Micropatterning as a tool to decipher cell morphogenesis and functions

In situ, cells are highly sensitive to geometrical and mechanical constraints from their microenvironment. These parameters are, however, uncontrolled under classic culture conditions, which are thus highly artefactual. Micro-engineering techniques provide tools to modify the chemical properties of cell culture substrates at sub-cellular scales. These can be used to restrict the location and shape of the substrate regions, in which cells can attach, so-called micropatterns. Recent progress in micropatterning techniques has enabled the control of most of the crucial parameters of the cell microenvironment. Engineered micropatterns can provide a micrometer-scale, soft, 3-dimensional, complex and dynamic microenvironment for individual cells or for multi-cellular arrangements. Although artificial, micropatterned substrates allow the reconstitution of physiological in situ conditions for controlled in vitro cell culture and have been used to reveal fundamental cell morphogenetic processes as highlighted in this review. By manipulating micropattern shapes, cells were shown to precisely adapt their cytoskeleton architecture to the geometry of their microenvironment. Remodelling of actin and microtubule networks participates in the adaptation of the entire cell polarity with respect to external constraints. These modifications further impact cell migration, growth and differentiation.

Improved visualization and quantitative analysis of drug effects using micropatterned cells

To date, most HCA (High Content Analysis) studies are carried out with adherent cell lines grown on a homogenous substrate in tissue-culture treated micro-plates. Under these conditions, cells spread and divide in all directions resulting in an inherent variability in cell shape, morphology and behavior. The high cell-to-cell variance of the overall population impedes the success of HCA, especially for drug development. The ability of micropatterns to normalize the shape and internal polarity of every individual cell provides a tremendous opportunity for solving this critical bottleneck (1-2). To facilitate access and use of the micropatterning technology, CYTOO has developed a range of ready to use micropatterns, available in coverslip and microwell formats. In this video article, we provide detailed protocols of all the procedures from cell seeding on CYTOOchip micropatterns, drug treatment, fixation and staining to automated acquisition, automated image processing and final data analysis. With this example, we illustrate how micropatterns can facilitate cell-based assays. Alterations of the cell cytoskeleton are difficult to quantify in cells cultured on homogenous substrates, but culturing cells on micropatterns results in a reproducible organization of the actin meshwork due to systematic positioning of the cell adhesion contacts in every cell. Such normalization of the intracellular architecture allows quantification of even small effects on the actin cytoskeleton as demonstrated in these set of protocols using blebbistatin, an inhibitor of the actin-myosin interaction.

The centrosome neither persistently leads migration nor determines the site of axonogenesis in migrating neurons in vivo

The position of the centrosome ahead of the nucleus has been considered crucial for coordinating neuronal migration in most developmental situations. The proximity of the centrosome has also been correlated with the site of axonogenesis in certain differentiating neurons. Despite these positive correlations, accumulating experimental findings appear to negate a universal role of the centrosome in determining where an axon forms, or in leading the migration of neurons. To further examine this controversy in an in vivo setting, we have generated cell type-specific multi-cistronic gene expression to monitor subcellular dynamics in the developing zebrafish cerebellum. We show that migration of rhombic lip-derived neurons is characterized by a centrosome that does not persistently lead the nucleus, but which is instead regularly overtaken by the nucleus. In addition, axonogenesis is initiated during the onset of neuronal migration and occurs independently of centrosome proximity. These in vivo data reveal a new temporal orchestration of organelle dynamics and provide important insights into the variation in intracellular processes during vertebrate brain differentiation.

