Embryonic death of Mek1-deficient mice reveals a role for this kinase in angiogenesis in the labyrinthine region of the placenta.
Mek is a dual-specificity kinase that activates the extracellular-signal-regulated (Erk) mitogen-activated protein (MAP) kinases upon agonist binding to receptors. The Erk MAP kinase cascade is involved in cell-fate determination in many organisms. In mammals, this pathway is proposed to regulate cell growth and differentiation. Genetic studies have shown that although a single mek gene is present in Caenorhabditis elegans, Drosophila and Xenopus, two mek homologs, Mek1 and Mek2, are present in the mammalian cascade. In the present study, we describe a mutant mouse line in which the mek1 gene has been disrupted by insertional mutagenesis. The null mutation was recessive lethal, as the homozygous mutant embryos died at 10.5 days of gestation. Histopathological analyses revealed a reduction in vascularization of the placenta that was due to a marked decrease of vascular endothelial cells in the labyrinthine region. The failure to establish a functional placenta probably explains the death of the mek1-/- embryos. Cell-migration assays indicated that mek1-/- fibroblasts could not be induced to migrate by fibronectin, although the levels of Mek2 protein and Erk activation were normal. Re-expression of Mek1 in the mutant mouse embryonic fibroblasts (MEFs) restored their ability to migrate. Our findings provide genetic evidence that establishes the unique role played by Mek1 in signal transduction. They also suggest that mek1 function is required for normal response to angiogenic signals that might promote vascularization of the labyrinthine region of the placenta.
Giroux
S
S
Centre de recherche en cancérologie de l'Université Laval, Centre Hospitalier Universitaire de Québec, Pavillon L'Hôtel-Dieu de Québec, 9, a rue McMahon, Québec, Canada, G1R 2J6.
Tremblay
M
M
Bernard
D
D
Cardin-Girard
J F
JF
Aubry
S
S
Larouche
L
L
Rousseau
S
S
Huot
J
J
Landry
J
J
Jeannotte
L
L
Charron
J
J
D000818:Animals; D001808:Blood Vessels / Q000196:embryology / Q000378:metabolism*; D002465:Cell Movement / Q000187:drug effects / Q000235:genetics; D004622:Embryo, Mammalian / Q000166:cytology / Q000201:enzymology; D005260:Female; D005313:Fetal Death / Q000235:genetics*; D005353:Fibronectins / Q000494:pharmacology; D018507:Gene Expression Regulation, Developmental; D006651:Histocytochemistry; D017403:In Situ Hybridization; D048369:MAP Kinase Kinase 1; D051379:Mice; D018345:Mice, Knockout; D020929:Mitogen-Activated Protein Kinase Kinases; D018919:Neovascularization, Physiologic / Q000235:genetics; D010920:Placenta / Q000502:physiology*; D011247:Pregnancy; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency* / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000172:deficiency* / Q000235:genetics; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics; D017978:Receptors, Growth Factor / Q000235:genetics; D040262:Receptors, Vascular Endothelial Growth Factor
D005353:Fibronectins; D017978:Receptors, Growth Factor; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse; D020929:Mitogen-Activated Protein Kinase Kinases