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Dard N. [Compaction and lineage divergence during mouse preimplantation embryo development]. ACTA ACUST UNITED AC 2008; 36:1133-8. [PMID: 18922731 DOI: 10.1016/j.gyobfe.2008.07.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2008] [Accepted: 07/15/2008] [Indexed: 11/17/2022]
Abstract
The preimplantation embryo development leads to the formation of a blastocyst made of two cell lineages: an outer layer of epithelial cells, the trophectoderm, that will give rise to some embryonic annexes, and a mass of undifferentiated cells, the inner cell mass, that will form the foetus and the remaining embryonic annexes. The trophectoderm encloses the inner cell mass and protects it from the external medium. Moreover, after hatching, the trophectoderm invades the uterine tissue, a crucial step for the implantation of the embryo. Therefore, the divergence between these two lineages is of crucial importance for the emergence of the foetus itself and for the postimplantation development to take place correctly. The setting up of cell polarity during compaction at the eight-cell stage allows asymmetric divisions to take place, thereby leading to lineage divergence. Phenotypic properties of these two cell populations are progressively reinforced through cell-cell interactions, outer cells undergoing epithelial differentiation while inner cells remain undifferentiated. Although cellular mechanisms controlling the divergence of the first two lineages are quite well known, important efforts have been carried out this last decade to identify the molecular machinery involved in this process and will be presented in this review.
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Affiliation(s)
- N Dard
- CNRS, UMR7622, Laboratoire Biologie du Développement, UPMC Université Paris-6, quai Saint-Bernard, 75005 Paris, France.
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52
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Schiffmann Y. The Turing-Child energy field as a driver of early mammalian development. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 98:107-17. [DOI: 10.1016/j.pbiomolbio.2008.07.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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53
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Zachos NC, Burch MG, Billiar RB, Li C, Albrecht ED, Pepe GJ. Regulation of expression of microvillus membrane proteins by estrogen in baboon fetal ovarian oocytes. Biol Reprod 2008; 79:1160-8. [PMID: 18716290 DOI: 10.1095/biolreprod.108.067900] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
We previously demonstrated that the number and height of oocyte microvilli were reduced in baboon fetuses deprived of estrogen in utero and restored to normal in animals supplemented with estradiol. Phosphorylated ezrin and Na+/H+ exchange regulatory factor 1 (NHERF, now termed SLC9A3R1) link f-actin bundles to the membrane, whereas alpha-actinin cross-links f-actin to form microvilli. Therefore, we determined whether these proteins were expressed in oocytes of the fetal baboon ovary and whether expression and/or localization were altered between mid and late gestation in association with an increase in estrogen and in late gestation in animals in which estrogen was suppressed (>95%) or restored by treatment with an aromatase inhibitor with or without estradiol. Expression of alpha-actinin was low at mid gestation, increased on the surface of oocytes of primordial follicles in late gestation, and was negligible in the ovaries of estrogen-suppressed fetuses and normal in animals treated with estrogen. Ezrin (total and phosphorylated) and SLC9A3R1 expression was localized to the surface of oocytes at mid and late gestation in estrogen-replete baboons and to the cytoplasm in late gestation after estrogen suppression. These results are the first to show that the fetal baboon oocyte expressed ezrin, SLC9A3R1, and alpha-actinin, and that these proteins were localized to the oocyte surface consistent with their role in microvilli development in epithelial cells. The current study also showed that the developmental increase in oocyte expression of alpha-actinin is regulated by estrogen and correlated with the estrogen-dependent increase in oocyte microvilli demonstrated previously. Therefore, we propose that development of oocyte microvilli requires expression of alpha-actinin and that expression of alpha-actinin and localization of ezrin-phosphate and SLC9A3R1 to the oocyte membrane are regulated by estrogen.