Short-term molecular polarization of cells on symmetric and asymmetric micropatterns

The ability of cells to sense geometrical/physical constraints of local environment is important for cell movements during development, immune surveillance, and in cancer invasion. In this paper, we quantify "front-rear" polarization - the crucial step in initiating cell migration - based on cytoskeleton and substrate adhesion anisotropy in micropatterned cells of well-defined shapes. We then show that the general viewpoint that asymmetric cell shape is one of the defining characteristics of polarized cells is incomplete. Specifically, we demonstrate that cells on circular micropatterned islands can exhibit asymmetric distribution of both filamentous actin (f-actin) and focal adhesions (FAs) as well as directional, lamellipodial-like ruffling activity. This asymmetry, however, is transient and persists only for the period of several hours during which actin filaments and adhesion structures reorganize into symmetric peripheral arrangement. Cells on asymmetric tear-drop shape islands also display polarized f-actin and FAs, but polarization axes are oriented towards the wide end of the islands. Polarization of actin filaments on tear-drop islands is short-term, while focal adhesions remain asymmetrically distributed for long times. From a practical perspective, circular cells constitute a convenient experimental system, in which phenomena related to cell polarization are "decoupled" from the effects of cells' local curvature (constant along circular cell's perimeter), while asymmetric (tear-drop) micropatterned cells standardize the organization of motility machinery of polarized/ moving cells. Both systems may prove useful for the design of diagnostic tools with which to probe and quantify ex vivo the motility/invasiveness status of cells from cancer patients.

Coordinate control of host centrosome position, organelle distribution, and migratory response by Toxoplasma gondii via host mTORC2

The invasion of host cells by Toxoplasma gondii is accompanied by a reorganization of host cell structure, in which the host centrosome and Golgi apparatus are localized to the vacuole, and mitochondria, microtubules, and endolysosomes are recruited to the vacuole perimeter. The mechanism and functional significance of this process have not been well defined. Here, we report that the centrosome-vacuole association was abolished in mammalian target of rapamycin complex 2 (mTORC2)-deficient cells, which also displayed a disordered distribution of perivacuolar host mitochondria and lysosomes. Infection of fibroblasts led to stable, mTORC2-dependent activation of Akt, and Akt inhibition mimicked the effect of mTORC2 ablation on centrosome, mitochondria, and lysosome localization. Mobilization of the centrosome by Akt inhibition was abrogated by inhibitors of glycogen synthase kinase 3 (GSK3), implying that the centrosome is constrained to the vacuole through an mTORC2-Akt-GSK3 pathway. Infected cells were incapable of migration in a wounded monolayer model, and this effect was associated with the inability of centrosomes to reorient in the direction of migration. Both migration and centrosome reorientation were fully restored upon ablation of mTORC2. These findings provide the first linkage of host signals to parasite-mediated host cell reorganization and demonstrate migratory suppression as a novel functional consequence of this process that is associated with mTORC2-mediated centrosome constraint.

The Golgi and the centrosome: building a functional partnership

The mammalian Golgi apparatus is characterized by a ribbon-like organization adjacent to the centrosome during interphase and extensive fragmentation and dispersal away from the centrosome during mitosis. It is not clear whether this dynamic association between the Golgi and centrosome is of functional significance. We discuss recent findings indicating that the Golgi–centrosome relationship may be important for directional protein transport and centrosome positioning, which are both required for cell polarization. We also summarize our current knowledge of the link between Golgi organization and cell cycle progression.

Monomeric red fluorescent proteins with a large Stokes shift

Two-photon microscopy has advanced fluorescence imaging of cellular processes in living animals. Fluorescent proteins in the blue-green wavelength range are widely used in two-photon microscopy; however, the use of red fluorescent proteins is limited by the low power output of Ti-Sapphire lasers above 1,000 nm. To overcome this limitation we have developed two red fluorescent proteins, LSS-mKate1 and LSS-mKate2, which possess large Stokes shifts with excitation/emission maxima at 463/624 and 460/605 nm, respectively. These LSS-mKates are characterized by high pH stability, photostability, rapid chromophore maturation, and monomeric behavior. They lack absorbance in the green region, providing an additional red color to the commonly used red fluorescent proteins. Substantial overlap between the two-photon excitation spectra of the LSS-mKates and blue-green fluorophores enables multicolor imaging using a single laser. We applied this approach to a mouse xenograft model of breast cancer to intravitally study the motility and Golgi-nucleus alignment of tumor cells as a function of their distance from blood vessels. Our data indicate that within 40 mum the breast cancer cells show significant polarization towards vessels in living mice.

