Biomedical subjects

M Klemm

Publications and source records attributed to M Klemm.

At least 37 records · Page 2Linked to original sources

PubMed1998

Utility of C57BL/6J x 129/SvJae embryonic stem cells for generating chromosomal deletions: tolerance to gamma radiation and microsatellite polymorphism.

We have previously reported a method for making nested deletion complexes in mice by irradiation of ES cells. The key to this technology is that F1 hybrid ES cells (called v17.2) of the genotype (BALB/cTa x 129/SvJae) retain germline colonizing ability after exposure to levels of ionizing radiation that induce chromosomal deletions. In an effort to identify other genotypes of ES cells that are suitable for this technology, the radiation sensitivity of the cell line v6.4, which is of the genotype (C57BL/6J x 129/SvJae), was investigated. After treatment with a range of radiation exposures, the developmental potential of these cells was assayed by injecting them into blastocysts to generate chimeric mice. These experiments showed that while cell lethality increased as the level of radiation increased, the surviving ES cells retained full totipotency at all exposure levels, up to 400 Rads. Because polymorphism between parental microsatellite alleles in the F1 hybrid ES cells is important for ascertaining the sizes of induced deletions, the 129/SvJ and 129/SvJae allele sizes of 48 microsatellite loci on chromosome (Chr) 17 were determined. This revealed a higher level of polymorphism between 129 and C57BL/6J on Chr 17. The radiation tolerance, high polymorphism between parental strains, and presence of the widely used C57BL/6J strain component make v6.4 ES cells an attractive cell line for generating radiation-induced chromosomal deletions.

Animals↗

PubMed1998

Endothelial cell loss secondary to two different phacoemulsification techniques.

BACKGROUND AND OBJECTIVE: The endothelial cell count after phacoemulsification serves as a sensitive indicator for the level of corneal damage caused by different phacoemulsification techniques. PATIENTS AND METHODS: In a prospective and randomized study, the "Reversed Tip and Snip" technique and the "Divide and Conquer" technique were performed in groups of 30 patients each. The corneal endothelial cell count was measured preoperatively as well as 4 weeks and 3 months postoperatively. RESULTS: The endothelial cell count showed significant (P < .001) reduction by approximately 10% after the "Reversed Tip and Snip" technique and by approximately 15% (P < .001) after the "Divide and Conquer" technique. The latter produced a significantly (P < .001) greater cell loss. CONCLUSIONS: The "Reversed Tip and Snip" phacoemulsification technique produces less endothelial cell loss than the "Divide and Conquer" technique.

Aged↗

PubMed1997

Regulation of ES cell differentiation by functional and conformational modulation of p53.

Embryonic stem (ES) cell lines were used to examine the role of p53 during in vitro differentiation. Undifferentiated ES cells express high levels of p53 exclusively in the wild-type conformation, immunoprecipitable by monoclonal antibody PAb246, and p53 was found to be functionally active as determined by its ability to bind DNA specifically and to activate transcription of target genes. Differentiation in vitro resulted in a decrease in the levels of p53 and in a shift in its conformational status to the mutant form, detectable by monoclonal antibody PAb240, with a concomitant loss of functional activity. The presence of functional p53 in the undifferentiated ES cells renders them hypersensitive to UV irradiation, whereas the differentiated cells were resistant to UV treatment. ES cells lacking p53 exhibit enhanced proliferation in both the undifferentiated and differentiated state, and apoptosis accompanying differentiation was found to be reduced. Furthermore, wild-type ES cells undergoing apoptosis expressed functional p53. Expression of the temperature-sensitive p53val135 mutant in wild-type ES cells resulted in a reduction of apoptosis accompanying differentiation when it adopted a mutant conformation at 39 degrees C. These data demonstrate that functional inactivation of p53 allows differentiating cells to escape from apoptosis, and suggest that the conformational switch could regulate the inactivation process.

Animals↗

PubMed1997

Targeting of a functional Escherichia coli RecA protein to the nucleus of plant cells.

We have characterised a RecA protein fused to the simian virus 40 large T nuclear-localisation signal. The fusion protein was targeted to the nucleus in transgenic tobacco plants with high efficiency. By contrast, authentic RecA was not enriched in the nuclei of plant cells expressing comparable amounts of protein. For detailed characterisation of the strand-exchange activity of the nuclear-targeted RecA protein, a nearly identical protein was expressed in Escherichia coli and purified to homogeneity. This protein was found to bind to single-stranded DNA with the same stoichiometry and to promote the exchange of homologous DNA strands with the same kinetics as authentic RecA. It was concluded that the amino-terminal modification did not alter any of the essential properties of RecA and that the fusion protein is a fully functional strand-exchange protein. However, the ATPase activity of this protein was 20 times greater than that of RecA in the absence of single-stranded DNA. As with RecA, this activity was further stimulated by the addition of single-stranded DNA. Since ATPase activity is correlated with the ability of RecA to assume its high affinity state for DNA, the nuclear-targeted RecA protein might be regarded as a constitutively stimulated RecA variant, fully functional in promoting homologous recombination.

