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Current Topics in Developmental Biology 2023By the time a Drosophila egg is laid, both major body axes have already been defined and it contains all the nutrients needed to develop into a free-living larva in... (Review)
Review
By the time a Drosophila egg is laid, both major body axes have already been defined and it contains all the nutrients needed to develop into a free-living larva in 24 h. By contrast, it takes almost a week to make an egg from a female germline stem cell, during the complex process of oogenesis. This review will discuss key symmetry-breaking steps in Drosophila oogenesis that lead to the polarisation of both body axes: the asymmetric divisions of the germline stem cells; the selection of the oocyte from the 16-cell germline cyst; the positioning of the oocyte at the posterior of the cyst; Gurken signalling from the oocyte to polarise the anterior-posterior axis of the somatic follicle cell epithelium around the developing germline cyst; the signalling back from the posterior follicle cells to polarise the anterior-posterior axis of the oocyte; and the migration of the oocyte nucleus that specifies the dorsal-ventral axis. Since each event creates the preconditions for the next, I will focus on the mechanisms that drive these symmetry-breaking steps, how they are linked and the outstanding questions that remain to be answered.
Topics: Animals; Drosophila; Oocytes; Oogenesis; Germ Cells; Drosophila Proteins; Cell Polarity
PubMed: 37100524
DOI: 10.1016/bs.ctdb.2023.02.002 -
Journal of Integrative Plant Biology Jan 2020Cell polarity plays an important role in a wide range of biological processes in plant growth and development. Cell polarity is manifested as the asymmetric distribution... (Review)
Review
Cell polarity plays an important role in a wide range of biological processes in plant growth and development. Cell polarity is manifested as the asymmetric distribution of molecules, for example, proteins and lipids, at the plasma membrane and/or inside of a cell. Here, we summarize a few polarized proteins that have been characterized in plants and we review recent advances towards understanding the molecular mechanism for them to polarize at the plasma membrane. Multiple mechanisms, including membrane trafficking, cytoskeletal activities, and protein phosphorylation, and so forth define the polarized plasma membrane domains. Recent discoveries suggest that the polar positioning of the proteo-lipid membrane domain may instruct the formation of polarity complexes in plants. In this review, we highlight the factors and regulators for their functions in establishing the membrane asymmetries in plant development. Furthermore, we discuss a few outstanding questions to be addressed to better understand the mechanisms by which cell polarity is regulated in plants.
Topics: Cell Membrane; Cell Polarity; Homeostasis; Plant Cells; Plant Proteins; Plants
PubMed: 31889400
DOI: 10.1111/jipb.12904 -
Current Topics in Developmental Biology 2023Epithelia are tissues with diverse morphologies and functions across metazoans, ranging from vast cell sheets encasing internal organs to internal tubes facilitating... (Review)
Review
Epithelia are tissues with diverse morphologies and functions across metazoans, ranging from vast cell sheets encasing internal organs to internal tubes facilitating nutrient uptake, all of which require establishment of apical-basolateral polarity axes. While all epithelia tend to polarize the same components, how these components are deployed to drive polarization is largely context-dependent and likely shaped by tissue-specific differences in development and ultimate functions of polarizing primordia. The nematode Caenorhabditis elegans (C. elegans) offers exceptional imaging and genetic tools and possesses unique epithelia with well-described origins and roles, making it an excellent model to investigate polarity mechanisms. In this review, we highlight the interplay between epithelial polarization, development, and function by describing symmetry breaking and polarity establishment in a particularly well-characterized epithelium, the C. elegans intestine. We compare intestinal polarization to polarity programs in two other C. elegans epithelia, the pharynx and epidermis, correlating divergent mechanisms with tissue-specific differences in geometry, embryonic environment, and function. Together, we emphasize the importance of investigating polarization mechanisms against the backdrop of tissue-specific contexts, while also underscoring the benefits of cross-tissue comparisons of polarity.
Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Intestines; Epithelium; Morphogenesis; Cell Polarity; Epithelial Cells
PubMed: 37100523
DOI: 10.1016/bs.ctdb.2023.02.007 -
Journal of Cell Science Aug 2014Cell polarity is characterised by differences in structure, composition and function between at least two poles of a cell. In epithelial cells, these spatial differences... (Review)
Review
Cell polarity is characterised by differences in structure, composition and function between at least two poles of a cell. In epithelial cells, these spatial differences allow for the formation of defined apical and basal membranes. It has been increasingly recognised that cell-matrix interactions and integrins play an essential role in creating epithelial cell polarity, although key gaps in our knowledge remain. This Commentary will discuss the mounting evidence for the role of integrins in polarising epithelial cells. We build a model in which both inside-out signals to polarise basement membrane assembly at the basal surface, and outside-in signals to control microtubule apical-basal orientation and vesicular trafficking are required for establishing and maintaining the orientation of epithelial cell polarity. Finally, we discuss the relevance of the basal integrin polarity axis to cancer. This article is part of a Minifocus on Establishing polarity.
Topics: Animals; Basement Membrane; Cell Polarity; Epithelial Cells; Humans; Integrins; Microtubules; Neoplasms
PubMed: 24994933
DOI: 10.1242/jcs.146142 -
Molecular Biology of the Cell May 2021Cells polarize their growth or movement in many different physiological contexts. A key driver of polarity is the Rho GTPase Cdc42, which when activated becomes...
Cells polarize their growth or movement in many different physiological contexts. A key driver of polarity is the Rho GTPase Cdc42, which when activated becomes clustered or concentrated at polar sites. Multiple models for polarity establishment have been proposed. All of them rely on positive feedback to reinforce regions of high Cdc42 activity. Positive feedback can lead to bistability, a scenario in which cells can exist in either a polarized or unpolarized state under identical external conditions. Determining if the signaling circuit that drives Cdc42 polarity is bistable would provide important information about the mechanism that underlies polarity establishment and insights into the design features required for proper cellular function. We studied polarity establishment during the mating response of yeast. Using microfluidics to precisely control the temporal profile of mating pheromone and live-cell imaging to monitor the polarity process in single living cells, we found that the polarity circuit of yeast shows hysteresis, a characteristic feature of bistable systems. Our analysis also revealed that cells exposed to high pheromone concentrations rapidly lose polarity following a precipitous removal of pheromone. We used a reaction-diffusion model for polarity establishment to demonstrate that delayed negative regulation is sufficient to explain our experimental results. [Media: see text] [Media: see text] [Media: see text] [Media: see text].
PubMed: 33956497
DOI: 10.1091/mbc.E20-07-0445 -
Current Opinion in Plant Biology Feb 2009Plants have acquired the ability for organized multicellular development independent from animals. Because of this, they represent an independent example in nature for... (Review)
Review
Plants have acquired the ability for organized multicellular development independent from animals. Because of this, they represent an independent example in nature for the development of coordinated, complex cell polarity from the simple polarity found in unicellular eukaryotes. Plants display a striking array of polarized cell types, with different axes of polarity being defined in one cell. The most investigated and best understood aspect of plant polarity is the apical-basal polarity of the PIN family of auxin efflux facilitators, which are of crucial importance for the organization of the entire plant body. Striking differences exist between the PAR-polarity modules known in animals and the ways PINs polarize plant cells. Nonetheless, a common regulatory logic probably applies to all polarizing eukaryotic cells, which includes self-reinforcing, positive feedback loops, intricate interactions between membrane-attached proteins, lipid signatures, and the targeting of transmembrane proteins to the correct domains of the plasma membrane.
Topics: Biological Transport; Cell Polarity; Cytoskeleton; Indoleacetic Acids; Plant Cells; Plant Proteins; Plants
PubMed: 18993110
DOI: 10.1016/j.pbi.2008.09.009 -
BioEssays : News and Reviews in... Feb 1990In the 4 1/2 to 5 days between fertilization and implantation, the mouse conceptus must gain the abilities to implant and produce an embryo. Each of these is the sole... (Review)
Review
In the 4 1/2 to 5 days between fertilization and implantation, the mouse conceptus must gain the abilities to implant and produce an embryo. Each of these is the sole developmental responsibility of one of two cell types forming the blastocyst, trophectoderm and inner cell mass (ICM), respectively. Trophectoderm is a polarized transporting epithelium while the ICM is an aggregate of non-epithelial pluripotent stem cells. These two cell types originate from the division of polar blastomeres when their cleavage furrows parallel their apical surfaces. Blastomeres polarize in response to asymmetric cell--cell contact, and understanding the mechanism of this induction is regarded as the key to understanding the origin of trophectoderm and ICM. Here we propose a model based on transcellular ion current loops for the induction of cell polarity during the development of the first epithelium, trophectoderm.
