Label‐free multi‐parametric imaging of single cells: dual picosecond optoacoustic microscopy

Advances in microscopy with new visualization possibilities often bring dramatic progress to our understanding of the intriguing cellular machinery. Picosecond optoacoustic micro‐spectroscopy is an optical technique based on ultrafast pump‐probe generation and detection of hypersound on time durations of picoseconds and length scales of nanometers. It is experiencing a renaissance as a versatile imaging tool for cell biology research after a plethora of applications in solid‐state physics. In this emerging context, this work reports on a dual‐probe architecture to carry out real‐time parallel detection of the hypersound propagation inside a cell that is cultured on a metallic substrate, and of the hypersound reflection at the metal/cell adhesion interface. Using this optoacoustic modality, several biophysical properties of the cell can be measured in a noncontact and label‐free manner. Its abilities are demonstrated with the multiple imaging of a mitotic macrophage‐like cell in a single run experiment.      

A Surface-Induced Asymmetric Program Promotes Tissue Colonization by Pseudomonas aeruginosa

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The NAD-Booster Nicotinamide Riboside Potently Stimulates Hematopoiesis through Increased Mitochondrial Clearance

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Unbalanced biparental care during colony foundation in two subterranean termites

Parental care is a major component of reproduction in social organisms, particularly during the foundation steps. Because investment into parental care is often costly, each parent is predicted to maximize its fitness by providing less care than its partner. However, this sexual conflict is expected to be low in species with lifelong monogamy, because the fitness of each parent is typically tied to the other's input. Somewhat surprisingly, the outcomes of this tug‐of‐war between maternal and paternal investments have received important attention in vertebrate species, but remain less known in invertebrates. In this study, we investigated how queens and kings share their investment into parental care and other social interactions during colony foundation in two termites with lifelong monogamy: the invasive species Reticulitermes flavipes and the native species R. grassei. Behaviors of royal pairs were recorded during six months using a non‐invasive approach. Our results showed that queens and kings exhibit unbalanced investment in terms of grooming, antennation, trophallaxis, and vibration behavior. Moreover, both parents show behavioral differences toward their partner or their descendants. Our results also revealed differences among species, with R. flavipes exhibiting shorter periods of grooming and antennation toward eggs or partners. They also did more stomodeal trophallaxis and less vibration behavior. Overall, this study emphasizes that despite lifelong monogamy, the two parents are not equally involved in the measured forms of parental care and suggests that kings might be specialized in other tasks. It also indicates that males could play a central, yet poorly studied role in the evolution and maintenance of the eusocial organization.     

Decoupling the Roles of Cell Shape and Mechanical Stress in Orienting and Cueing Epithelial Mitosis

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《中国植被志》研编规范的若干说明、补充与修订

前期编制的《中国植被志》研编技术规范为《中国植被志》的研编工作提供了标准和指南。但在后续研编过程中发现存在一些具体问题和不足。针对这些问题和不足, 该文主要就《中国植被志》研编中的“植被类型”及志书卷册划分、中低级植被分类单元群落数量特征的记述以及文献记载的群落类型的收录等内容进行了补充和修订, 并对植被分类方法做了进一步说明。这些补充和修订内容与前期的技术规范共同成为《中国植被志》研编的依据和标准。     

重组细菌多药外排泵AcrAB-TolC的转运功能和动态组装

【背景】多药外排泵多以膜蛋白复合体形式存在,是导致细菌耐药性的重要原因。外排泵的转运功能和组装过程对于细菌耐药性和药物研发具有重要意义。【目的】以多药外排泵耐药结节细胞分化家族(resistance-nodulation-division family, RND)的重要成员AcrAB-TolC复合体为对象,研究其转运活性和体外组装特性。【方法】基于大肠杆菌AcrAB-TolC复合体基因序列,分别构建含有acrA、acrB、tolC基因的重组质粒,表达和纯化复合体各亚基,利用荧光光谱、等温滴定量热法(isothermal titration calorimetry,ITC)等技术分析复合体及亚基的转运功能、亚基与底物的相互作用,以及亚基间的相互作用和动态装配。【结果】实现了AcrAB-TolC复合体各组分的表达和纯化(纯度>98%),证实表达有各组分的活细胞提高了对于溴化乙锭(ethidium bromide,EB)的转运活性,并发现群体感应效应信号分子N-hexanoyl-L-homoserine lactone (C6-HSL)能够抑制AcrB、TolC对于EB的转运活性。ITC结果进一步证实了C6-HSL与AcrB、TolC的相互作用。ITC结果还显示AcrA分别与AcrB、TolC之间存在明显的相互作用,而AcrB与TolC之间无明显的相互作用。在体外装配实验中观测到AcrAB-TolC亚基的单分子荧光强度随时间增加,证实了复合体亚基在膜上的动态组装过程。【结论】实现了AcrAB-TolC外排泵及亚基的表达和纯化,证实了AcrAB-TolC对底物的转运活性及与底物的相互作用,观察到AcrAB-TolC的动态组装过程。以上结果为研究多药外排泵导致的细菌耐药性及抗菌策略具有重要意义。     

The Soluble Periplasmic Domains of Escherichia coli Cell Division Proteins FtsQ/FtsB/FtsL Form a Trimeric Complex with Submicromolar Affinity

Cell division in Escherichia coli involves a set of essential proteins that assembles at midcell to form the so-called divisome. The divisome regulates the invagination of the inner membrane, cell wall synthesis, and inward growth of the outer membrane. One of the divisome proteins, FtsQ, plays a central but enigmatic role in cell division. This protein associates with FtsB and FtsL, which, like FtsQ, are bitopic inner membrane proteins with a large periplasmic domain (denoted FtsQ_p, FtsB_p, and FtsL_p) that is indispensable for the function of each protein. Considering the vital nature and accessible location of the FtsQBL complex, it is an attractive target for protein-protein interaction inhibitors intended to block bacterial cell division. In this study, we expressed FtsQ_p, FtsB_p, and FtsL_p individually and in combination. Upon co-expression, FtsQ_p was co-purified with FtsB_p and FtsL_p from E. coli extracts as a stable trimeric complex. FtsB_p was also shown to interact with FtsQ_p in the absence of FtsL_p albeit with lower affinity. Interactions were mapped at the C terminus of the respective domains by site-specific cross-linking. The binding affinity and 1:1:1 stoichiometry of the FtsQ_pB_pL_p complex and the FtsQ_pB_p subcomplex were determined in complementary surface plasmon resonance, analytical ultracentrifugation, and native mass spectrometry experiments.     

The Cell Division Protein FtsZ from Streptococcus pneumoniae Exhibits a GTPase Activity Delay

The cell division protein FtsZ assembles in vitro by a mechanism of cooperative association dependent on GTP, monovalent cations, and Mg²⁺. We have analyzed the GTPase activity and assembly dynamics of Streptococcus pneumoniae FtsZ (SpnFtsZ). SpnFtsZ assembled in an apparently cooperative process, with a higher critical concentration than values reported for other FtsZ proteins. It sedimented in the presence of GTP as a high molecular mass polymer with a well defined size and tended to form double-stranded filaments in electron microscope preparations. GTPase activity depended on K⁺ and Mg²⁺ and was inhibited by Na⁺. GTP hydrolysis exhibited a delay that included a lag phase followed by a GTP hydrolysis activation step, until reaction reached the GTPase rate. The lag phase was not found in polymer assembly, suggesting a transition from an initial non-GTP-hydrolyzing polymer that switches to a GTP-hydrolyzing polymer, supporting models that explain FtsZ polymer cooperativity.