Filopodia assemble unique integrin-adhesion complexes to sense the extracellular matrix. However, the mechanisms of integrin localization and regulation in filopodia are poorly defined. Here, we observed that active integrins accumulate at the tip of myosin-X (MYO10)-positive filopodia while inactive integrins are uniformly distributed. RNAi depletion of 10 integrin activity modulators identified talin as the principal integrin activator in filopodia. Deletion of the MYO10-FERM domain, or mutation of the β1-integrin-binding residues within, revealed MYO10 as facilitating integrin activation but not transport in filopodia. However, MYO10-FERM alone could not activate integrins, potentially due to dual binding to both a- and β-integrin tails. As swapping MYO10-FERM with talin-FERM enabled integrin activation in filopodia, our data indicate that an integrin-binding FERM domain coupled to a myosin motor is a core requirement for integrin activation in filopodia. Therefore, we propose a two-step integrin activation model in filopodia: receptor tethering by MYO10 followed by talin-mediated integrin activation.
Mitro Miihkinen, Max L.B. Grönloh, Helena Vihinen, Eija Jokitalo, Benjamin T. Goult, Johanna Ivaska, Guillaume Jacquemet
Deep Learning (DL) methods are powerful analytical tools for microscopy and can outperform conventional image processing pipelines. Despite the enthusiasm and innovations fuelled by DL technology, the need to access powerful and compatible resources to train DL networks leads to an accessibility barrier that novice users often find difficult to overcome. Here, we present ZeroCostDL4Mic, an entry-level platform simplifying DL access by leveraging the free, cloud-based computational resources of Google Colab. ZeroCostDL4Mic allows researchers with no coding expertise to train and apply key DL networks to perform tasks including segmentation (using U-Net and StarDist), object detection (using YOLOv2), denoising (using CARE and Noise2Void), super-resolution microscopy (using Deep-STORM), and image-to-image translation (using Label-free prediction – fnet, pix2pix and CycleGAN). Importantly, we provide suitable quantitative tools for each network to evaluate model performance, allowing model optimisation. We demonstrate the application of the platform to study multiple biological processes.
Lucas von Chamier, Romain F. Laine, Johanna Jukkala, Christoph Spahn, Daniel Krentzel, Elias Nehme, Martina Lerche, Sara Hernández-Pérez, Pieta K. Mattila, Eleni Karinou, Séamus Holden, Ahmet Can Solak, Alexander Krull, Tim-Oliver Buchholz, Martin L. Jones, Loïc A Royer, Christophe Leterrier, Yoav Shechtman, Florian Jug, Mike Heilemann, Guillaume Jacquemet, Ricardo Henriques
The ability of cells to migrate is a fundamental physiological process involved in embryonic development, tissue homeostasis, immune surveillance, and wound healing. Therefore, the mechanisms governing cellular locomotion have been under intense scrutiny over the last 50 years. One of the main tools of this scrutiny is live-cell quantitative imaging, where researchers image cells over time to study their migration and quantitatively analyze their dynamics by tracking them using the recorded images. Despite the availability of computational tools, manual tracking remains widely used among researchers due to the difficulty setting up robust automated cell tracking and large-scale analysis. Here we provide a detailed analysis pipeline illustrating how the deep learning network StarDist can be combined with the popular tracking software TrackMate to perform 2D automated cell tracking and provide fully quantitative readouts. Our proposed protocol is compatible with both fluorescent and widefield images. It only requires freely available and open-source software (ZeroCostDL4Mic and Fiji), and does not require any coding knowledge from the users, making it a versatile and powerful tool for the field. We demonstrate this pipeline’s usability by automatically tracking cancer cells and T cells using fluorescent and brightfield images. Importantly, we provide, as supplementary information, a detailed step-by-step protocol to allow researchers to implement it with their images.
