Fate of Quasiparticles at High Temperature in the Correlated Metal Sr_{2}RuO_{4}

We study the temperature evolution of quasiparticles in the correlated metal Sr_{2}RuO_{4}. Our angle resolved photoemission data show that quasiparticles persist up to temperatures above 200 K, far beyond the Fermi liquid regime. Extracting the quasiparticle self-energy, we demonstrate that the quasiparticle residue Z increases with increasing temperature. Quasiparticles eventually disappear on approaching the bad metal state of Sr_{2}RuO_{4} not by losing weight but via excessive broadening from super-Planckian scattering. We further show that the Fermi surface of Sr_{2}RuO_{4}-defined as the loci where the spectral function peaks-deflates with increasing temperature. These findings are in semiquantitative agreement with dynamical mean field theory calculations.

Flat Γ Moiré Bands in Twisted Bilayer WSe_{2}

The recent observation of correlated phases in transition metal dichalcogenide moiré systems at integer and fractional filling promises new insight into metal-insulator transitions and the unusual states of matter that can emerge near such transitions. Here, we combine real- and momentum-space mapping techniques to study moiré superlattice effects in 57.4° twisted WSe_{2} (tWSe_{2}). Our data reveal a split-off flat band that derives from the monolayer Γ states. Using advanced data analysis, we directly quantify the moiré potential from our data. We further demonstrate that the global valence band maximum in tWSe_{2} is close in energy to this flat band but derives from the monolayer K states which show weaker superlattice effects. These results constrain theoretical models and open the perspective that Γ-valley flat bands might be involved in the correlated physics of twisted WSe_{2}.

Tomographic mapping of the hidden dimension in quasi-particle interference

Quasiparticle interference (QPI) imaging is well established to study the low-energy electronic structure in strongly correlated electron materials with unrivalled energy resolution. Yet, being a surface-sensitive technique, the interpretation of QPI only works well for anisotropic materials, where the dispersion in the direction perpendicular to the surface can be neglected and the quasiparticle interference is dominated by a quasi-2D electronic structure. Here, we explore QPI imaging of galena, a material with an electronic structure that does not exhibit pronounced anisotropy. We find that the quasiparticle interference signal is dominated by scattering vectors which are parallel to the surface plane however originate from bias-dependent cuts of the 3D electronic structure. We develop a formalism for the theoretical description of the QPI signal and demonstrate how this quasiparticle tomography can be used to obtain information about the 3D electronic structure and orbital character of the bands.

Effect of Surgical Approach on Node Harvest in Gastrectomy: Analysis of the National Cancer Database

BACKGROUND

Gastrectomy is the cornerstone of treatment for gastric cancer. Recent studies demonstrated significant surgical outcome advantages for patients undergoing minimally invasive versus open gastrectomy. Lymph node harvest is an indicator of adequate surgical resection, and greater harvest is associated with improved staging and patient outcomes. This study evaluated lymph node harvest based on surgical approach.

METHODS

Gastric adenocarcinoma patients were identified from NCDB who underwent gastrectomy between 2010 and 2016. Patients were classified by surgical approach into three cohorts: robotic, laparoscopic, or open gastrectomy. Clinical and demographic data were collected. Lymph node harvest was compared with univariate analysis and multivariable generalized linear mixed model. Univariate analysis with propensity matching was also performed to control for differences in patient population across cohorts.

RESULTS

We identified 10,690 patients that underwent gastrectomy for gastric adenocarcinoma, with 68% males and median age of 66 (IQR 5774) years. 7161 (67%) underwent open, 2841 (26.6%) laparoscopic, and 688 (6.4%) robotic gastrectomy. Multivariable analysis revealed robotic was associated with a significantly higher median node harvest (18, IQR 1326) compared to laparoscopic (17, IQR 1125) and open gastrectomy (16, IQR 1023). Laparoscopic was also associated with significantly higher node harvest then open gastrectomy. Propensity-matched analysis (6950 patients) showed robotic gastrectomy was still associated with significantly higher node harvest (18, IQR 1226) compared to laparoscopic (17, IQR 1125) and open (17, IQR 1124); however, laparoscopic and open were not significantly different.

CONCLUSION

Robotic approach is associated with increased node harvest compared to laparoscopic and open approach in gastrectomy patients.

Pure and Hybrid Deep Learning Models can Predict Pathologic Tumor Response to Neoadjuvant Therapy in Pancreatic Adenocarcinoma: A Pilot Study

BACKGROUND

Neoadjuvant therapy may improve survival of patients with pancreatic adenocarcinoma; however, determining response to therapy is difficult. Artificial intelligence allows for novel analysis of images. We hypothesized that a deep learning model can predict tumor response to NAC.

METHODS

Patients with pancreatic cancer receiving neoadjuvant therapy prior to pancreatoduodenectomy were identified between November 2009 and January 2018. The College of American Pathologists Tumor Regression Grades 0-2 were defined as pathologic response (PR) and grade 3 as no response (NR). Axial images from preoperative computed tomography scans were used to create a 5-layer convolutional neural network and LeNet deep learning model to predict PRs. The hybrid model incorporated decrease in carbohydrate antigen 19-9 (CA19-9) of 10%. Accuracy was determined by area under the curve.

RESULTS

A total of 81 patients were included in the study. Patients were divided between PR (333 images) and NR (443 images). The pure model had an area under the curve (AUC) of .738 (P < .001), whereas the hybrid model had an AUC of .785 (P < .001). CA19-9 decrease alone was a poor predictor of response with an AUC of .564 (P = .096).

CONCLUSIONS

A deep learning model can predict pathologic tumor response to neoadjuvant therapy for patients with pancreatic adenocarcinoma and the model is improved with the incorporation of decreases in serum CA19-9. Further model development is needed before clinical application.

Effect of Margin Status on Survival After Resection of Hilar Cholangiocarcinoma in the Modern Era of Adjuvant Therapies

INTRODUCTION

Studies have shown that for patients with hilar cholangiocarcinoma (HC), survival is associated with negative resection margins (R0). This requires increasingly proximal resection, putting patients at higher risk for complications, which may delay chemotherapy. For patients with microscopically positive resection margins (R1), the use of modern adjuvant therapies may offset the effect of R1 resection.

METHODS

Patients at our institution with HC undergoing curative-intent resection between January 2008 and July 2019 were identified by retrospective record review. Demographic data, operative details, tumor characteristics, postoperative outcomes, recurrence, survival, and follow-up were recorded. Patients with R0 margin were compared to those with R1 margin. Patients with R2 resection were excluded.