TBCCD1, a new centrosomal protein, is required for centrosome and Golgi apparatus positioning

In animal cells the centrosome is positioned at the cell centre in close association with the nucleus. The mechanisms responsible for this are not completely understood. Here, we report the first characterization of human TBCC-domain containing 1 (TBCCD1), a protein related to tubulin cofactor C. TBCCD1 localizes at the centrosome and at the spindle midzone, midbody and basal bodies of primary and motile cilia. Knockdown of TBCCD1 in RPE-1 cells caused the dissociation of the centrosome from the nucleus and disorganization of the Golgi apparatus. TBCCD1-depleted cells are larger, less efficient in primary cilia assembly and their migration is slower in wound-healing assays. However, the major microtubule-nucleating activity of the centrosome is not affected by TBCCD1 silencing. We propose that TBCCD1 is a key regulator of centrosome positioning and consequently of internal cell organization.

Impact of tumor cell cytoskeleton organization on invasiveness and migration: a microchannel-based approach

Cell migration is a fundamental feature of the interaction of cells with their surrounding. The cell's stiffness and ability to deform itself are two major characteristics that rule migration behavior especially in three-dimensional tissue. We simulate this situation making use of a micro-fabricated migration chip to test the active invasive behavior of pancreatic cancer cells (Panc-1) into narrow channels. At a channel width of 7 microm cell migration through the channels was significantly impeded due to size exclusion. A striking increase in cell invasiveness was observed once the cells were treated with the bioactive lipid sphingosylphosphorylcholine (SPC) that leads to a reorganization of the cell's keratin network, an enhancement of the cell's deformability, and also an increase in the cell's migration speed on flat surfaces. The migration speed of the highly deformed cells inside the channels was three times higher than of cells on flat substrates but was not affected upon SPC treatment. Cells inside the channels migrated predominantly by smooth sliding while maintaining constant cell length. In contrast, cells on adhesion mediating narrow lines moved in a stepwise way, characterized by fluctuations in cell length. Taken together, with our migration chip we demonstrate that the dimensionality of the environment strongly affects the migration phenotype and we suggest that the spatial cytoskeletal keratin organization correlates with the tumor cell's invasive potential.

Protein micropatterns: A direct printing protocol using deep UVs

The described protocol is a simple method to make protein micropatterns with a micron size resolution. It can be applied to control cell shape and adhesive geometry, and also for any other assay requiring protein patterning. It is based on the use of a photomask with microfeatures to locally irradiate with deep UV light (below 200 nm) an antifouling substrate, making it locally adsorbing for proteins. The entire process can be subdivided into three main parts. The first part describes the design of a photomask. The second part describes the passivation (antifouling treatment) of the substrate, its irradiation, and the binding of proteins. The entire process can be completed in a couple of hours. It requires no expensive equipment and can be performed in any biology lab. The last part describes cell deposition on the micropatterned substrate. We also provide a discussion with pitfalls and alternative techniques adapted to various substrates, including silicone elastomers.

The neural crest epithelial-mesenchymal transition in 4D: a 'tail' of multiple non-obligatory cellular mechanisms

An epithelial-mesenchymal transition (EMT) is the process whereby epithelial cells become mesenchymal cells, and is typified by the generation of neural crest cells from the neuroepithelium of the dorsal neural tube. To investigate the neural crest EMT, we performed live cell confocal time-lapse imaging to determine the sequence of cellular events and the role of cell division in the EMT. It was observed that in most EMTs, the apical cell tail is retracted cleanly from the lumen of the neuroepithelium, followed by movement of the cell body out of the neural tube. However, exceptions to this sequence include the rupture of the neural crest cell tail during retraction (junctional complexes not completely downregulated), or translocation of the cell body away from the apical surface while morphologically rounded up in M phase (no cell tail retraction event). We also noted that cell tail retraction can occur either before or after the redistribution of apical-basolateral epithelial polarity markers. Surprisingly, we discovered that when an EMT was preceded by a mitotic event, the plane of cytokinesis does not predict neural crest cell fate. Moreover, when daughter cells are separated from the adherens junctions by a parallel mitotic cleavage furrow, most re-establish contact with the apical surface. The diversity of cellular mechanisms by which neural crest cells can separate from the neural tube suggests that the EMT program is a complex network of non-linear mechanisms that can occur in multiple orders and combinations to allow neural crest cells to escape from the neuroepithelium.

