In vivo and photophysical studies on photooxidative damage to lens proteins and their protection by radioprotectors

Photooxidation, whether initiated by an endogenous or exogenous sensitizer, is an important mechanism in light induced damage to the lens. One of the substrates for this damage is lens protein. A porphyrin sensitizer which binds to lens proteins [mesotetra(p-sulfonatophenyl) porphyrin (TPPS)] was found to photooxidize Skh-2 pigmented mice lens protein in vivo. Uroporphyrin, a model for a non-binding photosensitizer, did not induce photooxidative damage to the mouse lens. The radioprotector 3-amino-2-hydroxypropyl phosphorothioate (WR-77913) was investigated as an agent to retard or negate in vivo photooxidative damage to the lens. Intraperitoneal injections of WR-77913 prior to irradiation reduced the TPPS induced photodestruction of lens protein in Skh-2 pigmented mice. The mechanism of protection was also investigated. Thiols were found to quench both the triplet state of porphyrins and the reactive intermediate singlet oxygen on the order of 10(5) and 10(6) M-1 s-1 respectively. These are probably not fast enough to explain most of the protection afforded by thiols. An additional mechanism may be the accelerated photobleaching of porphyrins by thiols which protects tissue by reducing the absorptions due to the porphyrins.

An evaluation of triple-lumen catheter infections using a guidewire exchange technique

One hundred fifty-six triple-lumen central venous catheters placed into 65 different sites in 52 surgical or trauma patients were prospectively evaluated to determine the frequency of catheter-related infection and the efficacy of multiple guidewire exchanges. Thirty-four anatomic sites in 33 patients without clinical signs of sepsis were compared to 31 anatomic sites in 19 patients with a clinical diagnosis of sepsis based on clinical, microbiologic, and radiologic evaluation. Anatomic sites were used indefinitely unless a positive semiquantitative catheter culture (greater than or equal to 15 cfu) or catheter-associated bacteremia developed. Seven catheter-related infections developed in five septic patients (26.3%) while no infections developed in the nonseptic group (p = 0.004). Three of 31 anatomic sites (9.6%) were associated with bacteremia. The number of hospital days to initial catheter insertion and the length of catheter site use were considerably higher in the septic patients compared to the nonseptic group. We conclude that triple-lumen catheter-related infections are uncommon in patients with no evidence of infection and can be safely guidewire-exchanged to prolong site use. Catheter-related infections in septic patients are much more frequent and unpredictable. Although guidewire exchange has a role in septic patients, multiple exchanges cannot routinely be recommended.

Inducible ribosomal RNA methylation in Streptomyces lividans, conferring resistance to lincomycin

Streptomyces lividans TK21 possesses inducible ribosomal RNA methylase activity that confers high-level resistance to lincomycin and lower levels of resistance to certain macrolides. The methylase gene (designated lrm) is inducible by erythromycin and other macrolides and also by celesticetin (a lincosamide) but not by lincomycin. The lrm enzyme monomethylates the N6-amino group of adenosine at position 2058 within 23S-like ribosomal RNA.

Elimination of multivalents during meiotic prophase in Scilla autumnalis. II. Tetraploid

The pairing behaviour of chromosomes during meiotic prophase in two Scilla autumnalis tetraploids was investigated by observing synaptonemal complexes from serial sections and whole-mount surface spreads. In one of the tetraploids with the genomic constitution AAB7B7 pairing at first metaphase of meiosis is restricted to homologous chromosomes and only bivalents appear. In the second tetraploid, AB7B7B7, some multivalents are found at first metaphase, but most of the configurations are bivalent. The bivalents, however, result from chiasma formation between homoeologous as well as homologous chromosomes. Both tetraploids show extensive multivalent formation at zygotene. The transformation of these multivalents to bivalents is described and interpreted in the two tetraploid forms.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination, polyploids.

