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Gheisari E, Aakhte M, Müller HAJ. Gastrulation in Drosophila melanogaster: Genetic control, cellular basis and biomechanics. Mech Dev 2020; 163:103629. [PMID: 32615151 DOI: 10.1016/j.mod.2020.103629] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 06/08/2020] [Accepted: 06/24/2020] [Indexed: 01/31/2023]
Abstract
Gastrulation is generally understood as the morphogenetic processes that result in the spatial organization of the blastomere into the three germ layers, ectoderm, mesoderm and endoderm. This review summarizes our current knowledge of the morphogenetic mechanisms in Drosophila gastrulation. In addition to the events that drive mesoderm invagination and germband elongation, we pay particular attention to other, less well-known mechanisms including midgut invagination, cephalic furrow formation, dorsal fold formation, and mesoderm layer formation. This review covers topics ranging from the identification and functional characterization of developmental and morphogenetic control genes to the analysis of the physical properties of cells and tissues and the control of cell and tissue mechanics of the morphogenetic movements in the gastrula.
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Affiliation(s)
- Elham Gheisari
- Institute for Biology, Dept. Developmental Genetics, University of Kassel, Germany
| | - Mostafa Aakhte
- Institute for Biology, Dept. Developmental Genetics, University of Kassel, Germany
| | - H-Arno J Müller
- Institute for Biology, Dept. Developmental Genetics, University of Kassel, Germany.
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2
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WASH phosphorylation balances endosomal versus cortical actin network integrities during epithelial morphogenesis. Nat Commun 2019; 10:2193. [PMID: 31097705 PMCID: PMC6522504 DOI: 10.1038/s41467-019-10229-6] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2018] [Accepted: 04/24/2019] [Indexed: 12/16/2022] Open
Abstract
Filamentous actin (F-actin) networks facilitate key processes like cell shape control, division, polarization and motility. The dynamic coordination of F-actin networks and its impact on cellular activities are poorly understood. We report an antagonistic relationship between endosomal F-actin assembly and cortical actin bundle integrity during Drosophila airway maturation. Double mutants lacking receptor tyrosine phosphatases (PTP) Ptp10D and Ptp4E, clear luminal proteins and disassemble apical actin bundles prematurely. These defects are counterbalanced by reduction of endosomal trafficking and by mutations affecting the tyrosine kinase Btk29A, and the actin nucleation factor WASH. Btk29A forms protein complexes with Ptp10D and WASH, and Btk29A phosphorylates WASH. This phosphorylation activates endosomal WASH function in flies and mice. In contrast, a phospho-mimetic WASH variant induces endosomal actin accumulation, premature luminal endocytosis and cortical F-actin disassembly. We conclude that PTPs and Btk29A regulate WASH activity to balance the endosomal and cortical F-actin networks during epithelial tube maturation.
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Tsikala G, Karagogeos D, Strigini M. Btk-dependent epithelial cell rearrangements contribute to the invagination of nearby tubular structures in the posterior spiracles of Drosophila. Dev Biol 2014; 396:42-56. [PMID: 25305143 DOI: 10.1016/j.ydbio.2014.09.019] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Revised: 09/16/2014] [Accepted: 09/18/2014] [Indexed: 01/08/2023]
Abstract
The Drosophila respiratory system consists of two connected organs, the tracheae and the spiracles. Together they ensure the efficient delivery of air-borne oxygen to all tissues. The posterior spiracles consist internally of the spiracular chamber, an invaginated tube with filtering properties that connects the main tracheal branch to the environment, and externally of the stigmatophore, an extensible epidermal structure that covers the spiracular chamber. The primordia of both components are first specified in the plane of the epidermis and subsequently the spiracular chamber is internalized through the process of invagination accompanied by apical cell constriction. It has become clear that invagination processes do not always or only rely on apical constriction. We show here that in mutants for the src-like kinase Btk29A spiracle cells constrict apically but do not complete invagination, giving rise to shorter spiracular chambers. This defect can be rescued by using different GAL4 drivers to express Btk29A throughout the ectoderm, in cells of posterior segments only, or in the stigmatophore pointing to a non cell-autonomous role for Btk29A. Our analysis suggests that complete invagination of the spiracular chamber requires Btk29A-dependent planar cell rearrangements of adjacent non-invaginating cells of the stigmatophore. These results highlight the complex physical interactions that take place among organ components during morphogenesis, which contribute to their final form and function.