Adenosine Triphosphatases↗

PubMed1997

Chromosomal deletion complexes in mice by radiation of embryonic stem cells.

Chromosomal deletions ("deficiencies') are powerful tools in the genetic analysis of complex genomes. They have been exploited extensively in Drosophila melanogaster, an organism in which deficiencies can be efficiently induced and selected. Spontaneous deletions in humans have facilitated the dissection of phenotypes in contiguous gene syndromes and led to the positional cloning of critical genes. In mice, deletion complexes created by whole animal irradiation experiments have enabled a systematic characterization of functional units along defined chromosomal regions. However, classical mutagenesis in mice is logistically impractical for generating deletion sets on a genome-wide scale. Here, we report a high-throughput method for generating radiation-induced deletion complexes at defined regions in the genome using ES cells. Dozens of deletions of up to several centiMorgans, encompassing a specific locus, can be created in a single experiment and transmitted through the germline. The ability to rapidly create deletion complexes along chromosomes will facilitate systematic functional analyses of the mammalian genome.

Animals↗

PubMed1997

[Ultrasound biomicroscopy as a criterium of functional assessment of the supra-choroidal cleft after chamber angle surgical interventions].

BACKGROUND: The new technique of ultrasonic biomicroscopy provides detailed information about the extension and width of suprachoroidal clefts during the follow-up period after cyclodialysis ab interno. PATIENTS AND METHODS: We examined a group of 9 patients suffering from dysgenetic glaucoma and secondary glaucoma. Ultrasonic biomicroscopy was performed before and after cyclodialysis ab interno. The results were compared to those of gonioscopy. RESULTS: These examinations revealed that even cyclodialysis clefts which appeared to be closed by gonioscopy were still open. This was proven by a broad choroidal cleft in the cyclodialysis area. CONCLUSIONS: Thus, ultrasonic biomicroscopy is a means of checking the outcome of cyclodialysis ab interno and may influence the indications for further surgical procedures.

Adolescent↗

PubMed1997

[Endothelial cell loss after phacoemulsification with the "reversed tip and snip" technique compared with the "divide and conquer" technique].

BACKGROUND: The endothelial cell count after phakoemulsification is a sensitive parameter to compare different phakoemulsification techniques. PATIENTS AND METHOD: In a prospective study 30 patients in each group were operated upon the "Reversed Tip and Snip" and with the "Divide and Conquer"-Technique. The corneal endothelial cell count was measured before surgery and 4 weeks and 3 months after the operation. RESULTS: The endothelial cell count was reduced significantly about 10% after the the "Reversed Tip and Snip" and about 15% after the "Divide and Conquer"-Technique. The first mentioned technique had a significantly reduced cell loss than the latter. CONCLUSION: The "Reversed Tip and Snip" phakoemulsification technique causes less endothelial cell loss than the "Divide and Conquer"-Technique.

Aged↗

PubMed1996

RecA protein stimulates homologous recombination in plants.

A number of RecA-like proteins have been found in eukaryotic organisms. We demonstrate that the prokaryotic recombination protein RecA itself is capable of interacting with genomic homologous DNA in somatic plant cells. Resistance to the DNA crosslinking agent mitomycin C requires homologous recombination as well as excision repair activity. Tobacco protoplasts expressing a nucleus-targeted RecA protein were at least three times as efficient as wild-type cells in repairing mitomycin C-induced damage. Moreover, homologous recombination at a defined locus carrying an endogenous nuclear marker gene was stimulated at least 10-fold in transgenic plant cells expressing nucleus-targeted RecA. The increase in resistance to mitomycin C and the stimulation of intrachromosomal recombination demonstrate that Escherichia coli RecA protein is functional in genomic homologous recombination in plants, especially when targeted to the plant nucleus.

Agrobacterium tumefaciens↗

PubMed1996

[Glaucoma and aircraft pilot fitness].

Two completely different questions arise when considering glaucoma and fitness to fly: Firstly, what is the risk for a passenger with glaucoma? Secondly, what is the flight safety risk connected with pilots suffering from glaucoma? National requirements and international standards pay little regard to this disease. This is astonishing, given that the perception of flight information in the peripheral visual field is of great importance in the cockpit. On one hand, diagnostic glaucoma examinations for pilots are mainly insufficient, and on the other, progressive visual field deficiencies may go undetected because of long intervals between examinations. Intraocular pressure may increase while flying in aircraft, e.g. in the case of negative g-load. Frequent flights at high altitudes without pressurized cabin air and with decreased oxygen supply, and therefore decreased tissue oxygen saturation, may represent a risk, especially for patients with progressive nerve fibre loss.