Elimination of multivalents during meiotic prophase in Scilla autumnalis. I. Diploid and triploid

The ultrastructure and pairing behaviour of the chromosomes of two diploid cytotypes and a triploid of Scilla autumnalis were investigated using the techniques of three-dimensional reconstruction from serial electron micrographs and whole-mount surface spreading of synaptonemal complexes. The diploids, designated AA and B7B7, have karyotypes that are virtually identical in appearance at mitotic metaphase but differ in length by 47% and in DNA content by 66%. All the chromosomes were identified during meiotic prophase in both diploids, enabling construction of accurate karyotypes, which were the same as those derived from root tip metaphases. Chromosome pairing was largely regular with very few structural chromosome rearrangements. These two observations permitted confident interpretations of multivalent configurations observed in polyploids containing multiples of the A and B7 genomes. In the triploid (AB7B7) during meiotic prophase lateral components are associated in groups of three, either as trivalents with several exchanges of pairing partners, or as bivalents and univalents in close alignment. The overall difference in length between A and B7 chromosomes is close to expected, but varies to some degree depending on the extent of pairing between the two chromosome types. Most of the synaptonemal complexes between A and B7 homoeologues are ineffective in terms of chiasma formation, as revealed by the low frequency of multivalents and heteromorphic bivalents at metaphase I. In other words, there is an elimination of multivalents during meiotic prophase in the triploid.Key words: Scilla autumnalis, synaptonemal complex, multivalents, elimination.

Molecular cloning of multiple xylanase genes from Pseudomonas fluorescens subsp. cellulosa

Pseudomonas fluorescens subsp. cellulosa was shown to express extracellular xylanases. Genes encoding these enzymes were isolated from a gene library of P. fluorescens subsp. cellulosa DNA, constructed in bacteriophage lambda 47.1. One of the phages (PXC) that expressed xylanase also conferred the ability to hydrolyse carboxymethylcellulose. An 11.8 kb HindIII DNA restriction fragment and a 6.2 kb EcoRI DNA fragment were subcloned from two distinct xylanase-expressing phages, into pUC18, to yield recombinant plasmids pGHJ4 and pGHJ5 respectively. Cells of Escherichia coli harbouring either of these two plasmids, or plasmid pJHH1 (comprising the cellulase gene from PXC, previously cloned on a 7.3 kb partial EcoRI DNA fragment in pUC18), expressed xylanase activity. The positions of the xylanase genes in the recombinant plasmids were elucidated by subcloning and transposon mutagenesis. In pJHH1 the xylanase gene was adjacent to the DNA region encoding the endoglucanase. The polysaccharide-degrading genes in pJHH1 were transcribed from different promotors. Hybridization studies revealed that the xylanase genes encoded by pGHJ4 and pGHJ5 showed strong homology. All three cloned enzymes cleaved p-nitrophenyl beta-D-glucopyranoside and 4-methylumbelliferyl beta-D-cellobioside. Xylan and glucose did not affect expression of xylanase in E. coli strains harbouring pJHH1, pGHJ4 or pGHJ5.

Effects of hypervitaminosis A on the bone and mineral metabolism of the rat

Vitamin A toxicity has been associated with alterations in mineral metabolism and may result in osteopenia, fractures, deformities, and growth arrest. The pathogenesis of the bone lesions that occur in vitamin A toxicity is, however, ill defined and was examined in the present study. The administration of pharmacological doses of vitamin A to growing male rats resulted in weakness and spontaneous fractures. Undecalcified bone histology of vitamin A toxic animals was characterized by increased bone resorption, osteoclastosis, a paucity of trabecular surfaces covered with osteoid, and lesions which appear to be pathognomonic of hypervitaminosis A. The serum calcium and magnesium levels of vitamin A-toxic animals were unremarkable, but serum phosphate levels were significantly higher than control values. Urinary hydroxyproline excretion reflected bone histology and was significantly increased in experimental rats. Circulating levels of the potent bone resorbers, PTH, 1,25-dihydroxyvitamin D, and 25-hydroxyvitamin D, were, however, comparable in vitamin A-toxic and control animals, suggesting a possible direct effect of vitamin A on bone. Subsequently, the effects of vitamin A (retinol) on in vitro collagen synthesis (incorporation of [3H]proline into collagen) and bone resorption (45Ca release from bone) were examined using a fetal rat calvarial culture. Retinol added to the culture medium for 20-24 h in concentrations ranging from 0.5-10 micrograms/ml selectively inhibited collagen synthesis in a dose-dependent fashion. Higher concentrations of retinol were toxic and resulted in a general inhibition of protein synthesis. Bone resorption was stimulated by 0.5 and 2.5 micrograms/ml retinol. We conclude that vitamin A toxicity in rats causes bone lesions, the genesis of which can be explained, at least in part, by a direct effect of the vitamin on skeletal tissue.