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Affiliation(s)
- Georgia Tsikala
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology Hellas (FORTH), Nikolaou Plastira 100, GR-70013 Heraklion, Crete, Greece; Department of Basic Sciences, Faculty of Medicine, University of Crete, P.O. Box 2208, GR-71003 Heraklion, Crete, Greece
| | - Domna Karagogeos
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology Hellas (FORTH), Nikolaou Plastira 100, GR-70013 Heraklion, Crete, Greece; Department of Basic Sciences, Faculty of Medicine, University of Crete, P.O. Box 2208, GR-71003 Heraklion, Crete, Greece
| | - Maura Strigini
- Institute of Molecular Biology and Biotechnology (IMBB), Foundation for Research and Technology Hellas (FORTH), Nikolaou Plastira 100, GR-70013 Heraklion, Crete, Greece.
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Jennings BH. Pausing for thought: disrupting the early transcription elongation checkpoint leads to developmental defects and tumourigenesis. Bioessays 2013; 35:553-60. [PMID: 23575664 PMCID: PMC3698693 DOI: 10.1002/bies.201200179] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Accepted: 03/04/2013] [Indexed: 12/30/2022]
Abstract
Factors affecting transcriptional elongation have been characterized extensively in in vitro, single cell (yeast) and cell culture systems; however, data from the context of multicellular organisms has been relatively scarce. While studies in homogeneous cell populations have been highly informative about the underlying molecular mechanisms and prevalence of polymerase pausing, they do not reveal the biological impact of perturbing this regulation in an animal. The core components regulating pausing are expressed in all animal cells and are recruited to the majority of genes, however, disrupting their function often results in discrete phenotypic effects. Mutations in genes encoding key regulators of transcriptional pausing have been recovered from several genetic screens for specific phenotypes or interactions with specific factors in mice, zebrafish and flies. Analysis of these mutations has revealed that control of transcriptional pausing is critical for a diverse range of biological pathways essential for animal development and survival.
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A novel conserved phosphotyrosine motif in the Drosophila fibroblast growth factor signaling adaptor Dof with a redundant role in signal transmission. Mol Cell Biol 2010; 30:2017-27. [PMID: 20154139 DOI: 10.1128/mcb.01436-09] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The fibroblast growth factor receptor (FGFR) signals through adaptors constitutively associated with the receptor. In Drosophila melanogaster, the FGFR-specific adaptor protein Downstream-of-FGFR (Dof) becomes phosphorylated upon receptor activation at several tyrosine residues, one of which recruits Corkscrew (Csw), the Drosophila homolog of SHP2, which provides a molecular link to mitogen-activated protein kinase (MAPK) activation. However, the Csw pathway is not the only link from Dof to MAPK. In this study, we identify a novel phosphotyrosine motif present in four copies in Dof and also found in other insect and vertebrate signaling molecules. We show that these motifs are phosphorylated and contribute to FGF signal transduction. They constitute one of three sets of phosphotyrosines that act redundantly in signal transmission: (i) a Csw binding site, (ii) four consensus Grb2 recognition sites, and (iii) four novel tyrosine motifs. We show that Src64B binds to Dof and that Src kinases contribute to FGFR-dependent MAPK activation. Phosphorylation of the novel tyrosine motifs is required for the interaction of Dof with Src64B. Thus, Src64B recruitment to Dof through the novel phosphosites can provide a new link to MAPK activation and other cellular responses. This may give a molecular explanation for the involvement of Src kinases in FGF-dependent developmental events.
