Legumain/asparaginyl endopeptidase-resistant tau fibril fold produces corticobasal degeneration-specific C-terminal tau fragment.

Corticobasal degeneration (CBD) is a major four-repeat tauopathy along with progressive supranuclear palsy (PSP). Although detergent-insoluble 37-40-kDa carboxyl-terminal tau fragments (CTFs) are hallmarks of CBD pathology, the process of their formation is unknown. This study monitored the formation of CBD-type fibrils that exhibit astrocytic plaques, a characteristic CBD pathology, using its biochemical properties different from those of Alzheimer's disease/PSP-type fibrils. Tau fibrils from patients with CBD were amplified in non-astrocytic cultured cells, which maintained CBD-specific biochemical properties. We found that the lysosomal protease Legumain (LGMN) was involved in the generation of CBD-specific 37-40-kDa CTFs. While LGMN cleaved tau fibrils at Asn167 and Asn368 in the brain tissues of patients with Alzheimer's disease and PSP, tau fibrils from patients with CBD were predominantly resistant to cleavage at Asn368 by LGMN, resulting in the generation of CBD-specific CTFs. LGMN preference in tau fibrils was lost upon unraveling the tau fibril fold, suggesting that the CBD-specific tau fibril fold contributes to CBD-specific CTF production. From these findings, we found a way to differentiate astrocytic plaque from tufted astrocyte using the anti-Asn368 LGMN cleavage site-specific antibody. Inoculation of tau fibrils amplified in non-astrocytic cells into the mouse brain reproduced LGMN-resistant tau fibrils and recapitulated anti-Asn368-negative astrocytic plaques, which are characteristic of CBD pathology. This study supports the existence of disease-specific tau fibrils and contribute to further understanding of the tauopathy diagnosis. Our tau propagation mouse model using cellular tau seeds may contribute to uncovering disease mechanisms and screening for potential therapeutic compounds.

Clinical characteristics and pathophysiological properties of newly discovered LRRK2 variants associated with Parkinson's disease.

Leucine-rich repeat kinase 2 (LRRK2) is the most common gene responsible for familial Parkinson's disease (PD). The gene product of LRRK2 contains multiple protein domains, including armadillo repeat, ankyrin repeat, leucine-rich repeat (LRR), Ras-of-complex (ROC), C-terminal of ROC (COR), kinase, and WD40 domains. In this study, we performed genetic screening of LRRK2 in our PD cohort, detecting sixteen LRRK2 rare variants. Among them, we selected seven variants that are likely to be familial and characterized them in terms of LRRK2 protein function, along with clinical information and one pathological analysis. The seven variants were S1120P and N1221K in the LRR domain; I1339M, S1403R, and V1447M in the ROC domain; and I1658F and D1873H in the COR domain. The kinase activity of the LRRK2 variants N1221K, S1403R, V1447M, and I1658F toward Rab10, a well-known phosphorylation substrate, was higher than that of wild-type LRRK2. LRRK2 D1873H showed enhanced self-association activity, whereas LRRK2 S1403R and D1873H showed reduced microtubule-binding activity. Pathological analysis of a patient with the LRRK2 V1447M variant was also performed, which revealed Lewy pathology in the brainstem. No functional alterations in terms of kinase activity, self-association activity, and microtubule-binding activity were detected in LRRK2 S1120P and I1339M variants. However, the patient with PD carrying LRRK2 S1120P variant also had a heterozygous Glucosylceramidase beta 1 (GBA1) L444P variant. In conclusion, we characterized seven LRRK2 variants potentially associated with PD. Five of the seven variants in different LRRK2 domains exhibited altered properties in kinase activity, self-association, and microtubule-binding activity, suggesting that each domain variant may contribute to disease progression in different ways.

Ligation of left gastric vein may cause delayed gastric emptying after pancreatoduodenectomy: a retrospective study.

