In this study, we synthesized Pt/g-C3N4 photocatalysts modified by a solvent etching process wher... more In this study, we synthesized Pt/g-C3N4 photocatalysts modified by a solvent etching process where ethanol (Pt/CN0), water (Pt/CN100), and a 50:50 mixture (Pt/CN50) were used as a solvent, and investigated the optimal properties of g-C3N4 to prepare the best Pt/g-C3N4 for photocatalytic hydrogen evolution. From diverse characterizations, water was proven to be a stronger solvent agent, resulting in not only the introduction of more O-functional groups onto the g-C3N4 surface, but also the degradation of a regular array of tri-s-triazine units in the g-C3N4 structure. While the addition of O-functional groups positively influenced the oxidation state of the Pt cocatalyst and the hydrogen production rate, the changes to g-C3N4 structure retarded charge transfer on its surface, inducing negative effects such as fast recombination and less oxidized Pt species. Pt/CN50 that was synthesized with the 50:50 solvent mixture exhibited the highest hydrogen production rate of 590.9 µmol g−1h−1,...
In this work, the growth of extended tri-s-triazine units (melem units) on g-C3N4 (CN) by hydroth... more In this work, the growth of extended tri-s-triazine units (melem units) on g-C3N4 (CN) by hydrothermal treatment and its effect on the photodegradation efficiency of tetracycline hydrochloride (TC) is investigated. The CN-180-x and CN-200-6 samples were prepared using different hydrolysis times and temperatures, and they were characterized by multiple physicochemical techniques. In addition, their photodegradation performance was evaluated under visible light irradiation. Compared to the CN, CN-180-6 possesses remarkable photocatalytic degradation efficiency at 97.17% towards TC removal in an aqueous solution. The high visible-light-induced photo-reactivity of CN-180-6 directly correlates to charge transfer efficiency, numerous structural defects with a high specific surface area (75.0 m2 g−1), and sufficient O-functional groups over g-C3N4. However, hydrothermal treatment at a higher temperature or during a longer time additionally induces the growth of extended melem units on the ...
Vietnamese Journal of Radiology and Nuclear Medicine
TÓM TẮTMục tiêu: Đánh giá hiệu quả bước đầu trong xử lý các tổn thương vú lành tính ... more TÓM TẮTMục tiêu: Đánh giá hiệu quả bước đầu trong xử lý các tổn thương vú lành tính bằng phương pháp sinh thiết vú có hỗ trợ hút chân không tại trung tâm Điện quang, bệnh viện Bạch MaiĐối tượng và phương pháp nghiên cứu: nghiên cứu tiến cứu can thiệp không đối chứng trên các bệnh nhân nữ có tổn thương vú lành tính được loại bỏ hoàn toàn bằng kim sinh thiết có hỗ trợ hút chân không dưới hướng dẫn siêu âm từ tháng 1 năm 2018 đến tháng 12 năm 2018 tại Trung tâm điện quang bệnh viện Bạch Mai. Tiêu chuẩn lựa chọn bệnh nhân:- Tổn thương đã được chọc tế bào có kết quả tế bào học không có tế bào ác tính.- Có chỉ định điều trị, ưu tiên các trường hợp sau:1. Những tổn thương vú sờ thấy được chắc chắn hoặc không chắc chắn gây lo âu cho bệnh nhân.2. Không thể kết luận được giữa kết quả lâm sàng và nhũ ảnh, MRI.3. Tiền sử gia đình về ung thư.- Có hồ sơ bệnh án đầy đủ- Bệnh nhân đồng ý tham gia nghiên cứu.Kết quả: 32 bệnh nhân nữ được loại bỏ 45 tổn thương vú lành tính...