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Xia F, Li J, Hickey GW, Tsurumi A, Larson K, Guo D, Yan SJ, Silver-Morse L, Li WX. Raf activation is regulated by tyrosine 510 phosphorylation in Drosophila. PLoS Biol 2008; 6:e128. [PMID: 18494562 PMCID: PMC2386837 DOI: 10.1371/journal.pbio.0060128] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2007] [Accepted: 04/15/2008] [Indexed: 12/22/2022] Open
Abstract
The proto-oncoprotein Raf is pivotal for mitogen-activated protein kinase (MAPK) signaling, and its aberrant activation has been implicated in multiple human cancers. However, the precise molecular mechanism of Raf activation, especially for B-Raf, remains unresolved. By genetic and biochemical studies, we demonstrate that phosphorylation of tyrosine 510 is essential for activation of Drosophila Raf (Draf), which is an ortholog of mammalian B-Raf. Y510 of Draf is phosphorylated by the c-src homolog Src64B. Acidic substitution of Y510 promotes and phenylalanine substitution impairs Draf activation without affecting its enzymatic activity, suggesting that Y510 plays a purely regulatory role. We further show that Y510 regulates Draf activation by affecting the autoinhibitory interaction between the N- and C-terminal fragments of the protein. Finally, we show that Src64B is required for Draf activation in several developmental processes. Together, these results suggest a novel mechanism of Raf activation via Src-mediated tyrosine phosphorylation. Since Y510 is a conserved residue in the kinase domain of all Raf proteins, this mechanism is likely evolutionarily conserved. Receptor tyrosine kinase (RTK)/Ras signaling pathways control many different biological processes during metazoan development. Mutations that disrupt this signaling pathway cause many human diseases, including cancer. The proto-oncoprotein Raf functions downstream of Ras in transducing signals from RTK. Activating mutations in both Ras and Raf have been linked to many types of human cancers. Despite the importance of these oncoproteins in tumorigenesis, the molecular mechanisms of Raf activation remains unresolved. Here, using a genetic screen in Drosophila, we show that the Src homolog Src64B is an activator of Drosophila Raf (Draf) .Src64B phosphorylates tyrosine Y510, in the Draf kinase domain and will activate a full-length Draf, but not a truncated Draf that contains only its kinase domain, suggesting that Y510 phosphorylation may relieve the autoinhibition of full-length Draf. Since Y510 is conserved among all the members of the Raf protein family, its phosphorylation may serve as a mechanism of Raf regulation in general. Phosphorylation of a conserved tyrosine residue located in the kinase domain of Raf family proteins can serve as a mechanism of Raf activation.
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Affiliation(s)
- Fan Xia
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Jinghong Li
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Gavin W Hickey
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Amy Tsurumi
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Kimberly Larson
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Dongdong Guo
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Shian-Jang Yan
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Louis Silver-Morse
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Willis X Li
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York, United States of America
- * To whom correspondence should be addressed. E-mail:
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Acevedo SF, Tsigkari KK, Grammenoudi S, Skoulakis EMC. In vivo functional specificity and homeostasis of Drosophila 14-3-3 proteins. Genetics 2007; 177:239-53. [PMID: 17660572 PMCID: PMC2013677 DOI: 10.1534/genetics.107.072280] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The functional specialization or redundancy of the ubiquitous 14-3-3 proteins constitutes a fundamental question in their biology and stems from their highly conserved structure and multiplicity of coexpressed isotypes. We address this question in vivo using mutations in the two Drosophila 14-3-3 genes, leonardo (14-3-3zeta) and D14-3-3epsilon. We demonstrate that D14-3-3epsilon is essential for embryonic hatching. Nevertheless, D14-3-3epsilon null homozygotes survive because they upregulate transcripts encoding the LEOII isoform at the time of hatching, compensating D14-3-3epsilon loss. This novel homeostatic response explains the reported functional redundancy of the Drosophila 14-3-3 isotypes and survival of D14-3-3epsilon mutants. The response appears unidirectional, as D14-3-3epsilon elevation upon LEO loss was not observed and elevation of leo transcripts was stage and tissue specific. In contrast, LEO levels are not changed in the wing disks, resulting in the aberrant wing veins characterizing D14-3-3epsilon mutants. Nevertheless, conditional overexpression of LEOI, but not of LEOII, in the wing disk can partially rescue the venation deficits. Thus, excess of a particular LEO isoform can functionally compensate for D14-3-3epsilon loss in a cellular-context-specific manner. These results demonstrate functional differences both among Drosophila 14-3-3 proteins and between the two LEO isoforms in vivo, which likely underlie differential dimer affinities toward 14-3-3 targets.
