RESUMO
RAC1 activity is critical for intestinal homeostasis, and is required for hyperproliferation driven by loss of the tumour suppressor gene Apc in the murine intestine. To avoid the impact of direct targeting upon homeostasis, we reasoned that indirect targeting of RAC1 via RAC-GEFs might be effective. Transcriptional profiling of Apc deficient intestinal tissue identified Vav3 and Tiam1 as key targets. Deletion of these indicated that while TIAM1 deficiency could suppress Apc-driven hyperproliferation, it had no impact upon tumourigenesis, while VAV3 deficiency had no effect. Intriguingly, deletion of either gene resulted in upregulation of Vav2, with subsequent targeting of all three (Vav2-/- Vav3-/- Tiam1-/-), profoundly suppressing hyperproliferation, tumourigenesis and RAC1 activity, without impacting normal homeostasis. Critically, the observed RAC-GEF dependency was negated by oncogenic KRAS mutation. Together, these data demonstrate that while targeting RAC-GEF molecules may have therapeutic impact at early stages, this benefit may be lost in late stage disease.
Assuntos
Carcinogênese/metabolismo , Carcinogênese/patologia , Fatores de Troca do Nucleotídeo Guanina/metabolismo , Intestinos/patologia , Transdução de Sinais , Proteínas rac1 de Ligação ao GTP/metabolismo , Proteína da Polipose Adenomatosa do Colo/metabolismo , Animais , Carcinogênese/genética , Homeostase , Intestinos/ultraestrutura , Camundongos Knockout , Mutação/genética , Especificidade de Órgãos , Fenótipo , Proteínas Proto-Oncogênicas c-vav/metabolismo , Proteínas Proto-Oncogênicas p21(ras)/genética , Proteína 1 Indutora de Invasão e Metástase de Linfoma de Células T/metabolismo , Regulação para Cima , Via de Sinalização WntRESUMO
Liver disease represents an increasing cause of global morbidity and mortality. Currently, liver transplant is the only treatment curative for end-stage liver disease. Donor organs cannot meet the demand and therefore scalable treatments and new disease models are required to improve clinical intervention. Pluripotent stem cells represent a renewable source of human tissue. Recent advances in three-dimensional cell culture have provided the field with more complex systems that better mimic liver physiology and function. Despite these improvements, current cell-based models are variable in performance and expensive to manufacture at scale. This is due, in part, to the use of poorly defined or cross-species materials within the process, severely affecting technology translation. To address this issue, we have developed an automated and economical platform to produce liver tissue at scale for modelling disease and small molecule screening. Stem cell derived liver spheres were formed by combining hepatic progenitors with endothelial cells and stellate cells, in the ratios found within the liver. The resulting tissue permitted the study of human liver biology 'in the dish' and could be scaled for screening. In summary, we have developed an automated differentiation system that permits reliable self-assembly of human liver tissue for biomedical application. Going forward we believe that this technology will not only serve as anin vitroresource, and may have an important role to play in supporting failing liver function in humans.
Assuntos
Células Endoteliais , Células-Tronco Pluripotentes , Diferenciação Celular , Análise Custo-Benefício , Humanos , FígadoRESUMO
The formation of epithelial tissues allows organisms to specialise and form tissues with diverse functions and compartmentalised environments. The tight controls on cell growth and migration required to maintain epithelia can present problems such as the development and spread of cancer when normal pathways are disrupted. By attaining a deeper understanding of how cell migration is suppressed to maintain the epithelial organisation and how it is reactivated when epithelial tissues become mesenchymal, new insights into both cancer and development can be gained. Here we discuss recent developments in our understanding of epithelial and mesenchymal regulation of the actin cytoskeleton in normal and cancerous tissue, with a focus on the pancreas and intestinal tract.
