RESUMO
The evolutionary emergence of the mesenchymal phenotype greatly increased the complexity of tissue architecture and composition in early Metazoan species. At the molecular level, an epithelial-to-mesenchymal transition (EMT) was permitted by the innovation of specific transcription factors whose expression is sufficient to repress the epithelial transcriptional program. The reverse process, mesenchymal-to-epithelial transition (MET), involves direct inhibition of EMT transcription factors by numerous mechanisms including tissue-specific MET-inducing transcription factors (MET-TFs), micro-RNAs, and changes to cell and tissue architecture, thus providing an elegant solution to the need for tight temporal and spatial control over EMT and MET events during development and adult tissue homeostasis.
Assuntos
Desenvolvimento Embrionário/genética , Transição Epitelial-Mesenquimal/genética , MicroRNAs/genética , Neoplasias/genética , Animais , Homeostase/genética , Humanos , Fenótipo , Fatores de Transcrição/genéticaRESUMO
Morphogenesis is an essential process by which a given tissue, organ or organism acquires its final shape. A select number of mechanisms are used in order to drive epithelial morphogenesis, including cell shape changes as well as cell death or cell division. A cell's shape results from the combination of intrinsic properties of the actomyosin and microtubule (MTs) cytoskeletons, and extrinsic properties due to physical interactions with the neighbouring environment. While we now have a good understanding of the genetic pathways and some of the signalling pathways controlling cell shape changes, the mechanical properties of cells and their role in morphogenesis remain largely unexplored. Recent improvements in microscopy techniques and the development of modelling and quantitative methods have enabled a better understanding of the bio-mechanical events controlling cell shape during morphogenesis. This review aims to highlight recent findings elegantly unravelling and quantifying the contribution of mechanical forces during morphogenesis.
Assuntos
Citoesqueleto de Actina , Forma Celular , Células Epiteliais/citologia , Células Epiteliais/fisiologia , Morfogênese , Animais , HumanosRESUMO
The budding of tubular organs from flat epithelial sheets is a vital morphogenetic process. Cell behaviours that drive such processes are only starting to be unraveled. Using live-imaging and novel morphometric methods, we show that in addition to apical constriction, radially oriented directional intercalation of cells plays a major contribution to early stages of invagination of the salivary gland tube in the Drosophila embryo. Extending analyses in 3D, we find that near the pit of invagination, isotropic apical constriction leads to strong cell-wedging. Further from the pit cells interleave circumferentially, suggesting apically driven behaviours. Supporting this, junctional myosin is enriched in, and neighbour exchanges are biased towards the circumferential orientation. In a mutant failing pit specification, neither are biased due to an inactive pit. Thus, tube budding involves radially patterned pools of apical myosin, medial as well as junctional, and radially patterned 3D-cell behaviours, with a close mechanical interplay between invagination and intercalation.
Assuntos
Células Epiteliais/citologia , Epitélio/embriologia , Morfogênese , Animais , Polaridade Celular , Forma Celular , Drosophila melanogaster/citologia , Drosophila melanogaster/embriologia , Embrião não Mamífero , Epitélio/metabolismo , Fluorescência , Imageamento Tridimensional , Mutação/genética , Miosina Tipo II/metabolismo , Glândulas Salivares/embriologia , Imagem com Lapso de TempoRESUMO
Neural stem cells or neuroblasts in the Drosophila melanogaster embryo delaminate as single cells from the embryonic epidermis to give rise to the nervous system. Using this accessible system to examine the molecular mechanisms of cell ingression at a high temporal and spatial resolution, in this issue, Simões et al. (2017. J. Cell Biol. https://doi.org/10.1083/jcb.201608038) reveal that myosin-driven anisotropic junction loss and apical constriction are the main drivers of this process.