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Affiliation(s)
- Summer F Acevedo
- Institute of Molecular Biology and Genetics, Biomedical Sciences Research Centre Alexander Fleming, 16672 Vari, Greece
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Pepple KL, Anderson AE, Frankfort BJ, Mardon G. A genetic screen in Drosophila for genes interacting with senseless during neuronal development identifies the importin moleskin. Genetics 2006; 175:125-41. [PMID: 17110483 PMCID: PMC1774993 DOI: 10.1534/genetics.106.065680] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Senseless (Sens) is a conserved transcription factor required for normal development of the Drosophila peripheral nervous system. In the Drosophila retina, sens is necessary and sufficient for differentiation of R8 photoreceptors and interommatidial bristles (IOBs). When Sens is expressed in undifferentiated cells posterior to the morphogenetic furrow, ectopic IOBs are formed. This phenotype was used to identify new members of the sens pathway in a dominant modifier screen. Seven suppressor and three enhancer complementation groups were isolated. Three groups from the screen are the known genes Delta, lilliputian, and moleskin/DIM-7 (msk), while the remaining seven groups represent novel genes with previously undefined functions in neural development. The nuclear import gene msk was identified as a potent suppressor of the ectopic interommatidial bristle phenotype. In addition, msk mutant adult eyes are extremely disrupted with defects in multiple cell types. Reminiscent of the sens mutant phenotype, msk eyes demonstrate reductions in the number of R8 photoreceptors due to an R8 to R2,5 fate switch, providing genetic evidence that Msk is a component of the sens pathway. Interestingly, in msk tissue, the loss of R8 fate occurs earlier than with sens and suggests a previously unidentified stage of R8 development between atonal and sens.
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Affiliation(s)
- Kathryn L Pepple
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA
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Li WX. Functions and mechanisms of receptor tyrosine kinase Torso signaling: lessons from Drosophila embryonic terminal development. Dev Dyn 2005; 232:656-72. [PMID: 15704136 PMCID: PMC3092428 DOI: 10.1002/dvdy.20295] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The Torso receptor tyrosine kinase (RTK) is required for cell fate specification in the terminal regions (head and tail) of the early Drosophila embryo. Torso contains a split tyrosine kinase domain and belongs to the type III subgroup of the RTK superfamily that also includes the platelet-derived growth factor receptors, stem cell or steel factor receptor c-Kit proto-oncoprotein, colony-stimulating factor-1 receptor, and vascular endothelial growth factor receptor. The Torso pathway has been a model system for studying RTK signal transduction. Genetic and biochemical studies of Torso signaling have provided valuable insights into the biological functions and mechanisms of RTK signaling during early Drosophila embryogenesis.
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Affiliation(s)
- Willis X Li
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York 14642, USA.
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Laberge G, Douziech M, Therrien M. Src42 binding activity regulates Drosophila RAF by a novel CNK-dependent derepression mechanism. EMBO J 2005; 24:487-98. [PMID: 15660123 PMCID: PMC548663 DOI: 10.1038/sj.emboj.7600558] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2004] [Accepted: 12/15/2004] [Indexed: 01/05/2023] Open
Abstract
Connector enhancer of KSR (CNK), an essential component of Drosophila receptor tyrosine kinase/mitogen-activated protein kinase pathways, regulates oppositely RAF function. This bimodal property depends on the N-terminal region of CNK, which integrates RAS activity to stimulate RAF and a bipartite element, called the RAF-inhibitory region (RIR), which binds and inhibits RAF catalytic activity. Here, we show that the repressive effect of the RIR is counteracted by the ability of Src42 to associate, in an RTK-dependent manner, with a conserved region located immediately C-terminal to the RIR. Strikingly, we found that several cnk loss-of-function alleles have mutations clustered in this area and provide evidence that these mutations impair Src42 binding. Surprisingly, the derepressing effect of Src42 does not appear to involve its catalytic function, but critically depends on the ability of its SH3 and SH2 domains to associate with CNK. Together, these findings suggest that the integration of RTK-induced RAS and Src42 signals by CNK as a two-component input is essential for RAF activation in Drosophila.