RESULTS

Seventy-five patients underwent attempted resection with 34 (45.3%) cases aborted due to metastatic disease or locally advanced disease. Forty-one (54.7%) patients underwent curative-intent resection with R1 rate of 43.9%. Both groups had similar rates of adjuvant therapy (56.5% vs. 61.1%, P = .7672). Complication rates and 30 mortality were similar between groups (all P > .05). Both groups had similar median recurrence-free survival (R0 29.2 months vs. R1 27.8 months, P = .540) and median overall survival (R0 31.2 months vs. R1 38.8 months, P = .736) with similar median follow-up time (R0 29.9 months vs. R1 28.5 months, P = .8864).

CONCLUSIONS

At our institution, patients undergoing hepatic resection for HC with R1 margins have similar recurrence-free and overall survival to those with R0 margins. Complications and short-term mortality were similar. This may indicate that with use of modern adjuvant therapies obtaining an R0 resection is not an absolute mandate.

Surgery Residents Spend Nearly 8 Months of Their 5-Year Training on the Electronic Health Record (EHR)

OBJECTIVE

Electronic health records (EHRs) are an integral part of the medical system and are used in all aspects of care. Despite multiple advantages of an EHR, concerns exist over the amount of time that residents spend on computers rather than in direct patient care. This study aims to quantify the time a general surgery resident spends on the EHR during their training.

DESIGN/PARTICIPANTS

Active usage time data from our institution's EHR were extracted for 34 unique general surgery residents from October 2014 to June 2019. Career time on the EHR was calculated and a "work month" was defined as a 4-week period of 80 hours per week.

SETTING

Carolinas Medical Center, Charlotte, NC.

RESULTS

Total career EHR usage for a general surgery resident was 2512 continuous hours, corresponding to 31.4 work weeks or 7.9 work months. In total, 7133 charts were opened with an average of 20.5 minutes on the EHR per patient chart. Career time spent on specific tasks included: chart review 10.6 work weeks, documentation 10.4 work weeks, and order entry 5.4 work weeks. The total number of orders entered were 57,739 and total number of documents created were 9222. EHR time in all aspects, patient charts opened, documents created, and number of orders entered decreased as postgraduate year increased.

CONCLUSIONS

This is the first study quantifying the total time a general surgery resident spends on the EHR during their clinical training. Total EHR time equated to nearly 8 work months. General surgery residents spend considerable time on the EHR and this underscores the importance of implementing methods to improve EHR efficiency and maximize time for clinical training.

Distractions During Patient Handoff: The Application-Based Messaging Volume on General Surgery Interns

OBJECTIVE

Mobile phone-based paging systems have become increasingly common for communication within hospitals. Surgical interns receive the most pages, and our aim is to objectively quantify and evaluate this burden to allow for targeted improvement.

DESIGN

We performed a retrospective review of our institutions mobile phone-based paging system data (Halo Health, Cincinnati, OH) from July 2019 to September 2019.

SETTING

Carolinas Medical Center, Charlotte, NC, USA.

PARTICIPANTS

Seven general surgery postgraduate year (PGY) 1 residents.

RESULTS

Forty-five thousand eight hundred and one messages met inclusion criteria, with 27,397 messages received and 18,404 sent. PGY 1 residents each received an average of 48 ± 41 messages per shift, with 8 ± 17 messages per day while off-duty. Night shifts averaged more messages than day shifts (80 ± 39 vs 38 ± 32, p < 0.0001), and had more shifts with high message volume (30% vs 11%, p = 0.0005). Evaluating the total number of messages received per minute of the day, the largest number of high-volume message intervals (21) occurred during patient handoff (1700-1900 hours). Most messages were sent by nursing staff (55.8%), followed by medical providers (38.2%).

CONCLUSIONS

PGY 1 residents receive a large number of pages using a messaging application, with many occurring at critical times. Residents received a higher volume of pages on night shifts, during patient handoff, and while off-duty. Since most pages are from nursing staff, targeted education and preventative actions may help decrease the volume of pages during these critical times.

Use of Artificial Intelligence Deep Learning to Determine the Malignant Potential of Pancreatic Cystic Neoplasms With Preoperative Computed Tomography Imaging

BACKGROUND

Society consensus guidelines are commonly used to guide management of pancreatic cystic neoplasms (PCNs). However, downsides of these guidelines include unnecessary surgery and missed malignancy. The aim of this study was to use computed tomography (CT)-guided deep learning techniques to predict malignancy of PCNs.

MATERIALS AND METHODS

Patients with PCNs who underwent resection were retrospectively reviewed. Axial images of the mucinous cystic neoplasms were collected and based on final pathology were assigned a binary outcome of advanced neoplasia or benign. Advanced neoplasia was defined as adenocarcinoma or intraductal papillary mucinous neoplasm with high-grade dysplasia. A convolutional neural network (CNN) deep learning model was trained on 66% of images, and this trained model was used to test 33% of images. Predictions from the deep learning model were compared to Fukuoka guidelines.

RESULTS

Twenty-seven patients met the inclusion criteria, with 18 used for training and 9 for model testing. The trained deep learning model correctly predicted 3 of 3 malignant lesions and 5 of 6 benign lesions. Fukuoka guidelines correctly classified 2 of 3 malignant lesions as high risk and 4 of 6 benign lesions as worrisome. Following deep learning model predictions would have avoided 1 missed malignancy and 1 unnecessary operation.

DISCUSSION

In this pilot study, a deep learning model correctly classified 8 of 9 PCNs and performed better than consensus guidelines. Deep learning can be used to predict malignancy of PCNs; however, further model improvements are necessary before clinical use.

The treatment sequence may matter in patients undergoing pancreatoduodenectomy for early stage pancreatic cancer in the era of modern chemotherapy

BACKGROUND

The aim of this study was to investigate outcomes associated with neoadjuvant chemotherapy in patients undergoing pancreatoduodenectomy for early stage pancreatic adenocarcinoma in the era of modern chemotherapy.

METHODS

The National Cancer Database (2010-2016) was queried for patients with clinical stage 0-2 pancreatic adenocarcinoma who underwent pancreatoduodenectomy. Patients who underwent up-front pancreatoduodenectomy were propensity matched to patients who received neoadjuvant chemotherapy. Postoperative outcomes, pathologic outcomes, and overall survival were compared.

