The state of the septin cytoskeleton from assembly to function

Septins are conserved guanine nucleotide-binding proteins that polymerize into filaments at the cell cortex or in association with other cytoskeletal proteins, such as actin or microtubules. As integral players in many morphogenic and signaling events, septins form scaffolds important for the recruitment of the cytokinetic machinery, organization of the plasma membrane, and orientation of cell polarity. Mutations in septins or their misregulation are associated with numerous diseases. Despite growing appreciation for the importance of septins in different aspects of cell biology and disease, septins remain relatively poorly understood compared with other cytoskeletal proteins. Here in this review, we highlight some of the recent developments of the last two years in the field of septin cell biology.     

High-efficacy subcellular micropatterning of proteins using fibrinogen anchors

Protein micropatterning allows proteins to be precisely deposited onto a substrate of choice and is now routinely used in cell biology and in vitro reconstitution. However, drawbacks of current technology are that micropatterning efficiency can be variable between proteins and that proteins may lose activity on the micropatterns. Here, we describe a general method to enable micropatterning of virtually any protein at high specificity and homogeneity while maintaining its activity. Our method is based on an anchor that micropatterns well, fibrinogen, which we functionalized to bind to common purification tags. This enhances micropatterning on various substrates, facilitates multiplexed micropatterning, and dramatically improves the on-pattern activity of fragile proteins like molecular motors. Furthermore, it enhances the micropatterning of hard-to-micropattern cells. Last, this method enables subcellular micropatterning, whereby complex micropatterns simultaneously control cell shape and the distribution of transmembrane receptors within that cell. Altogether, these results open new avenues for cell biology.     

Biologic functions of the G12 subfamily of heterotrimeric g proteins: growth, migration, and metastasis

The G12 subfamily of heterotrimeric G proteins has been the subject of intense scientific interest for more than 15 years. During this period, studies have revealed more than 20 potential G12-interacting proteins and numerous signaling axes emanating from the G12 proteins, Galpha12 and Galpha13. In addition, more recent studies have begun to illuminate the various and sundry functions that the G12 subfamily plays in biology. In this review, we summarize the diverse range of proteins that have been identified as Galpha12 and/or Galpha13 interactors and describe ongoing studies designed to dissect the biological roles of specific Galpha-effector protein interactions. Further, we describe and discuss the expanding role of G12 proteins in the biology of cells, focusing on the distinct properties of this subfamily in regulating cell proliferation, cell migration, and metastatic invasion.     

The regulation of bacterial cell division: a time and place for it

Temporal and spatial regulation of cell division assures that each daughter cell receives a copy of the chromosome. Within the past year, the application of fluorescence microscopy to the cell biology of bacteria has revealed an increasing number of proteins that are localized within the bacterial cell to carry out DNA segregation and cell division. The localization of these proteins implies the existence of positional information in the cell, but how this information is established is unknown.     

Automated Learning of Subcellular Variation among Punctate Protein Patterns and a Generative Model of Their Relation to Microtubules

Characterizing the spatial distribution of proteins directly from microscopy images is a difficult problem with numerous applications in cell biology (e.g. identifying motor-related proteins) and clinical research (e.g. identification of cancer biomarkers). Here we describe the design of a system that provides automated analysis of punctate protein patterns in microscope images, including quantification of their relationships to microtubules. We constructed the system using confocal immunofluorescence microscopy images from the Human Protein Atlas project for 11 punctate proteins in three cultured cell lines. These proteins have previously been characterized as being primarily located in punctate structures, but their images had all been annotated by visual examination as being simply “vesicular”. We were able to show that these patterns could be distinguished from each other with high accuracy, and we were able to assign to one of these subclasses hundreds of proteins whose subcellular localization had not previously been well defined. In addition to providing these novel annotations, we built a generative approach to modeling of punctate distributions that captures the essential characteristics of the distinct patterns. Such models are expected to be valuable for representing and summarizing each pattern and for constructing systems biology simulations of cell behaviors.     

A rich and bountiful harvest: Key discoveries in plant cell biology

The field of plant cell biology has a rich history of discovery, going back to Robert Hooke’s discovery of cells themselves. The development of microscopes and preparation techniques has allowed for the visualization of subcellular structures, and the use of protein biochemistry, genetics, and molecular biology has enabled the identification of proteins and mechanisms that regulate key cellular processes. In this review, seven senior plant cell biologists reflect on the development of this research field in the past decades, including the foundational contributions that their teams have made to our rich, current insights into cell biology. Topics covered include signaling and cell morphogenesis, membrane trafficking, cytokinesis, cytoskeletal regulation, and cell wall biology. In addition, these scientists illustrate the pathways to discovery in this exciting research field.

Seven senior plant cell biologists reflect on foundational contributions to a variety of topics, including pollen tube signaling, cell morphogenesis, membrane trafficking, cytokinesis, cytoskeletal regulation, and cell wall biology.     