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Affiliation(s)
- Gino Laberge
- Institut de Recherche en Immunologie et en Cancérologie, Laboratory of Intracellular Signaling, Université de Montréal, Montréal, Québec, Canada
| | - Mélanie Douziech
- Institut de Recherche en Immunologie et en Cancérologie, Laboratory of Intracellular Signaling, Université de Montréal, Montréal, Québec, Canada
| | - Marc Therrien
- Institut de Recherche en Immunologie et en Cancérologie, Laboratory of Intracellular Signaling, Université de Montréal, Montréal, Québec, Canada
- Institut de Recherche en Immunologie et en Cancérologie, Laboratory of Intracellular Signaling, Université de Montréal, CP 6128 Succursale Centre-Ville, Montreal, Quebec, Canada H3C 3J7. Tel.: +1 514 343 7837; Fax: +1 514 343 6965; E-mail:
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Abstract
Overactivation of receptor tyrosine kinases (RTKs) has been linked to tumorigenesis. To understand how a hyperactivated RTK functions differently from wild-type RTK, we conducted a genome-wide systematic survey for genes that are required for signaling by a gain-of-function mutant Drosophila RTK Torso (Tor). We screened chromosomal deficiencies for suppression of a gain-of-function mutation tor (tor(GOF)), which led to the identification of 26 genomic regions that, when in half dosage, suppressed the defects caused by tor(GOF). Testing of candidate genes in these regions revealed many genes known to be involved in Tor signaling (such as those encoding the Ras-MAPK cassette, adaptor and structural molecules of RTK signaling, and downstream target genes of Tor), confirming the specificity of this genetic screen. Importantly, this screen also identified components of the TGFbeta (Dpp) and JAK/STAT pathways as being required for Tor(GOF) signaling. Specifically, we found that reducing the dosage of thickveins (tkv), Mothers against dpp (Mad), or STAT92E (aka marelle), respectively, suppressed tor(GOF) phenotypes. Furthermore, we demonstrate that in tor(GOF) embryos, dpp is ectopically expressed and thus may contribute to the patterning defects. These results demonstrate an essential requirement of noncanonical signaling pathways for a persistently activated RTK to cause pathological defects in an organism.
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Affiliation(s)
- Jinghong Li
- Department of Biomedical Genetics, University of Rochester Medical Center, Rochester, New York 14642, USA
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Ji JY, Haghnia M, Trusty C, Goldstein LSB, Schubiger G. A genetic screen for suppressors and enhancers of the Drosophila cdk1-cyclin B identifies maternal factors that regulate microtubule and microfilament stability. Genetics 2002; 162:1179-95. [PMID: 12454065 PMCID: PMC1462342 DOI: 10.1093/genetics/162.3.1179] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Coordination between cell-cycle progression and cytoskeletal dynamics is important for faithful transmission of genetic information. In early Drosophila embryos, increasing maternal cyclin B leads to higher Cdk1-CycB activity, shorter microtubules, and slower nuclear movement during cycles 5-7 and delays in nuclear migration to the cortex at cycle 10. Later during cycle 14 interphase of six cycB embryos, we observed patches of mitotic nuclei, chromosome bridges, abnormal nuclear distribution, and small and large nuclei. These phenotypes indicate disrupted coordination between the cell-cycle machinery and cytoskeletal function. Using these sensitized phenotypes, we performed a dosage-sensitive genetic screen to identify maternal proteins involved in this process. We identified 10 suppressors classified into three groups: (1) gene products regulating Cdk1 activities, cdk1 and cyclin A; (2) gene products interacting with both microtubules and microfilaments, Actin-related protein 87C; and (3) gene products interacting with microfilaments, chickadee, diaphanous, Cdc42, quail, spaghetti-squash, zipper, and scrambled. Interestingly, most of the suppressors that rescue the astral microtubule phenotype also reduce Cdk1-CycB activities and are microfilament-related genes. This suggests that the major mechanism of suppression relies on the interactions among Cdk1-CycB, microtubule, and microfilament networks. Our results indicate that the balance among these different components is vital for normal early cell cycles and for embryonic development. Our observations also indicate that microtubules and cortical microfilaments antagonize each other during the preblastoderm stage.
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Affiliation(s)
- Jun-Yuan Ji
- Department of Zoology, University of Washington, Seattle 98195-1800, USA
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Hindley A, Kolch W. Extracellular signal regulated kinase (ERK)/mitogen activated protein kinase (MAPK)-independent functions of Raf kinases. J Cell Sci 2002; 115:1575-81. [PMID: 11950876 DOI: 10.1242/jcs.115.8.1575] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Raf comprises a family of three kinases, A-Raf, B-Raf and Raf-1, which are best known as key regulators of the MEK—MAPK/ERK cascade. This module is often perceived as a linear pathway in which ERK is the effector. However,recent advances have unveiled a role for Raf outside this established signalling unit. Current evidence, including gene-knockout studies in mice,suggests that there are ERK-independent functions of Raf kinases. Regulation of apoptosis is one area in which Raf may function independently of ERK,although its substrates remain to be identified. Other studies have suggested that Raf has kinase-independent functions and may act as a scaffold protein.
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Affiliation(s)
- Alison Hindley
- The Beatson Institute for Cancer Research, CRC Beatson Laboratories, Glasgow, G61 1BD, UK
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