This paper is concerned with the problem of secure transmission for amplify-and-forward multi-ant... more This paper is concerned with the problem of secure transmission for amplify-and-forward multi-antenna relay systems in the presence of multiple eavesdroppers. Specifically, spatial beamforming and artificial noise broadcasting are chosen as the strategy for secure transmission with robustness against imperfect channel state information of the intended receiver and the eavesdroppers. In such a scenario, the objective is to maximize the worst-case secrecy rate while guaranteeing the transmit power constraint at the relay and the norm-bounded channel uncertainty. We reformulate the problem as a general DC (Difference-of-Convex functions) program (i.e. minimizing a DC function under DC constraints) and develop a very inexpensive DCA based algorithm for solving it. Numerical results illustrate the effectiveness of the proposed algorithm and its superiority versus the existing approach.
Viễn thám radar khẩu độ tổng hợp (SAR) cung cấp một phương pháp tiếp cận linh hoạt và mang đến cơ... more Viễn thám radar khẩu độ tổng hợp (SAR) cung cấp một phương pháp tiếp cận linh hoạt và mang đến cơ hội thu thập thông tin cây trồng mà không bị hạn chế bởi các yếu tố điều kiện thời tiết. Khả năng ứng dụng của dữ liệu Sentinel-1 SAR với phân cực kép cho phép nhận diện các ruộng lúa riêng lẻ, và với chu kỳ chụp lặp đủ để giám sát tình trạng sinh trưởng của các loại cây trồng khác nhau. Trong những năm gần đây, với sự phát triển không ngừng của các thuật toán học máy, học sâu trên thế giới, đặc biệt là mạng nơ-ron tích chập (CNN) đã thu được nhiều kết quả tốt trong phát hiện và chiết tách thông tin trên ảnh viễn thám. Nghiên cứu này, đề xuất mô hình phân loại dựa trên mạng nơ-ron tích chập sâu (DCNN) để chiết tách ruộng lúa từ dữ liệu Sentinel-1 SAR. Các chỉ số vật lý đã được tính toán từ phân cực (VH và VV) và một đội di động kiểm tra hình thái sinh trưởng của cây lúa. Đối với kết quả trích xuất ruộng lúa được xác minh bằng độ chính xác tổng thể (OA) và xác nhận chéo (CV) đều đạt kết ...
Advances in Intelligent Systems and Computing, 2019
This paper studies the worst-case secrecy rate maximization problem under the total transmit powe... more This paper studies the worst-case secrecy rate maximization problem under the total transmit power, the energy harvesting and the outage probability requirements. The problem is nonconvex, thus, hard to solve. Exploiting the special structure of the problem, we first reformulate as a DC (Difference of Convex functions) program. Then, we develop an efficient approach based on DCA (DC Algorithm) and alternating method for solving the problem. The computational results confirm the efficiency of the proposed approach.
This paper addresses the emerging practical requirement that wireless information and power trans... more This paper addresses the emerging practical requirement that wireless information and power transfer are employed simultaneously in a multiple-input single-output (MISO) secrecy channel. Transmit beamforming without artificial noise and that with artificial noise are considered. In addition, perfect and imperfect channel state information of both the legitimate receivers and eavesdroppers are investigated. These four scenarios correspond to four optimization problems. The considered problems aim to maximize the secrecy rate with constraints on the transmit power and the harvested energy at each receiver. Since these optimization problems are nonconvex, we propose the efficient algorithms based on Difference of Convex (DC) functions programming and DC Algorithm (DCA)-an innovative approach in nonconvex optimization. Exploiting the special structure of these problems, we utilize the semidefinite relaxation technique and S-procedure to reformulate them as general DC programs. The efficient algorithms based on general DCA are developed to solve the corresponding general DC programs. Numerical results are presented which illustrate the effectiveness of our proposed algorithms, they outperform the existing approaches in terms of both quality and rapidity.