RESULTS

A total of 2036 patients were in each group. Neoadjuvant chemotherapy was associated with shorter length of stay, lower 30-day readmission rate, and lower 30 and 90-day mortality rates (all p < 0.05). Neoadjuvant chemotherapy was associated with lower rates of positives nodes and positive resection margins (all p < 0.0001). Neoadjuvant chemotherapy was associated with longer survival (26.8 vs. 22.1months, p < 0.0001). Patients who received neoadjuvant chemotherapy followed by surgery and adjuvant therapy had the longest OS, followed by neoadjuvant + surgery, surgery + adjuvant therapy, and surgery alone (29.8 vs. 25.6 vs. 23.9 vs. 13.1 months; p < 0.0001).

CONCLUSIONS

Neoadjuvant chemotherapy is associated with improved postoperative outcomes, oncologic outcomes, and overall survival in patients with early stage pancreatic adenocarcinoma. Neoadjuvant chemotherapy should be considered in all patients with early stage pancreatic adenocarcinoma.

Factors Associated with Treatment and Survival of Early Stage Pancreatic Cancer in the Era of Modern Chemotherapy: An Analysis of the National Cancer Database

Background: Underutilization of operative management of early stage pancreatic cancer is associated with sociodemographic variables, including age, race, facility type, insurance, and education. It is currently unclear how these variables are associated with survival in patients who undergo surgery.

Methods: Patients with clinical stage I pancreatic adenocarcinoma were identified within the National Cancer Database (2010–2016). Utilization of surgery and nonoperative management was determined. Nonclinical factors associated with nonoperative management were identified by multivariable analysis. The association between nonclinical factors and survival was assessed in patients who received operative management.

Results: A total of 17,833 patients with clinical stage I pancreatic cancer were identified, and 41.2% underwent operative intervention. Approximately 46% of nonoperatively managed patients lacked a contraindication. Operatively managed patients had longer overall survival (OS) than those who were nonoperatively managed or untreated (25.1 months vs. 11.1 months vs. 5.1 months, p < 0.0001). Factors associated with nonoperative management included age, black/Hispanic race, nonacademic facilities, nonprivate health insurance, lower education level, and lower income. In operatively managed patients, nonclinical factors associated with lower OS included Medicaid (hazard ratio [HR] 1.27) and treatment at nonacademic facilities (HR 1.20–1.22). Patients on Medicaid received less adjuvant therapy and had higher 30- and 90-day mortality rates. Patients treated at nonacademic facilities received less neoadjuvant therapy, had worse pathologic outcomes, and had higher 30- and 90-day mortality rates.

Conclusions: Surgical management is underutilized in clinical stage I pancreatic cancer. Primary insurance payor and facility type appear to be associated with OS in patients who undergo operative management.

Improved oncologic outcomes for minimally invasive left pancreatectomy: Propensity-score matched analysis of the National Cancer Database

BACKGROUND AND OBJECTIVES

Minimally invasive (MIS) left pancreatectomy (LP) is increasingly used to treat pancreatic adenocarcinoma (PDAC). Despite improved short-term outcomes, no studies have demonstrated long-term benefits over open resection.

METHODS

The National Cancer Database was queried between 2010 and 2016 for patients with PDAC, grouped by surgical approach (MIS vs open). Demographics, comorbidities, clinical staging, and pathologic staging were used for propensity-score matching. Perioperative, short-term oncologic, and survival outcomes were compared.

RESULTS

After matching, both cohorts included 805 patients. There were no differences in baseline characteristics, staging, or preoperative therapy between cohorts. The MIS cohort had a shorter length of stay (6.8 ± 5.5 vs 8.5 ± 7.3 days; P < .0001) with the trend toward improved time to chemotherapy (53.9 ± 26.1 vs 57.9 ± 29.9 days; P = .0511) and margin-positive resection rate (15.3% vs 18.9%; P = .0605). Lymph node retrieval and receipt of chemotherapy were similar. The MIS cohort had higher median overall survival (28.0 vs 22.1 months; P = .0067). Subgroup analysis demonstrated the highest survival for robotic compared with laparoscopic and open LP (41.9 vs 26.6 vs 22.1 months; P < .0001).

CONCLUSIONS

This study demonstrates the safety of MIS LP and favorable long-term oncologic outcomes. The improved survival after MIS LP warrants further study with prospective, randomized trials.

Electronic health record usage among nurse practitioners, physician assistants, and junior residents

BACKGROUND

Studies demonstrate significant electronic health record (EHR) use by junior residents; however, few studies have investigated this for nurse practitioners and physician assistants (NPs/PAs).

PURPOSE

The aim of this study was to quantify the time spent on the EHR by NPs/PAs and junior residents.

METHODS

Electronic health record usage data were collected from April 2015 through April 2016. Monthly EHR usage was compared between NPs/PAs and postgraduate second and third year residents. Further subgroup analysis of NPs/PAs and residents from surgical or nonsurgical fields was conducted.

RESULTS

Data for 22 NPs/PAs (16 surgical and six nonsurgical) and 125 residents (31 surgical and 94 nonsurgical) were analyzed. Nurse practitioners/physician assistants opened fewer charts per day (4.9 ± 1.5 vs. 5.4 ± 3.1), placed more orders per month, and spent more daily time on the EHR (176.5 ± 51.7 minutes vs. 152.3 ± 71.9 minutes; p < .0001). Compared with residents, NPs/PAs spent more time per patient in all categories (chart review, documentation, order entry) and in total time per patient chart (all p < .05). Comparing surgical NPs/PAs to surgical residents, findings were similar with fewer charts per day, more total daily EHR time, and more EHR time per patient in every tracked category (all p < .05).

IMPLICATIONS FOR PRACTICE

This is the first study to quantify time on the EHR for NPs/PAs. Nurse practitioners/physician assistants spent more time on the EHR than residents, and this is accentuated with surgical NPs/PAs. Electronic health record utilization appears more burdensome for NPs/PAs; however, the reason for this is unclear and highlights the need for targeted interventions.

