title: Serum response factor is crucial for actin cytoskeletal organization and focal adhesion assembly in embryonic stem cells.
abstract: The activity of serum response factor (SRF), an essential transcription factor in mouse gastrulation, is regulated by changes in actin dynamics. Using Srf(-/-) embryonic stem (ES) cells, we demonstrate that SRF deficiency causes impairments in ES cell spreading, adhesion, and migration. These defects correlate with defective formation of cytoskeletal structures, namely actin stress fibers and focal adhesion (FA) plaques. The FA proteins FA kinase (FAK), beta1-integrin, talin, zyxin, and vinculin were downregulated and/or mislocalized in ES cells lacking SRF, leading to inefficient activation of the FA signaling kinase FAK. Reduced overall actin expression levels in Srf(-/-) ES cells were accompanied by an offset treadmilling equilibrium, resulting in lowered F-actin levels. Expression of active RhoA-V14 rescued F-actin synthesis but not stress fiber formation. Introduction of constitutively active SRF-VP16 into Srf(-/-) ES cells, on the other hand, strongly induced expression of FA components and F-actin synthesis, leading to a dramatic reorganization of actin filaments into stress fibers and lamellipodia. Thus, using ES cell genetics, we demonstrate for the first time the importance of SRF for the formation of actin-directed cytoskeletal structures that determine cell spreading, adhesion, and migration. Our findings suggest an involvement of SRF in cell migratory processes in multicellular organisms.
authors.affiliation: Interfakultäres Institut für Zellbiologie, Abteilung Molekularbiologie, Universität Tübingen, 72076 Tübingen, Germany.
authors.forename: Gerhard
authors.initials: G
authors.lastname: Schratt
authors.forename: Ulrike
authors.initials: U
authors.lastname: Philippar
authors.forename: Jürgen
authors.initials: J
authors.lastname: Berger
authors.forename: Heinz
authors.initials: H
authors.lastname: Schwarz
authors.forename: Olaf
authors.initials: O
authors.lastname: Heidenreich
authors.forename: Alfred
authors.initials: A
authors.lastname: Nordheim
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D002465:Cell Movement / Q000502:physiology; D003599:Cytoskeleton / Q000378:metabolism / Q000502:physiology*; D004789:Enzyme Activation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D022001:Focal Adhesions / Q000502:physiology*; D005786:Gene Expression Regulation; D017405:Herpes Simplex Virus Protein Vmw65 / Q000235:genetics / Q000378:metabolism; D019012:Integrin beta1 / Q000235:genetics / Q000378:metabolism; D008667:Metalloproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D026362:Serum Response Factor / Q000235:genetics / Q000502:physiology*; D013234:Stem Cells / Q000166:cytology; D016608:Talin / Q000235:genetics / Q000378:metabolism; D016596:Vinculin / Q000235:genetics / Q000378:metabolism; D060589:Zyxin; D020742:rhoA GTP-Binding Protein / Q000378:metabolism
chemical_list: D000199:Actins; D017405:Herpes Simplex Virus Protein Vmw65; D019012:Integrin beta1; D008667:Metalloproteins; D011993:Recombinant Fusion Proteins; D026362:Serum Response Factor; D016608:Talin; C498285:Zyx protein, mouse; D060589:Zyxin; D016596:Vinculin; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496051:Ptk2 protein, mouse; D020742:rhoA GTP-Binding Protein