Poly(-isopropyl acrylamide) (pNIPAM) is a stimulus-responsive polymer that has been of great inte... more Poly(-isopropyl acrylamide) (pNIPAM) is a stimulus-responsive polymer that has been of great interest to the bioengineering community. When the temperature is lowered below its lower critical solution temperature (∼32 °C), pNIPAM rapidly hydrates, and adherent cells detach as intact cell sheets. This cell-releasing behavior in a physiologically relevant temperature range has led to NIPAM's use for engineered tissues and other devices. In a previous study, however, the authors found that although most techniques used to polymerize NIPAM yield biocompatible films, some formulations from commercially-available NIPAM (cpNIPAM) can be cytotoxic. In this work, the authors investigate the reasons underlying this anomaly. The authors evaluated the response of a variety of cell types (e.g., bovine aortic endothelial cells, BAECs; monkey kidney epithelial cells, Vero cells; and mouse embryonic fibroblasts, 3T3s) after culture on substrates spin-coated with sol-gel (spNIPAM) and commercial...
Each year, the United States spends about $20 billion to treat people who have been infected with... more Each year, the United States spends about $20 billion to treat people who have been infected with antibiotic resistant bacteria. Even so, the development of new antibiotics has slowed considerably since the mid-20th century. As a result, researchers are looking into developing synthetic compounds and materials with antimicrobial activities such as those made by the Schanze and Whitten groups [ACS Appl. Mater. Interfaces 3, 2820 (2011)]. Previously, they have demonstrated that poly(phenylene ethynylene) (PPE) based electrolytes and oligomeric end-only phenylene ethynylene (EO-OPE) based electrolytes possess strong biocidal activity. However, before the PPE and OPE can be used with humans, skin irritation tests are required to ensure their safety. In this work, in vitro skin assays are used to predict in vivo irritation. Tissues were conditioned for 24 h, exposed to test substances for 1 h, and then tested for viability using colorimetric and cytokine assays. Concentrations up to 50 μ...
Although there is a great deal of research focused on cell sheet engineering from polymers such a... more Although there is a great deal of research focused on cell sheet engineering from polymers such as poly(N-isopropyl acrylamide) (pNIPAM), the biocompatibility of pNIPAM surfaces and the nature of cellular detachment from this polymer is still unclear. The most extensive study of the mechanism of detachment proposed a two-step process, with a first (passive) phase involving hydration of pNIPAM chains, and the second (active) phase involving cellular metabolism. However, a number of studies performed successful cell sheet detachment from pNIPAM-grafted surfaces at low temperatures which calls this hypothesis into question. Furthermore, although it has been demonstrated that low-temperature cell sheet detachment using pNIPAM-grafted surfaces is less destructive than other methods of detachment, it has not been investigated if cell sheet detachment removes a portion of pNIPAM from the surfaces as well. It is essential to know if any fragments of the polymer are removed along with the ce...
Mitotic spindles specify cleavage planes in early embryos by communicating their position and ori... more Mitotic spindles specify cleavage planes in early embryos by communicating their position and orientation to the cell cortex using microtubule asters that grow out from the spindle poles during anaphase. Chromatin also plays a poorly understood role. Polyspermic fertilization provides a natural experiment where aster pairs from the same spindle (sister asters) have chromatin between them, while asters pairs from different spindles (non-sisters) do not. In frogs, only sister aster pairs induce furrows. We found that only sister asters recruited two conserved furrow-inducing signaling complexes, Chromosome Passenger Complex (CPC) and Centralspindlin, to a plane between them. This explains why only sister pairs induce furrows. We then investigated factors that influenced CPC recruitment to microtubule bundles in intact eggs and a cytokinesis extract system. We found that microtubule stabilization, optimal starting distance between asters, and proximity to chromatin all favored CPC recr...
Cell division in prokaryotes and eukaryotes is commonly initiated by the well-controlled binding ... more Cell division in prokaryotes and eukaryotes is commonly initiated by the well-controlled binding of proteins to the cytoplasmic side of the cell membrane. However, a precise characterization of the spatiotemporal dynamics of membrane-bound proteins is often difficult to achieve in vivo. Here, we present protocols for the use of supported lipid bilayers to rebuild the cytokinetic machineries of cells with greatly different dimensions: the bacterium Escherichia coli and eggs of the vertebrate Xenopus laevis. Combined with total internal reflection fluorescence microscopy, these experimental setups allow for precise quantitative analyses of membrane-bound proteins. The protocols described to obtain glass-supported membranes from bacterial and vertebrate lipids can be used as starting points for other reconstitution experiments. We believe that similar biochemical assays will be instrumental to study the biochemistry and biophysics underlying a variety of complex cellular tasks, such as...