Publisher Correction: A weak topological insulator state in quasi-one-dimensional bismuth iodide

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Effect of Surgical Approach on Node Harvest in Robotic Gastrectomy

There has been increasing utilization of minimally invasive surgical approaches. This study evaluates the effect of surgical approach on total lymph node harvest in gastrectomy. Patients undergoing gastrectomy for gastric adenocarcinoma between 2007 and 2018 were reviewed retrospectively. Data collected included age, gender, race, BMI, neoadjuvant therapy, tumor stage, surgical approach, and total number of lymph nodes harvested. The total number of harvested lymph nodes for open, laparoscopic, and robotic gastrectomy was compared using the Kruskal-Wallis test for univariate analysis and a Poisson regression model for multivariable analysis. One hundred four patients were identified. Median node harvest for open, laparoscopic, and robotic approaches were 16, 17, and 36, respectively. Multivariable analysis controlling for gender, BMI, pathological T stage, and year of operation demonstrates that surgical approach is statistically significantly associated with lymph node harvest ( F = 83.4, P < 0.0001). In multivariable analysis, robotic approach was associated with greater lymph node harvest than both open ( P < 0.0001) and laparoscopic ( P < 0.0001) approaches, whereas laparoscopic approach was associated with greater lymph node harvest than open ( P < 0.0001) approach. These data demonstrate that for patients undergoing gastrectomy for gastric adenocarcinoma at our institution, robotic approach is associated with greater lymph node harvest than both laparoscopic and open approaches.

Effect of age on swallowing dysfunction after esophagectomy

455

Background: Patients undergoing esophagectomy frequently experience malnutrition, which in combination with the catabolic effects of surgery can result in loss of muscle mass and function. Safe swallowing requires the preservation of muscle mass. Modified barium swallow (MBS) enables assessment of postoperative swallowing impairments. We assessed the incidence and risk factors of swallowing dysfunction post-esophagectomy. Methods: Patients with a MBS post-esophagectomy were identified between January 2015-June 2019 at Levine Cancer Institute at Carolinas Medical Center. Swallowing was evaluated with the Penetration Aspiration Scale. Muscle loss was evaluated with pre-operative hand-grip strength (HGS) and skeletal muscle index (SMI) and skeletal muscle density (SMD) from axial CT images. Uni- and multivariable GLM analyses were performed. Results: 91 patients (79 men, 12 women) underwent esophagectomy with an average age of 64.0 + 10.1. Pre-operative HGS, SMI, and SMD all decreased with age. Significant differences existed between sexes in HGS, SMI, and SMD, so the cohort was stratified by sex for analysis. Univariate analysis of male patients revealed older age, lower body mass index (BMI), smoking history, prior feeding tube, and lower pre-operative HGS and SMI were associated with aspiration or penetration on MBS. Among women, no factors analyzed were significantly associated with swallowing dysfunction. Conclusions: Swallowing dysfunction after esophagectomy is correlated with increased age and lower BMI. The role of muscle loss in the risk of aspiration after esophagectomy is not clear. Further research is needed to determine the relationship between these factors with the goal of enabling preoperative physiologic optimization and patient selection. [Table: see text]

Preoperative muscle strength as a predictor of complications after esophagectomy

454

Background: Sarcopenia has been associated with post-operative complications and length of stay (LOS) in patients undergoing esophagectomy. A variety of methods exist to measure muscle mass and strength, with few comparisons between methods. We compared hand-grip strength (HGS), muscle mass and intramuscular adipose tissue as predictors of post-operative outcomes. Methods: Patients with esophageal cancer undergoing esophagectomy were identified between January 2015 – June 2019 at Levine Cancer Institute. Skeletal muscle index (SMI) and skeletal muscle density (SMD), a measure of intramuscular adipose tissue, were derived from CT. HGS was measured using a dynamometer. Uni- and multivariable GLM analyses were performed. Results: 115 patients (100 male, 15 female) underwent esophagectomy with an average age of 64.3 +/- 9.8. The analysis was stratified by sex due to significant differences in HGS, SMI, and SMD. Among men, univariable analysis revealed a significant association between pre-operative HGS <25 kg and increased risk of post-operative pneumonia ( p=0.02), ventilation >48hrs ( p=0.02), LOS ( p=0.002), discharge to home ( p=0.001), and one-year mortality ( p=0.005). All associations except discharge home remained significant in multivariable analyses (Table). Among women, no factors analyzed were significantly associated with postoperative outcomes. Conclusions: HGS is a more powerful predictor of postoperative complications and LOS than either muscle mass or intramuscular adipose tissue among men undergoing esophagectomy. HGS is cost-effective and easily incorporated into routine clinical care, allowing for preoperative intervention to optimize patients for esophagectomy. To better understand the implications in women, additional research with a larger cohort is needed. [Table: see text]

Weyl-like points from band inversions of spin-polarised surface states in NbGeSb

Band inversions are key to stabilising a variety of novel electronic states in solids, from topological surface states to the formation of symmetry-protected three-dimensional Dirac and Weyl points and nodal-line semimetals. Here, we create a band inversion not of bulk states, but rather between manifolds of surface states. We realise this by aliovalent substitution of Nb for Zr and Sb for S in the ZrSiS family of nonsymmorphic semimetals. Using angle-resolved photoemission and density-functional theory, we show how two pairs of surface states, known from ZrSiS, are driven to intersect each other near the Fermi level in NbGeSb, and to develop pronounced spin splittings. We demonstrate how mirror symmetry leads to protected crossing points in the resulting spin-orbital entangled surface band structure, thereby stabilising surface state analogues of three-dimensional Weyl points. More generally, our observations suggest new opportunities for engineering topologically and symmetry-protected states via band inversions of surface states.

Effect of Surgical Approach on Node Harvest in Robotic Gastrectomy

There has been increasing utilization of minimally invasive surgical approaches. This study evaluates the effect of surgical approach on total lymph node harvest in gastrectomy. Patients undergoing gastrectomy for gastric adenocarcinoma between 2007 and 2018 were reviewed retrospectively. Data collected included age, gender, race, BMI, neoadjuvant therapy, tumor stage, surgical approach, and total number of lymph nodes harvested. The total number of harvested lymph nodes for open, laparoscopic, and robotic gastrectomy was compared using the Kruskal-Wallis test for univariate analysis and a Poisson regression model for multivariable analysis. One hundred four patients were identified. Median node harvest for open, laparoscopic, and robotic approaches were 16, 17, and 36, respectively. Multivariable analysis controlling for gender, BMI, pathological T stage, and year of operation demonstrates that surgical approach is statistically significantly associated with lymph node harvest (F = 83.4, P < 0.0001). In multivariable analysis, robotic approach was associated with greater lymph node harvest than both open (P < 0.0001) and laparoscopic (P < 0.0001) approaches, whereas laparoscopic approach was associated with greater lymph node harvest than open (P < 0.0001) approach. These data demonstrate that for patients undergoing gastrectomy for gastric adenocarcinoma at our institution, robotic approach is associated with greater lymph node harvest than both laparoscopic and open approaches.

