Identification of plant cytoskeletal, cell cycle-related and polarity-related proteins using Schizosaccharomyces pombe

The fission yeast Schizosaccharomyces pombe has been used to identify Arabidopsis thaliana proteins that may play a role in cell shape maintenance or cell cycle regulation. An Arabidopsis thaliana cDNA library was constructed in pREP5N vector under the control of the inducible nmt1 promoter and transformed into S. pombe. Expression of the A. thaliana sequences was induced and clones showing severe morphological changes were identified and analysed. Comparison of the sequences of the inserts with the sequence data bases revealed that several cDNAs encode proteins known to play a role in function of the cytoskeleton, the cell cycle and establishment of cell polarity. These include alpha-1, alpha-2, alpha-6 and beta-6 tubulins, myosin heavy chain-like protein, ubiquitin conjugating enzymes UBC9 (E2), 26S protease subunits, Ranbinding protein, myb protein, PRL1 gene product and rho protein. Approximately 30% of the clones encode novel sequences. The results suggest that S. pombe phenotypic screening can be used to identify plant proteins involved in cell shape maintenance and regulation during cell cycle and development.

Huntingtin is ubiquitinated and interacts with a specific ubiquitin-conjugating enzyme

Using the yeast two-hybrid system, we have identified a human ubiquitin-conjugating enzyme (hE2-25K) as a protein that interacts with the gene product for Huntington disease (HD) (Huntingtin). This protein has complete amino acid identity with the bovine E2-25K protein and has striking similarity to the UBC-1, -4 and -5 enzymes of Saccharomyces cerevisiae. This protein is highly expressed in brain and a slightly larger protein recognized by an anti-E2-25K polyclonal antibody is selectively expressed in brain regions affected in HD. The huntingtin-E2-25K interaction is not obviously modulated by CAG length. We also demonstrate that huntingtin is ubiquitinated. These findings have implications for the regulated catabolism of the gene product for HD.

Surface hydrophobic residues of multiubiquitin chains essential for proteolytic targeting

Ubiquitin conjugation is a signal for degradation of eukaryotic proteins by the 26S protease. Conjugation of a homopolymeric multiubiquitin chain to a substrate lysine residue results in 10-fold faster degradation than does conjugation of monoubiquitin, but the molecular basis of enhanced targeting by chains is unknown. We show that ubiquitin residues L8, I44, and V70 are critical for targeting. Mutation of pairs of these residues to alanine had little effect on attachment of ubiquitin to substrates but severely inhibited degradation of the resulting conjugates. The same mutations blocked the binding of chains to a specific subunit (S5a) of the regulatory complex of the 26S protease. The side chains implicated in this binding--L8, I44, and V70--form repeating patches on the chain surface. Thus, hydrophobic interactions between these patches and S5a apparently contribute to enhanced proteolytic targeting by multiubiquitin chains.

Simple equations used to study the wavelengths of two-segment bistable diode lasers

The physical fact that the competition between modes in homogeneously broadened media will eventually settle the overall gain down to the threshold level has been turned into an extra equation for the mathematical study of the wavelength-dependent rate equations applicable to two-segment bistable diode lasers. This has made the simultaneous determination of bistable laser operation parameters including the wavelength much simpler. Calculations of laser wavelength indicate that the switch-on and switch-off processes are accompanied by upward and downward wavelength chirps, respectively.

Chemical structure of sterols that activate oocyte meiosis

Gonadotrophins and various growth factors, but not sex steroids, can induce resumption of meiosis in vitro, but only in oocytes enclosed by cumulus-granulosa cells. Follicular purines prevent resumption of meiosis. This process can be overcome, in vitro, by a transient elevation of cyclic AMP resulting in the production of a diffusible meiosis-inducing substance secreted by the cumulus cells. A meiosis-inducing activity has been detected in gonads of different species, for example, in preovulatory follicular fluid of women and in mouse testes. We report here the isolation and characterization of meiosis-activating sterols from human follicular fluid and bull testes and the synthesis of two closely related C29 sterols. All these sterols induce a resumption of meiosis in cultured cumulus-enclosed and naked mouse oocytes indicating their nonspecificity across species and sex. This family of sterols is for the first time considered crucial to meiosis.

