title: Serum response factor is required for cell contact maintenance but dispensable for proliferation in visceral yolk sac endothelium.
abstract: BACKGROUND
  Endothelial-specific knockout of the transcription factor serum response factor (SRF) results in embryonic lethality by mid-gestation. The associated phenotype exhibits vascular failure in embryos as well as visceral yolk sac (VYS) tissues. Previous data suggest that this vascular failure is caused by alterations in cell-cell and cell-matrix contacts. In the current study, we sought to more carefully address the role of SRF in endothelial function and cell contact interactions in VYS tissues.
  
  
  RESULTS
  Tie2-Cre recombinase-mediated knockout of SRF expression resulted in loss of detectable SRF from VYS mesoderm by E12.5. This loss was accompanied by decreased expression of smooth muscle alpha-actin as well as vascular endothelial cadherin and claudin 5, endothelial-specific components of adherens and tight junctions, respectively. Focal adhesion (FA) integrins alpha5 and beta1 were largely unchanged in contrast to loss of the FA-associated molecule vinculin. The integrin binding partner fibronectin-1 was also profoundly decreased in the extracellular matrix, indicating another aspect of impaired adhesive function and integrin signaling. Additionally, cells in SRF-null VYS mesoderm failed to reduce proliferation, suggesting not only that integrin-mediated contact inhibition is impaired but also that SRF protein is not required for proliferation in these cells.
  
  
  CONCLUSIONS
  Our data support a model in which SRF is critical in maintaining functional cell-cell and cell-matrix adhesion in endothelial cells. Furthermore, we provide evidence that supports a model in which loss of SRF protein results in a sustained proliferation defect due in part to failed integrin signaling.
authors.affiliation: Department of Biochemistry, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, Wisconsin 53226, USA. rmisra@mcw.edu
authors.forename: Mary L
authors.initials: ML
authors.lastname: Holtz
authors.forename: Ravi P
authors.initials: RP
authors.lastname: Misra
mesh_terms: D000199:Actins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D015703:Antigens, CD / Q000235:genetics; D001808:Blood Vessels / Q000196:embryology* / Q000378:metabolism; D015820:Cadherins / Q000235:genetics; D002448:Cell Adhesion; D049109:Cell Proliferation; D021982:Cell-Matrix Junctions / Q000502:physiology; D062507:Claudin-5; D004622:Embryo, Mammalian / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology* / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000196:embryology* / Q000378:metabolism; D005353:Fibronectins / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D055786:Gene Knockout Techniques; D039482:Integrin alpha5 / Q000235:genetics; D019012:Integrin beta1 / Q000235:genetics; D008565:Membrane Proteins / Q000235:genetics; D008648:Mesoderm / Q000166:cytology / Q000196:embryology / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D016133:Polymerase Chain Reaction; D042787:Receptor, TIE-2 / Q000235:genetics; D026362:Serum Response Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D015017:Yolk Sac / Q000098:blood supply* / Q000378:metabolism*; D000099152:Cadherin 5
chemical_list: D000199:Actins; D015703:Antigens, CD; D015820:Cadherins; D062507:Claudin-5; D005353:Fibronectins; D039482:Integrin alpha5; D019012:Integrin beta1; D008565:Membrane Proteins; D042787:Receptor, TIE-2; D026362:Serum Response Factor; D000099152:Cadherin 5; C491511:Cldn5 protein, mouse