Crossover from lattice to plasmonic polarons of a spin-polarised electron gas in ferromagnetic EuO

Strong many-body interactions in solids yield a host of fascinating and potentially useful physical properties. Here, from angle-resolved photoemission experiments and ab initio many-body calculations, we demonstrate how a strong coupling of conduction electrons with collective plasmon excitations of their own Fermi sea leads to the formation of plasmonic polarons in the doped ferromagnetic semiconductor EuO. We observe how these exhibit a significant tunability with charge carrier doping, leading to a polaronic liquid that is qualitatively distinct from its more conventional lattice-dominated analogue. Our study thus suggests powerful opportunities for tailoring quantum many-body interactions in solids via dilute charge carrier doping.

Multiband One-Dimensional Electronic Structure and Spectroscopic Signature of Tomonaga-Luttinger Liquid Behavior in K_{2}Cr_{3}As_{3}

We present angle-resolved photoemission spectroscopy measurements of the quasi-one-dimensional superconductor K_{2}Cr_{3}As_{3}. We find that the Fermi surface contains two Fermi surface sheets, with linearly dispersing bands not displaying any significant band renormalizations. The one-dimensional band dispersions display a suppression of spectral intensity approaching the Fermi level according to a linear power law, over an energy range of ∼200  meV. This is interpreted as a signature of Tomonoga-Luttinger liquid physics, which provides a new perspective on the possibly unconventional superconductivity in this family of compounds.

Linear magnetoresistance caused by mobility fluctuations in n-doped Cd(3)As(2)

Cd(3)As(2) is a candidate three-dimensional Dirac semimetal which has exceedingly high mobility and nonsaturating linear magnetoresistance that may be relevant for future practical applications. We report magnetotransport and tunnel diode oscillation measurements on Cd(3)As(2), in magnetic fields up to 65 T and temperatures between 1.5 and 300 K. We find that the nonsaturating linear magnetoresistance persists up to 65 T and it is likely caused by disorder effects, as it scales with the high mobility rather than directly linked to Fermi surface changes even when approaching the quantum limit. From the observed quantum oscillations, we determine the bulk three-dimensional Fermi surface having signatures of Dirac behavior with a nontrivial Berry phase shift, very light effective quasiparticle masses, and clear deviations from the band-structure predictions. In very high fields we also detect signatures of large Zeeman spin splitting (g∼16).

Quasiparticle mass enhancement close to the quantum critical point in BaFe2(As(1-x)P(x))2

We report a combined study of the specific heat and de Haas-van Alphen effect in the iron-pnictide superconductor BaFe2(As(1-x)P(x))2. Our data when combined with results for the magnetic penetration depth give compelling evidence for the existence of a quantum critical point close to x=0.30 which affects the majority of the Fermi surface by enhancing the quasiparticle mass. The results show that the sharp peak in the inverse superfluid density seen in this system results from a strong increase in the quasiparticle mass at the quantum critical point.

de Haas-van Alphen study of the Fermi surfaces of superconducting LiFeP and LiFeAs

We report a de Haas-van Alphen oscillation study of the 111 iron pnictide superconductors LiFeAs with T(c) ≈ 18 K and LiFeP with T(c) ≈ 5 K. We find that for both compounds the Fermi surface topology is in good agreement with density functional band-structure calculations and has almost nested electron and hole bands. The effective masses generally show significant enhancement, up to ~3 for LiFeP and ~5 for LiFeAs. However, one hole Fermi surface in LiFeP shows a very small enhancement, as compared with its other sheets. This difference probably results from k-dependent coupling to spin fluctuations and may be the origin of the different nodal and nodeless superconducting gap structures in LiFeP and LiFeAs, respectively.

Prototypical single-molecule chemical-field-effect transistor with nanometer-sized gates

A prototypical single-molecule chemical-field-effect transistor is presented, in which the current through a hybrid-molecular diode is modified by nanometer-sized charge transfer complexes covalently linked to a molecule in an STM junction. The effect is attributed to an interface dipole which shifts the substrate work function by approximately 120 meV. It is induced by the complexes from electron acceptors covalently bound to the molecule in the gap and electron donors coming from the ambient fluid. This proof of principle is regarded as a major step towards monomolecular electronic devices.

Hippocampal nitric oxide upregulation precedes memory loss and A beta 1-40 accumulation after chronic brain hypoperfusion in rats

Chronic brain hypoperfusion (CBH) using permanent occlusion of both common carotid arteries in an aging rat model, has been shown to mimic human mild cognitive impairment (MCI), an acknowledged high risk condition that often converts to Alzheimer's disease. An aging rat model was used to determine whether hippocampal nitric oxide (NO) is abnormally expressed following CBH for two or eight weeks. At each time point, spatial memory was measured with the Morris water maze and hippocampal A beta 1-40/1-42 concentrations were obtained using sandwich ELISA. Real-time amperometric measures of NO representing the constitutive isoforms of neuronal nitric oxide synthase (nNOS) and endothelial (e)NOS were also taken at each time point to ascertain whether NO levels changed as a result of CBH, and if so, whether such NO changes preceded or followed any memory or amyloid-beta pathology. We found that two weeks after CBH, NO hippocampal levels were upregulated nearly four-fold when compared to nonoccluded rats but no alteration in spatial memory of A beta products were observed at this time point. By contrast, NO concentration had declined to control levels by eight weeks but spatial memory was found significantly impaired and A beta 1-40 (but not A beta 1-42) had increased in the CBH group when compared to control rats. Since changes in shear stress are known to upregulate eNOS but generally not nNOS, these results suggest that shear stress induced by CBH hyperactivated vascular NO derived from eNOS in the first two weeks as a reaction by the capillary endothelium to maintain homeostasis of local cerebral blood flow. The return of vascular NO to basal levels after eight weeks of CBH may have triggered metabolic changes within hippocampal cells resulting in hippocampal dysfunction as reflected by spatial memory impairment and by accumulation of A beta 1-40 peptide. In conclusion, our study shows that CBH initiates spatial memory loss in aging rats thus mimicking human MCI and also increases A beta 1-40 in the hippocampus. The memory and amyloid changes are preceded by NO upregulation in the hippocampus. These preliminary findings may be important in understanding, at least in part, the molecular mechanisms that precede memory impairment during chronic brain ischemia and as such, the pre-clinical stage leading to Alzheimer's disease.