Elnaz Fazeli, Nathan H. Roy, Gautier Follain, Romain F. Laine, Lucas von Chamier, Pekka E. Hänninen, John E. Eriksson, Jean-Yves Tinevez, Guillaume Jacquemet
This review discusses recent advances in our understanding of the role filopodia and filopodia-like structures in cell adhesion and three dimensional (3D) cell migration both in vitro and in vivo. In particular, we focus on recent advances demonstrating that filopodia are involved in substrate tethering and environment sensing in vivo. We further discuss the emerging role of filopodia and filopodial proteins in tumor dissemination as mounting in vitro, in vivo and clinical evidence suggest that filopodia drive cancer cell invasion and highlight filopodia proteins as attractive therapeutic targets. Finally, we outline outstanding questions that remain to be addressed to elucidate the role of filopodia during 3D cell migration.
Guillaume Jacquemet, Hellyeh Hamidi & Johanna Ivaska
Cellular mechanics play a crucial role in tissue homeostasis and are often misregulated in disease. Traction force microscopy is one of the key methods that has enabled researchers to study fundamental aspects of mechanobiology; however, traction force microscopy is limited by poor resolution. Here, we propose a simplified protocol and imaging strategy that enhances the output of traction force microscopy by increasing i) achievable bead density and ii) the accuracy of bead tracking. Our approach relies on super-resolution microscopy, enabled by fluorescence fluctuation analysis. Our pipeline can be used on spinning-disk confocal or widefield microscopes and is compatible with available analysis software. In addition, we demonstrate that our workflow can be used to gain biologically relevant information and is suitable for fast long-term live measurement of traction forces even in light-sensitive cells. Finally, using fluctuation-based traction force microscopy, we observe that filopodia align to the force field generated by focal adhesions.
Aki Stubb, Romain F. Laine, Mitro Miihkinen, Hellyeh Hamidi, Camilo Guzmán, Ricardo Henriques, Guillaume Jacquemet*, Johanna Ivaska*
2D surfaces offer simple analysis of cells in culture, yet these often
yield different cell morphologies and responses from those observed in vivo.
Considerable effort has therefore been expended on the generation of
more tissue-like environments for the study of cell behavior in vitro. Purified matrix proteins provide a 3D scaffold that better mimics the in vivo situation; however, these are far removed from the complex tissue composition seen in vivo. Cell-derived matrices (CDMs) offer a more physiologically relevant alternative for studying in vivo-like cell behavior in vitro.
In the protocol described here, fibroblasts cultured on gelatin-coated
surfaces are maintained in the presence of ascorbic acid to strengthen
matrix deposition over 1–3 weeks. The resulting fibrillar CDMs are
denuded of cells, and other cells are subsequently cultured on them,
after which their behavior is monitored. We also demonstrate how to use
CDMs as an in vivo-relevant reductionist model for studying tumor-stroma-induced changes in carcinoma cell proliferation and migration.
Riina Kaukonen, Guillaume Jacquemet, Hellyeh Hamidi & Johanna Ivaska
Defective filopodia formation is linked to pathologies such as cancer, wherein actively protruding filopodia, at the invasive front, accompany cancer cell dissemination. Despite wide biological significance, delineating filopodia function in complex systems remains challenging and is particularly hindered by lack of compatible methods to quantify filopodia properties. Here, we present FiloQuant, a freely available ImageJ plugin, to detect filopodia-like protrusions in both fixed- and live-cell microscopy data. We demonstrate that FiloQuant can extract quantifiable information, including protrusion dynamics, density, and length, from multiple cell types and in a range of microenvironments. In cellular models of breast ductal carcinoma in situ, we reveal a link between filopodia formation at the cell–matrix interface, in collectively invading cells and 3D tumor spheroids, and the in vitro invasive capacity of the carcinoma. Finally, using intravital microscopy, we observe that tumor spheroids display filopodia in vivo, supporting a potential role for these protrusions during tumorigenesis.