Live imaging of development in fish embryos

Understanding the cellular and molecular mechanisms that drive the development of embryos requires a detailed knowledge of the way cells divide, move, change shape, interact with one another and die during embryogenesis. Ideally this should be analysed in intact embryos using minimally invasive techniques. Because of their easy accessibility, external development and excellent transparency the teleost embryo has emerged as probably the premier vertebrate model for this type of study. This review will discuss some of the recent advances in this field including attempts to image every cell and their movements during the first 24h of development as well as other studies that focus on the development of specific organs or high resolution analyses of the behaviour of individual cells.

The epithelial cell adhesion molecule EpCAM is required for epithelial morphogenesis and integrity during zebrafish epiboly and skin development

The aberrant expression of the transmembrane protein EpCAM is associated with tumor progression, affecting different cellular processes such as cell–cell adhesion, migration, proliferation, differentiation, signaling, and invasion. However, the in vivo function of EpCAM still remains elusive due to the lack of genetic loss-of-function studies. Here, we describe epcam (tacstd) null mutants in zebrafish. Maternal-zygotic mutants display compromised basal protrusive activity and epithelial morphogenesis in cells of the enveloping layer (EVL) during epiboly. In partial redundancy with E-cadherin (Ecad), EpCAM made by EVL cells is further required for cell–cell adhesion within the EVL and, possibly, for proper attachment of underlying deep cells to the inner surface of the EVL, thereby also affecting deep cell epiboly movements. During later development, EpCAM per se becomes indispensable for epithelial integrity within the periderm of the skin, secondarily leading to disrupted morphology of the underlying basal epidermis and moderate hyper-proliferation of skin cells. On the molecular level, EVL cells of epcam mutant embryos display reduced levels of membranous Ecad, accompanied by an enrichment of tight junction proteins and a basal extension of apical junction complexes (AJCs). Our data suggest that EpCAM acts as a partner of E-cadherin to control adhesiveness and integrity as well as plasticity and morphogenesis within simple epithelia. In addition, EpCAM is required for the interaction of the epithelia with underlying cell layers.

EpCAM is a well-established marker for carcinomas of epithelial origin and a potential target for immunotherapy. In vitro analyses have implicated EpCAM in a plethora of different cellular processes, such as adhesion, motility, proliferation, differentiation, and signaling. Strikingly, depending on the context, EpCAM displayed rather opposite effects, either promoting or attenuating cell–cell adhesion versus cell migration and tissue invasion, a phenomenon described as the “double-face” of EpCAM. However, the in vivo relevance of its different effects remained largely unclear. Here, we present the first genetic analysis of EpCAM function in vivo, based on loss-of-function mutants in the zebrafish. As it is in mammals, zebrafish EpCAM is expressed in simple epithelia. Mutant embryos display defects both in epithelial morphogenesis and in epithelial integrity. Reduced epithelial morphogenesis is accompanied, and possibly caused, by an extension of apical junctional complexes and compromised basal protrusive activity. Furthermore, mutant epithelia display alterations in the relative abundance of adherence junction versus tight junction components. In addition, EpCAM tightly cooperates with E-cadherin and has a previously unrecognized trans effect on the morphogenesis and integrity of underlying cell layers. Cell differentiation and proliferation in EpCAM mutants are not, or only secondarily, affected. During later development and adulthood, EpCAM is largely dispensable, reinforcing its suitability as a target for anti-carcinoma immunotherapy with minimal side effects.