Studying semiconductor lasers with multimode rate equations

After the summation over terms that describe interactions between carriers and photons of various diode modes is worked out, implicit-form analytical solutions to the multimode rate equations of a semiconductor laser are obtained within the framework of the mean field approximation. With emphasis on the threshold region, several laser characteristics of importance, such as the carrier density, photon density, and output spectral width, have been investigated theoretically and experimentally.

Identifying the output spectra from end facets of semiconductor lasers

We report a simple way of determining the spontaneous-emission spectrum from the output spectrum directly detected at the end facet of a semiconductor laser and measuring the wavelength difference between the peaks of the gain and the spontaneous emission. This difference can be used to explain the blue shift of the peak wavelength of the output spectrum after the facets of the diode have been antireflection coated during the process of making a traveling-wave semiconductor amplifier.

Cumulus cells secrete a meiosis-inducing substance by stimulation with forskolin and dibutyric cyclic adenosine monophosphate

The role of the cumulus cells in initiating the resumption of meiosis after exposure to forskolin and dbcAMP was studied in the mouse. The resumption of meiosis was monitored by the percentage of germinal vesicle breakdown (GVBD) and polar body formation (PB). The cumulus-enclosed oocytes (CEO) and denuded oocytes (DO) were cultured with and without hypoxanthine (HX) in the culture medium. Three types of experiments were performed: (1) Effect of forskolin on spontaneous resumption of meiosis, i.e. cultures without HX, and two experiments in which HX is present throughout the culture: (2) Effect of transient exposure to forskolin or dibutyric-cyclic adenosinemonophosphate (dbcAMP) on GVBD prior to continued culture without forskolin or dbcAMP (oocyte priming). (3) Priming of CEO with forskolin for 2 hr, separation of cumulus cells and oocytes, followed by coculture of rejoined cumulus cells and oocytes, or coculture of the cumulus cells and new, unprimed DO. (1) Forskolin inhibited a spontaneous resumption of meiosis in a dose-dependent manner during the first 5 hr of culturing. After 22 hr all controls and CEO resumed meiosis, whereas only half of the DO did. (2) At least 1 hr of priming the CEO with forskolin is needed to induce GVBD and PB formation, but forskolin inhibited the resumption of meiosis when present for 24 hr. Similar results were obtained with a high concentration of dbcAMP. (3) A separation and rejoining of oocytes and cumulus cells after priming induced the resumption of meiosis in a significantly greater number of oocytes than in the control oocytes which were not primed.(ABSTRACT TRUNCATED AT 250 WORDS)

EMB30 is essential for normal cell division, cell expansion, and cell adhesion in Arabidopsis and encodes a protein that has similarity to Sec7

The EMB30 gene is involved in apical-basal pattern formation in the Arabidopsis embryo. Mutations in this locus produce mutants with a wide range of seedling phenotypes, but all of the mutants lack a root and a true hypocotyl. We have cloned the EMB30 gene, and it encodes a protein that has similarity to the yeast Sec7 protein and to two other open reading frames identified in clones from humans and C. elegans. We refer to the region of similarity among these four sequences as the Sec7 domain. The emb30-1 allele has a mutation in the Sec7 domain that alters a residue conserved in all four of these sequences, suggesting that this domain may be important for EMB30 function. Molecular data and microscopy studies of emb30 seedlings presented here indicate that EMB30 affects cell division, elongation, and adhesion and functions in seedling and adult plants as well as during embryogenic pattern formation.