BACKGROUND: This study aimed to determine which running pattern of the left gastric vein (LGV) is most frequently ligated in subtotal stomach-preserving pancreatoduodenectomy (SSPPD) and how LGV ligation affects delayed gastric emptying (DGE) after SSPPD. METHODS: We retrospectively analysed 105 patients who underwent SSPPD between January 2016 and September 2021. We classified the running pattern of LGV as follows: type 1 runs dorsal to the common hepatic artery (CHA) or splenic artery (SpA) to join the portal vein (PV), type 2 runs dorsal to the CHA or SpA and joins the splenic vein, type 3 runs ventral to the CHA or SpA and joins the PV, and type 4 runs ventral to the CHA or SpA and joins the SpV. Univariate and multivariate analyses were used to identify differences between patients with and without DGE after SSPPD. RESULTS: Type 1 LGV running pattern was observed in 47 cases (44.8%), type 2 in 23 (21.9%), type 3 in 12 (11.4%), and type 4 in 23 (21.9%). The ligation rate was significantly higher in type 3 (75.0%) LGVs (p < 0.0001). Preoperative obstructive jaundice (p = 0.0306), LGV ligation (p < 0.0001), grade B or C pancreatic fistula (p = 0.0116), and sepsis (p = 0.0123) were risk factors for DGE in the univariate analysis. Multivariate analysis showed that LGV ligation was an independent risk factor for DGE (odds ratio: 13.60, 95% confidence interval: 3.80-48.68, p < 0.0001). CONCLUSION: Type 3 LGVs are often ligated because they impede lymph node dissection; however, LGV preservation may reduce the occurrence of DGE after SSPPD.

A new method using a vessel-sealing system provides coagulation effects to various types of bleeding with less thermal damage.

BACKGROUND: Hemostasis is very important for a safe surgery, particularly in endoscopic surgery. Accordingly, in the last decade, vessel-sealing systems became popular as hemostatic devices. However, their use is limited due to thermal damage to organs, such as intestines and nerves. We developed a new method for safe coagulation using a vessel-sealing system, termed flat coagulation (FC). This study aimed to evaluate the efficacy of this new FC method compared to conventional coagulation methods. METHODS: We evaluated the thermal damage caused by various energy devices, such as the vessel-sealing system (FC method using LigaSure™), ultrasonic scissors (Sonicision™), and monopolar electrosurgery (cut/coagulation/spray/soft coagulation (SC) mode), on porcine organs, including the small intestine and liver. Furthermore, we compared the hemostasis time between the FC method and conventional methods in the superficial bleeding model using porcine mesentery. RESULTS: FC caused less thermal damage than monopolar electrosurgery's SC mode in the porcine liver and small intestine (liver: mean depth of thermal damage, 1.91 ± 0.35 vs 3.37 ± 0.28 mm; p = 0.0015). In the superficial bleeding model, the hemostasis time of FC was significantly shorter than that of electrosurgery's SC mode (mean, 19.54 ± 22.51 s vs 44.99 ± 21.18 s; p = 0.0046). CONCLUSION: This study showed that the FC method caused less thermal damage to porcine small intestine and liver than conventional methods. This FC method could provide easier and faster coagulation of superficial bleeds compared to that achieved by electrosurgery's SC mode. Therefore, this study motivates for the use of this new method to achieve hemostasis with various types of bleeds involving internal organs during endoscopic surgeries.

Lamellipodium tip actin barbed ends serve as a force sensor.

Cells change direction of migration by sensing rigidity of environment and traction force, yet its underlying mechanism is unclear. Here, we show that tip actin barbed ends serve as an active "force sensor" at the leading edge. We established a method to visualize intracellular single-molecule fluorescent actin through an elastic culture substrate. We found that immediately after cell edge stretch, actin assembly increased specifically at the lamellipodium tip. The rate of actin assembly increased with increasing stretch speed. Furthermore, tip actin polymerization remained elevated at the subsequent hold step, which was accompanied by a decrease in the load on the tip barbed ends. Stretch-induced tip actin polymerization was still observed without either the WAVE complex or Ena/VASP proteins. The observed relationships between forces and tip actin polymerization are consistent with a force-velocity relationship as predicted by the Brownian ratchet mechanism. Stretch caused extra membrane protrusion with respect to the stretched substrate and increased local tip polymerization by >5% of total cellular actin in 30 s. Our data reveal that augmentation of lamellipodium tip actin assembly is directly coupled to the load decrease, which may serve as a force sensor for directed cell protrusion.

Convection-Induced Biased Distribution of Actin Probes in Live Cells.

Fluorescent markers that bind endogenous target proteins are frequently employed for quantitative live-cell imaging. To visualize the actin cytoskeleton in live cells, several actin-binding probes have been widely used. Among them, Lifeact is the most popular probe with ideal properties, including fast exchangeable binding kinetics. Because of its fast kinetics, Lifeact is generally believed to distribute evenly throughout cellular actin structures. In this study, however, we demonstrate misdistribution of Lifeact toward the rear of lamellipodia where actin filaments continuously move inward along the retrograde flow. Similarly, phalloidin showed biased misdistribution toward the rear of lamellipodia in live cells. We show evidence of convection-induced misdistribution of actin probes by both experimental data and physical models. Our findings warn about the potential error arising from the use of target-binding probes in quantitative live imaging.