We report optimized methods for preparing Xenopus egg extracts without cytochalasin D, that we te... more We report optimized methods for preparing Xenopus egg extracts without cytochalasin D, that we term "actin-intact egg…
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, Jan 5, 2014
The large cells in early vertebrate development face an extreme physical challenge in organizing ... more The large cells in early vertebrate development face an extreme physical challenge in organizing their cytoplasm. For example, amphibian embryos have to divide cytoplasm that spans hundreds of micrometres every 30 min according to a precise geometry, a remarkable accomplishment given the extreme difference between molecular and cellular scales in this system. How do the biochemical reactions occurring at the molecular scale lead to this emergent behaviour of the cell as a whole? Based on recent findings, we propose that the centrosome plays a crucial role by initiating two autocatalytic reactions that travel across the large cytoplasm as chemical waves. Waves of mitotic entry and exit propagate out from centrosomes using the Cdk1 oscillator to coordinate the timing of cell division. Waves of microtubule-stimulated microtubule nucleation propagate out to assemble large asters that position spindles for the following mitosis and establish cleavage plane geometry. By initiating these c...
During animal cell division, the cleavage furrow is positioned by microtubules that signal to the... more During animal cell division, the cleavage furrow is positioned by microtubules that signal to the actin cortex at the cell midplane. We developed a cell-free system to recapitulate cytokinesis signaling using cytoplasmic extract from Xenopus eggs. Microtubules grew out as asters from artificial centrosomes and met to organize antiparallel overlap zones. These zones blocked the interpenetration of neighboring asters and recruited cytokinesis midzone proteins, including the chromosomal passenger complex (CPC) and centralspindlin. The CPC was transported to overlap zones, which required two motor proteins, Kif4A and a Kif20A paralog. Using supported lipid bilayers to mimic the plasma membrane, we observed the recruitment of cleavage furrow markers, including an active RhoA reporter, at microtubule overlaps. This system opens further approaches to understanding the biophysics of cytokinesis signaling.
Proceedings of the National Academy of Sciences of the United States of America, Jan 16, 2014
A major challenge in cell biology is to understand how nanometer-sized molecules can organize mic... more A major challenge in cell biology is to understand how nanometer-sized molecules can organize micrometer-sized cells in space and time. One solution in many animal cells is a radial array of microtubules called an aster, which is nucleated by a central organizing center and spans the entire cytoplasm. Frog (here Xenopus laevis) embryos are more than 1 mm in diameter and divide with a defined geometry every 30 min. Like smaller cells, they are organized by asters, which grow, interact, and move to precisely position the cleavage planes. It has been unclear whether asters grow to fill the enormous egg by the same mechanism used in smaller somatic cells, or whether special mechanisms are required. We addressed this question by imaging growing asters in a cell-free system derived from eggs, where asters grew to hundreds of microns in diameter. By tracking marks on the lattice, we found that microtubules could slide outward, but this was not essential for rapid aster growth. Polymer trea...
There is very little information or analysis on middle class youth in Vietnam. This paper begins ... more There is very little information or analysis on middle class youth in Vietnam. This paper begins to fill this gap in our knowledge by utilising data on urban, educated professional youth from the Survey Assessment of Vietnamese Youth (2003–04) and an ethnographic investigation in Hanoi between 1999 and 2002. It considers some of the conceptual and analytical issues in addressing the character and definition of the middle class in Southeast Asia more generally, and provides contextual information on the emergence of the middle class in Vietnam and the transformation of the class structure there. The information available suggests that the expanding young middle class in Vietnam exhibits many of the characteristics of the middle class everywhere—possession of cultural capital, a firm interest in and commitment to education, an orientation to consumption and to accessing news and information, and aspirations to improve and develop in personal and career terms. However, the continuing c...