Topics: Animals; Blastomeres; Cell Differentiation; Cell Membrane; Epithelial Cells; Epithelium
PubMed: 2188651
DOI: 10.1002/bies.950120204 -
The Journal of Histochemistry and... Oct 2021Collagen has a major role in the structural organization of tendons. Picrosirius red (PSR) staining viewed under polarized light microscopy is the standard method to...
Collagen has a major role in the structural organization of tendons. Picrosirius red (PSR) staining viewed under polarized light microscopy is the standard method to evaluate the organization of collagen fibers in tissues. It is also used to distinguish between type I and type III collagen in tissue sections. However, accurate analysis and interpretation of PSR images are challenging because of technical factors and historical misconceptions. The aim of this study was to clarify whether collagen types I and III can be distinguished by PSR staining in rat Achilles tendons, using double immunohistochemistry as the positive control. Our findings showed that PSR staining viewed with polarized light microscopy was suitable for qualitative and quantitative assessment of total collagen but was not able to distinguish collagen types. We found it critical to use a polarizing microscope equipped with a rotating stage; tendon section orientation at 45° with respect to crossed polarizers was optimal for the qualitative and quantitative assessment of collagen organization. Immunohistochemistry was superior to PSR staining for detection of collagen type III. We also compared formalin and Bouin solution as fixatives. Both produced similar birefringence, but formalin-fixed tendons provided higher quality histological detail with both hematoxylin-eosin and immunostaining.
Topics: Animals; Azo Compounds; Collagen Type I; Collagen Type III; Rats; Rats, Sprague-Dawley; Staining and Labeling; Tendons
PubMed: 34549650
DOI: 10.1369/00221554211046777 -
Current Opinion in Genetics &... Oct 2000The polarised character of a cell is often obvious from its shape and is largely dependent on the actin cytoskeleton and the membrane-associated cell cortex---a dense... (Review)
Review
The polarised character of a cell is often obvious from its shape and is largely dependent on the actin cytoskeleton and the membrane-associated cell cortex---a dense network comprising spectrin and other related proteins. Spatially and functionally distinct protein scaffolds, assembled from transmembrane and cytoplasmic proteins, provide the cues for polarisation. Recent data have provided new insights into the molecular nature of these cues and the mechanisms by which they may be translated into a polarised phenotype.
Topics: Animals; Cell Polarity; Cell Size; Drosophila; Epithelial Cells; Membrane Proteins
PubMed: 10980423
DOI: 10.1016/s0959-437x(00)00115-5 -
Seminars in Cell & Developmental Biology Oct 2004The first developmental lineage allocation during the generation of the mouse blastocyst is to outer trophoblast or to inner pluriblast (inner cell mass; ICM) cells.... (Review)
Review
The first developmental lineage allocation during the generation of the mouse blastocyst is to outer trophoblast or to inner pluriblast (inner cell mass; ICM) cells. This allocation seems to be initiated at the 8-cell stage, when blastomeres polarise. Polarisation is followed by differentiative divisions at the subsequent two cleavage divisions to generate polar outer and non-polar inner 16- and 32-cells. The key events in polarisation are regulated post-translationally through a cell contact-mediated pathway, which imposes a heritable determinant-like organisation on the blastomere cortex. Two proteins in particular, E-cadherin and ezrin, are intimately involved in the generation and stabilisation of developmentally significant information. Transcriptional differences between lineages appear to follow and may coincide with the lineage commitment of cells.
Topics: Animals; Blastomeres; Body Patterning; Cadherins; Cell Lineage; Cytoskeletal Proteins; Female; Mice; Ovum; Phosphoproteins; Trophoblasts
PubMed: 15271304
DOI: 10.1016/j.semcdb.2004.04.002