Assuntos
Citoesqueleto de Actina/fisiologia , Transição Epitelial-Mesenquimal , Neoplasias Intestinais/patologia , Intestinos/crescimento & desenvolvimento , Pâncreas/crescimento & desenvolvimento , Neoplasias Pancreáticas/patologia , Animais , Transição Epitelial-Mesenquimal/genética , Humanos , Mucosa Intestinal/metabolismo , Neoplasias Intestinais/genética , Pâncreas/metabolismo , Neoplasias Pancreáticas/genéticaRESUMO
Mtss1 is located within chromosomal region 8q23-24, which is one of the three most commonly amplified regions in head and neck squamous cell carcinoma (HNSCC). Mtss1 is lost in metastatic cells, but confusingly is commonly overexpressed in primary tumors. Here we address possible reasons why Mtss1 is positively selected for in primary tumors. We find that Mtss1 enhances the localization of the epidermal growth factor (EGF) receptor to the plasma membrane, prolonging EGF signaling and resulting in enhanced proliferation in HNSCC. Depletion of Mtss1 results in decreased EGF receptor levels and decreased phosphorylation of Erk1/2 and Akt. However, when cells are at high density and adherent to each other, analogous to conditions in a solid tumor, Mtss1 does not confer any growth advantage, either in basal conditions or following EGF stimulation. This could indicate why Mtss1 might be lost in metastases, but preserved in early primary tumors. This is supported by an organotypic assay showing that Mtss1-expressing cells display a less proliferative more epithelial-like morphology on top of a collagen matrix. Furthermore, xenograft tumors expressing Mtss1 initially grow more rapidly, but later show less proliferation and more differentiation. Mtss1 positively modulates EGF signaling at low cell densities to promote proliferation and, therefore, may be beneficial for the early stages of primary HNSCC tumor growth. However, at high cell densities, Mtss1 impacts negatively on EGF signaling and this suggests why it inhibits metastasis.
Assuntos
Carcinoma de Células Escamosas/metabolismo , Receptores ErbB/metabolismo , Neoplasias de Cabeça e Pescoço/metabolismo , Proteínas dos Microfilamentos/fisiologia , Proteínas de Neoplasias/fisiologia , Animais , Linhagem Celular Tumoral , Fator de Crescimento Epidérmico/metabolismo , Humanos , Camundongos , Camundongos Nus , Transplante de Neoplasias , Transdução de Sinais , Carcinoma de Células Escamosas de Cabeça e PescoçoAssuntos
Plaquetas/enzimologia , Proteínas Fetais/metabolismo , Proteínas Nucleares/metabolismo , Receptores Acoplados a Proteínas G/metabolismo , Quinases Associadas a rho/metabolismo , Difosfato de Adenosina/metabolismo , Animais , Plaquetas/efeitos dos fármacos , Proteínas de Transporte/genética , Proteínas de Transporte/metabolismo , Proteínas Fetais/genética , Forminas , Humanos , Cinética , Camundongos , Camundongos Knockout , Proteínas Nucleares/genética , Peptídeos/metabolismo , Fosforilação , Inibidores de Proteínas Quinases/farmacologia , Trombina/metabolismo , Tromboxano A2/metabolismo , Quinases Associadas a rho/antagonistas & inibidoresRESUMO
BACKGROUND: During platelet spreading, the actin cytoskeleton undergoes marked changes, forming filopodia, lamellipodia and stress fibres. In the present study, we report the identification of a novel actin-rich structure, termed an actin nodule, which appears prior to lamellipodia and stress fibre formation. METHODS: Platelet spreading was monitored using human platelets and mouse GFP-actin platelets using real-time and end-point DIC, and fluorescent and electron microscopy (EM). RESULTS: We identified a small, novel actin structure, the actin nodule, in the early stages of adhesion and spreading, which we hypothesize to be a precursor of lamellipodia and stress fibres. Nodule formation shows an inverse correlation to Rho kinase and myosin-II activity, is independent of PI3-kinase, but dependent on Src kinase activity. Actin nodules contain multiple proteins, including Arp2/3, Fyn, Rac, and beta1- and beta3- integrins, but not Src. EM analysis revealed that actin filaments extend in all directions from the nodules. Actin nodules are present on multiple matrices, including fibrinogen, laminin and VWF + botrocetin. CONCLUSION: This work identifies a novel platelet actin structure, which we propose is a precursor to both lamellipodia and stress fibres and acts to drive platelet spreading.