In this study, we synthesized Pt/g-C3N4 photocatalysts modified by a solvent etching process wher... more In this study, we synthesized Pt/g-C3N4 photocatalysts modified by a solvent etching process where ethanol (Pt/CN0), water (Pt/CN100), and a 50:50 mixture (Pt/CN50) were used as a solvent, and investigated the optimal properties of g-C3N4 to prepare the best Pt/g-C3N4 for photocatalytic hydrogen evolution. From diverse characterizations, water was proven to be a stronger solvent agent, resulting in not only the introduction of more O-functional groups onto the g-C3N4 surface, but also the degradation of a regular array of tri-s-triazine units in the g-C3N4 structure. While the addition of O-functional groups positively influenced the oxidation state of the Pt cocatalyst and the hydrogen production rate, the changes to g-C3N4 structure retarded charge transfer on its surface, inducing negative effects such as fast recombination and less oxidized Pt species. Pt/CN50 that was synthesized with the 50:50 solvent mixture exhibited the highest hydrogen production rate of 590.9 µmol g−1h−1,...
In this work, the growth of extended tri-s-triazine units (melem units) on g-C3N4 (CN) by hydroth... more In this work, the growth of extended tri-s-triazine units (melem units) on g-C3N4 (CN) by hydrothermal treatment and its effect on the photodegradation efficiency of tetracycline hydrochloride (TC) is investigated. The CN-180-x and CN-200-6 samples were prepared using different hydrolysis times and temperatures, and they were characterized by multiple physicochemical techniques. In addition, their photodegradation performance was evaluated under visible light irradiation. Compared to the CN, CN-180-6 possesses remarkable photocatalytic degradation efficiency at 97.17% towards TC removal in an aqueous solution. The high visible-light-induced photo-reactivity of CN-180-6 directly correlates to charge transfer efficiency, numerous structural defects with a high specific surface area (75.0 m2 g−1), and sufficient O-functional groups over g-C3N4. However, hydrothermal treatment at a higher temperature or during a longer time additionally induces the growth of extended melem units on the ...
Vietnamese Journal of Radiology and Nuclear Medicine
TÓM TẮTMục tiêu: Đánh giá hiệu quả bước đầu trong xử lý các tổn thương vú lành tính ... more TÓM TẮTMục tiêu: Đánh giá hiệu quả bước đầu trong xử lý các tổn thương vú lành tính bằng phương pháp sinh thiết vú có hỗ trợ hút chân không tại trung tâm Điện quang, bệnh viện Bạch MaiĐối tượng và phương pháp nghiên cứu: nghiên cứu tiến cứu can thiệp không đối chứng trên các bệnh nhân nữ có tổn thương vú lành tính được loại bỏ hoàn toàn bằng kim sinh thiết có hỗ trợ hút chân không dưới hướng dẫn siêu âm từ tháng 1 năm 2018 đến tháng 12 năm 2018 tại Trung tâm điện quang bệnh viện Bạch Mai. Tiêu chuẩn lựa chọn bệnh nhân:- Tổn thương đã được chọc tế bào có kết quả tế bào học không có tế bào ác tính.- Có chỉ định điều trị, ưu tiên các trường hợp sau:1. Những tổn thương vú sờ thấy được chắc chắn hoặc không chắc chắn gây lo âu cho bệnh nhân.2. Không thể kết luận được giữa kết quả lâm sàng và nhũ ảnh, MRI.3. Tiền sử gia đình về ung thư.- Có hồ sơ bệnh án đầy đủ- Bệnh nhân đồng ý tham gia nghiên cứu.Kết quả: 32 bệnh nhân nữ được loại bỏ 45 tổn thương vú lành tính...