New steps toward the nucleocytoplasmic traffic of macromolecules

The nucleocytoplasmic transport of functional molecules is mediated bidirectionally through the nuclear pore complex (NPC), which spans the double membranes of the nuclear envelope. It has recently been shown that signaling between the nucleus and the cytoplasm plays a key role in coordinating the cellular processes such as the cell cycle and cell differentiation (Yoneda, 2000). As the result of recent extensive analysis, significant progress has been made in our understanding of the fundamental mechanism of nuclear transport of proteins and RNAs and numerous transport factors have now been identified. In this special issue of review articles, we focus on our rapid growing knowledge of nucleocytoplasmic transport, especially the translocation of proteins through the NPC and mRNA export, and review this exciting field from various points of view including cell biology, structural biology and yeast genetics.     

活细胞单分子实时视见研究

我们对细胞生物学与分子生物学中有关分子事件和相互作用的认识,大部分都是集团平均水平研究的结果,并且基于所有的分子在给定时间内以完全相同的方式运动这样一种不真实的假设。现在,激光技术和全内反射显微镜的应用,以及绿色荧光蛋白(green fluorescent proteins,GFPs)等新的分子荧光探针的出现,使得显示活细胞单个生物分子的运动行为和轨迹成为可能。单分子水平的研究将会加深人们对分子和细胞生物学的基本概念的认识。     

A quick guide to light microscopy in cell biology

Light microscopy is a key tool in modern cell biology. Light microscopy has several features that make it ideally suited for imaging biology in living cells: the resolution is well-matched to the sizes of subcellular structures, a diverse range of available fluorescent probes makes it possible to mark proteins, organelles, and other structures for imaging, and the relatively nonperturbing nature of light means that living cells can be imaged for long periods of time to follow their dynamics. Here I provide a brief introduction to using light microscopy in cell biology, with particular emphasis on factors to be considered when starting microscopy experiments.     

Restitution at the cellular level: regulation of the migrating phenotype.

Intestinal epithelial cells migrating across a mucosal defect are generally described as dedifferentiated, a term that suggests a loss of regulatory biology. Since cell biology may be more readily studied in established cell lines than in vivo, a model is developed using the human Caco-2 intestinal epithelial cell migrating across matrix proteins. This resembles in vivo models of mucosal healing in its sheet migration and loss of the brush border enzymes, which are conventional markers for intestinal epithelial differentiation. Immunohistochemical studies of migrating Caco-2 cells suggest, however, that the rearrangements of cytoskeletal, cell-cell and cell-matrix proteins during migration are not random but seem adapted to the migratory state. Indeed, Caco-2 migration may be substantially regulated by a variety of physiologic and pharmacologic stimuli and differentiation, measured by the specific activity of the intestinal epithelial brush border enzymes alkaline phosphatase and dipeptidyl dipeptidase, may be independently pharmacologically programmed during the stimulation or inhibition of cell motility.     

被子植物生殖细胞和精细胞

随着被子植物精细胞分离技术的突破和细胞生物学以及分子生物学技术的发展,对被子植物精细胞的研究不断深入。在以前细胞生物学研究的基础上结合近年来的分子生物学研究结果对被子植物雄性生殖细胞的产生、精细胞的形成和发育以及有关精细胞的表面蛋白质、精细胞的特异启动子、精细胞cDNA文库的构建等分子生物学研究进展和今后的发展趋势进行了综述。     

Fluorescent proteins: physical-chemical properties and application in cell biology

Green fluorescent protein (GFP) from jellyfish Aequorea victoria is the most extensively studied and widely used in cell biology protein. At present novel naturally occurring GFP-like proteins have been discovered and enhanced mutants of Aequorea GFP have been created. These mutants differ from wild-type GFP by stability, value of quantum yield, absorption and fluorescence spectra position and photochemical properties. GFP-like proteins are the fast growing family. This review is an attempt to characterize the main groups of GFP-like proteins, describe their structure and mechanisms of chromophore formation and summarize the main trends of their utilization as markers and biosensors in cell and molecular biology.     

Biogenesis of lipid droplets--how cells get fatter

Lipid droplets are discrete organelles present in most cell types and organisms including bacteria, yeast, plants, insects and animals. Long considered as passive storage deposits, recent cell biology, proteomic and lipidomic analysis show that lipid droplets are dynamic organelles involved in multiple cellular functions. They have a central function in lipid distribution to different membrane-bound organelles and serve not only as main reservoirs of neutral lipids such as triglycerides and cholesterol but in addition, contain structural proteins, proteins involved in lipid synthesis and transmembrane proteins. A detailed model for how transmembrane proteins such as SNARE proteins can exist in lipid droplets is proposed.     