Disruption and basic phenotypic analysis of six novel genes from the right arm of chromosome XII of Saccharomyces cerevisiae

Six open reading frames (ORFs) of unknown function from the right arm of Saccharomyces cerevisiae chromosome XII were deleted in two genetic backgrounds by disruption cassettes with regions of short flanking homology. This work was carried out within the framework of the EUROFAN consortium. The SFH disruption cassettes, obtained by PCR, were made by amplification of the kanMX marker module with oligonucleotides containing approximately 40 bp of homology to either the promoter or translation terminator regions of the relevant ORF. Transformants resistant to geneticin (G418) were selected. The SFH disruption cassettes were cloned into a bacterial vector. Each cognate gene was also cloned into a yeast centromeric plasmid. Sporulation and tetrad analysis of the disrupted heterozygous strains revealed that ORF YLR153c (now known as ACS2) is essential. Basic phenotypic analysis was performed on haploid deletants of both mating types of the five non-essential ORFs, YLR082c (now known as SRL2), YLR149c, YLR151c, YLR152c and YLR154c. Plate growth tests on different media at 15 degrees C, 30 degrees C and 37 degrees C did not reveal any significant differences between parental and mutant cells. Mating and sporulation efficiencies were not affected in any of the viable disruptants as compared to wild-type cells.

Current awareness on yeast

In order to keep subscribers up-to-date with the latest developments in their field, this current awareness service is provided by John Wiley & Sons and contains newly-published material on yeasts. Each bibliography is divided into 10 sections. 1 Books, Reviews & Symposia; 2 General; 3 Biochemistry; 4 Biotechnology; 5 Cell Biology; 6 Gene Expression; 7 Genetics; 8 Physiology; 9 Medical Mycology; 10 Recombinant DNA Technology. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted. (4 weeks journals - search completed 3rd Jan. 2001)

The role of complement in Alzheimer's disease pathology

Complement proteins are integral components of amyloid plaques and cerebral vascular amyloid in Alzheimer brains. They can be found at the earliest stages of amyloid deposition and their activation coincides with the clinical expression of Alzheimer's dementia. This review will examine the origins of complement in the brain and the role of beta-amyloid peptide (Abeta) in complement activation in Alzheimer's disease, an event that might serve as a nidus of chronic inflammation. Pharmacology therapies that may serve to inhibit Abeta-mediated complement activation will also be discussed.

Traumatic brain injury elevates the Alzheimer's amyloid peptide A beta 42 in human CSF. A possible role for nerve cell injury

The increased risk for Alzheimer's Disease (AD) associated with traumatic brain injury (TBI) suggests that environmental insults may influence the development of this age-related dementia. Recently, we have shown that the levels of the beta-amyloid peptide (A beta 1-42) increase in the cerebrospinal fluid (CSF) of patients after severe brain injury and remain elevated for some time after the initial event. The relationships of elevated A beta with markers of blood-brain barrier (BBB) disruption, inflammation, and nerve cell or axonal injury were evaluated in CSF samples taken daily from TBI patients. This analysis reveals that the rise in A beta 1-42 is best correlated with possible markers of neuronal or axonal injury, the cytoskeletal protein tau, neuron-specific enolase (NSE), and apolipoprotein E (ApoE). Similar or better correlations were observed between A beta 1-40 and the three aforementioned markers. These results imply that the degree of brain injury may play a decisive role in determining the levels of A beta 1-42 and A beta 1-40 in the CSF of TBI patients. Inflammation and alterations in BBB may play lesser, but nonetheless significant, roles in determining the A beta level in CSF after brain injury.

Xenopus NK cells identified by novel monoclonal antibodies

Early-thymectomized (Tx) Xenopus frogs, which are permanently deficient in T cells, are used as a model sytem for the characterization of novel monoclonal antibodies (mAb) which identify candidate NK cells at the amphibian level of evolution. Hybridomas, generated from mice immunized with splenocytes from Tx Xenopus following B cell and thrombocyte depletion, were screened by flow cytometry. Three mAb (1F8, 4D4 and 1G5) were identified that stained increased proportions of splenocytes from Tx compared with control frogs. These mAb identified lymphoid populations from Xenopus spleen, liver and gut which, after 48 h culture in growth factor-rich medium, exhibited spontanous killing of MHC-deficient allotumor targets. mAb-defined splenocytes also rapidly induced apoptosis of such tumor targets. Dual color analysis confirmed that NK cells are neither T nor B cells. Cytospins of splenocytes isolated with anti-NK mAb revealed large lymphoid cells with distinct pseudopodia. Immunohistology indicated each anti-NK mAb routinely labeled cells within the gut epithelium but NK cells were difficult to visualize in spleen sections. Western blotting of spleen, liver and intestinal lysates subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis showed that 1G5 reacted strongly with protein bands of approximately 70 - 85 kDa, whereas mAb 1F8 and 4D4 stained less intensely, but identified similar protein bands.

Inhibitors of V-type ATPases, bafilomycin A1 and concanamycin A, protect against beta-amyloid-mediated effects on 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction

The functional viability of cells can be evaluated using a number of different assay determinants. One common assay involves exposing cells to 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), which is converted intracellularly to a colored formazan precipitate and often used to assess amyloid peptide-induced cytotoxic effects. The MTT assay was employed to evaluate the role of endosomal uptake and lysosomal acidification in amyloid peptide-treated differentiated PC12 cell cultures using selective vacuolar-type (V-type) ATPase inhibitors. The macrolides bafilomycin A1 (BAF) and concanamycin A (CON) block lysosomal acidification through selective inhibition of the V-type ATPase. Treating nerve growth factor-differentiated PC12 cells with nanomolar concentrations of BAF or CON provides complete protection against the effects of beta-amyloid peptides Abeta(1-42), Abeta(1-40), and Abeta(25-35) and of amylin on MTT dye conversion. These macrolides do not inhibit peptide aggregation, act as antioxidants, or inhibit Abeta uptake by cells. Measurements of lysosomal acidification reveal that the concentrations of BAF and CON effective in reversing Abeta-mediated MTT dye conversion also reverse lysosomal pH. These results suggest that lysosomal acidification is necessary for Abeta effects on MTT dye conversion.

Benzenesulfonamide derivatives of 2-substituted 4H-3,1-benzoxazin-4-ones and benzthiazin-4-ones as inhibitors of complement C1r protease

A series of 2-sulfonyl-4H-3,1-benzoxazinones was prepared that inhibit C1r protease in vitro. Several compounds were found to be selective for C1r verses the related serine protease trypsin. Selected compounds demonstrated functional activity in a hemolysis assay.