Guillaume Jacquemet , Ilkka Paatero, Alexandre F. Carisey, Artur Padzik, Jordan S. Orange, Hellyeh Hamidi & Johanna Ivaska
Filopodia are fingerlike membrane protrusions that are extended by cells in vitro and in vivo. Due to important roles in sensing the extracellular microenvironment, filopodia and filopodia-like protrusions have been implicated in numerous biological processes including epithelial sheet zippering in development and wound healing and in cancer progression. Recently, there has been an explosion in the number of software available to analyze specific features of cell protrusions with the aim of gaining mechanistic insights into the action of filopodia and filopodia-like structures. In this methods chapter, we highlight an open-access software called FiloQuant that has been developed to specifically quantify the length, density, and dynamics of filopodia and filopodia-like structures from in vitro and in vivo generated samples. We provide step-by-step protocols on (i) how to install FiloQuant in the ImageJ platform (Fiji), (ii) how to quantify filopodia and filopodia-like protrusions from single images using FiloQuant, and (iii) how to track filopodial protrusions from live-cell imaging experiments using FiloQuant and TrackMate.
Guillaume Jacquemet, Hellyeh Hamidi & Johanna Ivaska
Mounting in vitro, in vivo and clinical evidence suggest an important role for filopodia in driving cancer cell invasion. Using a high-throughput microscopic-based drug screen, we identify FDA-approved calcium channel blockers (CCBs) as potent inhibitors of filopodia formation in cancer cells. Unexpectedly, we discover that L-type calcium channels are functional and frequently expressed in cancer cells suggesting a previously unappreciated role for these channels during tumorigenesis. We further demonstrate that, at filopodia, L-type calcium channels are activated by integrin inside-out signalling, integrin activation and Src. Moreover, L-type calcium channels promote filopodia stability and maturation into talin-rich adhesions through the spatially restricted regulation of calcium entry and subsequent activation of the protease calpain-1. Altogether we uncover a novel and clinically relevant signalling pathway that regulates filopodia formation in cancer cells and propose that cycles of filopodia stabilization, followed by maturation into focal adhesions, directs cancer cell migration and invasion.
Guillaume Jacquemet, Habib Baghirov, Maria Georgiadou, Harri Sihto, Emilia Peuhu, Pierre Cettour-Janet, Tao He, Merja Perälä, Pauliina Kronqvist, Heikki Joensuu & Johanna Ivaska
Filopodia are adhesive cellular protrusions specialized in the detection of extracellular matrix (ECM)-derived cues. Although ECM engagement at focal adhesions is known to trigger the recruitment of hundreds of proteins (“adhesome”) to fine-tune cellular behavior, the components of the filopodia adhesions remain undefined. Here, we performed a structured-illumination-microscopy-based screen to map the localization of 80 target proteins, linked to cell adhesion and migration, within myosin-X-induced filopodia. We demonstrate preferential enrichment of several adhesion proteins to either filopodia tips, filopodia shafts, or shaft subdomains, suggesting divergent, spatially restricted functions for these proteins. Moreover, proteins with phosphoinositide (PI) binding sites are particularly enriched in filopodia. This, together with the strong localization of PI(3,4)P2 in filopodia tips, predicts critical roles for PIs in regulating filopodia ultra-structure and function. Our mapping further reveals that filopodia adhesions consist of a unique set of proteins, the filopodome, that are distinct from classical nascent adhesions, focal adhesions, and fibrillar adhesions. Using live imaging, we observe that filopodia adhesions can give rise to nascent adhesions, which, in turn, form focal adhesions. We demonstrate that p130Cas (BCAR1) is recruited to filopodia tips via its C-terminal Cas family homology domain (CCHD) and acts as a mechanosensitive regulator of filopodia stability. Finally, we demonstrate that our map based on myosin-X-induced filopodia can be translated to endogenous filopodia and fascin- and IRSp53-mediated filopodia.
Guillaume Jacquemet, Aki Stubb, Rafael Saup, Mitro Miihkinen, Elena Kremneva, Hellyeh Hamidi & Johanna Ivaska
The ability of cells to migrate is a fundamental physiological process involved in embryonic development, tissue homeostasis, immune surveillance and wound healing. In order for cells to migrate, they must interact with their environment using adhesion receptors, such as integrins, and form specialized adhesion complexes that mediate responses to different extracellular cues. In this review, we discuss the role of integrin adhesion complexes (IACs) in cell migration, highlighting the layers of regulation that are involved, including intracellular signalling cascades, mechanosensing and reciprocal feedback to the extracellular environment. We also discuss the role of IACs in extracellular matrix remodeling and how they impact upon cell migration.