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Biomedical subjects

S Clemens

Publications and source records attributed to S Clemens.

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

Tolerance to toxic metals by a gene family of phytochelatin synthases from plants and yeast.

Phytochelatins play major roles in metal detoxification in plants and fungi. However, genes encoding phytochelatin synthases have not yet been identified. By screening for plant genes mediating metal tolerance we identified a wheat cDNA, TaPCS1, whose expression in Saccharomyces cerevisiae results in a dramatic increase in cadmium tolerance. TaPCS1 encodes a protein of approximately 55 kDa with no similarity to proteins of known function. We identified homologs of this new gene family from Arabidopsis thaliana, Schizosaccharomyces pombe, and interestingly also Caenorhabditis elegans. The Arabidopsis and S.pombe genes were also demonstrated to confer substantial increases in metal tolerance in yeast. PCS-expressing cells accumulate more Cd2+ than controls. PCS expression mediates Cd2+ tolerance even in yeast mutants that are either deficient in vacuolar acidification or impaired in vacuolar biogenesis. PCS-induced metal resistance is lost upon exposure to an inhibitor of glutathione biosynthesis, a process necessary for phytochelatin formation. Schizosaccharomyces pombe cells disrupted in the PCS gene exhibit hypersensitivity to Cd2+ and Cu2+ and are unable to synthesize phytochelatins upon Cd2+ exposure as determined by HPLC analysis. Saccharomyces cerevisiae cells expressing PCS produce phytochelatins. Moreover, the recombinant purified S.pombe PCS protein displays phytochelatin synthase activity. These data demonstrate that PCS genes encode phytochelatin synthases and mediate metal detoxification in eukaryotes.

Amino Acid Sequence↗
PubMed1999

Suppression of inward-rectifying K+ channels KAT1 and AKT2 by dominant negative point mutations in the KAT1 alpha-subunit.

The Arabidopsis thaliana cDNA, KAT1 encodes a hyperpolarization-activated K+ (K+in) channel. In the present study, we identify and characterize dominant negative point mutations that suppress K+in channel function. Effects of two mutations located in the H5 region of KAT1, at positions 256 (T256R) and 262 (G262K), were studied. The co-expression of either T256R or G262K mutants with KAT1 produced an inhibition of K+ currents upon membrane hyperpolarization. The magnitude of this inhibition was dependent upon the molar ratio of cRNA for wild-type to mutant channel subunits injected. Inhibition of KAT1 currents by the co-expression of T256R or G262K did not greatly affect the ion selectivity of residual currents for Rb+, Na+, Li+, or Cs+. When T256R or G262K were co-expressed with a different K+ channel, AKT2, an inhibition of the channel currents was also observed. Voltage-dependent Cs+ block experiments with co-expressed wild type, KAT1 and AKT2, channels further indicated that KAT1 and AKT2 formed heteromultimers. These data show that AKT2 and KAT1 are able to co-assemble and suggest that suppression of channel function can be pursued in vivo by the expression of the dominant negative K+in channel mutants described here.

Animals↗
PubMed1999

Assessment of RS1 in X-linked juvenile retinoschisis and sporadic senile retinoschisis.

The RS1 gene is the causative gene in X-linked juvenile retinoschisis (RS). We have screened this gene for mutations in 13 patients with RS and in 7 probands with senile retinoschisis, a sporadic, later-onset form of retinoschisis. Mutations were detected in all RS patients. Of the 11 different mutations identified, six have been reported previously and live are novel. We did not find mutations in any of the senile retinoschisis patients and conclude that senile retinoschisis is not the result of germline mutations in the RS1 gene.

Adult↗
PubMed1999

CUT1, an Arabidopsis gene required for cuticular wax biosynthesis and pollen fertility, encodes a very-long-chain fatty acid condensing enzyme.