Carrier deficit from the nominal threshold density and mode-suppression ratio of an above-threshold biased semiconductor laser

An analytical expression for the carrier deficit DeltaN from the nominal threshold carrier density N(t) of an above-threshold biased semiconductor laser has been deduced. As a result, both the mode spectra and the mode-suppression ratio of a semiconductor laser can be studied analytically. The measured dependence of the mode-suppression ratio on the wavelength difference between the gain peak and its nearest cavity mode of the semiconductor laser confirms the theoretical predictions.

In vitro studies on the effect of thromboxane receptor blockade on platelet deposition on vascular surfaces

The efficacy of platelet inhibition by a thromboxane receptor antagonist (Bay U3405) and acetylsalicylic acid was investigated in vitro using a new perfusion system. Rabbit 51Cr-labeled platelets were suspended in saline as perfusate. Vascular grafts, PTFE or Dacron (precoated with blood or uncoated) as well as native aorta were perfused in vitro. Three sets of grafts (vessels) were perfused simultaneously with either acetylsalicylic acid (10(-5) M), Bay U3405 (10(-6) M) treated or untreated (control) labeled platelets. Platelet deposition on the grafts (vessels) was measured in a gamma counter. Values were normalised to graft weight or vessel surface area respectively and to the platelet concentration of perfusate. The results of these experiments indicated that thromboxane receptor inhibition was superior to cyclooxygenase blockade in preventing platelet deposition on synthetic grafts and native aorta vessels in vitro. Whether this is valid in vivo has to be confirmed.

The impact of starch-powdered gloves on the formation of adhesions in rats

OBJECTIVE

To assess the influence of starch powdered surgical gloves on the postoperative formation of adhesions in a standard rat model.

DESIGN

Prospective, randomised, double-blind study.

MATERIAL

197 rats.

INTERVENTIONS

Abdominal cavity was exposed to gloves during the induction of adhesions and for an additional two minutes. Animals were operated on with the operator wearing either starch-powdered or powder-free gloves.

MAIN OUTCOME MEASURES

Formation of adhesions and starch particles present in the adhesions after one, three, 12, or 24 weeks.

RESULTS

When powdered gloves were worn the percentage of adhesions formed was significantly greater (n = 197, p < 0.01) than when powder-free gloves were worn. Starch particles were found in biopsy specimens from rats operated on with powdered gloves, but not when powder-free gloves were used.

CONCLUSION

Even the small amount of starch that settles in the abdominal cavity during an operation increases the amount of adhesions formed.

A locus involved in the regulation of replication in plasmid pSC101

The origin of replication of plasmid pSC101 contains three directly repeated sequences RS1, RS2, and RS3 separated by 22 bp from two palindromic sequences, IR1 and IR2, which are partially homologous to the direct repeats. These inverted repeat (IR) sequences overlap the promoter of the repA gene which encodes a protein essential for plasmid replication. We have shown that RepA binds to the RS sites as a monomer and to the IR sites as a dimer. The influence of the IR1 site, and of the DNA segment that separates it from RS3, on plasmid copy number control has been studied in detail. We show that the integrity of IR1 is essential for efficient replication and plasmid stability, the critical site extending to the left of IR1 proper. We also show that the presence of IR1 modifies profoundly the binding properties of purified RepA protein to a segment of DNA containing the RS sequences. IR1 is separated from its homologous site on RS3 by approximately four turns of the DNA helix. Replication is abolished if this distance is increased by half a turn of the helix but it is restored if the distance is increased by a whole turn. These results suggest a DNA looping interaction, in the initiation of replication, between the RepA dimer that binds IR1 and the RepA monomers that bind the RS sequences.