Aircraft↗

PubMed1995

Experimental use of space-retaining substances with extended duration: functional and morphological results.

BACKGROUND: In glaucoma surgery, e.g. cyclodialysis ab interno, to date no viscous substances have been available that stay in the cyclodialysis cleft long enough to prevent scarring. We examined the qualities of two different viscoelastic substances that stay longer in the place of instillation than hyaluronic acid. METHODS: We performed cyclodialysis ab interno in 12 eyes of six owl monkeys. The right eyes were treated with the gel with the higher molecular weight, the left eyes using the gel with the lower molecular weight. The baseline data of intraocular pressure and outflow facility were compared to the values measured postoperatively up to the 140th day. Histological examination of the eyes followed. RESULTS: There was no statistically significant difference between the two substances. The mean intraocular pressure decrease was 7.9 (+/- 2.9) mmHg in the right eyes and 4.8 (+/- 2.7) mmHg in the left eyes. The histological examination showed that the gel had remained in the cyclodialysis cleft without signs of inflammation. In contrast to other viscoelastic substances studied previously, the substances in this study performed their space-retaining function without decreasing outflow facility. CONCLUSION: Both substances are suitable means of improving the rate of success of cyclodialysis ab interno, as they remain where they are instilled long enough to prevent wound scarring in the cyclodialysis cleft.

Animals↗

PubMed1995

[Corneal reinnervation after keratomileusis in situ and keratomileusis myopica--a comparison].

BACKGROUND: In a retrospective study corneal sensitivity after keratomileusis in situ and keratomileusis myopica was measured. METHOD: 5 points on the cornea were measured with the Draeger aesthesiometer at 18 eyes after keratomileusis myopica and at 66 eyes after keratomileusis in situ. RESULTS: The ingrowth of corneal nerve fibres is delayed after keratomileusis myopica compared to keratomileusis in situ because of delayed stromal repopulation of keratocytes and disturbances of stromal metabolism due to toxic effects of the cryopreservation solution.

Adolescent↗

PubMed1995

[Results of cyclodialysis combined goniotomy in treatment of dysgenetic glaucoma].

This study was performed in order to investigate the results of "cyclodialysis ab interno," i.e., a combination of goniotomy and cyclodialysis, in patients suffering from dysgenetic glaucoma. From 1985 to 1993, 69 patients (98 eyes) underwent at least one cyclodialysis ab interno. The development of intraocular pressure was examined 2 days, 4 weeks, 1/2 year, 1 year and 3 years postoperatively after the first and last cyclodialysis ab interno. Additionally, we examined intraoperative bleeding, preoperative pressure level, previous operations, reoperations, age at manifestation, and monocular or binocular manifestation for their influence on the results. The effect the operation had on visual acuity was also examined. One year after the last cyclodialysis ab interno, the IOP was regulated in 77% of the eyes. The prognosis was better for eyes with preoperative pressure values of less than 30 mmHg than for eyes with pressure values of more than 30 mmHg. It was also clearly better when the glaucoma had become manifest at the age of more than one year. Previous operations, intraoperative bleeding, and monocular or binocular manifestation had no influence on the results. In comparison with the data available for goniotomy and trabeculotomy, cyclodialysis ab interno shows a tendency for better results.

Adolescent↗

PubMed1995

[Cyclocryocoagulation in treatment of special types of glaucoma].

In this retrospective study, we examine the efficiency of cyclocryocoagulation in eyes with secondary and congenital glaucoma. We studied 137 eyes with advanced, inadequately controlled glaucoma, which were operated from 1984 to 1993. Besides the intraocular pressure (IOP), we assessed the effect on the visual acuity and the optic nerve. We also compared the efficiency of two different cryomethods (CO2/N2 cyclocryocoagulation). Fifty eyes were cyclocryocoagulated with CO2 and 87 with N2. After a period of 6 months, 90 eyes were regulated (IOP between 7 and 21 mm Hg). At this time the mean IOP was 16 mmHg, whereas it had been 40 mm Hg before the cyclocryocoagulation. Serious complications like a phthisis bulbi were seen in only 18 eyes. Five eyes became blind despite therapy because of an absolute glaucoma. Concerning the different types of glaucoma, the neovascular glaucoma was the most difficult type to regulate. We obtained better and more lasting results with N2 cyclocryocoagulation (68% regulation) than with CO2 cyclocryocoagulation (62% regulation). Thus, cyclocryocoagulation represents a good method for the treatment of advanced, inadequately controlled glaucoma eyes when other methods have failed.

Adult↗

PubMed1995

Reporter genes.

