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WASP and SCAR have distinct roles in activating the Arp2/3 complex during myoblast fusion
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2008 (English)In: Journal of Cell Science, ISSN 0021-9533, E-ISSN 1477-9137, Vol. 121, no Pt 8, 1303-1313 p.Article in journal (Refereed) Published
Abstract [en]

Myoblast fusion takes place in two steps in mammals and in Drosophila. First, founder cells (FCs) and fusion-competent myoblasts (FCMs) fuse to form a trinucleated precursor, which then recruits further FCMs. This process depends on the formation of the fusion-restricted myogenic-adhesive structure (FuRMAS), which contains filamentous actin (F-actin) plugs at the sites of cell contact. Fusion relies on the HEM2 (NAP1) homolog Kette, as well as Blow and WASP, a member of the Wiskott-Aldrich-syndrome protein family. Here, we show the identification and characterization of schwächling--a new Arp3-null allele. Ultrastructural analyses demonstrate that Arp3 schwächling mutants can form a fusion pore, but fail to integrate the fusing FCM. Double-mutant experiments revealed that fusion is blocked completely in Arp3 and wasp double mutants, suggesting the involvement of a further F-actin regulator. Indeed, double-mutant analyses with scar/WAVE and with the WASP-interacting partner vrp1 (sltr, wip)/WIP show that the F-actin regulator scar also controls F-actin formation during myoblast fusion. Furthermore, the synergistic phenotype observed in Arp3 wasp and in scar vrp1 double mutants suggests that WASP and SCAR have distinct roles in controlling F-actin formation. From these findings we derived a new model for actin regulation during myoblast fusion.

Place, publisher, year, edition, pages
2008. Vol. 121, no Pt 8, 1303-1313 p.
Keyword [en]
Drosophila, Myogenesis, F-actin, Arp3, FuRMAS, Actin cytoskeleton, kette
National Category
Cell and Molecular Biology
Research subject
Molecular Biology
Identifiers
URN: urn:nbn:se:umu:diva-20623DOI: 10.1242/jcs.022269PubMedID: 18388318OAI: oai:DiVA.org:umu-20623DiVA: diva2:209175
Available from: 2009-03-24 Created: 2009-03-24 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Exploiting Drosophila as a model system for studying anaplastic lymphoma kinase in vivo
Open this publication in new window or tab >>Exploiting Drosophila as a model system for studying anaplastic lymphoma kinase in vivo
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Anaplastic Lymphoma Kinase (ALK) is a Receptor Tyrosine Kinase (RTK) and an oncogene associated with several human diseases, but its normal function in humans and other vertebrates is unclear. Drosophila melanogaster has an ALK homolog, demonstrating that the RTK has been conserved throughout evolution. This makes Drosophila a suitable model organism for studying not only Drosophila ALK function, but also to study mammalian forms of ALK. In Drosophila the ligand Jeb activates ALK, initiating signaling crucial for visceral mesoderm development. The activating ligand for mammalian ALK is unclear, and for this reason Drosophila was employed in a cross-species approach to investigate whether Drosophila Jeb can activate mouse ALK. Jeb is unable to activate mouse ALK, and therefore mouse ALK is unable to substitute for and rescue the Drosophila ALK mutant phenotype. This suggests that there has been significant evolution in the ALK-ligand relationship between the mouse and Drosophila.

In humans ALK has recently been shown to be involved in the development of neuroblastoma, a cancer tumor in children. I have developed a Drosophila model for examining human gain of function ALK mutants found in neuroblastoma patients. The various ALK variants have acquired point mutations in the kinase domain that have been predicted to activate the RTK in a constitutive and ligand independent manner. When expressed in the fly eye, active human ALK mutants result in a rough eye phenotype, while inactive wild type ALK does not, due to the lack of an activating ligand in the fly. In this way  several of the ALK mutations identified in neuroblastoma patients could be confirmed to be activated in a ligand independent manner. Moreover, a novel ALK mutant; ALKF1174S, was discovered in a neuroblastoma patient and was in the Drosophila model shown to be a gain of function mutation, and a previously predicted gain of function mutation; ALKI1250T, was shown to be a kinase dead mutation. This fly model can also be used for testing ALK selective inhibitors, for identifying activating ligands for human ALK and for identifying conserved components of the ALK signaling pathway.

Gut musculature development in Drosophila is dependent on ALK signaling, while somatic muscle development is not. Proteins of the Wasp-Scar signaling network regulate Arp2/3-complex mediated actin polymerization, and I have investigated their function in visceral and somatic muscle fusion. I found that Verprolin and other members of this protein family are essential for somatic but not visceral muscle development. Despite fusion defects in both tissues in Verprolin and other examined mutants, gut development proceeds, suggesting that fusion is not crucial for visceral mesoderm development. Hence the actin polymerization machinery functions in both somatic and visceral muscle fusion, but this process only appears to be essential in somatic muscle development.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2010. 58 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1376
Keyword
Anaplastic lymphoma kinase, Receptor tyrosine kinase, Jeb, neuroblastoma, actin polymerization, Wasp, Scar, Vrp1, Arp2/3
National Category
Cell and Molecular Biology
Research subject
Molecular Biology
Identifiers
urn:nbn:se:umu:diva-36991 (URN)978-91-7459-090-6 (ISBN)
Public defence
2010-11-05, Major Groove, Byggnad 6L, Umeå universitet, Umeå, 09:00 (English)
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Exploiting Drosophila as a model system for studying Anaplastic Lymphoma Kinase in vivo
Available from: 2010-10-15 Created: 2010-10-14 Last updated: 2010-10-15Bibliographically approved

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