T-cell and natural killer cell development in thymectomized Xenopus

The Xenopus early-thymectomy model system is used to investigate the extent to which the thymus controls T-cell development and to probe the evolution of natural killer (NK) cells. Loss of T-cell function following thymectomy, together with the paucity of cells expressing monoclonal antibody-defined T-cell surface markers, and greatly reduced expression of T-cell receptor beta transcripts in spleen, liver and intestine, indicate that T-cell development in minimal in the absence of the thymus. Our findings therefore mitigate against the idea that a substantial extrathymic pathway of T-cell development exists in early vertebrate evolution. Rather, they suggest that in this amphibian representative T cells are predominately thymus dependent. In vitro studies with control and thymectomized Xenopus splenocytes reveal that a non-T/non-B population and also two T-cell subsets all display natural cytotoxicity towards allogeneic thymus lymphoid tumour cells (which are deficient in MHC antigen expression). Since Xenopus thymectomized early in larval development are permanently deficient in T cells, they may provide a useful phylogenetic model for the study of NK cells.

Traumatic brain injury increases beta-amyloid peptide 1-42 in cerebrospinal fluid

The beta-amyloid peptides, A beta1-42 and A beta1-40, were quantified in ventricular CSF taken daily for up to 3 weeks from six individuals with severe traumatic brain injury (TBI). There was considerable interindividual variability in the levels of A beta peptides, but in general A beta1-42 levels equalled or exceeded those of A beta1-40. Averaging the daily totals of our trauma cohort revealed that the levels of A beta1-42 and A beta1-40 rose after injury, peaking in the first week and then declining toward control levels over the next 2 weeks. A beta1-42 levels were on average two to three times higher in the trauma cohort than in CSF from nontrauma samples. Compared with nontrauma samples, the A beta1-40/A beta1-42 ratio decreased about fivefold in the trauma patients, further indicative of increased A beta1-42 levels. The ratio remained low at all time points studied. No change was measured in the levels of beta-amyloid precursor protein during the same interval. These results suggest that A beta1-42 becomes elevated in the CSF after severe brain trauma.

Natural cytotoxicity towards allogeneic tumour targets in Xenopus mediated by diverse splenocyte populations

We have recently demonstrated NK-like activity in the spleen of the clawed frog, Xenopus laevis. This paper investigates the cellular basis of this natural cytotoxicity. Significant levels of cytotoxicity towards B3B7 allogeneic thymus tumour targets, that express neither class Ia nor class II MHC proteins, occurred after splenocytes from either control or early-thymectomized (Tx) year-old Xenopus were cultured for 48 hours. Killing by Tx cells required their culture in growth factor-rich medium (GFM) obtained from concanavalin A-stimulated cells. Immunomagnetic cell sorting revealed that cytotoxic effectors in both control and Tx frogs were found in the B cell-depleted population, but never in the B cell-enriched fraction. Splenocytes from control Xenopus, depleted of T cells by magnetic sorting and following culture in GFM, also developed natural cytotoxicity towards allotumour cells. Magnetic cell sorting also revealed that purified (CD5+) T cells cultured for 48 hours in GFM also became able to lyse the allogeneic tumour targets. Cytotoxicity mediated by T cells resided not only in the CD5+, CD8+ population, but also in the CD5+, CD8- (putative CD4+) T cell subset. Ontogenetic studies revealed that splenocytes from 6-7 week-old (stage 56-57) control larvae, even after 48 hr culture in GFM, were unable to spontaneously lyse the allotumour targets, whereas cultured splenocytes from 6 month old froglets were effective killers. Thymocytes from larvae or adults routinely failed to kill tumour cells. The work highlights the need to use Tx Xenopus to further explore non-T-cell-mediated, NK-like cytotoxicity at the amphibian level of evolution.

Inhibiting the formation of classical C3-convertase on the Alzheimer's beta-amyloid peptide

Amyloid plaques are the pathological hallmark of Alzheimer Disease (AD) brains, being found primarily in the hippocampus and neocortex, where AD pathology is most evident. Complement activation is associated with amyloid plaques which are made from fibrils of aggregated amyloid peptides, 39-42 amino acids long. In vitro studies show that aggregated amyloid peptides activate complement via the classical pathway, implying that amyloid plaques themselves cause complement activation in AD brains. In order to test this hypothesis, we sought to determine if a major peptide component of amyloid plaques, A beta 1-42, supports the formation of the classical pathway C3 convertase. Using normal human serum depleted of C3, we are able to detect C3 convertase activity on aggregated A beta 1-42 in vitro. The convertase activity is associated with the binding of C1q and activation of C4 on the aggregated peptide. Inhibitors of C1 esterase and the cation chelator EGTA both block the formation of the convertase activity. Congo red, a histochemical stain for amyloid deposits and an inhibitor of amyloid aggregation, reduces C3 convertase activity on aggregated A beta 1-42, indicated by decreased C3a production. Our results provide further evidence that aggregated A beta 1-42 alone is sufficient to serve as a nidus for complement activation, and thus may be involved directly in initiating the inflammation seen in AD brains.

NK-like activity against allogeneic tumour cells demonstrated in the spleen of control and thymectomized Xenopus

This paper addresses the issue of natural killer (NK) cell evolution by searching for NK-like activity in an amphibian representative, the immunologically well-characterized clawed frog, Xenopus laevis. Using in vitro 6 h 51chromium release assays, we have shown that splenocyte effectors from early thymectomized (Tx) year-old frogs, but not from control siblings, are able to spontaneously lyse allogeneic thymus tumour cell lines that lack MHC antigen expression. Such lytic capacity can be readily induced in control Xenopus and elevated in Tx frogs by a single injection of tumour cells, with maximal splenocyte cytotoxicity occurring 3 days postinjection, the amount of 51Cr-release correlating directly with effector: target ratios. Splenocytes, even those from tumour-injected frogs, are unable to lyse allogeneic splenic lymphoblasts or erythrocyte targets, even when the latter are coated with IgY (the Xenopus IgG equivalent); moreover, we were unable to demonstrate any splenocyte-induced lysis of the human NK cell target K562. Lymphokine-activated killing (LAK) in Xenopus is suggested, since Tx splenocytes cultured in cytokine-rich medium (from concanavalin A-stimulated control splenocytes) display significantly elevated killing of allogeneic tumour targets. Flow cytometric analysis highlights the loss of T cell markers from the spleen of Tx frogs and reveals a variable staining pattern of both control and Tx splenocytes when treated with a mAb that binds to both fish non-specific cytotoxic cells and human NK cells. Prospects for identifying the cellular basis of NK-like activity in Xenopus are discussed in the light of these experiments.