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Chloramphenicol O-Acetyltransferase↗

PubMed1994

[Surgical therapy of liver metastases. Therapeutic procedures, results and prognostic factors].

In a period of 7 years, 151 patients were treated by resection and/or regional chemotherapy after liver metastases from various primary tumours. The subgroup of patients with colorectal liver metastases was evaluated separately from the heterogeneous group with any other primaries. Radical resection of colorectal liver metastases was followed by a 5-year survival of 17%. The time from resection of the primary to development of the metastatic lesions was shown by univariate and multivariate analysis to be the most important prognostic factor. Adjuvant regional chemotherapy failed to improve outcome after curative resection of liver metastases. Neither palliative regional chemotherapy in cases of diffuse hepatic metastases nor the combination of palliative resection with regional or systemic chemotherapy significantly prolonged survival.

Adult↗

PubMed1994

[Reversible translimbal suture fixation of the ciliary body in treatment of ocular persistent hypotonia after surgical cyclodialysis].

UNLABELLED: After surgical or traumatical cyclodialysis dangerous hypotony can occur. In cases with peripheral anterior synechia the fixation of the ciliary body by reversible suture can bring about the desired pressure rise. PATIENTS: In nine eyes with persistent ocular hypotony after cyclodialysis 13 ciliary body fixations were performed. RESULTS: In four eyes the operation was successful. In two eyes a second operation was necessary. In two cases there was a high postoperative pressure rise. Cutting of the sutures led to a sudden decrease in pressure. In these eyes a second operation with slightly different fixation position was successful. One eye remained hypotonic. CONCLUSIONS: This operative technique entail only slight risk while having good results in patients with aphakia and extensive peripheral anterior synechia. During the early postoperative periods there is the opportunity to reverse the operative effect.

Adolescent↗

PubMed1993

Sympathetic transmission to the dilator muscle of the rat iris.

The responses of the dilator layer of the rat iris to sympathetic nerve stimulation were examined using intracellular recording techniques. Three different cell types were detected. In two of these, which were assumed to reflect recordings from myoepithelial cells, sympathetic nerve stimulation initiated excitatory junction potentials. These started after a delay of several hundred milliseconds and lasted for several seconds. The excitatory junction potentials were abolished by low concentrations of prazosin and were relatively insensitive to yohimbine, indicating that neurally released noradrenaline activated an alpha 1-adrenoceptor. The adrenoceptor was further characterised as being of the alpha 1b subtype using chlorethylclonidine. The time course of excitatory junction potentials was slowed when the preparation was cooled, suggesting that a second messenger pathway was being activated. The contractions triggered by sympathetic nerve stimulation persisted after excitatory junction potentials had been abolished by reducing the external concentration of chloride ions and after adding the organic calcium antagonist, nifedipine. Thus it seems likely that contractions of the dilator are triggered by the release of calcium ions from internal stores. These observations are discussed in relation to the idea that alpha 1b-adrenoceptors are coupled to a messenger pathway which involves inositol triphosphate and the pulsatile release of calcium ions from internal stores. The second section of the paper deals with the structure of neuro-myoepithelial contacts in the dilator layer. The majority of sympathetic varicosities formed organized neuroeffector junctions with either myoepithelial cells or melanophores. At the junctions the effector cell membrane and varicosity membrane were separated by less than 80 nm, with synaptic vesicles concentrated towards the neuroeffector junction. The synaptic vesicles in varicosities that failed to form junctions did not aggregate towards their regions of exposed membrane. These observations are discussed in relation to the idea that transmission at autonomic varicosities occurs at organised neuroeffector junctions.

Adrenergic alpha-Antagonists↗

PubMed1993

Sympathetic and parasympathetic neuromuscular junctions in the guinea-pig sino-atrial node.

The structure and organization of cholinergic and adrenergic varicosities in the sino-atrial node of the guinea-pig heart was determined by electron microscopy. When random sections of tissue were examined, some varicosities were found in close proximity (less than 90 nm) to a muscle cell, while others appeared to be some distance (greater than 90 nm) from the nearest muscle cell. When the organization of individual varicosities and their relationships with nearby cardiac muscle cells were determined by examining serial sections of tissue, it was found that most varicosities which lost all or part of their Schwann cell wrap formed close appositions with one or more cardiac muscle cells. At the regions of close apposition, the neuromuscular clefts were filled with a single layer of basal lamina, giving neuromuscular separations of about 80 nm. Although evidence of pre-synaptic or post-synaptic thickenings was not found, there was an accumulation of synaptic vesicles towards the regions of close apposition. These observations are discussed in relation to the idea that in a number of different tissues, most autonomic varicosities which lose part of their Schwann cell wrap, form organized neuromuscular junctions and that these junctions may be the sites of neuromuscular transmission.

Adrenergic Fibers↗