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Affiliation(s)
- Nicholas C Zachos
- Department of Physiological Sciences, Eastern Virginia Medical School, Norfolk, Virginia 23501, USA
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Zhu L, Hatakeyama J, Chen C, Shastri A, Poon K, Forte JG. Comparative study of ezrin phosphorylation among different tissues: more is good; too much is bad. Am J Physiol Cell Physiol 2008; 295:C192-202. [PMID: 18480298 DOI: 10.1152/ajpcell.00159.2008] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In a comparison of three different tissues, the membrane cytoskeleton linker protein ezrin was found to assume high levels of phosphorylation on threonine-567 (T567) in the brush border membranes of renal proximal tubule cells and small intestine enterocytes, in contrast to the apical canalicular membrane of gastric parietal cells. Together with an earlier observation that increased T567 phosphorylation is associated with more elaborate microvilli in parietal cells, this comparative study suggested a higher phosphorylation level requirement for the denser and more uniform distribution of microvilli at brush border surfaces. Using a kinase inhibitor, staurosporin, and metabolic inhibitor, sodium azide, relatively high turnover of ezrin T567 phosphorylation was observed in all three epithelia. Aiming to understand the role of phosphorylation turnover in these tissues, detergent extraction analysis of gastric glands and proximal tubules revealed that an increased phosphorylation on ezrin T567 greatly enhanced its association with F-actin, while ezrin-membrane interaction persisted regardless of the changes of phosphorylation level on ezrin T567. Finally, expression of Thr567Asp mutant ezrin, which mimics the phospho-ezrin state but does not allow turnover, caused aberrant growth of membrane projections in cultured proximal tubule cells, consistent with what had previously been observed in several cell lines and gastric parietal cells. These results fit into a model of surface plasticity, which posits that the turnover of phosphorylation on T567 empowers ezrin to relax and reposition membrane to the underlying cytoskeleton under varying conditions of filament growth or rapid membrane expansion (or depletion).
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Affiliation(s)
- Lixin Zhu
- Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, CA 94720-3200, USA
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55
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Eckert JJ, Fleming TP. Tight junction biogenesis during early development. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1778:717-28. [DOI: 10.1016/j.bbamem.2007.09.031] [Citation(s) in RCA: 82] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/01/2007] [Revised: 09/13/2007] [Accepted: 09/17/2007] [Indexed: 01/12/2023]
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Abstract
The first 4 days of mouse pre-implantation development are characterized by a period of segmentation, including morphogenetic events that are required for the divergence of embryonic and extra-embryonic lineages. These extra-embryonic tissues are essential for the implantation into the maternal uterus and for the development of the foetus. In this review, we first discuss data showing unambiguously that no essential axis of development is set up before the late blastocyst stage, and explain why the pre-patterning described during the early phases (segmentation) of development in other vertebrates cannot apply to mammalian pre-implantation period. Then, we describe important cellular and molecular events that are required for the morphogenesis of the blastocyst.
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Affiliation(s)
- Nicolas Dard
- Laboratoire de Biologie Cellulaire du Développement, UMR 7622, CNRS, Université Pierre et Marie Curie, 9 Quai St Bernard, 75252 Paris Cedex 05, France
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Abstract
This review explores possible mechanisms by which the neurofibromatosis type-2 tumour suppressor Merlin regulates contact-dependent inhibition of proliferation. Starting from an evolutionary perspective, the concurrent emergence of intercellular contacts and proliferation control in multicellular organisms is first considered. Following a brief survey of the molecular and subcellular milieus in which merlin performs its function, the importance of different cellular and biological contexts in defining the function of merlin is discussed. Finally, an integrated model for merlin and the Ezrin, Radixin, and Moesin (ERM) proteins functioning in the regulation of cellular interfaces is proposed.