This paper is concerned with the problem of secure transmission for amplify-and-forward multi-ant... more This paper is concerned with the problem of secure transmission for amplify-and-forward multi-antenna relay systems in the presence of multiple eavesdroppers. Specifically, spatial beamforming and artificial noise broadcasting are chosen as the strategy for secure transmission with robustness against imperfect channel state information of the intended receiver and the eavesdroppers. In such a scenario, the objective is to maximize the worst-case secrecy rate while guaranteeing the transmit power constraint at the relay and the norm-bounded channel uncertainty. We reformulate the problem as a general DC (Difference-of-Convex functions) program (i.e. minimizing a DC function under DC constraints) and develop a very inexpensive DCA based algorithm for solving it. Numerical results illustrate the effectiveness of the proposed algorithm and its superiority versus the existing approach.
Viễn thám radar khẩu độ tổng hợp (SAR) cung cấp một phương pháp tiếp cận linh hoạt và mang đến cơ... more Viễn thám radar khẩu độ tổng hợp (SAR) cung cấp một phương pháp tiếp cận linh hoạt và mang đến cơ hội thu thập thông tin cây trồng mà không bị hạn chế bởi các yếu tố điều kiện thời tiết. Khả năng ứng dụng của dữ liệu Sentinel-1 SAR với phân cực kép cho phép nhận diện các ruộng lúa riêng lẻ, và với chu kỳ chụp lặp đủ để giám sát tình trạng sinh trưởng của các loại cây trồng khác nhau. Trong những năm gần đây, với sự phát triển không ngừng của các thuật toán học máy, học sâu trên thế giới, đặc biệt là mạng nơ-ron tích chập (CNN) đã thu được nhiều kết quả tốt trong phát hiện và chiết tách thông tin trên ảnh viễn thám. Nghiên cứu này, đề xuất mô hình phân loại dựa trên mạng nơ-ron tích chập sâu (DCNN) để chiết tách ruộng lúa từ dữ liệu Sentinel-1 SAR. Các chỉ số vật lý đã được tính toán từ phân cực (VH và VV) và một đội di động kiểm tra hình thái sinh trưởng của cây lúa. Đối với kết quả trích xuất ruộng lúa được xác minh bằng độ chính xác tổng thể (OA) và xác nhận chéo (CV) đều đạt kết ...
Advances in Intelligent Systems and Computing, 2019
This paper studies the worst-case secrecy rate maximization problem under the total transmit powe... more This paper studies the worst-case secrecy rate maximization problem under the total transmit power, the energy harvesting and the outage probability requirements. The problem is nonconvex, thus, hard to solve. Exploiting the special structure of the problem, we first reformulate as a DC (Difference of Convex functions) program. Then, we develop an efficient approach based on DCA (DC Algorithm) and alternating method for solving the problem. The computational results confirm the efficiency of the proposed approach.
This paper addresses the emerging practical requirement that wireless information and power trans... more This paper addresses the emerging practical requirement that wireless information and power transfer are employed simultaneously in a multiple-input single-output (MISO) secrecy channel. Transmit beamforming without artificial noise and that with artificial noise are considered. In addition, perfect and imperfect channel state information of both the legitimate receivers and eavesdroppers are investigated. These four scenarios correspond to four optimization problems. The considered problems aim to maximize the secrecy rate with constraints on the transmit power and the harvested energy at each receiver. Since these optimization problems are nonconvex, we propose the efficient algorithms based on Difference of Convex (DC) functions programming and DC Algorithm (DCA)-an innovative approach in nonconvex optimization. Exploiting the special structure of these problems, we utilize the semidefinite relaxation technique and S-procedure to reformulate them as general DC programs. The efficient algorithms based on general DCA are developed to solve the corresponding general DC programs. Numerical results are presented which illustrate the effectiveness of our proposed algorithms, they outperform the existing approaches in terms of both quality and rapidity.