Postoperative acute exacerbation of interstitial pneumonia in pulmonary and non-pulmonary surgery: a retrospective study.

BACKGROUND: Acute exacerbation of interstitial pneumonia (AE-IP) is a serious complication of pulmonary surgery in patients with IP. However, little is known about AE-IP after non-pulmonary surgery. The aim of this study was to determine the frequency of AE-IP after non-pulmonary surgery and identify its risk factors. METHODS: One hundred and fifty-one patients with IP who underwent pulmonary surgery and 291 who underwent non-pulmonary surgery were retrospectively investigated. RESULTS: AE-IP developed in 5 (3.3%) of the 151 patients in the pulmonary surgery group and 4 (1.4%) of the 291 in the non-pulmonary surgery group; the difference was not statistically significant. A logistic regression model showed that serum C-reactive protein (CRP) was a predictor of AE-IP in the non-pulmonary surgery group (odds ratio 1.187, 95% confidence interval 1.073-1.344, P = 0.002). CONCLUSIONS: This is the first study to compare the frequency of AE-IP after pulmonary surgery with that after non-pulmonary surgery performed under the same conditions. The results suggest that the frequency of AE-IP after non-pulmonary surgery is similar to that after pulmonary surgery. A high preoperative C-reactive protein level is a potential risk factor for AE-IP after non-pulmonary surgery.

New Concept for a Thoracic Drainage System Using Magnetic Actuation.

Objectives. Thoracic drainage is a common procedure to drain fluid, blood, or air from the pleural cavity. Some attempts to develop approaches to new thoracic drainage systems have been made; however, a simple tube is often currently used. The existing drain presupposes that it is placed correctly and that the tip does not require moving after insertion into the thoracic cavity. However, in some cases, the drain is not correctly placed and reinsertion of an additional drain is required, resulting in significant invasiveness to the patient. Therefore, a more effective drainage system is needed. This study aimed to develop and assess a new thoracic drain via a collaboration between medical and engineering personnel. Methods. We developed the concept of a controllable drain system using magnetic actuation. A dry laboratory trial and accompanying questionnaire assessment were performed by a group of thoracic and general surgeons. Objective mechanical measurements were obtained. Porcine experiments were also carried out. Results. In a dry laboratory trial, use of the controllable drain required significantly less time than that required by replacing the drain. The average satisfaction score of the new drainage system was 4.07 out of 5, indicating that most of the research participants were satisfied with the quality of the drain with a magnetic actuation. During the porcine experiment, the transfer of the tip of the drain was possible inside the thoracic cavity and abdominal cavity. Conclusion. This controllable thoracic drain could reduce the invasiveness for patients requiring thoracic or abdominal cavity drainage.

Neuromelanin imaging and midbrain volumetry in progressive supranuclear palsy and Parkinson's disease.

Background Nigral degeneration patterns differ between PSP and PD. However, the relationship between nigral degeneration and midbrain atrophy in PSP remains unclear. Objective We analyzed differences and relationships between nigral degeneration and midbrain atrophy in PSP and PD. Methods Neuromelanin-sensitive MRI and midbrain volumetry were performed in 11 PSP patients, 24 PD patients, and 10 controls to measure the neuromelanin-sensitive SNpc area and midbrain volume. Results The neuromelanin-sensitive SNpc area and midbrain volume were significantly smaller in PSP patients compared with PD patients and controls. Motor deficits were inversely correlated with neuromelanin-sensitive SNpc area in PD, but not PSP patients. There was no significant correlation between neuromelanin-sensitive SNpc area and midbrain volume in either disease group. Midbrain volumetry discriminated PSP from PD. Diagnostic accuracy was improved when neuromelanin-sensitive MRI analysis was added. Conclusions Neuromelanin-sensitive MRI and midbrain volumetry may reflect the clinical and pathological characteristics of PSP and PD. Combining neuromelanin-sensitive MRI and midbrain volumetry may be useful for differentiating PSP from PD. © 2018 International Parkinson and Movement Disorder Society.