Evidence for multiple carboxymethylcellulase genes in Pseudomonas fluorescens subsp. cellulosa

A genomic library of Pseudomonas fluorescens subsp. cellulosa DNA was constructed in bacteriophage lambda 47.1 and recombinants expressing carboxymethylcellulase (CMCase) activity isolated. A 7.3 kb partial EcoRI fragment, a 9.4 kb EcoRI fragment and a 5.8 kb HindIII fragment were subcloned from three different phages into pUC18 to yield recombinant plasmids pJHH1, pJHH3 and pGJH2 respectively. Cells of Escherichia coli harbouring these plasmids expressed CMCase activity. The positions of the CMCase genes in the three plasmids were determined by subcloning and transposon mutagenesis. pJHH1 contained two distinct DNA regions encoding CMCases, which were controlled by the same promoter. All four cloned enzymes cleaved p-nitrophenyl-beta-D-glucopyranoside, although at a very low rate, but none exhibited exoglucanase activity. In common with other extracellular enzymes cloned in E. coli, all the CMCases were exported to the periplasmic space in the enteric bacterium. The carboxymethylcellulase genes encoded by pJHH1 and pJHH3, were subject to glucose repression in E. coli.

Chromosome pairing in a Lolium temulentum X Lolium perenne diploid hybrid with a low chiasma frequency

Despite an average difference of about 50% in DNA amount, homoeologous chromosomes pair effectively at first metaphase in the diploid interspecific hybrid between Lolium temulentum and Lolium perenne. However, in the presence of accessory B chromosomes and "diploidising genes" pairing at metaphase I is severely reduced. Reconstruction of serial electron micrographs through pollen mother cell nuclei show that synaptonemal complexes are formed at pachytene between not only homoeologous but also non-homologous chromosome segments resulting in multivalent formation. These associations are largely ineffective in terms of chiasma formation and degenerate at late pachytene. It is highly probable that the pairing determinants exercise their control on chromosome pairing largely by prohibiting the siting of crossovers in homoeologously paired chromosome segments.

Quantitative DNA variation and chromosome homology

In many genera, of both plants and animals, divergence and speciation is often accompanied by massive changes in the amount of nuclear DNA. These changes, in turn, result from amplification or repetition of base sequences within the chromosomal DNA. The chromosomes of different species are consequently of different size and structure. Observations in hybrids between species differing in nuclear DNA amount show that, despite large differences in DNA content, homoeologous chromosomes pair effectively at pachytene and form chiasmata. Only when the DNA differences are very large, of the order of 60% or more, is pairing at pachytene and chiasma formation impaired. The conclusion is that large scale chromosome structural change due to the repetition of DNA base sequences has surprisingly little effect upon the homology of chromosomes, i.e. their ability to pair effectively and form chiasmata at meiosis. Similar repetitive sequences are frequently distributed widely among non-homologous chromosomes within complements. The question then arises as to what prevents chiasma formation between the non-homologous chromosomes which have in common DNA segments of similar sequences? Evidence is presented which indicates that prevention is under the control of the genotype. The control is effected in one of two ways, either by the suppression of pairing at zygotene or pachytene or by suppression of chiasma formation subsequent to pairing.