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Zhu L, Zhou R, Mettler S, Wu T, Abbas A, Delaney J, Forte JG. High turnover of ezrin T567 phosphorylation: conformation, activity, and cellular function. Am J Physiol Cell Physiol 2007; 293:C874-84. [PMID: 17553936 DOI: 10.1152/ajpcell.00111.2007] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In its dormant state, the membrane cytoskeletal linker protein ezrin takes on a NH(2) terminal-to-COOH terminal (N-C) binding conformation. In vitro evidence suggests that eliminating the N-C binding conformation by Thr(567) phosphorylation leads to ezrin activation. Here, we found for resting gastric parietal cells that the levels of ezrin phosphorylation on Thr(567) are low and can be increased to a small extent ( approximately 40%) by stimulating secretion via the cAMP pathway. Treatment of cells with protein phosphatase inhibitors led to a rapid, dramatic increase in Thr(567) phosphorylation by 400% over resting levels, prompting the hypothesis that ezrin activity is regulated by turnover of phosphorylation on Thr(567). In vitro and in vivo fluorescence resonance energy transfer analysis demonstrated that Thr(567) phosphorylation opens the N-C interaction. However, even in the closed conformation, ezrin localizes to membranes by an exposed NH(2) terminal binding site. Importantly, the opened phosphorylated form of ezrin more readily cosediments with F-actin and binds more tightly to membrane than the closed forms. Furthermore, fluorescence recovery after photobleaching analysis in live cells showed that the Thr567Asp mutant had longer recovery times than the wild type or the Thr567Ala mutant, indicating the Thr(567)-phosphorylated form of ezrin is tightly associated with F-actin and the membrane, restricting normal activity. These data demonstrate and emphasize the functional importance of reversible phosphorylation of ezrin on F-actin binding. A novel model is proposed whereby ezrin and closely associated kinase and phosphatase proteins represent a motor complex to maintain a dynamic relationship between the varying membrane surface area and filamentous actin length.
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Affiliation(s)
- Lixin Zhu
- 241 LSA, Dept. of Molecular and Cell Biology, Univ. of California, Berkeley, CA 94720-3200, USA
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59
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Krawetz R, MacKenzie MJ, Sun Q, Walton PA, Kelly GM. Gα13 activation rescues moesin-depletion induced apoptosis in F9 teratocarcinoma cells. Exp Cell Res 2006; 312:3224-40. [PMID: 16860319 DOI: 10.1016/j.yexcr.2006.06.016] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2006] [Revised: 05/25/2006] [Accepted: 06/14/2006] [Indexed: 11/17/2022]
Abstract
Mouse F9 cells differentiate into primitive endoderm when treated with retinoic acid (RA) and into parietal endoderm in response to RA and dibutyryl (db-) cAMP. G protein signaling either blocks or mimics RA-induced differentiation, the latter signaling through the Wnt-beta-catenin pathway. In our study, we found that a constitutively active Galpha13 mutant induces F9 cells to differentiate into parietal endoderm in the absence of exogenous agents. Galpha13 expression and subsequent differentiation are accompanied by beta-catenin translocation to the nucleus. Differentiation and changes in cell morphology are supported by rearrangements to the F-actin cytoskeleton. ERM (ezrin-radixin-moesin) proteins, known to link F-actin to transmembrane receptors, are also redistributed during differentiation. Furthermore, morpholino antisense and shRNA approaches show that moesin expression is essential since its knockdown leads to altered F-actin distribution and subsequent apoptosis. Moesin-depleted cells, however, remain attached to the substrate when Galpha13 is constitutively expressed, but they do not differentiate into extraembryonic endoderm. Our study demonstrates a link between Galpha13 signaling that regulates differentiation of F9 cells through primitive to parietal endoderm and a moesin requirement for cell survival.
