Regulation of cell motile behavior by crosstalk between cadherin- and integrin-mediated adhesions

During normal development and in disease, cohesive tissues undergo rearrangements that require integration of signals from cell adhesions to neighboring cells and to the extracellular matrix (ECM). How a range of cell behaviors is coordinated by these different adhesion complexes is unknown. To analyze epithelial cell motile behavior in response to combinations of cell-ECM and cell-cell adhesion cues, we took a reductionist approach at the single-cell scale by using unique, functionalized micropatterned surfaces comprising alternating stripes of ECM (collagenIV) and adjustable amounts of E-cadherin-Fc (EcadFc). On these surfaces, individual cells spatially segregated integrin- and cadherin-based complexes between collagenIV and EcadFc surfaces, respectively. Cell migration required collagenIV and did not occur on surfaces functionalized with only EcadFc. However, E-cadherin adhesion dampened lamellipodia activity on both collagenIV and EcadFc surfaces and biased the direction of cell migration without affecting the migration rate, all in an EcadFc concentration-dependent manner. Traction force microscopy showed that spatial confinement of integrin-based adhesions to collagenIV stripes induced anisotropic cell traction on collagenIV and migration directional bias. Selective depletion of different pools of alphaE-catenin, an E-cadherin and actin binding protein, identified a membrane-associated pool required for E-cadherin-mediated adhesion and down-regulation of lamellipodia activity and a cytosolic pool that down-regulated the migration rate in an E-cadherin adhesion-independent manner. These results demonstrate that there is crosstalk between E-cadherin- and integrin-based adhesion complexes and that E-cadherin regulates lamellipodia activity and cell migration directionality, but not cell migration rate.

Different roles of cadherins in the assembly and structural integrity of the desmosome complex

Adhesion between cells is established by the formation of specialized intercellular junctional complexes, such as desmosomes. Desmosomes contain isoforms of two members of the cadherin superfamily of cell adhesion proteins, desmocollins (Dsc) and desmogleins (Dsg), but their combinatorial roles in desmosome assembly are not understood. To uncouple desmosome assembly from other cell-cell adhesion complexes, we used micro-patterned substrates of Dsc2aFc and/or Dsg2Fc and collagen IV; we show that Dsc2aFc, but not Dsg2Fc, was necessary and sufficient to recruit desmosome-specific desmoplakin into desmosome puncta and produce strong adhesive binding. Single-molecule force spectroscopy showed that monomeric Dsc2a, but not Dsg2, formed Ca(2+)-dependent homophilic bonds, and that Dsg2 formed Ca(2+)-independent heterophilic bonds with Dsc2a. A W2A mutation in Dsc2a inhibited Ca(2+)-dependent homophilic binding, similar to classical cadherins, and Dsc2aW2A, but not Dsg2W2A, was excluded from desmosomes in MDCK cells. These results indicate that Dsc2a, but not Dsg2, is required for desmosome assembly through homophilic Ca(2+)- and W2-dependent binding, and that Dsg2 might be involved later in regulating a switch to Ca(2+)-independent adhesion in mature desmosomes.

Dendritic spine density in the lobus parolfactorius of the domestic chick is increased 24 h after one-trial passive avoidance training

One to three day old chicks spontaneously peck at small objects. When presented with a chrome bead coated with the bitter tasting substance methyl anthranilate (MeA), chicks peck once, display a characteristic disgust response and subsequently avoid a similar bead. Chicks that are trained on a water coated bead continue to peck a similar bead on retrial. Twenty four hours after training on this one-trial passive avoidance paradigm, chicks were tested for retention. The brains of chicks displaying the correct behavioural response (> 90%) were removed and the lobus parolfactorius from each hemisphere was dissected from the brain and impregnated using a rapid Golgi technique. Analysis of large multipolar neurones by centrifugal dendritic branch order showed that there were significantly more spines on all orders examined in the left hemispheres of MeA-trained chicks compared to water-trained control chicks. Significantly higher spine densities were also found on 4th and 5th order branches of neurones in the right lobus parolfactorius of MeA-trained chicks compared to water-trained chicks. No significant difference in dendritic length was observed. These results suggest that substantial plasticity occurs in post-synaptic structures in the lobus parolfactorius following passive avoidance training. It is suggested that this plasticity is related to processes involved in long term information storage.