Neoadjuvant Chemoradiotherapy for Patients with cT3/Nearly T4 Esophageal Cancer: Is Sarcopenia Correlated with Postoperative Complications and Prognosis?

BACKGROUND: Since the clinical impact of sarcopenia on multimodal therapy for patients with esophageal cancer is not well understood, this study was conducted to determine the influence of sarcopenia on the efficacy of neoadjuvant chemoradiotherapy (NACRT) for locally advanced esophageal cancer. METHODS: The skeletal muscle index was quantified at the level of the third lumbar vertebra on computed tomography images, and sarcopenia was defined as a skeletal muscle index that was less than the average for each gender. We compared treatment outcomes in patients with cT3 and nearly T4 thoracic esophageal squamous cell carcinoma between the sarcopenia group (n = 85) and the non-sarcopenia group (n = 72). RESULTS: The 5-year survival rates were 33.4% in the non-sarcopenia group and 31.5% in the sarcopenia group; these differences were not significant. The prognosis of the patients with sarcopenia was worse than that of the patients without sarcopenia in the surgery-alone group, but there was no difference between patients with and without sarcopenia in the NACRT group. CONCLUSIONS: NACRT could be a useful option for patients with locally advanced esophageal squamous cell carcinoma, even for those with sarcopenia, without increasing the incidence of morbidity and mortality.

Sarcopenia is an independent predictor of complications after colorectal cancer surgery.

PURPOSE: The significance of sarcopenia after colorectal cancer (CRC) resection has only been discussed with relatively small samples or short follow-up periods. This study aimed to clarify the clinical significance of sarcopenia in a large-sample study. METHODS: We retrospectively analyzed the relationship between sarcopenia and clinical factors, surgical outcomes, and the survival in 494 patients who underwent CRC surgery between 2004 and 2013. Sarcopenia was defined based on the sex-specific skeletal muscle mass index measured by preoperative computed tomography. RESULTS: Sarcopenia was associated with sex (higher rate of male, P < 0.0001), and low body mass index (P < 0.0001), but not age or tumor stage. Sarcopenia was associated with higher incidence of all postoperative complications (P = 0.02), especially for patients with Clavien-Dindo classification grade ≥2 (CDC; P = 0.0007). Postoperative hospital stays were significantly longer for sarcopenic patients than for non-sarcopenic patients (P = 0.02). In a multivariate analysis, sarcopenia was an independent predictor for postoperative complications (P = 0.01, odds ratio 1.82, 95% confidence interval 1.13-3.00). Among postoperative complications (CDC grade ≥2), sarcopenia was correlated with non-surgical-site infections (P = 0.03). Sarcopenia was not correlated with the overall or recurrence-free survival. CONCLUSIONS: Sarcopenia was an independent predictive factor for postoperative complications after CRC surgery.

Balloon-Based Organ Retractor With Increased Safety and Reduced Invasiveness During Video-Assisted Thoracoscopic Surgery.

OBJECTIVES: In recent years, video-assisted thoracoscopic surgery (VATS) has increasingly become the preferred technique for thoracic surgery. However, the inherent characteristics of the lungs as large, soft, slippery, and delicate creates difficulties for pulmonary surgery. In this article, we outline the development and assessment of a balloon-based organ retractor for VATS via collaboration between medical and engineering personnel. METHODS: A dry lab trial and accompanying questionnaire assessment were performed by a group of thoracic surgeons. Objective pressure measurements were obtained, and animal experiment on pigs was performed. RESULTS: In the dry lab trial, use of the developed organ retractor required significantly less time and resulted in fewer difficulties than using a Cherry Dissector. The measured pressure per mm2 of the developed retractor was clearly lower than that for the Cherry Dissector. The questionnaire completed by the surgeons following the dry lab and animal experiments showed that most of the surgeons (7 surgeons out of 9) were satisfied with the quality of the balloon-based retractor based on a score of 3.13 ± 0.28 (mean ± standard deviation) out of 4.0. During the animal experiment, the balloon-based retractor provided stable and clear viewing with minimal need for adjustment. CONCLUSION: This balloon-based retractor could contribute to increased safety and less-invasive VATS.

Prognostic Significance of Sarcopenia in Patients with Esophagogastric Junction Cancer or Upper Gastric Cancer.