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Affiliation(s)
- Roman Krawetz
- Department of Biology, Molecular Genetics Unit, University of Western Ontario, London, ON, Canada N6A 5B7
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60
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Yamanaka Y, Ralston A, Stephenson RO, Rossant J. Cell and molecular regulation of the mouse blastocyst. Dev Dyn 2006; 235:2301-14. [PMID: 16773657 DOI: 10.1002/dvdy.20844] [Citation(s) in RCA: 208] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Animals use diverse strategies to specify tissue lineages during development. A common strategy is to partition maternally supplied and localized lineage determinants into progenitor cells. The mouse embryo appears to use a different, more regulative strategy to specify the first three lineages: the epiblast (EPI: future embryo), the trophectoderm (TE: future placenta), and the primitive endoderm (PE: future yolk sac). These lineages are specified during two successive differentiation steps leading to formation of the blastocyst. Here, we review classic and contemporary models of early lineage specification in the mouse, and describe recent efforts to understand the molecular regulation of these events. We describe evidence that trophectoderm differentiation bears resemblance to the process of epithelialization and describe the importance of apical/basal protein complexes in regulating this process. Next, we present a revised model of PE specification, and describe evidence that PE cells in the inner cell mass sort out to occupy their ultimate position on the surface of the EPI. Finally, we describe factors that reinforce these lineages and three distinct stem cell types that can be isolated from them. Together, these mechanisms guide the differentiation of the first lineages of the mouse and thereby set up tissues that will be important for the first steps of embryonic body patterning.
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Affiliation(s)
- Yojiro Yamanaka
- Program of Developmental Biology, Hospital for Sick Children, Toronto, Ontario, Canada
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61
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Golovnina K, Blinov A, Akhmametyeva EM, Omelyanchuk LV, Chang LS. Evolution and origin of merlin, the product of the Neurofibromatosis type 2 (NF2) tumor-suppressor gene. BMC Evol Biol 2005; 5:69. [PMID: 16324214 PMCID: PMC1315344 DOI: 10.1186/1471-2148-5-69] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2005] [Accepted: 12/02/2005] [Indexed: 11/10/2022] Open
Abstract
Background Merlin, the product of the Neurofibromatosis type 2 (NF2) tumor suppressor gene, belongs to the ezrin-radixin-moesin (ERM) subgroup of the protein 4.1 superfamily, which links cell surface glycoproteins to the actin cytoskeleton. While merlin's functional activity has been examined in mammalian and Drosophila models, little is understood about its evolution, diversity, and overall distribution among different taxa. Results By combining bioinformatic and phylogenetic approaches, we demonstrate that merlin homologs are present across a wide range of metazoan lineages. While the phylogenetic tree shows a monophyletic origin of the ERM family, the origin of the merlin proteins is robustly separated from that of the ERM proteins. The derivation of merlin is thought to be in early metazoa. We have also observed the expansion of the ERM-like proteins within the vertebrate clade, which occurred after its separation from Urochordata (Ciona intestinalis). Amino acid sequence alignment reveals the absence of an actin-binding site in the C-terminal region of all merlin proteins from various species but the presence of a conserved internal binding site in the N-terminal domain of the merlin and ERM proteins. In addition, a more conserved pattern of amino acid residues is found in the region containing the so-called "Blue Box," although some amino acid substitutions in this region exist in the merlin sequences of worms, fish, and Ciona. Examination of sequence variability at functionally significant sites, including the serine-518 residue, the phosphorylation of which modulates merlin's intra-molecular association and function as a tumor suppressor, identifies several potentially important sites that are conserved among all merlin proteins but divergent in the ERM proteins. Secondary structure prediction reveals the presence of a conserved α-helical domain in the central to C-terminal region of the merlin proteins of various species. The conserved residues and structures identified correspond to the important sites highlighted by the available crystal structures of the merlin and ERM proteins. Furthermore, analysis of the merlin gene structures from various organisms reveals the increase of gene length during evolution due to the expansion of introns; however, a reduction of intron number and length appears to occur in the merlin gene of the insect group. Conclusion Our results demonstrate a monophyletic origin of the merlin proteins with their root in the early metazoa. The overall similarity among the primary and secondary structures of all merlin proteins and the conservation of several functionally important residues suggest a universal role for merlin in a wide range of metazoa.