Combining nanosurface chemistry and microfluidics for molecular analysis and cell biology

Development of new tools catalyzes progress in biochemical sciences [G.M. Whitesides, E. Ostuni, S. Takayama, X.Y. Jiang, D.E. Ingber, Annual Review of Biomedical Engineering 3 (2001) 335]. Recent advances in micro-/nano-technology have resulted in an explosion of the number of new tools available for biochemical sciences. We have used surface chemistry, nano-structures and microfluidics to create a set of tools applicable for problems ranging from molecular to cellular analysis. These tools will promote the understanding of fundamental problems in cell biology, development and neurobiology, and become useful for real-world applications such as molecular diagnostics, food analysis and environmental monitoring.

Following the fate in vivo of COPI vesicles generated in vitro

COPI vesicles are a class of transport carriers that function in the early secretory pathway. Their fate and function are still controversial. This includes their contribution to bidirectional transport within the Golgi apparatus and their role during cell division. Here we describe a method that should address several open questions about the fate and function of COPI vesicles in vivo. To this end, fluorescently labeled COPI vesicles were generated in vitro from isolated rat liver Golgi membranes, labeled with the fluorescent dyes Alexa-488 or Alexa-568. These vesicles appeared to be active and colocalized with endogenous Golgi membranes within 30 min after microinjection into mammalian cells. The COPI vesicle-derived labeled membrane proteins could be classified into two types that behaved like endogenous proteins after Brefeldin A treatment.

One-dimensional topography underlies three-dimensional fibrillar cell migration

Current concepts of cell migration were established in regular two-dimensional (2D) cell culture, but the roles of topography are poorly understood for cells migrating in an oriented 3D fibrillar extracellular matrix (ECM). We use a novel micropatterning technique termed microphotopatterning (μPP) to identify functions for 1D fibrillar patterns in 3D cell migration. In striking contrast to 2D, cell migration in both 1D and 3D is rapid, uniaxial, independent of ECM ligand density, and dependent on myosin II contractility and microtubules (MTs). 1D and 3D migration are also characterized by an anterior MT bundle with a posterior centrosome. We propose that cells migrate rapidly through 3D fibrillar matrices by a 1D migratory mechanism not mimicked by 2D matrices.

Organelle positioning and cell polarity

In spite of conspicuous differences in their polarized architecture, swimming unicellular eukaryotes and migrating cells from metazoa display a conserved hierarchical interlocking of the main cellular compartments, in which the microtubule network has a dominant role. A microtubule array can organize the distribution of endomembranes owing to a cell-wide and polarized extension around a unique nucleus-associated structure. The nucleus-associated structure in animal cells contains a highly conserved organelle, the centriole or basal body. This organelle has a defined polarity that can be transmitted to the cell. Its conservative mode of duplication seems to be a core mechanism for the transmission of polarities through cell division.

Dynamic Fgf signaling couples morphogenesis and migration in the zebrafish lateral line primordium

The collective migration of cells in the form of cohesive tissues is a hallmark of both morphogenesis and repair. The extrinsic cues that direct these complex migrations usually act by regulating the dynamics of a specific subset of cells, those at the leading edge. Given that normally the function of tissue migration is to lay down multicellular structures, such as branched epithelial networks or sensory organs, it is surprising how little is known about the mechanisms that organize cells behind the leading edge. Cells of the zebrafish lateral line primordium switch from mesenchyme-like leader cells to epithelial rosettes that develop into mechanosensory organs. Here, we show that this transition is regulated by an Fgf signaling circuit that is active within the migrating primordium. Point sources of Fgf ligand drive surrounding cells towards a ;non-leader' fate by increasing their epithelial character, a prerequisite for rosette formation. We demonstrate that the dynamic expression of Fgf ligands determines the spatiotemporal pattern of epithelialization underlying sensory organ formation in the lateral line. Furthermore, this work uncovers a surprising link between internal tissue organization and collective migration.