Land plants secrete a layer of wax onto their aerial surfaces that is essential for survival in a terrestrial environment. This wax is composed of long-chain, aliphatic hydrocarbons derived from very-long-chain fatty acids (VLCFAs). Using the Arabidopsis expressed sequence tag database, we have identified a gene, designated CUT1, that encodes a VLCFA condensing enzyme required for cuticular wax production. Sense suppression of CUT1 in transgenic Arabidopsis plants results in waxless (eceriferum) stems and siliques as well as conditional male sterility. Scanning electron microscopy revealed that this was a severe waxless phenotype, because stems of CUT1-suppressed plants were completely devoid of wax crystals. Furthermore, chemical analyses of waxless plants demonstrated that the stem wax load was reduced to 6 to 7% of wild-type levels. This value is lower than that reported for any of the known eceriferum mutants. The severe waxless phenotype resulted from the downregulation of both the decarbonylation and acyl reduction wax biosynthetic pathways. This result indicates that CUT1 is involved in the production of VLCFA precursors used for the synthesis of all stem wax components in Arabidopsis. In CUT1-suppressed plants, the C24 chain-length wax components predominate, suggesting that CUT1 is required for elongation of C24 VLCFAs. The unique wax composition of CUT1-suppressed plants together with the fact that the location of CUT1 on the genetic map did not coincide with any of the known ECERIFERUM loci suggest that we have identified a novel gene involved in wax biosynthesis. CUT1 is currently the only known gene with a clearly established function in wax production.

Acetyltransferases↗
PubMed1999

Changes in motor network expression related to moulting behaviour in lobster: role of moult-induced deep hypoxia

The well known rhythmically active pyloric neural network in intact and freely behaving lobsters Homarus gammarus was monitored prior to and following ecdysis. Despite long-lasting hormonal and metabolic alterations associated with this process, spontaneous pyloric network activity remained largely unaltered until the last 12-48 h before exuviation. At this time, the most notable change was a progressive lengthening of pyloric cycle period, which eventually attained 500-600 % of control values. It was only in the very last minutes before ecdysis that burst patterning became irregular and the otherwise strictly alternating motor sequence broke down. After the moult, coordinated rhythmicity was re-established within 10 min. Concomitant with these final changes in motor network expression at ecdysis was a drastic reduction in blood oxygen levels which led to a temporary near-anoxia. By imposing similarly deep hypoxic conditions both on intermoult animals and on the pyloric network in vitro, we mimicked to a large extent the moult-induced changes in pyloric network performance. Our data suggest that, despite major surrounding physiological perturbations, the pyloric network in vivo retains stable pattern-generating properties throughout much of the moulting process. Moreover, some of the most significant modifications in motor expression just prior to ecdysis can be related to a substantial reduction in oxygen levels in the blood.

Journal Article↗
PubMed1998

The plant cDNA LCT1 mediates the uptake of calcium and cadmium in yeast.

Nonessential metal ions such as cadmium are most likely transported across plant membranes via transporters for essential cations. To identify possible pathways for Cd2+ transport we tested putative plant cation transporters for Cd2+ uptake activity by expressing cDNAs in Saccharomyces cerevisiae and found that expression of one clone, LCT1, renders the growth of yeast more sensitive to cadmium. Ion flux assays showed that Cd2+ sensitivity is correlated with an increase in Cd2+ uptake. LCT1-dependent Cd2+ uptake is saturable, lies in the high-affinity range (apparent KM for Cd2+ = 33 microM) and is sensitive to block by La3+ and Ca2+. Growth assays demonstrated a sensitivity of LCT1-expressing yeast cells to extracellular millimolar Ca2+ concentrations. LCT1-dependent increase in Ca2+ uptake correlated with the observed phenotype. Furthermore, LCT1 complements a yeast disruption mutant in the MID1 gene, a non-LCT1-homologous yeast gene encoding a membrane Ca2+ influx system required for recovery from the mating response. We conclude that LCT1 mediates the uptake of Ca2+ and Cd2+ in yeast and may therefore represent a first plant cDNA encoding a plant Ca2+ uptake or an organellar Ca2+ transport pathway in plants and may contribute to transport of the toxic metal Cd2+ across plant membranes.