Stress and coping among hospice nurses: test of an analytic model

Nursing is a profession with high levels of occupational stress, especially for those employed in hospice settings. This study considered the stressors, mediators, and adaptations evident among 100 hospice nurses from 20 facilities. The research tested an analytic model of stress that included social and predisposing conditioning factors, stress appraisals, coping strategies, social resources, and adaptive status. Entered as sets in a hierarchical regression analysis, stress appraisals and coping strategies proved to be the best predictors of adaptive status. Social resources exerted a more indirect influence.

The intranuclear relationship between centromere volume and chromosome size in Festuca scariosa X drymeja

In the hybrid Festuca scarisoa X drymeja where pairing is incomplete at pachytene, there is preferential pairing between the longer chromosomes of the complement. EM serial-section reconstruction of nuclei at zygotene and pachytene reveals that there is equally pronounced preferential pairing between larger centromeres. This evidence suggests that the longer chromosomes have large centromeres and that centromere volume is correlated with chromosome length. Confirmation of this comes from the comparison of the frequency distributions of observed centromere volumes and those predicted on the basis of chromosome length. Although there is a positive correlation between centromere volume and chromosome length, it is not possible to identify the centromeres of each individual chromosome within the complement because (a) the differences between the lengths of each chromosome are small and (b) the estimates of relative centromere volumes vary significantly between cells.

The relationship between nuclear DNA content and centromere volume in higher plants

The total volume of centromeres per nucleus varies widely within Triticum aestivum cv. Chinese Spring (7-fold) and between 11 higher plant species (24-fold). Such variation is closely correlated with nuclear DNA content, nuclear volume and, to a lesser extent, the total volume of nucleoli per nucleus. Centromere volume reflects minor intraspecific developmental fluctuations in nuclear size independent of variation in nuclear DNA content, but variation in nuclear DNA plays the major role in determining centromere volume. Thus, in general a given total volume of centromeric material is apparently characteristic of an approximately constant nuclear volume and mass of nuclear DNA, but largely independent of chromosome number. The range of volume of single centromeres in 4 taxa corresponds with the ranges of their single chromosome lengths or chromosome DNA contents. The centromere is, therefore, not a unit structure of constant size and mass but a chromosome segment whose highly variable volume closely reflects the volume and mass of the chromosome to which it belongs. The correlation between centromere size and chromosome size and DNA content is potentially useful for identifying single centromeres in unsquashed interphase and dividing nuclei; thereby facilitating studies of the intranuclear disposition of chromosomes. The present results for centromeres provide probably the first example to indicate that variation in the total DNA content of small segments present on each chromosome sometimes varies directly in proportion to large interspecific variation in nuclear DNA C-value. The close correlation between centromere volume, and nuclear DNA content is probably nucleotypic in origin. The functional significance of the variation in centromere volume is unknown, as is the nature of the mechanism which determines that centromere volume closely reflects nuclear and chromosome size and mass.

An improved methodology for the extraction and partial purification of porcine hypothalamic corticotrophin releasing factor

In most previous reports material with corticotrophin releasing factor (CRF) activity has been obtained from hypothalami after extraction with dilute aqueous acid. Such conditions allow substantial proteolytic degradation. By adopting conditions designed to precipitate proteases and by using information on the nature of CRF gained from earlier studies, rapid large scale extraction and partial purification of porcine hypothalamic CRF in high yield was achieved. After extraction with 0.2 m-HCl; acetone (1:1, v/v), centrifugation and ultrafiltration, considerable preliminary purification of the CRF activity was achieved by adsorption onto carboxymethylcellulose and subsequent elution at increased salt concentration. Following ion-exchange chromatography of the extract on carboxymethylcellulose, CRF activity was obtained in good yield (minimal effective dose of about 1-2 micrograms/ml) for ACTH release in an in-vitro CRF bioassay utilizing a coupled isolated pituitary cell-adrenal cell system. The data indicated that the previously reported heterogeneous corticotrophin releasing factors of low activity may be a consequence of proteolytic degradation.