Essential role of B-Raf in ERK activation during extraembryonic development

doi:10.1073/pnas.0507399103

Essential role of B-Raf in ERK activation during extraembryonic development

^*Max F. Perutz Laboratories, Vienna Biocenter, Dr. Bohr Gasse 9, 1030 Vienna, Austria; and ^§Departments of Neurobiology, Psychiatry, and Psychology, and Brain Research Institute, University of California, Los Angeles, CA 90095-1761

Edited by Kathryn V. Anderson, Sloan-Kettering Institute, New York, NY (received for review August 24, 2005)

Abstract

The kinases of the Raf family have been intensively studied as activators of the mitogen-activated protein kinase kinase/extra-cellular signal-regulated kinase (ERK) module in regulated and deregulated proliferation. Genetic evidence that Raf is required for ERK activation in vivo has been obtained in lower organisms, which express only one Raf kinase, but was hitherto lacking in mammals, which express more than one Raf kinase. Ablation of the two best studied Raf kinases, B-Raf and Raf-1, is lethal at midgestation in mice, hampering the detailed study of the essential functions of these proteins. Here, we have combined conventional and conditional gene ablation to show that B-Raf is essential for ERK activation and for vascular development in the placenta. B-Raf-deficient placentae show complete absence of phosphorylated ERK and strongly reduced HIF-1α and VEGF levels, whereas all these parameters are normal in Raf-1-deficient placentae. In addition, neither ERK phosphorylation nor development are affected in B-raf-deficient embryos that are born alive obtained by epiblast-restricted gene inactivation. The data demonstrate that B-Raf plays a nonredundant role in ERK activation during extraembyronic mammalian development in vivo.

Footnotes

↵ ¶ To whom correspondence should be addressed. E-mail: manuela.baccarini{at}univie.ac.at.
↵ † G.G.-K. and D.M. contributed equally to this work.
↵ ‡ Present address: Department of Vascular Biology and Thrombosis Research, Medical University of Vienna, 1090 Vienna, Austria.
Author contributions: M.B. designed research; G.G.-K., D.M., D.P., K.M., and T.P. performed research; A.P.C. and A.S. contributed new reagents/analytic tools; G.G.-K., D.M., and M.B. analyzed data; and M.B. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: En, embryonic day n; ERK, extracellular signal-regulated kinase; KO, knockout; MEF, mouse embryonic fibroblast; MEK, mitogen-activated protein kinase kinase; pERK, phosphorylated ERK; VEGF-A, A isoform of VEGF.