Assuntos
Actinas/ultraestrutura , Plaquetas/ultraestrutura , Actinas/metabolismo , Animais , Plaquetas/citologia , Forma Celular , Citoesqueleto , Humanos , Camundongos , Microscopia Eletrônica , Adesividade Plaquetária , Pseudópodes , Fibras de EstresseRESUMO
BACKGROUND: MyosinIIs are adenosine triphosphate-driven molecular motors that form part of a cell's contractile machinery. They are activated by phosphorylation of their light chains, by either activation of myosin light chain (MLC) kinase or inhibition of MLC phosphatase via Rho kinase (ROCK). MyosinIIa phosphorylation underlies platelet rounding and stress fiber formation. OBJECTIVE: To identify the functional significance of myosinIIa in platelet spreading and thrombus formation on collagen using inhibitors of ROCK (Y27632) and myosinII (blebbistatin). RESULTS: Stress fiber formation on collagen is inhibited by both Y27632 and blebbistatin. A substantial proportion of spread platelets generate internal holes or splits on collagen, presumably because of a reduction in contractile strength. Platelet integrity, however, is maintained. In an in vitro model, thrombus embolization on collagen is increased in the presence of Y27632 and blebbistatin at intermediate shear, leading to a reduction in platelet aggregate growth. Moreover, Y27632 causes a marked reduction in thrombus formation in an in vivo laser-injury model. CONCLUSIONS: MyosinIIa contractility is required for maintenance of platelet structure during spreading on collagen and contributes to thrombus stability.
Assuntos
Miosina não Muscular Tipo IIA/biossíntese , Miosina não Muscular Tipo IIA/fisiologia , Actinas/metabolismo , Amidas/farmacologia , Plaquetas/citologia , Plaquetas/metabolismo , Movimento Celular , Colágeno/química , Colágeno/metabolismo , Citoesqueleto/metabolismo , Compostos Heterocíclicos de 4 ou mais Anéis/farmacologia , Humanos , Modelos Biológicos , Cadeias Leves de Miosina/química , Fosforilação , Agregação Plaquetária , Piridinas/farmacologia , Trombose/metabolismo , Quinases Associadas a rho/metabolismoRESUMO
BACKGROUND: The small GTPase Rac1 plays a critical role in lamellipodia assembly in platelets on matrix proteins in the absence or presence of G protein-coupled receptor (GPCR) agonists. Rac mediates actin assembly via Scar/WAVE, a family of scaffolding proteins that direct actin reorganization by relaying signals from Rac to the Arp2/3 complex. OBJECTIVE: To evaluate the role of Scar/WAVE-1 in mediating platelet activation and cytoskeletal reorganization. METHODS AND RESULTS: Using specific antibodies, we demonstrate that murine platelets, like human platelets, express Scar/WAVE-1 and Scar/WAVE-2. Lamellipodia formation in Scar/WAVE-1(-/-) platelets is markedly inhibited on immobilized collagen-related peptide (CRP) and on laminin, both of which signal through the collagen receptor GPVI. In contrast, lamellipodia formation on collagen, which requires release of the GPCR agonists ADP and thromboxane A(2), is not altered. Immobilized fibrinogen supports limited formation of lamellipodia in murine platelets, which is not altered in Scar/WAVE-1(-/-) platelets. As with Rac1(-/-) platelets, Scar/WAVE-1(-/-) platelets exhibit a marked inhibition of aggregation in response to CRP, whereas the response to the GPCR agonist thrombin is not altered. Platelet aggregation on immobilized collagen under shear, which is dependent on signaling by matrix and GPCR agonists, was unaltered in the absence of Scar/WAVE-1. CONCLUSION: This study demonstrates a major role for Scar/WAVE-1 in mediating platelet cytoskeletal reorganization and aggregate formation downstream of activation by GPVI but not by GPCR agonists.