Poly(-isopropyl acrylamide) (pNIPAM) is a stimulus-responsive polymer that has been of great inte... more Poly(-isopropyl acrylamide) (pNIPAM) is a stimulus-responsive polymer that has been of great interest to the bioengineering community. When the temperature is lowered below its lower critical solution temperature (∼32 °C), pNIPAM rapidly hydrates, and adherent cells detach as intact cell sheets. This cell-releasing behavior in a physiologically relevant temperature range has led to NIPAM's use for engineered tissues and other devices. In a previous study, however, the authors found that although most techniques used to polymerize NIPAM yield biocompatible films, some formulations from commercially-available NIPAM (cpNIPAM) can be cytotoxic. In this work, the authors investigate the reasons underlying this anomaly. The authors evaluated the response of a variety of cell types (e.g., bovine aortic endothelial cells, BAECs; monkey kidney epithelial cells, Vero cells; and mouse embryonic fibroblasts, 3T3s) after culture on substrates spin-coated with sol-gel (spNIPAM) and commercial...
Each year, the United States spends about $20 billion to treat people who have been infected with... more Each year, the United States spends about $20 billion to treat people who have been infected with antibiotic resistant bacteria. Even so, the development of new antibiotics has slowed considerably since the mid-20th century. As a result, researchers are looking into developing synthetic compounds and materials with antimicrobial activities such as those made by the Schanze and Whitten groups [ACS Appl. Mater. Interfaces 3, 2820 (2011)]. Previously, they have demonstrated that poly(phenylene ethynylene) (PPE) based electrolytes and oligomeric end-only phenylene ethynylene (EO-OPE) based electrolytes possess strong biocidal activity. However, before the PPE and OPE can be used with humans, skin irritation tests are required to ensure their safety. In this work, in vitro skin assays are used to predict in vivo irritation. Tissues were conditioned for 24 h, exposed to test substances for 1 h, and then tested for viability using colorimetric and cytokine assays. Concentrations up to 50 μ...
Although there is a great deal of research focused on cell sheet engineering from polymers such a... more Although there is a great deal of research focused on cell sheet engineering from polymers such as poly(N-isopropyl acrylamide) (pNIPAM), the biocompatibility of pNIPAM surfaces and the nature of cellular detachment from this polymer is still unclear. The most extensive study of the mechanism of detachment proposed a two-step process, with a first (passive) phase involving hydration of pNIPAM chains, and the second (active) phase involving cellular metabolism. However, a number of studies performed successful cell sheet detachment from pNIPAM-grafted surfaces at low temperatures which calls this hypothesis into question. Furthermore, although it has been demonstrated that low-temperature cell sheet detachment using pNIPAM-grafted surfaces is less destructive than other methods of detachment, it has not been investigated if cell sheet detachment removes a portion of pNIPAM from the surfaces as well. It is essential to know if any fragments of the polymer are removed along with the ce...
Mitotic spindles specify cleavage planes in early embryos by communicating their position and ori... more Mitotic spindles specify cleavage planes in early embryos by communicating their position and orientation to the cell cortex using microtubule asters that grow out from the spindle poles during anaphase. Chromatin also plays a poorly understood role. Polyspermic fertilization provides a natural experiment where aster pairs from the same spindle (sister asters) have chromatin between them, while asters pairs from different spindles (non-sisters) do not. In frogs, only sister aster pairs induce furrows. We found that only sister asters recruited two conserved furrow-inducing signaling complexes, Chromosome Passenger Complex (CPC) and Centralspindlin, to a plane between them. This explains why only sister pairs induce furrows. We then investigated factors that influenced CPC recruitment to microtubule bundles in intact eggs and a cytokinesis extract system. We found that microtubule stabilization, optimal starting distance between asters, and proximity to chromatin all favored CPC recr...
Cell division in prokaryotes and eukaryotes is commonly initiated by the well-controlled binding ... more Cell division in prokaryotes and eukaryotes is commonly initiated by the well-controlled binding of proteins to the cytoplasmic side of the cell membrane. However, a precise characterization of the spatiotemporal dynamics of membrane-bound proteins is often difficult to achieve in vivo. Here, we present protocols for the use of supported lipid bilayers to rebuild the cytokinetic machineries of cells with greatly different dimensions: the bacterium Escherichia coli and eggs of the vertebrate Xenopus laevis. Combined with total internal reflection fluorescence microscopy, these experimental setups allow for precise quantitative analyses of membrane-bound proteins. The protocols described to obtain glass-supported membranes from bacterial and vertebrate lipids can be used as starting points for other reconstitution experiments. We believe that similar biochemical assays will be instrumental to study the biochemistry and biophysics underlying a variety of complex cellular tasks, such as...