Base Sequence↗
PubMed1998

Feeding-induced changes in temporal patterning of muscle activity in the lobster stomatogastric system.

In the lobster Homarus gammarus, rhythmic masticatory movements of the foregut gastric mill are generated by a small neural network in the stomatogastric ganglion. We have used EMG recordings from intact animals to analyse gastric network output in relation to cycle period before and after feeding. In pre-prandial conditions, muscles controlling lateral teeth closure and medial tooth protraction (driven by MG and GM motor neurons, respectively) express relatively constant, return stroke-like burst durations, but change to a variable-duration power stroke-like phenotype after feeding. In contrast, the LPG neuron-innervated lateral teeth opener muscle switches from power stroke to return stroke-like behavior. Thus alternate phases within a single motor program may invert their temporal properties according to the behavioral situation.

Animals↗
PubMed1998

In vivo modulation of interacting central pattern generators in lobster stomatogastric ganglion: influence of feeding and partial pressure of oxygen.

The stomatogastric ganglion (STG) of the European lobster Homarus gammarus contains two rhythm-generating networks (the gastric and pyloric circuits) that in resting, unfed animals produce two distinct, yet strongly interacting, motor patterns. By using simultaneous EMG recordings from the gastric and pyloric muscles in vivo, we found that after feeding, the gastropyloric interaction disappears as the two networks express accelerated motor rhythms. The return to control levels of network activity occurs progressively over the following 1-2 d and is associated with a gradual reappearance of the gastropyloric interaction. In parallel with this change in network activity is an alteration of oxygen levels in the blood. In resting, unfed animals, arterial partial pressure of oxygen (PO2) is most often between 1 and 2 kPa and then doubles within 1 hr after feeding, before returning to control values some 24 hr later. In vivo, experimental prevention of the arterial PO2 increase after feeding leads to a slowing of pyloric rhythmicity toward control values and a reappearance of the gastropyloric interaction, without apparent effect on gastric network operation. Using in vitro preparations of the stomatogastric nervous system and by changing oxygen levels uniquely at the level of the STG within the range observed in the intact animal, we were able to mimic most of the effects observed in vivo. Our data indicate that the gastropyloric interaction appears only during a "free run" mode of foregut activity and that the coordinated operation of multiple neural networks may be modulated by local changes in oxygenation.

Animals↗
PubMed1998

Steep central islands after myopic photorefractive keratectomy.

PURPOSE: To investigate the formation of steep central islands and their reduction under modified experimental conditions. SETTING: University Eye Hospital Münster and Schwind Co., Kleinostheim, Germany. METHODS: Corneas of enucleated intact bovine eyes were treated with the Schwind Keratom. All experimental conditions were repeated six times in six different corneas. Eight experimental groups were looked at. Fluence was 180 to 200 mJ/cm2. Ablation mode (phototherapeutic keratectomy ([PTK] and standard myopic photorefractive keratectomy [PRK]), internal repetition rate (3 to 30 Hz), and ablation diameter (5 to 8 mm) and depth (4 to 15 diopters [D] in PRK) were varied. Modifications to reduce or avoid steep central islands included blowing nitrogen gas and aerosol over the cornea, cleaning the cornea of fluid, and using an anti-central-island software program. RESULTS: In PTK, an increase in the internal repetition rate resulted in a decrease in the height of the steep central island. In standard PRK, increasing refractive correction up to -8.0 D and increasing the ablation diameter resulted in an increase in steep central island power. The anti-central-island program, blowing aerosol, and cleaning the cornea reduced the formation of steep central islands and blowing nitrogen gas eliminated them. CONCLUSION: Steep central islands are created by a wide-field ablation process and are probably caused by many factors. Both software and hardware modifications can be used to reduce their formation.

Animals↗
PubMed1998

[Primary high malignancy B-cell lymphoma of the lacrimal sac].

Case report on a 44-year-old woman in good health with the symptoms of epiphora, a plump elastic, not distressing swelling under the medial canthal tendon of 1 cm size on the right side. In ultrasonography and intraoperatively a tumour of moderate reflectivity with infiltration of the lacrimal sac was found. The histological evaluation, including immunohistochemical studies of the removed lesion, revealed a malignant B-cell lymphoma.