Effects of antioxidants and PAF receptor antagonist in intestinal shock in the rat

In a model of intestinal ischemia-reperfusion resulting in hypotension, mucosal lesions in the small intestine and mortality, the effects of a combination of superoxide dismutase (SOD) and catalase (cat) or a PAF receptor antagonist were tested. Intestinal ischemia was induced in rats and continued for 60 min. After this, the intestine was reperfused. A PAF receptor antagonist, BN 52021, was given 50 min before ischemia in one group, and SOD + cat was given 10 min before reperfusion in one group. One group received normal saline and one group were controls. Blood pressure, mucosal lesions, plasma volume, and endotoxin in plasma were determined up to 3 hr after reperfusion. Mortality was determined over 4 days. Endogenous endotoxin was not found in any of the groups, but the first types of SOD and cat used were contaminated with endotoxin, resulting in exogenous endotoxemia in animals which received those substances. Later endotoxin-free enzymes were used. Neither SOD + cat nor PAF antagonist had any effect on the hypotension or mucosal lesions. Plasma volume remained at the level of the control group after administration of either regimen. Mortality decreased in the group that received SOD + cat. The effects of SOD + cat indicate that free radicals were released in this model at reperfusion, and the effects of the PAF receptor antagonist indicate that PAF participates in membrane damage, but is an intermediary mechanism in the shock model used. The clearance of infused endotoxin from plasma was less effective in the shocked animals, possibly due to a shock effect on reticuloendothelial system (RES).(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo and in vitro studies of a copy number mutation of the RepA replication protein of plasmid pSC101

The RepA replication protein of plasmid pSC101 binds as a monomer to three repeated sequences (RS1, RS2, and RS3) in the replication origin of the plasmid to initiate duplication and binds as a dimer to two inversely repeated sequences (IR1 and IR2) in its promoter region (D. Manen, L. C. Upegui-Gonzalez, and L. Caro, Proc. Natl. Acad. Sci. USA 89:8923-8927, 1992). The binding to IR2 autoregulates repA transcription (P. Linder, G. Churchward, G. X. Xia, Y. Y. Yu, and L. Caro, J. Mol. Biol. 181:383-393, 1985). A mutation in the protein RepA(cop) that affects a single amino acid increases the plasmid copy number fourfold. In vivo experiments show that, when provided in trans under a foreign promoter, the RepA(cop) protein increases the replication of a plasmid containing the origin of replication without repA, whereas it decreases the repression of its own promoter. In vitro experiments show that the purified RepA(cop) protein binds more efficiently to the repeated sequences within the origin than does RepA and that its binding to these sequences is more specific than that of RepA. Binding to an inversely repeated sequence within the repA promoter gives opposite results: the wild-type protein binds efficiently to that sequence, whereas the mutated protein binds less efficiently and less specifically. Footprint experiments confirmed these results and, in addition, showed a difference in the pattern of protection of the inversely repeated sequences by the mutant protein. Equilibrium binding experiments showed that the formation of protein-probe complexes at increasing concentrations of protein had a sigmoidal shape for binding to RS sequences and a hyperbolic shape for binding to IR sequences. The results, together with earlier work (G.-X. Xia, D. Manen, T. Goebel, P. Linder, G. Churchward, and L. Caro, Mol. Microbiol. 5:631-640, 1991), confirm that the binding of RepA to RS sequences plays a crucial role in the regulation of plasmid replication and that its binding to IR sequences plays a role in the autoregulation of RepA expression. They also demonstrate that the two separate functions of the protein are effected by two different forms of binding to the target sites.

[Tetralogy of Fallot with absence of the left pulmonary artery]

Among 578 cases of Tetralogy of Fallot, 19 with absence left pulmonary artery were studied. When a patient has early and serious cyanosis and the stenosis of the outflow tract of right ventricle and/or the pulmonary artery is mild under echocardiographic examination, and at the same time, hemoglobin is markedly increased and SaO is rather low, the diagnosis of Tetralogy of Fallot with unilateral absence of pulmonary artery should be considered. The value of chest X-ray film is limited in this case. The diagnosis can be confirmed by selected angiography in the right ventricle which may reveal the anatomical deformity by the curved shadow or the drum-stick extremity in the left pulmonary artery.