Assuntos
Plaquetas/metabolismo , Citoesqueleto/metabolismo , Ativação Plaquetária , Glicoproteínas da Membrana de Plaquetas/metabolismo , Transdução de Sinais , Família de Proteínas da Síndrome de Wiskott-Aldrich/deficiência , Difosfato de Adenosina/metabolismo , Animais , Proteínas de Transporte/metabolismo , Colágeno/metabolismo , Fibrinogênio/metabolismo , Hemorreologia , Humanos , Técnicas In Vitro , Laminina/metabolismo , Camundongos , Camundongos Knockout , Selectina-P/metabolismo , Peptídeos/metabolismo , Pseudópodes/metabolismo , Estresse Mecânico , Trombina/metabolismo , Família de Proteínas da Síndrome de Wiskott-Aldrich/genética , Família de Proteínas da Síndrome de Wiskott-Aldrich/metabolismoRESUMO
BACKGROUND: von Willebrand factor (VWF) plays a critical role in the process of hemostasis by mediating flow-dependent adhesion and spreading of platelets on exposed extracellular matrix proteins following vascular injury. To accomplish this, VWF binds to two distinct platelet receptors: glycoprotein (GP)Ib-IX-V and integrin alpha(IIb)beta3. OBJECTIVE: To evaluate the ability of GPIb and alpha(IIb)beta3 to mediate platelet adhesion and lamellipodia formation on immobilized VWF in the presence of the biochemical modulators, ristocetin and botrocetin. RESULTS: In the presence of botrocetin and inhibitors of adenosine diphosphate (ADP) and thromboxane A2 (TxA2), VWF is able to support formation of lamellipodia through a GPIb-dependent mechanism that is independent of alpha(IIb)beta3 and PI3-kinase. Lamellipodia formation under these conditions is incomplete. In marked contrast, in the presence of ristocetin, VWF stimulates formation of fully spread lamellipodia through a pathway that is dependent upon alpha(IIb)beta3 and PI3-kinase. Furthermore, alpha(IIb)beta3 also supports platelet spreading on VWF alone, but only in the absence of inhibitors of ADP and TxA2. The localization of filamentous actin and the Arp2/3 complex in platelets on VWF in the presence of botrocetin and ristocetin are distinct, yielding disparate lamellipodium kinetic signatures. Interestingly, botrocetin significantly enhances platelet adhesion to VWF under flow in whole blood in an alpha(IIb)beta3-independent manner, while ristocetin augments washed platelet adhesion and spreading to VWF under flow in an alpha(IIb)beta3-dependent manner. CONCLUSIONS: These observations demonstrate that VWF is able to induce lamellipodia formation through distinct receptors, and has important consequences for investigation of the role of VWF-GPIb interactions in the context of platelet regulation.
Assuntos
Plaquetas/fisiologia , Adesividade Plaquetária/fisiologia , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/metabolismo , Complexo Glicoproteico GPIb-IX de Plaquetas/metabolismo , Pseudópodes/metabolismo , Fator de von Willebrand/metabolismo , Citoesqueleto de Actina/metabolismo , Animais , Benzodiazepinas/farmacologia , Plaquetas/citologia , Plaquetas/efeitos dos fármacos , Venenos de Crotalídeos/farmacologia , Citoesqueleto , Humanos , Técnicas In Vitro , Camundongos , Camundongos Knockout , Neuropeptídeos/genética , Fosfatidilinositol 3-Quinases/metabolismo , Piperidinas/farmacologia , Adesividade Plaquetária/efeitos dos fármacos , Inibidores da Agregação Plaquetária/farmacologia , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/antagonistas & inibidores , Pseudópodes/efeitos dos fármacos , Ristocetina/farmacologia , Transdução de Sinais , Proteínas rac de Ligação ao GTP/genética , Proteínas rac1 de Ligação ao GTP , Quinases da Família src/metabolismo , Proteína RAC2 de Ligação ao GTPRESUMO
BACKGROUND: Recent studies have shown that platelet adhesion and subsequent aggregation can occur in vivo in the absence of the two principal platelets adhesive ligands, von Willebrand factor and fibrinogen. These results highlight a possible role for fibronectin in supporting thrombus formation. OBJECTIVE AND METHODS: To evaluate the platelet integrins and subsequent activation pathways associated with fibronectin-dependent platelet adhesion utilizing both human and murine platelets. RESULTS: Platelets can adhere to fibronectin via the integrin alpha(IIb)beta(3), leading to formation of lamellipodia. This is mediated through an interaction with the tenth type III domain in fibronectin. Spreading on fibronectin promotes alpha(IIb)beta(3)-mediated Ca(2+) mobilization and tyrosine phosphorylation of focal adhesion kinase and phospholipase C gamma2. In contrast, studies with blocking antibodies and mice demonstrate that alpha(5)beta(1) and alpha(v)beta(3) support adhesion and promote formation of filopodia but not lamellipodia or tyrosine phosphorylation of these proteins. Further, neither alpha(5)beta(1) nor alpha(v)beta(3) is able to induce formation of lamellipodia in the presence of platelets agonists, such as collagen-related-peptide (CRP). CONCLUSIONS: These observations demonstrate that integrins alpha(5)beta(1) and alpha(v)beta(3) support platelet adhesion and the generation of filopodia but that, in contrast to the integrin alpha(IIb)beta(3), are unable to promote formation of lamellipodia.
