and sucrose density gradient centrifugation. An approximate 35-fold increase in the specific activity of the vanadate and sodium fluoride sensitive NTPase was obtained. Analysis of the partially purified NTPase by sodium dodecyl sulfate polyacrylamide gel electrophoresis revealed a single 37-kDa polypeptide that appeared to be associated with the activity. In support of this identification, it is demonstrated that the 37-kDa polypeptide can be photolabeled with 8-azido-ATP.

Properties of a Partially Purified Nucleoside Triphosphatase (NTPase) from the Chloroplast Envelope of Pea

The Mg-nucleoside triphosphatase activity associated with the inner envelope membrane of the pea chloroplast is comprised of at least two components, a major activity that is sensitive to vanadate and sodium fluoride and a minor insensitive activity. The vanadate/fluoride sensitive activity has been partially purified (about 35-fold) from Triton X-100 solubilized membranes by DEAE-Sephadex chromatography and sucrose density gradient centrifugation. The partially purified enzyme resembles the membrane-bound activity in requiring either Mg(2+) or Mn(2+), having a broad specificity for nucleoside triphosphates, having a K(m) for ATP of 0.18 millimolar, and being inhibited by N-ethylmaleimide, but insensitive to sodium azide and dicyclohexylcarbodiimide. The partially purified enzyme obtained after sucrose gradient centrifugation has a markedly increased sensitivity to inhibition by inorganic pyrophosphate compared with the less pure enzyme. Pyrophosphate is not a substrate of either the membrane-bound or partially purified enzyme.

Characterization and localization of the ATPase associated with pea chloroplast envelope membranes

Chloroplast envelope membranes isolated from Pisum sativum seedlings have been found to contain a Mg-ATPase activity (specific activity 50-175 nanomoles per minute per milligram protein). The ATPase had a broad pH optimum between 7.0 and 9.5. The activity was not inhibited by oligomycin, N,N'-dicyclohexylcarbodiimide, ouabain, or antibodies directed against chloroplast coupling factor 1; nor was the activity stimulated by monovalent cations. However, the ATPase was inhibited by vanadate, molybdate, and adenylyl imidodiphosphate.The ATPase hydrolyzed a broad range of nucleoside triphosphates, but did not hydrolyze ADP, AMP, or pyrophosphate. The K(m) for Mg-ATP was determined to be 0.2 millimolar. The ATPase was found to be distinct from ADPase and pyrophosphatase activities also present in pea envelope membranes.The ATPase was determined to be located on the inner membrane of the envelope after resolution of inner and outer membranes by sucrose density gradient centrifugation.