Assuntos
Drosophila melanogaster/citologia , Células-Tronco Neurais/citologia , Animais , Adesão Celular , MiosinasRESUMO
Dorsal closure of the Drosophila embryonic epithelium provides an excellent model system for the in vivo analysis of molecular mechanisms regulating cytoskeletal rearrangements. In this study, we investigated the function of the Drosophila spectraplakin Short stop (Shot), a conserved cytoskeletal structural protein, during closure of the dorsal embryonic epithelium. We show that Shot is essential for the efficient final zippering of the opposing epithelial margins. By using isoform-specific mutant alleles and genetic rescue experiments with truncated Shot variants, we demonstrate that Shot functions as an actin-microtubule cross-linker in mediating zippering. At the leading edge of epithelial cells, Shot regulates protrusion dynamics by promoting filopodia formation. Fluorescence recovery after photobleaching (FRAP) analysis and in vivo imaging of microtubule growth revealed that Shot stabilizes dynamic microtubules. The actin- and microtubule-binding activities of Shot are simultaneously required in the same molecule, indicating that Shot is engaged as a physical crosslinker in this process. We propose that Shot-mediated interactions between microtubules and actin filaments facilitate filopodia formation, which promotes zippering by initiating contact between opposing epithelial cells.
Assuntos
Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Células Epiteliais/metabolismo , Proteínas dos Microfilamentos/metabolismo , Microtúbulos/metabolismo , Morfogênese , Actinas/metabolismo , Animais , Proteínas de Drosophila/química , Drosophila melanogaster/embriologia , Embrião não Mamífero/metabolismo , Células Epiteliais/citologia , Proteínas de Fluorescência Verde/metabolismo , Proteínas dos Microfilamentos/química , Mutação/genética , Domínios Proteicos , Pseudópodes/metabolismoRESUMO
Coordination between different cytoskeletal systems is crucial for many cell biological functions, including cell migration and mitosis, and also plays an important role during tissue morphogenesis. Proteins of the class of cytoskeletal crosslinkers, or cytolinkers, have the ability to interact with more than one cytoskeletal system at a time and are prime candidates to mediate any coordination. One such class comprises the Gas2-like proteins, combining a conserved calponin-homology-type actin-binding domain and a Gas2 domain predicted to bind microtubules (MTs). This domain combination is also found in spectraplakins, huge cytolinkers that play important roles in many tissues in both invertebrates and vertebrates. Here, we dissect the ability of the single Drosophila Gas2-like protein Pigs to interact with both actin and MT cytoskeletons, both in vitro and in vivo, and illustrate complex regulatory interactions that determine the localisation of Pigs to and its effects on the cytoskeleton.
Assuntos
Polaridade Celular , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Peptídeos e Proteínas de Sinalização Intracelular/metabolismo , Microtúbulos/metabolismo , Citoesqueleto de Actina/metabolismo , Actinas/metabolismo , Motivos de Aminoácidos , Animais , Células Cultivadas , Proteínas de Drosophila/química , Proteínas de Drosophila/genética , Peptídeos e Proteínas de Sinalização Intracelular/química , Peptídeos e Proteínas de Sinalização Intracelular/genética , Mutação/genética , Ligação Proteica , Estrutura Terciária de ProteínaRESUMO
Cell polarity and cell-cell junctions have pivotal roles in organizing cells into tissues and in mediating cell-cell communication. The transmembrane protein Crumbs has a well-established role in the maintenance of epithelial polarity, and it can also regulate signalling via the Notch and Hippo pathways to influence tissue growth. The functions of Crumbs in epithelial polarity and Hippo-mediated growth depend on its short intracellular domain. Recent evidence now points to a conserved and fundamental role for the extracellular domain of Crumbs in mediating homophilic Crumbs-Crumbs interactions at cell-cell junctions.
Assuntos
Polaridade Celular/fisiologia , Junções Intercelulares/fisiologia , Proteínas de Membrana/fisiologia , Proteínas do Tecido Nervoso/fisiologia , Animais , Comunicação Celular/fisiologia , Células Epiteliais/citologia , Células Epiteliais/metabolismo , Células Epiteliais/fisiologia , Humanos , Junções Intercelulares/metabolismo , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismoRESUMO
During oogenesis in Drosophila an organelle called the fusome plays a crucial role in germline cyst development and oocyte selection. The fusome consists of cytoskeletal proteins and intracellular membranes and, whereas many cytoskeletal components have been characterized, the nature and function of the membrane component is poorly understood. I have found the reticulon-like 1 (Rtnl1) protein, a membrane protein resident in the endoplasmic reticulum (ER), to be highly enriched in the fusome. In other Drosophila tissues Rtnl1 marks a subset of ER membranes often derived from smooth ER. During oogenesis, Rtnl1-containing membranes are recruited to the fusome by the cytoskeletal components and become concentrated into the forming oocyte. On the central part of the fusome, which is contained within the future oocyte and also at later stages in the growing oocyte and the nurse cells, Rtnl1-containing membranes colocalize with components of ribonucleoprotein complexes that store translationally repressed mRNAs. As the ER is actively transported into the oocyte, this colocalization suggests a role for the Rtnl1-containing subdomain in anchoring the ribonucleoprotein complexes within and/or transporting them into the oocyte.