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Affiliation(s)
- Kseniya Golovnina
- Institute of Cytology and Genetics, Russian Academy of Sciences, 10 Lavrent'ev Ave., 630090, Novosibirsk, Russia
| | - Alexander Blinov
- Institute of Cytology and Genetics, Russian Academy of Sciences, 10 Lavrent'ev Ave., 630090, Novosibirsk, Russia
| | - Elena M Akhmametyeva
- Center for Childhood Cancer, Children's Research Institute, Children's Hospital and Department of Pediatrics, The Ohio State University, 700 Children's Drive, Columbus, OH 43205-2696, USA
| | - Leonid V Omelyanchuk
- Institute of Cytology and Genetics, Russian Academy of Sciences, 10 Lavrent'ev Ave., 630090, Novosibirsk, Russia
| | - Long-Sheng Chang
- Center for Childhood Cancer, Children's Research Institute, Children's Hospital and Department of Pediatrics, The Ohio State University, 700 Children's Drive, Columbus, OH 43205-2696, USA
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Lan M, Kojima T, Murata M, Osanai M, Takano KI, Chiba H, Sawada N. Phosphorylation of ezrin enhances microvillus length via a p38 MAP-kinase pathway in an immortalized mouse hepatic cell line. Exp Cell Res 2005; 312:111-20. [PMID: 16274688 DOI: 10.1016/j.yexcr.2005.09.018] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2005] [Revised: 08/05/2005] [Accepted: 09/29/2005] [Indexed: 11/27/2022]
Abstract
The apical microvilli are closely related with the development and the maintenance of cell polarization, and the length of microvilli varies in a regular way among cell types. Ezrin, a member of the ezrin/radixin/moesin (ERM) family, seems to be involved in the formation and stabilization of the apical microvilli. We found that phosphorylation of ezrin caused elongation of microvilli via a p38 MAP-kinase signaling pathway in an immortalized mouse hepatic cell line. When, in the oncogenic Raf-1-transfected mouse hepatic cell line, epithelial to mesenchymal transition (EMT) indicated as down-regulation of E-cadherin and up-regulation of Snail occurred, loss of microvilli and down-regulation of ezrin but not radixin and moesin were also observed. In the Raf-1 transfectants treated with the MAP-kinase inhibitor PD98059 and the p38 MAP-kinase inhibitor SB203580, the numbers of microvilli and the expression of ezrin, E-cadherin and Snail were recovered. More interestingly, treatment with SB203580 induced elongation of microvilli and increased phosphorylation of ezrin (at Thr-567 and Tyr-353). Phosphorylated ezrin-positive dots were colocalized with actin-positive dots on the surface of some Raf-1 transfectants treated with SB203580. These results suggested that phosphorylation of ezrin via the p38 MAP-kinase signaling pathway might be involved in the formation of microvilli during development of epithelial cell polarization.