Adult↗
PubMed1998

Long-term expression of two interacting motor pattern-generating networks in the stomatogastric system of freely behaving lobster.

Rhythmic movements of the gastric mill and pyloric regions of the crustacean foregut are controlled by two stomatogastric neuronal networks that have been intensively studied in vitro. By using electromyographic recordings from the European lobster, Homarus gammarus, we have monitored simultaneously the motor activity of pyloric and gastric mill muscles for </=3 mo in intact and freely behaving animals. Both pyloric and gastric mill networks are almost continuously active in vivo regardless of the presence of food. In unfed resting animals kept under "natural-like" conditions, the pyloric network expresses the typical triphasic pattern seen in vitro but at considerably slower cycle periods (2. 5-3.5 s instead of 1-1.5 s). Gastric mill activity occurs at mean cycle periods of 20-50 s compared with 5-10 s in vitro but may suddenly stop for up to tens of minutes, then restart without any apparent behavioral reason. When conjointly active, the two networks express a strict coupling that involves certain but not all motor neurons of the pyloric network. The posterior pyloric constrictor muscles, innervated by a total of 8 pyloric (PY) motor neurons, are influenced by the onset of each gastric mill medial gastric/lateral gastric(MG/LG) neuron powerstroke burst, and for one cycle, PY neuron bursts may attain >300% of their mean duration. However, the duration of activity in the lateral pyloric constrictor muscle, innervated by the unique lateral pyloric (LP) motor neuron, remains unaffected by this perturbation. During this period after gastric perturbation, LP neuron and PY neurons thus express opposite burst-to-period relationships in that LP neuron burst duration is independent of the ongoing cycle period, whereas PY neuron burst duration changes with period length. In vitro the same type of gastro-pyloric interaction is observed, indicating that it is not dependent on sensory inputs. Moreover, this interaction is intrinsic to the stomatogastric ganglion itself because the relationship between the two networks persists after suppression of descending inputs to the ganglion. Intracellular recordings reveal that this gastro-pyloric interaction originates from the gastric MG and LG neurons of the gastric network, which inhibit the pyloric pacemaker ensemble. As a consequence, the pyloric PY neurons, which are inhibited by the pyloric dilator (PD) neurons of the pyloric pacemaker group, extend their activity during the time that PD neuron is held silent. Moreover, there is evidence for a pyloro-gastric interaction, apparently rectifying, from the pyloric pacemakers back to the gastric MG/LG neuron group.

Animals↗
PubMed1997

[Rhegmatogenous retinal detachments. Seasonal variation and incidence].

UNLABELLED: Seasonal variations in the relative incidence of rhegmatogenous retinal detachment were reported as a trend in several studies on the database of relatively limited cohort sizes. PATIENTS AND METHODS: An analysis on this topic was performed with a long-term database. A total of 3073 files of patients with rhegmatogenous retinal detachment, covering 11 years of observation, were reviewed for this study. Patients with signs of long-standing detachment or other predisposing diseases were excluded, so that a basic study population of 2314 patients remained for the analysis. RESULTS: The averaged seasonal incidence of rhegmatogenous detachments revealed a significant (P < 0.005) mid-summer peak (n in July = 228) and a winter trough (mean of December-January = 161; difference = 36%). Phase and curve fitting of the seasonal variations in the number of retina detachment cases was similar to the seasonal variation of the astronomic duration of the day (P < 0.001). The relation was closer compared to the average duration of light exposure per day calculated from behavioural data and the astronomic length of light phase (P < 0.0002). CONCLUSION: This long-time study revealed a close correlation of the relative seasonal incidence of retinal detachment and the seasonal variation of light hours per day. So far, this observations cannot be explained pathogenetically. Two basic hypotheses ought to be investigated further: (1) The influence of light on the generation of toxic oxygen radicals and the subsequent destruction of the vitreous and (2) possible light-induced changes in vitreoretinal adhesion.