Assuntos
Plaquetas/citologia , Fibronectinas/fisiologia , Integrinas/fisiologia , Adesividade Plaquetária , Pseudópodes , Animais , Sítios de Ligação , Plaquetas/química , Sinalização do Cálcio , Quinase 1 de Adesão Focal , Proteína-Tirosina Quinases de Adesão Focal , Humanos , Integrina alfa5beta1/fisiologia , Integrina alfaVbeta3/fisiologia , Camundongos , Fosfolipase C gama , Fosforilação , Complexo Glicoproteico GPIIb-IIIa de Plaquetas/fisiologia , Proteínas Tirosina Quinases/metabolismo , Especificidade da Espécie , Trombose/etiologia , Fosfolipases Tipo C/metabolismoRESUMO
The involvement of Nck in pedestal formation by EPEC highlights the similar strategies adopted by this bacterium and the Vaccinia virus to hijack the host cell's cytoskeleton.
Assuntos
Actinas/metabolismo , Proteínas do Citoesqueleto , Citoesqueleto/metabolismo , Escherichia coli/metabolismo , Proteínas Oncogênicas/metabolismo , Vaccinia virus/metabolismo , Proteína 2 Relacionada a Actina , Proteína 3 Relacionada a Actina , Proteínas Adaptadoras de Transdução de Sinal , Extensões da Superfície Celular/metabolismo , Escherichia coli/patogenicidade , Modelos Biológicos , Proteínas do Tecido Nervoso/metabolismo , Isoformas de Proteínas , Transdução de Sinais , Vaccinia virus/genética , Proteína Neuronal da Síndrome de Wiskott-AldrichRESUMO
The intracellular protozoan parasite Cryptosporidium parvum accumulates host cell actin at the interface between the parasite and the host cell cytoplasm. Here we show that the actin polymerizing proteins Arp2/3, vasodilator-stimulated phosphoprotein (VASP), and neural Wiskott Aldrich syndrome protein (N-WASP) are present at this interface and that host cell actin polymerization is necessary for parasite infection.
Assuntos
Actinas/metabolismo , Criptosporidiose/parasitologia , Cryptosporidium parvum/patogenicidade , Proteínas do Citoesqueleto , Proteína 2 Relacionada a Actina , Proteína 3 Relacionada a Actina , Animais , Moléculas de Adesão Celular/metabolismo , Linhagem Celular , Interações Hospedeiro-Parasita , Humanos , Proteínas dos Microfilamentos , Proteínas do Tecido Nervoso/metabolismo , Fosfoproteínas/metabolismo , Polímeros , Proteína Neuronal da Síndrome de Wiskott-AldrichRESUMO
Recently, two new ligands of the Arp2/3 complex have been described that may shed light on the way cells organize complex networks of actin in response to signals. Abp1p, a yeast protein involved in endocytosis, and cortactin, a mammalian src substrate, both enhance the ability of the Arp2/3 complex to assemble branched actin filament networks.
Assuntos
Citoesqueleto de Actina/metabolismo , Actinas/metabolismo , Proteínas do Citoesqueleto , Proteínas Fúngicas/metabolismo , Proteínas dos Microfilamentos/metabolismo , Proteínas de Saccharomyces cerevisiae , Proteína 2 Relacionada a Actina , Proteína 3 Relacionada a Actina , Endocitose , Modelos Biológicos , Ligação Proteica , Transdução de SinaisAssuntos
Proteínas do Tecido Nervoso/química , Nucleopoliedrovírus/química , Homologia de Sequência de Aminoácidos , Proteínas Virais/química , Sequência de Aminoácidos/fisiologia , Animais , Humanos , Larva/virologia , Masculino , Dados de Sequência Molecular , Mariposas/virologia , Proteínas do Tecido Nervoso/fisiologia , Proteínas Virais/fisiologia , Síndrome de Wiskott-Aldrich/metabolismo , Proteína Neuronal da Síndrome de Wiskott-AldrichRESUMO
Most eukaryotic cells rely on localized actin polymerization to generate and sustain the protrusion activity necessary for cell movement [1, 2]. Such protrusions are often in the form of a flat lamellipod with a leading edge composed of a dense network of actin filaments [3, 4]. The Arp2/3 complex localizes within that network in vivo [3, 4] and nucleates actin polymerization and generates a branched network of actin filaments in vitro [5-7]. The complex has thus been proposed to generate the actin network at the leading edge of crawling cells in vivo [3, 4, 8]. However, the relative contributions of nucleation and branching to protrusive force are still unknown. We prepared antibodies to the p34 subunit of the Arp2/3 complex that selectively inhibit side binding of the complex to F-actin. We demonstrate that side binding is required for efficient nucleation and branching by the Arp2/3 complex in vitro. However, microinjection of these antibodies into cells specifically inhibits lamellipod extension without affecting the EGF-stimulated appearance of free barbed ends in situ. These results indicate that while the side binding activity of the Arp2/3 complex is required for nucleation in vitro and for protrusive force in vivo, it is not required for EGF-stimulated increases in free barbed ends in vivo. This suggests that the branching activity of the Arp2/3 complex is essential for lamellipod extension, while the generation of nucleation sites for actin polymerization is not sufficient.