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Affiliation(s)
- Mengdong Lan
- Department of Pathology, Sapporo Medical University School of Medicine, S1. W17. Sapporo 060-8556, Japan
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63
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Zhou R, Zhu L, Kodani A, Hauser P, Yao X, Forte JG. Phosphorylation of ezrin on threonine 567 produces a change in secretory phenotype and repolarizes the gastric parietal cell. J Cell Sci 2005; 118:4381-91. [PMID: 16144865 DOI: 10.1242/jcs.02559] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
Abstract
Phosphorylation of the membrane-cytoskeleton linker protein ezrin has been functionally linked to acid secretion and vesicle recruitment to the apical secretory membrane in gastric parietal cells. Phosphorylation of the conserved T567 residue of ezrin has been shown to alter the N/C oligomerization of ezrin and promote the formation of actin-rich surface projections in other cells. To test the importance of T567 as a regulatory site for ezrin in parietal cell activation, we incorporated wild-type (WT) and mutant forms of ezrin, including the nonphosphorylatable T567A mutation and a mutant mimicking permanent phosphorylation, T567D. All ezrin constructs included C-terminal cyan-fluorescent protein (CFP) and were incorporated into adenoviral constructs for efficient introduction into cultured parietal cells from rabbit stomach. Fluorescence microscopy was used to localize CFP-ezrin and monitor morphological responses. Accumulation of a weak base (aminopyrine) was used to monitor receptor-mediated acid secretory response of the cultured cells. Similar to endogenous ezrin, WT and T567A CFP-ezrin localized heavily to apical membrane vacuoles with considerably lower levels associated with the surrounding basolateral membrane. Interestingly, H,K-ATPase within cytoplasmic tubulovesicles was incorporated into the apical vacuoles along with WT and T567A mutant ezrin. In these parietal cells secretagogue stimulation produced a striking vacuolar expansion associated with HCl secretion and the secretory phenotype. Expression of T567D CFP-ezrin was quite different, being rarely associated with apical vacuoles. T567D was more typically localized to the basolateral membrane, often associated with long spikes and fingerlike projections. Moreover, the cells did not display secretagogue-dependent morphological changes and, to our surprise, H,K-ATPase was recruited to the T567D CFP-ezrin-enriched basolateral projections. We conclude that T567 phosphorylation, which is probably regulated through Rho signaling pathway, may direct ezrin to membrane-cytoskeletal activity at the basolateral membrane and away from apical secretory activity. The large basolateral expansion is predicted to recruit membranes from sources not normally targeted to that surface.
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Affiliation(s)
- Rihong Zhou
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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64
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Robb VA, Gerber MA, Hart-Mahon EK, Gutmann DH. Membrane localization of the U2 domain of Protein 4.1B is necessary and sufficient for meningioma growth suppression. Oncogene 2005; 24:1946-57. [PMID: 15688033 DOI: 10.1038/sj.onc.1208335] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Meningiomas are common central nervous system tumors; however, the molecular mechanisms underlying their pathogenesis are largely undefined. Previous work has implicated Protein 4.1B as an important tumor suppressor involved in the development of these neoplasms. In this report, we demonstrate that the U2 domain is necessary and sufficient for the ability of Protein 4.1B to function as a meningioma growth suppressor. Using a series of truncation and deletion constructs of DAL-1 (a fragment of Protein 4.1B that retains all the growth suppressive properties), we narrowed the domain required for 4.1B growth suppression to a fragment containing a portion of the FERM domain and the U2 domain using clonogenic assays on meningioma cells. Deletion of the U2 domain in the context of the full-length DAL-1 molecule eliminated growth suppressor function, as measured by thymidine incorporation and caspase-3 activation. Moreover, targeting the U2 domain to the plasma membrane using a membrane localization signal (MLS) reduced cell proliferation, similar to wild-type DAL-1. Collectively, the data suggest that the U2 domain, when properly targeted to the plasma membrane, contains all the residues necessary for mediating Protein 4.1B growth suppression.