The effects of archistriatal lesions on one-trial passive avoidance learning in the chick

The avian archistriatum, part of which may be homologous with the mammalian amygdala, has been implicated in fear and avoidance behaviour. There is also evidence to suggest its involvement in learning. One-trial passive avoidance learning (PAL) has been used extensively to study memory formation in the chick. Young chicks will peck spontaneously at a small, visually conspicuous bead. If the bead has been coated with an aversive substance, the chicks show a disgust response and learn in a single trial not to peck a similar bead on subsequent presentation. Successful acquisition of this one-trial PAL task involves the formation of a learned association between the bead and a noxious taste, followed by the expression of an avoidance response. In view of the possible involvement of the archistriatum in avoidance and learning behaviour, its role in one-trial PAL was investigated by ablation. Bilateral electrolytic lesions of the entire archistriatum prevented the acquisition of the one-trial PAL task. Neither bilateral lesions of the lateral cerebral area nor sham operation affected learning. The impairment of one-trial PAL caused by archistriatal lesions was not due to effects on the visual or motor components of pecking behaviour. The archistriatum could therefore be directly involved in memory formation. It could also be involved in the organization of avoidance behaviour associated with the task, or it could form part of a circuit linking two other forebrain regions previously implicated in one-trial PAL, the intermediate part of the medial hyperstriatum ventrale and the lobus parolfactorius.

Cell-state transitions and collective cell movement generate an endoderm-like region in gastruloids

Shaping the animal body plan is a complex process that involves the spatial organization and patterning of the different germ layers. Recent advances in live imaging have started to unravel the cellular choreography underlying this process in mammals, however, the sequence of events transforming an unpatterned cell ensemble into structured territories is largely unknown. Here, using gastruloids –3D aggregates of mouse embryonic stem cells- we study the formation of one of the three germ layers, the endoderm. We show that the endoderm is generated from an epiblast-like homogeneous state by a three-step mechanism: (i) a loss of E-cadherin mediated contacts in parts of the aggregate leading to the appearance of islands of E-cadherin expressing cells surrounded by cells devoid of E-cadherin, (ii) a separation of these two populations with islands of E-cadherin expressing cells flowing toward the aggregate tip, and (iii) their differentiation into an endoderm population. During the flow, the islands of E-cadherin expressing cells are surrounded by cells expressing T-Brachyury, reminiscent of the process occurring at the primitive streak. Consistent with recent in vivo observations, the endoderm formation in the gastruloids does not require an epithelial-to-mesenchymal transition, but rather a maintenance of an epithelial state for a subset of cells coupled with fragmentation of E-cadherin contacts in the vicinity, and a sorting process. Our data emphasize the role of signaling and tissue flows in the establishment of the body plan.

Archistriatal lesions impair the acquisition of filial preferences during imprinting in the domestic chick

The avian archistriatum has been demonstrated to play a role in agonistic behaviours and avoidance learning. However, the extent of its role in learning is unknown. The involvement of the archistriatum in the learning process of filial imprinting was therefore investigated in day-old chicks. Bilateral archistriatal lesions, lateral cerebral area lesions or sham archistriatal penetrations were made in dark-reared, day-old chicks, which were subsequently exposed to either a rotating red box or blue cylinder for 2 x 1 h training sessions. Three hours later, the approach of chicks to their training object and to the other, novel object was measured. Chicks with archistriatal lesions ran a similar distance towards each stimulus and therefore failed to display a preference for their training object. However, chicks with sham archistriatal penetrations or lateral cerebral area lesions exhibited a significant preference for the object they had been trained upon. These results demonstrate that the archistriatum is essential for the expression of an imprinted preference. All chicks approached their training object significantly more on their second compared to their first training exposure, suggesting that some aspects of imprinting behaviour remain intact in chicks with archistriatal lesions. Taken together with the results of previous work, the current data suggest that the archistriatum may be involved in retention of significant aspects of the imprinting experience, or in motivation to approach imprinting objects.

The effect of archistriatal lesions on 'open field' and fear/avoidance behaviour in the domestic chick

The chick archistriatum has been implicated in avoidance learning and filial imprinting. However, its role in these learning paradigms may be due to the inhibition of normal avoidance responses, since the avian archistriatum has been shown to play a role in fear/avoidance behaviour. The involvement of the archistriatum in the expression of unlearned fear/avoidance behaviour was therefore investigated in two day-old chicks. Chicks were exposed individually to a novel 'open field' for 5 min. Behaviour was recorded on videotape for analysis. In a separate but concurrent experiment, bilateral archistriatal lesions, sham archistriatal lesions or lateral cerebral lesions were made in day-old chicks which were then exposed to the 'open field' arena. At the end of each exposure a novel object was dropped near the chick. Chicks with archistriatal lesions generally displayed greater movement, more pecking behaviour and spent more time near the centre of the 'open field' than other chicks. There were no differences between the treatment groups in latencies to move or begin peeping. The behaviour of untreated chicks in the 'open field' was similar to that of sham-lesioned chicks and there was no effect of hatch on behaviour. Upon exposure to a novel object, indices of fear and avoidance were not changed in lesioned chicks. These results demonstrate that in the young chick, the archistriatum may be involved in the response to mild or intermediate levels of environment or isolation-related stress, but does not appear to be important for overt fear responses or avoidance of novel objects. Taken together with the results of previous work, the data suggests that the archistriatum may be directly involved in avoidance learning and imprinting.