The Pisum sativum MAP kinase homologue (PsMAPK) rescues the Saccharomyces cerevisiae hog1 deletion mutant under conditions of high osmotic stress

Previous analysis of the MAP kinase homologue from Pisum sativum (PsMAPK) revealed a potential MAP kinase motif homologous to that found in eukaryotic cdc2 kinases. Sequence comparison showed a 47% identity on amino acid sequence basis to the Saccharomyces cerevisiae Hog1p MAP kinase involved in the osmoregulatory pathway. Under conditions of salt-stress aberrant morphology of a hog1 deletion mutant was completely restored and growth was partially restored by expression of the PsMAPK. This shows that PsMAPK is functionally active as a MAP kinase in S. cerevisiae. Comparison of PsMAPK with other kinases involved in osmosensitivity, showed a high degree of homology and implicates a possible role for PsMAPK in a P. sativum osmosensing signal transduction pathway.

Popliteal vein thrombosis causing compartment syndrome: a case report

Compartment syndrome as a result of venous thrombosis is an uncommon occurrence. Generally, phlegmasia cerulea dolens or proximal venous thrombosis results in elevated compartment pressures. Distal venous occlusion rarely is reported as a cause of compartment syndrome. This is a case report of an otherwise healthy patient in whom popliteal vein thrombosis developed and resulted in elevation > 40 mm Hg of 3 leg muscle compartments requiring fasciotomies.

Isolation and characterisation of a maize cDNA that complements a 1-acyl sn-glycerol-3-phosphate acyltransferase mutant of Escherichia coli and encodes a protein which has similarities to other acyltransferases

We selected cDNA plasmid clones that corrected the temperature-sensitive phenotype of Escherichia coli strain JC201, which is deficient in 1-acyl-sn-glycerol-3-phosphate acyltransferase activity. A plasmid-based maize endosperm cDNA library was used for complementation and a plasmid that enabled the cells to grow at 44 degrees C on ampicillin was isolated. Addition of this plasmid (pMAT1) to JC201 restored 1-acyl-sn-glycerol-3-phosphate acyltransferase activity to the cells. Total phospholipid labelling showed that the substrate for the enzyme, lysophosphatidic acid, accumulated in JC201 and was further metabolised to phosphatidylethanolamine in complemented cells. Membranes isolated from such cells were able to convert lysophosphatidic acid to phosphatidic acid in acyltransferase assays. The cDNA insert of pMAT1 contains one long open reading frame of 374 amino acids which encodes a protein of relative molecular weight 42,543. The sequence of this protein is most similar to SLC1, which is thought to be able to acylate glycerol at the sn-2 position during synthesis of inositol-containing lipids. Homologies between the SLC1 protein, the 1-acyl-sn-glycerol-3-phosphate acyltransferase of E. coli (PlsC) and the maize ORF were found with blocks of conserved amino acids, whose spacing was conserved between the three proteins, identifiable.

Differential, temporal and spatial expression of genes involved in storage oil and oleosin accumulation in developing rapeseed embryos: implications for the role of oleosins and the mechanisms of oil-body formation

The temporal and spatial expression of oleosin and delta 9-stearoyl-ACP desaturase genes and their products has been examined in developing embryos of rapeseed, Brassica napus L. var. Topas. Expression of oleosin and stearate desaturase genes was measured by in situ hybridisation at five different stages of development ranging from the torpedo stage to a mature-desiccating embryo. The temporal pattern of gene expression varied dramatically between the two classes of gene. Stearate desaturase gene expression was relatively high, even at the torpedo stage, whereas oleosin gene expression was barely detectable at this stage. By the stage of maximum embryo fresh weight, stearate desaturase gene expression had declined considerably while oleosin gene expression was at its height. In contrast to their differential temporal expression, the in situ labelling of both classes of embryo-specific gene showed similar, relatively uniform patterns of spatial expression throughout the embryo sections. Immunogold labelling of ultra-thin sections from radicle tissue with anti-oleosin antibodies showed similar patterns to sections from cotyledon tissue. However, whereas at least three oleosin isoforms were detectable on western blots of homogenates from cotyledons, only one isoform was found in radicles. This suggests that some of the oleosin isoforms may be expressed differentially in the various types of embryo tissue. The differential timing of stearate desaturase and oleosin gene expression was mirrored by similar differences in the timing of the accumulation of their ultimate products, i.e. storage oil and oleosin proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence for a dual osmoregulatory mechanism in the yeast Saccharomyces cerevisiae

Osmoadaptation in S. cerevisiae occurs through intracellular accumulation of glycerol in response to an increase in osmolarity of the surrounding environment. Analysis of ssv1-2, a strain carrying a mutation in a gene required for vacuole biogenesis, protein-sorting and osmohomeostasis, shows that the strain is terminally inactivated by 1.5 M NaCl within 10 seconds while the isogenic wild type maintains slow growth and accumulates glycerol within 18 hours. This study provides the first evidence that the vacuole participates in an immediate osmoregulatory process permitting survival until the osmoadaptive glycerol accumulation allows growth under osmotically unfavorable conditions.

Targeting of oleosins to the oil bodies of oilseed rape (Brassica napus L.)

Oleosins of Brassica napus L. (oilseed rape) synthesized by in-vitro translation were found to be very efficiently targeted to microsomal membranes but only poorly translocated to oil bodies or emulsified oil. The use of other bilayer membranes as controls showed that this interaction was specific. The rate of oleosin synthesis in the presence of microsomes was enhanced about threefold, indicative of the involvement of the signal-recognition particle in the targeting process. There is no evidence for the cleavage of the protein during targeting and the protein sequence reveals no consensus cleavage site for the signal peptide. Protection experiments using Proteinase K revealed that about 6 kDa of the protein is exposed on the cytoplasmic side of the ER but the remainder is protected. Carbonate (pH 11) washing of microsomal membranes after in-vitro translation confirmed that oleosins have a domain which remains inserted in the ER rather than the protein being transported completely into the lumen of the ER. These results indicate that oleosins are transported via the ER prior to their accumulation on oil bodies.