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Affiliation(s)
- Victoria A Robb
- Department of Neurology, Washington University School of Medicine, St Louis, MO 63110, USA
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65
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Zhu L, Liu Y, Forte JG. Ezrin oligomers are the membrane-bound dormant form in gastric parietal cells. Am J Physiol Cell Physiol 2005; 288:C1242-54. [PMID: 15788482 DOI: 10.1152/ajpcell.00521.2004] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ezrin is a member of ezrin, radixin, moesin (ERM) protein family that links F-actin to membranes. The NH(2)- and COOH-terminal association domains of ERM proteins, known respectively as N-ERMAD and C-ERMAD, participate in interactions with membrane proteins and F-actin, and intramolecular and intermolecular interactions within and among ERM proteins. In gastric parietal cells, ezrin is heavily represented on the apical membrane and is associated with cell activation. Ezrin-ezrin interactions are presumably involved in functional regulation of ezrin and thus became a subject of our study. Fluorescence resonance energy transfer (FRET) was examined with cyan fluorescent protein (CFP)- and yellow fluorescent protein (YFP)-tagged ezrin incorporated into HeLa cells and primary cultures of parietal cells. Constructs included YFP at the NH(2) terminus of ezrin (YFP-Ez), CFP at the COOH terminus of ezrin (Ez-CFP), and double-labeled ezrin (N-YFP-ezrin-CFP-C). FRET was probed using fluorescence microscopy and spectrofluorometry. Evidence of ezrin oligomer formation was found using FRET in cells coexpressing Ez-CFP and YFP-Ez and by performing coimmunoprecipitation of endogenous ezrin with fluorescent protein-tagged ezrin. Thus intermolecular NH(2)- and COOH-terminal association domain (N-C) binding in vivo is consistent with the findings of earlier in vitro studies. After the ezrin oligomers were separated from monomers, FRET was observed in both forms, indicating intramolecular and intermolecular N-C binding. When the distribution of native ezrin as oligomers vs. monomers was examined in resting and maximally stimulated parietal cells, a shift of ezrin oligomers to the monomeric form was correlated with stimulation, suggesting that ezrin oligomers are the membrane-bound dormant form in gastric parietal cells.
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Affiliation(s)
- Lixin Zhu
- Department of Molecular and Cell Biology, University. of California, 245 Life Sciences Addition, MC 3200, Berkeley, CA 94720-3200, USA
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66
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Louvet-Vallée S, Vinot S, Maro B. Mitotic Spindles and Cleavage Planes Are Oriented Randomly in the Two-Cell Mouse Embryo. Curr Biol 2005; 15:464-9. [PMID: 15753042 DOI: 10.1016/j.cub.2004.12.078] [Citation(s) in RCA: 70] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Revised: 12/29/2004] [Accepted: 12/30/2004] [Indexed: 11/18/2022]
Abstract
Most experimental embryological studies performed on the early mouse embryo have led to the conclusion that there are no mosaically distributed developmental determinants in the zygote and early embryo (for example see [1-6]). It has been suggested recently that "the cleavage pattern of the early mouse embryo is not random and that the three-dimensional body plan is pre-patterned in the egg" (in [7] for review see [8-10]). Two major spatial cues influencing the pattern of cleavage divisions have been proposed: the site of the second meiotic division [11, 12] and the sperm entry point [13-14], although the latter is controversial [15-17]. An implication of this hypothesis is that the orientations of the first few cleavage divisions are stereotyped. Such a define cleavage pattern, leading to the segregation of developmental determinants, is observed in many species [18]. Recently, it was shown that the first cleavage plane is not predetermined but defined by the topology of the two apposing pronuclei [19]. Because the position of the female pronucleus is dependent upon the site of polar body extrusion and the position of the male pronuclei is dependent upon the sperm entry point [19-20], this observation leaves open the possibility that the sperm may provide some kind of directionality [7]. But, even if asymmetries were set up only after fertilization, a stereotyped cleavage pattern should take place during the following cleavage divisions. Thus, we studied the cleavage pattern of two-cell embryos by videomicroscopy to distinguish between the two hypotheses. After the mitotic spindle formed, its orientation did not change until cleavage. During late metaphase and anaphase, the spindle poles appear to be anchored to the cortex through astral microtubules and PARD6a. Only at the time of cleavage, during late anaphase, do the forming daughter cells change their relative positions. These studies show that cleavage planes are oriented randomly in two-cell embryos. This argues against a prepatterning of the mouse embryo before compaction.
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Affiliation(s)
- Sophie Louvet-Vallée
- Laboratoire de Biologie Cellulaire du Développement, UMR 7622, Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, 9 Quai St. Bernard, 75252 Paris cedex 05, France
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67
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Abstract
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.
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