Adult↗
PubMed1997

[Echographic diagnosis of efferent lacrimal ducts with contrast media].

BACKGROUND: Affections of the lacrimal drainage system are often seen by ophthalmologists. Inspection, palpation, diagnostic rinsing and sounding can distinguish anatomical stops before or after tear sac. For final diagnostics however more apparative examinations are necessary. The ultrasonic examination with contrast media is a simple method for diagnostics of affections of the lacrimal drainage system besides the dacryocystography, the scintigraphy and other ones. PATIENTS AND METHODS: On 12 patients with a dysfunctional lacrimal drainage system and 12 normal controls the ultrasonic examination with instillation of contrast media: silicon oil, glycerine, dispersions of almond oil and viscoelastic substances was performed. All examinations were performed with the 13 B-scan. RESULTS: The lacrimal drainage way was detectable from the canaliculus to the middle nasolacrimal duc CONCLUSION: An additional advantage of the ultrasonic examination with contrast-media is the neglect of radiation, the simple and often repeatable examination method, especially the enhancement of the contrast of different valves and stenoses and mucinous deposits in stationary anatomical variations and dynamic defects.

Contrast Media↗
PubMed1997

[Aicardi syndrome and acquired retinal detachment].

BACKGROUND: The Aicardi syndrome is a complex of congenital anomalies consisting of agenesis of the corpus callosum, infantile spasms and pathognomonic chorioretinal lacunar lesions. An acquired detachment of the retina was reported only in one patient. HISTORY AND SIGNS: We report about a nine-month-old girl with Aicardi syndrome. She presented the typical signs of this syndrome and an acquired detachment in both eyes. THERAPY AND OUTCOME: We performed a translimbal vitrectomy with silicon-oil instillation on the right eye. CONCLUSION: On the basis of histological findings reported in the literature we suggest a combined pathogenesis of the ablatio retinae in our patient with Aicardi syndrome: traction and foramina.

Abnormalities, Multiple↗
PubMed1997

[Possibilities and limits of extracranial vascular diagnosis with conventional echography].

BACKGROUND: For the extracranial and partial intracranial diagnosis of vessels Doppler ultrasonography has been the method of choice since a long time. If not the phenomenon of flow, but anatomical structures are of interest, or biopsy is planned, the conventional ultrasonography is often under-estimated. PATIENTS AND METHODS: A detection of the superficial temporal artery and its branches was performed in a clinical study of 50 patients by using a 10 Mhz ultrasonic system. The ultrasonic findings were correlated with clinical findings. RESULTS: The vessel course, the vessel was detectable diameter, plaques and stenosis and the perivascular tissue. CONCLUSIONS: The availability of conventional ultrasonic tools provides the possibility to achieve a fast first documentation of the extracranial vessels in a lot of inflammatory and arteriosclerotic diseases.

Adult↗
PubMed1995

[Treatment guidelines in various stages of senile retinoschisis].

BACKGROUND: Concerning the indications, progression in course and the possible complications, the different methods of treatment in cases of retinoschisis in its different expressions were examined. A staging of senile retinoschisis is presented. PATIENTS: Patients' natural course, prophylactic treatment against expansion and treatment of retinal detachment were examined. RESULTS: The lateral and central barrier of laser or cryo around the schisis is contradictory since a progression in direction to the macula is the result. Three of such cases could be found. In 6 of 52 cases with prophylactic treatment of an outer layer defect with cryo the result was a schisis detachment. In all these cases a retinal reattachment was performed with the Custodis procedure. The final anatomic result of 95 treated schisis retinal detachments was a 98% success. The symptomatic or progressive cases had a little less favourable outcome. CONCLUSIONS: The only indication for treatment of a schisis at present is the symptomatic or progressive schisis detachment with threatening of the macula. Lateral or central barring of a schisis or treatment of the borders of an outer layer retinal break should be avoided. The rate of reattachment and the functional results are better than in the group of rhegmatogenous retinal detachments including the 50.5% schisis retinal detachments without symptoms.

Adult↗