Assuntos
Actinas/metabolismo , Proteínas do Citoesqueleto , Proteína 2 Relacionada a Actina , Proteína 3 Relacionada a Actina , Humanos , Proteínas do Tecido Nervoso/metabolismo , Pseudópodes/fisiologia , Proteína Neuronal da Síndrome de Wiskott-AldrichRESUMO
Rab27a activity is affected in several mouse models of human disease including Griscelli (ashen mice) and Hermansky-Pudlak (gunmetal mice) syndromes. A loss of function mutation occurs in the Rab27a gene in ashen (ash), whereas in gunmetal (gm) Rab27a dysfunction is secondary to a mutation in the alpha subunit of Rab geranylgeranyl transferase, an enzyme required for prenylation and activation of Rabs. We show here that Rab27a is normally expressed in cytotoxic T lymphocytes (CTLs), but absent in ashen homozygotes (ash/ash). Cytotoxicity and secretion assays show that ash/ash CTLs are unable to kill target cells or to secrete granzyme A and hexosaminidase. By immunofluorescence and electron microscopy, we show polarization but no membrane docking of ash/ash lytic granules at the immunological synapse. In gunmetal CTLs, we show underprenylation and redistribution of Rab27a to the cytosol, implying reduced activity. Gunmetal CTLs show a reduced ability to kill target cells but retain the ability to secrete hexosaminidase and granzyme A. However, only some of the granules polarize to the immunological synapse, and many remain dispersed around the periphery of the CTLs. These results demonstrate that Rab27a is required in a final secretory step and that other Rab proteins also affected in gunmetal are likely to be involved in polarization of the granules to the immunological synapse.
Assuntos
Proteínas do Citoesqueleto , Vesículas Secretórias/metabolismo , Serina Endopeptidases/metabolismo , Linfócitos T Citotóxicos/imunologia , beta-N-Acetil-Hexosaminidases/metabolismo , Proteínas rab de Ligação ao GTP/metabolismo , Proteína 2 Relacionada a Actina , Proteína 3 Relacionada a Actina , Actinas/isolamento & purificação , Animais , Catepsina D , Membrana Celular/ultraestrutura , Polaridade Celular , Grânulos Citoplasmáticos/ultraestrutura , Complexo de Golgi/ultraestrutura , Granzimas , Síndrome de Hermanski-Pudlak , Hipopigmentação , Síndromes de Imunodeficiência , Camundongos , Camundongos Endogâmicos C3H , Camundongos Endogâmicos C57BL , Camundongos Mutantes , Vesículas Secretórias/ultraestrutura , Linfócitos T Citotóxicos/ultraestrutura , Talina/isolamento & purificação , Proteínas rab de Ligação ao GTP/genética , Proteínas rab27 de Ligação ao GTPRESUMO
The process of engulfing a foreign particle - phagocytosis - is of fundamental importance for a wide diversity of organisms. From simple unicellular organisms that use phagocytosis to obtain their next meal, to complex metazoans in which phagocytic cells represent an essential branch of the immune system, evolution has armed cells with a fantastic repertoire of molecules that serve to bring about this complex event. Regardless of the organism or specific molecules concerned, however, all phagocytic processes are driven by a finely controlled rearrangement of the actin cytoskeleton. A variety of signals can converge to locally reorganise the actin cytoskeleton at a phagosome, and there are significant similarities and differences between different organisms and between different engulfment processes within the same organism. Recent advances have demonstrated the complexity of phagocytic signalling, such as the involvement of phosphoinostide lipids and multicomponent signalling complexes in transducing signals from phagocytic receptors to the cytoskeleton. Similarly, a wide diversity of 'effector molecules' are now implicated in actin-remodelling downstream of these receptors.