BACKGROUND: The association between sarcopenia and postoperative outcomes for patients with gastrointestinal malignancies remains controversial. This study aimed to assess the impact of sarcopenia on short- and long-term outcomes after surgery for esophagogastric junction cancer (EGJC) or upper gastric cancer (UGC). METHODS: The study reviewed 148 patients with EGJC or UGC who underwent surgical resection. The patients were categorized into the sarcopenia group or the non-sarcopenia group according to their skeletal muscle index calculated using abdominal computed tomography images. The study compared clinicopathologic factors, postoperative complications, and prognosis between the two groups. RESULTS: Sarcopenia was present in 19 patients (32.2%) with EGJC and 23 patients (25.8%) with UGC. The 5-year overall survival (OS) and recurrence-free survival (RFS) rates were significantly poorer in the sarcopenia group than in the non-sarcopenia group (OS 85.5 vs 54.8%, P = 0.0010; RFS 78.7 vs 51.7%, P = 0.0054). The development of postoperative complications did not differ significantly between the two groups. Both the uni- and multivariate analyses showed that N stage (P < 0.0001) and sarcopenia (P = 0.0024 and 0.0293, respectively) were independent poor prognostic factors for OS. CONCLUSIONS: Sarcopenia was strongly associated with a poor long-term prognosis for patients with EGJC or UGC who underwent surgery. The results suggest that special attention might be needed during the development of treatment strategies for patients with sarcopenia who intend to undergo operations for EGJC and UGC.

Neuromelanin MRI is useful for monitoring motor complications in Parkinson's and PARK2 disease.

Parkinson's disease (PD) is caused by the loss of dopaminergic neurons. Recently, specific T1-weighted magnetic resonance imaging (MRI) at 3 Tesla was reported to visualize neuromelanin (NM)-related contrast of dopaminergic neurons. Using NM-MRI, we analyzed whether disease severity and motor complications (MC) are associated with the degree of dopaminergic neuronal degeneration in the substantia nigra pars compacta (SNc) in patients with idiopathic PD (PD) and PARK2. We examined 27 individuals with PD, 11 with PARK2, and a control group of 18. A 3T MRI was used to obtain a modified NM-sensitive T1-weighted fast-spin echo sequence. The size of the SNc was determined as the number of pixels with signal intensity higher than background signal intensity +2 standard deviations. NM-MRI indicated that the T1 hyperintense area in the SNc in patients with PD and PARK2 was significantly smaller than that in control subjects. When compared with the PD group without MC, both PD with MC and PARK2 showed a markedly smaller size of NM-rich SNc area. Receiver operating characteristic curve analysis revealed a sensitivity of 86.96% and a specificity of 100% in discriminating between patients with and without MC (area under the curve = 0.98). Correlation analysis between the T1 hyperintense SNc area and L-dopa and L-dopa equivalent dose demonstrated a significant negative correlation. The association between a reducing SNc NM-rich area and MC with increasing dopaminergic medication dose suggests that NM-MRI findings might be a useful tool for monitoring the development of MC in PD and PARK2.

Widespread enlarged perivascular spaces associated with dementia and focal brain dysfunction: case report.

BACKGROUND: Enlarged perivascular spaces (PVS) are common magnetic resonance imaging (MRI) findings, whereas widespread enlarged PVS are extremely rare. Although most patients with widespread enlarged PVS remain asymptomatic, some develop neurological dysfunctions; however, it remains unclear whether these are the consequence of widespread enlarged PVS. CASE PRESENTATION: A 64-year-old female patient developed consciousness disturbance, cognitive dysfunctions, fluent aphasia, agraphia, acalculia, and left-right disorientation after suffering from bronchopneumonia. Brain MRI revealed unusually widespread enlarged PVS predominantly in the left cerebral hemisphere. Following bronchopneumonia treatment, her cognitive dysfunction, fluent aphasia, agraphia, acalculia, and left-right disorientation persisted despite improvement of her general condition. Furthermore, the hypoperfusion area on single photon emission computed tomography and slow wave sites on electroencephalography were consistent with the location of enlarged PVS, indicating that severe enlarged PVS impaired focal brain functions. CONCLUSIONS: This case suggested that widespread enlarged PVS could be a potential cause of neurological deficits. We propose that impaired perivascular circulation due to enlarged PVS might lead to focal brain dysfunction.

The surgical outcomes of lung cancer combined with interstitial pneumonia: a single-institution report.