Molecular insights into the biochemical functions and signalling mechanisms of plant NLRs

Plant intracellular immune receptors known as NLR (nucleotide-binding leucine-rich repeat) proteins confer immunity and cause cell death. Plant NLR proteins that directly or indirectly recognize pathogen effector proteins to initiate immune signalling are regarded as sensor NLRs. Some NLR protein families function downstream of sensor NLRs to transduce immune signalling and are known as helper NLRs. Recent breakthrough studies on plant NLR protein structures and biochemical functions greatly advanced our understanding of NLR biology. Comprehensive and detailed knowledge on NLR biology requires future efforts to solve more NLR protein structures and investigate the signalling events between sensor and helper NLRs, and downstream of helper NLRs.     

Cytokinesis is blocked in mammalian cells transfected with Chlamydia trachomatis gene CT223

Background  

The chlamydiae alter many aspects of host cell biology, including the division process, but the molecular biology of these alterations remains poorly characterized. Chlamydial inclusion membrane proteins (Incs) are likely candidates for direct interactions with host cell cytosolic proteins, as they are secreted to the inclusion membrane and exposed to the cytosol. The inc gene CT223 is one of a sequential set of orfs that encode or are predicted to encode Inc proteins. CT223p is localized to the inclusion membrane in all tested C. trachomatis serovars.     

G proteins in development

The focus of developmental biologists has expanded from the analysis of gene expression to include the analysis of cell signalling. Heterotrimeric G proteins (G proteins) mediate signalling from a superfamily of heptahelical receptors (G-protein-coupled receptors) to a smaller number of effector units that include adenylyl cyclases, phospholipase C and various ion channels. The convergence of developmental biology with cell signalling has now revealed overlaps in which G proteins mediate complex pathways in embryonic development.     

What can proteomic analyses contribute to understanding the molecular biology and clinical behavior of prostate cancer?

Identifying the proteins and their complex interactions that promote and/or sustain the aggressive malignant phenotype is essential for understanding key effectors of the molecular biology of prostate cancer. This is also essential for development of new clinical applications. A variety of proteomic techniques, ranging from mass spectrometry to new methods of multiplexing protein identification, have great potential for rapidly achieving these goals. However, in order to obtain meaningful results, these techniques must be applied within the context of our knowledge of the heterogeneity of prostate tissues and tumors, the impact of specimen processing on both the quality and quantity of proteins detected and a thorough understanding of prostate cell biology. Collaboration between the protein chemist and the prostate cell biologist will expedite progress in this important field.     

Cell surface biology mediated by low affinity multivalent protein-glycan interactions

Glycan-binding proteins mediate diverse aspects of cell biology including pathogen recognition of host cells, cell trafficking, endocytosis and modulation of cell signaling. This is accomplished despite the intrinsic low affinity for their ligands through multivalent interactions that increase effective affinity and adhesive force. Recent successes in the rational design of high-affinity ligands for glycan-binding proteins offer the promise to create well-defined tools for exploring the structure and functions of this class of receptors.     

The time is right: proteome biology of stem cells

In stem cell biology, there is a growing need for advanced technologies that may help to unravel the molecular mechanisms of self-renewal and differentiation. Proteomics, the comprehensive analysis of proteins, is such an emerging technique. To facilitate interactions between specialists in proteomics and stem cell biology,a new initiative has been undertaken, supported by the Human Proteome Organization (HUPO) and the International Society for Stem Cell Research (ISSCR). Here we present the Proteome Biology of Stem Cells Initiative (PBSCI) and report on its goals and future activities.     

Toxoplasma gondii: the model apicomplexan

Toxoplasma gondii is an obligate intracellular protozoan parasite which is a significant human and veterinary pathogen. Other members of the phylum Apicomplexa are also important pathogens including Plasmodium species (i.e. malaria), Eimeria species, Neospora, Babesia, Theileria and Cryptosporidium. Unlike most of these organisms, T. gondii is readily amenable to genetic manipulation in the laboratory. Cell biology studies are more readily performed in T. gondii due to the high efficiency of transient and stable transfection, the availability of many cell markers, and the relative ease with which the parasite can be studied using advanced microscopic techniques. Thus, for many experimental questions, T. gondii remains the best model system to study the biology of the Apicomplexa. Our understanding of the mechanisms of drug resistance, the biology of the apicoplast, and the process of host cell invasion has been advanced by studies in T. gondii. Heterologous expression of apicomplexan proteins in T. gondii has frequently facilitated further characterisation of proteins that could not be easily studied. Recent studies of Apicomplexa have been complemented by genome sequencing projects that have facilitated discovery of surprising differences in cell biology and metabolism between Apicomplexa. While results in T. gondii will not always be applicable to other Apicomplexa, T. gondii remains an important model system for understanding the biology of apicomplexan parasites.