We report optimized methods for preparing Xenopus egg extracts without cytochalasin D, that we te... more We report optimized methods for preparing Xenopus egg extracts without cytochalasin D, that we term "actin-intact egg…
Philosophical transactions of the Royal Society of London. Series B, Biological sciences, Jan 5, 2014
The large cells in early vertebrate development face an extreme physical challenge in organizing ... more The large cells in early vertebrate development face an extreme physical challenge in organizing their cytoplasm. For example, amphibian embryos have to divide cytoplasm that spans hundreds of micrometres every 30 min according to a precise geometry, a remarkable accomplishment given the extreme difference between molecular and cellular scales in this system. How do the biochemical reactions occurring at the molecular scale lead to this emergent behaviour of the cell as a whole? Based on recent findings, we propose that the centrosome plays a crucial role by initiating two autocatalytic reactions that travel across the large cytoplasm as chemical waves. Waves of mitotic entry and exit propagate out from centrosomes using the Cdk1 oscillator to coordinate the timing of cell division. Waves of microtubule-stimulated microtubule nucleation propagate out to assemble large asters that position spindles for the following mitosis and establish cleavage plane geometry. By initiating these c...
During animal cell division, the cleavage furrow is positioned by microtubules that signal to the... more During animal cell division, the cleavage furrow is positioned by microtubules that signal to the actin cortex at the cell midplane. We developed a cell-free system to recapitulate cytokinesis signaling using cytoplasmic extract from Xenopus eggs. Microtubules grew out as asters from artificial centrosomes and met to organize antiparallel overlap zones. These zones blocked the interpenetration of neighboring asters and recruited cytokinesis midzone proteins, including the chromosomal passenger complex (CPC) and centralspindlin. The CPC was transported to overlap zones, which required two motor proteins, Kif4A and a Kif20A paralog. Using supported lipid bilayers to mimic the plasma membrane, we observed the recruitment of cleavage furrow markers, including an active RhoA reporter, at microtubule overlaps. This system opens further approaches to understanding the biophysics of cytokinesis signaling.
Proceedings of the National Academy of Sciences of the United States of America, Jan 16, 2014
A major challenge in cell biology is to understand how nanometer-sized molecules can organize mic... more A major challenge in cell biology is to understand how nanometer-sized molecules can organize micrometer-sized cells in space and time. One solution in many animal cells is a radial array of microtubules called an aster, which is nucleated by a central organizing center and spans the entire cytoplasm. Frog (here Xenopus laevis) embryos are more than 1 mm in diameter and divide with a defined geometry every 30 min. Like smaller cells, they are organized by asters, which grow, interact, and move to precisely position the cleavage planes. It has been unclear whether asters grow to fill the enormous egg by the same mechanism used in smaller somatic cells, or whether special mechanisms are required. We addressed this question by imaging growing asters in a cell-free system derived from eggs, where asters grew to hundreds of microns in diameter. By tracking marks on the lattice, we found that microtubules could slide outward, but this was not essential for rapid aster growth. Polymer trea...
There is very little information or analysis on middle class youth in Vietnam. This paper begins ... more There is very little information or analysis on middle class youth in Vietnam. This paper begins to fill this gap in our knowledge by utilising data on urban, educated professional youth from the Survey Assessment of Vietnamese Youth (2003–04) and an ethnographic investigation in Hanoi between 1999 and 2002. It considers some of the conceptual and analytical issues in addressing the character and definition of the middle class in Southeast Asia more generally, and provides contextual information on the emergence of the middle class in Vietnam and the transformation of the class structure there. The information available suggests that the expanding young middle class in Vietnam exhibits many of the characteristics of the middle class everywhere—possession of cultural capital, a firm interest in and commitment to education, an orientation to consumption and to accessing news and information, and aspirations to improve and develop in personal and career terms. However, the continuing c...
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