PURPOSE: Several studies have reported that an acute exacerbation (AE) of idiopathic interstitial pneumonia (IIP) can occur after lung resection in patients with non-small cell lung cancer (NSCLC); however, the perioperative management strategy is controversial. METHODS: The data of lung cancer patients at Nagasaki University Hospital from June 1994 to October 2013 were retrospectively reviewed. RESULTS: Among all 1701 NSCLC patients who underwent lung resection, 59 (3.5%) had IIP. Five patients (8.5%) had an AE of IIP following lung resection, three (60%) of whom died in hospital. Univariate and multivariate analyses were performed to identify possible risk factors for AE. The univariate analyses identified LDH and the volume of blood loss as risk factors. The multivariate analysis identified no factors. The treatment for an AE included steroid pulse therapy and neutrophil elastase inhibitor therapy. Direct hemoperfusion with polymyxin B immobilized the fiber column and immunosuppressant therapy was attempted in some of the patients who did not respond to these treatments. CONCLUSION: Patients with lung cancer and IIP have a higher risk of chest surgery and a poor prognosis. Very careful surgery and perioperative management are needed, because AEs are often difficult to AE predict.

Limb-Shaking Transient Ischemic Attack Induced by Middle Cerebral Artery Dissection after Lung Surgery.

We report a case of limb-shaking transient ischemic attack (TIA) caused by a dissection of the middle cerebral artery (MCA) following lung surgery under general anesthesia. An 81-year-old male patient who underwent lobectomy for lung cancer suddenly developed transient shaking movements of the neck and the left upper distal limb on postoperative day 1. On the basis of the double-barrel appearance of the right M1 segment of the MCA, a diagnosis of MCA dissection was made. Physicians should be aware that limb-shaking TIA is sometimes caused by MCA dissection and could be precipitated by any condition, including lung surgery under general anesthesia.

Spontaneous Formation of a Globally Connected Contractile Network in a Microtubule-Motor System.

Microtubule (MT) networks play key roles in cell division, intracellular transport, and cell motility. These functions of MT networks occur through interactions between MTs and various associated proteins, notably motor proteins that bundle and slide MTs. Our objective in this study was to address the question of how motors determine the nature of MT networks. We conducted in vitro assays using homotetrameric kinesin Eg5, a motor protein involved in the formation and maintenance of the mitotic spindle. The mixing of Eg5 and MTs produced a range of spatiotemporal dynamics depending on the motor/filament ratio. Low motor/filament ratios produced globally connected static MT networks with sparsely distributed contractile active nodes (motor-accumulating points with radially extending MTs). Increasing the motor/filament ratio facilitated the linking of contractile active nodes and led to a global contraction of the network. When the motor/filament ratio was further increased, densely distributed active nodes formed local clusters and segmented the network into pieces with their strong contractile forces. Altering the properties of the motor through the use of chimeric Eg5, which has kinesin-1 heads, resulted in the generation of many isolated asters. These results suggest that the spatial distribution of contractile active nodes determines the dynamics of MT-motor networks. We then developed a coarse-grained model of MT-motor networks and identified two essential features for reproducing the experimentally observed patterns: an accumulation of motors that form the active nodes necessary to generate contractile forces, and a nonlinear dependency of contractile force on motor densities. Our model also enabled us to characterize the mechanical properties of the contractile network. Our study provides insight into how local motor-MT interactions generate the spatiotemporal dynamics of macroscopic network structures.

Phase geometries of two-dimensional excitable waves govern self-organized morphodynamics of amoeboid cells.

In both randomly moving Dictyostelium and mammalian cells, phosphatidylinositol (3,4,5)-trisphosphate and F-actin are known to propagate as waves at the membrane and act to push out the protruding edge. To date, however, the relationship between the wave geometry and the patterns of amoeboid shape change remains elusive. Here, by using phase map analysis, we show that morphology dynamics of randomly moving Dictyostelium discoideum cells can be characterized by the number, topology, and position of spatial phase singularities, i.e., points that represent organizing centers of rotating waves. A single isolated singularity near the cellular edge induced a rotational protrusion, whereas a pair of singularities supported a symmetric extension. These singularities appeared by strong phase resetting due to de novo nucleation at the back of preexisting waves. Analysis of a theoretical model indicated excitability of the system that is governed by positive feedback from phosphatidylinositol (3,4,5)-trisphosphate to PI3-kinase activation, and we showed experimentally that this requires F-actin. Furthermore, by incorporating membrane deformation into the model, we demonstrated that geometries of competing waves explain most of the observed semiperiodic changes in amoeboid morphology.