Immobilized WNT Proteins Act as a Stem Cell Niche for Tissue Engineering

The timing, location, and level of WNT signaling are highly regulated during embryonic development and for the maintenance of adult tissues. Consequently the ability to provide a defined and directed source of WNT proteins is crucial to fully understand its role in tissue development and to mimic its activity in vitro. Here we describe a one-step immobilization technique to covalently bind WNT3A proteins as a basal surface with easy storage and long-lasting activity. We show that this platform is able to maintain adult and embryonic stem cells while also being adaptable for 3D systems. Therefore, this platform could be used for recapitulating specific stem cell niches with the goal of improving tissue engineering.

Constructing cellular niche properties by localized presentation of Wnt proteins on synthetic surfaces

Wnt signaling is crucial during embryonic development and for the maintenance of adult tissues. Depending on the tissue type, the Wnt pathway can promote stem cell self-renewal and/or direct lineage commitment. Wnt proteins are subject to lipid modification, often restricting them to act in a localized manner on responsive cells. Most methods for inducing Wnt signaling in stem cell cultures do not control the spatial presentation of the protein. To recreate the local presentation of Wnt proteins often seen in vivo, we previously developed a method to immobilize the protein onto synthetic surfaces. Here we describe a detailed protocol based on covalent binding of nucleophilic groups on Wnt proteins to activated carboxylic acid (COOH) or glutaraldehyde (COH) groups functionalized on synthetic surfaces. As an example, we describe how this method can be used to covalently immobilize Wnt3a proteins on microbeads or a glass surface. This procedure requires ∼3 h and allows for the hydrophobic protein to be stored in the absence of detergent. The immobilization efficiency of active Wnt proteins can be assessed using different T-cell factor (TCF) reporter assays as a readout for Wnt/β-catenin-dependent transcription. Immobilization efficiency can be measured 12-18 h after seeding the cells and takes 2-4 h. The covalent immobilization of Wnt proteins can also be used for single-cell analysis using Wnt-coated microbeads (12-18 h of live imaging) and to create a Wnt platform on a glass surface for stem cell maintenance and cell population analysis (3 d). The simple chemistry used for Wnt immobilization allows for adaptation to new materials and other developmental signals. Therefore, this method can also be incorporated into tissue engineering platforms in which depletion of the stem cell pool restricts the complexity and maturity of the tissue developed.

A system for the reconstruction and analysis of dendritic fields

We report here the development of a fast and 'user friendly' Semiautomatic Neuron Reconstruction and Analysis System (SANRAS) based on a Zeiss Universal microscope, Kontron Microscope Control Processor (MCP), and Apple Macintosh SE microcomputer. Four programs for digitisation and analysis have been written; STAGE, CONVERTZ, RECON and SHOLL. Cells are digitised by superimposing ocular crosshairs on a dendrite and tracing directly, the stage position in x, y, and z co-ordinates being recorded by the computer at points indicated by a keypress. Cells can be digitised from serial thick sections and dendritic reconstructions can be visualised on screen, rotated and viewed from any angle. Output is given either to a Hewlett Packard colour plotter or to a laser printer, in graphical form, and as a summary of various metrical and topological parameters. Radial Scholl diagrams of dendritic trees may also be produced. Dendritic branching patterns of Golgi-impregnated neurons of the left and right intermediate medial hyperstriatum ventrale of the chick are described.

Evolutionary origin of vertebrate OCT4/POU5 functions in supporting pluripotency

The support of pluripotent cells over time is an essential feature of development. In eutherian embryos, pluripotency is maintained from naïve states in peri-implantation to primed pluripotency at gastrulation. To understand how these states emerged, we reconstruct the evolutionary trajectory of the Pou5 gene family, which contains the central pluripotency factor OCT4. By coupling evolutionary sequence analysis with functional studies in mouse embryonic stem cells, we find that the ability of POU5 proteins to support pluripotency originated in the gnathostome lineage, prior to the generation of two paralogues, Pou5f1 and Pou5f3 via gene duplication. In osteichthyans, retaining both genes, the paralogues differ in their support of naïve and primed pluripotency. The specialization of these duplicates enables the diversification of function in self-renewal and differentiation. By integrating sequence evolution, cell phenotypes, developmental contexts and structural modelling, we pinpoint OCT4 regions sufficient for naïve pluripotency and describe their adaptation over evolutionary time.

Fabricating surfaces with distinct geometries and different combinations of cell adhesion proteins

A step-by-step procedure is described for functionalizing the surface of a glass coverslip so that a single cell contacts distinct patterns of extracellular matrix and cell-cell adhesion proteins. This dual-micropatterned substratum is accomplished through a two-step process. First, extracellular matrix (ECM) is microcontact-printed onto a silanized glass surface using electron beam lithography, etched resist-coated wafers, and Polydimethylsiloxane (PDMS) stamps of differing geometries. Then, non-ECM-coated surfaces are incubated sequentially with biotin, NeutrAvidin, and biotinylated Protein A to attach Fc-cadherin fusion proteins, Fc, or PEG. Cells are seeded at low density onto the functionalized surface for single-cell analysis of protein recruitment/turnover and cellular motility.