Assuntos
Proteínas de Drosophila/fisiologia , Drosophila/fisiologia , Retículo Endoplasmático/fisiologia , Membranas Intracelulares/fisiologia , Ribonucleoproteínas/fisiologia , Animais , Proteínas do Citoesqueleto/fisiologia , Drosophila/embriologia , Proteínas de Drosophila/genética , Feminino , Mutação , Oócitos/fisiologia , Oogênese , Organelas/fisiologia , Isoformas de Proteínas/genética , Isoformas de Proteínas/fisiologiaRESUMO
BACKGROUND: During Drosophila oogenesis a membranous organelle called the fusome has a key function in the establishment of oocyte fate and polarity, ultimately leading to the establishment of the major body axes of the animal. The fusome is necessary for the microtubule-driven restriction of markers of oocyte fate to the oocyte, but the mechanism by which the fusome organizes the microtubules is not known. RESULTS: We have identified the spectraplakin Short stop (Shot) as a new component of the fusome. Spectraplakins are giant cytoskeletal linker proteins, with multiple isoforms produced from each gene. Shot is the sole spectraplakin in Drosophila. The phenotype caused by the absence of Shot is not similar to that of other components of the fusome but instead is similar to the absence of the downstream components that interact with microtubules: the dynein/dynactin-complex-associated proteins Egalitarian and BicaudalD. Shot is required for the association of microtubules with the fusome and the subsequent specification of the oocyte in 16-cell cysts. Shot is also required for the concentration of centrosomes into the oocyte, a process thought to be independent of microtubules because it still occurs in the presence of microtubule depolymerizing drugs. This suggests that Shot may protect some microtubules from depolymerization and that these microtubules are sufficient for this process. CONCLUSIONS: Shot provides the missing link between the fusome and microtubules within meiotic cysts, which is essential for the establishment of the oocyte. Shot associates with the fusome and is required for microtubule organization. We suggest that it does this directly, via its microtubule binding GAS2 domain.
Assuntos
Microtúbulos/fisiologia , Oogênese/fisiologia , Organelas/fisiologia , Animais , Padronização Corporal/fisiologia , Diferenciação Celular/fisiologia , Polaridade Celular/fisiologia , Drosophila , Feminino , Imunofluorescência , Hibridização In Situ , Microscopia Confocal , Microtúbulos/metabolismo , Mutação/fisiologia , Organelas/metabolismo , Estrutura Terciária de Proteína/fisiologia , Transdução de SinaisRESUMO
The Short stop (Shot/Kakapo) spectraplakin is a giant cytoskeletal protein, which exists in multiple isoforms with characteristics of both spectrin and plakin superfamilies. Previously characterized Shot isoforms are similar to spectrin and dystrophin, with an actin-binding domain followed by spectrin repeats. We describe a new large exon within the shot locus, which encodes a series of plakin repeats similar to the COOH terminus of plakins such as plectin and BPAG1e. We find that the plakin repeats are inserted between the actin-binding domain and spectrin repeats, generating isoforms as large as 8,846 residues, which could span 400 nm. These novel isoforms localized to adherens junctions of embryonic and follicular epithelia. Loss of Shot within the follicle epithelium leads to double layering and accumulation of actin and ZO-1 in between, and a reduction of Armadillo and Discs lost within, mutant cells, indicative of a disruption of adherens junction integrity. Thus, we identify a new role for spectraplakins in mediating cell-cell adhesion.