Regulation of Raf-1-dependent signaling during early Xenopus development.
The Raf-1 gene product is activated in response to cellular stimulation by a variety of growth factors and hormones. Raf-1 activity has been implicated in both cellular differentiation and proliferation. We have examined the regulation of the Raf-1/MEK/MAP kinase (MAPK) pathway during embryonic development in the frog Xenopus laevis. We report that Raf-1, MEK, and MAPK activities are turned off following fertilization and remain undetectable up until blastula stages (stage 8), some 4 h later. Tight regulation of the Raf-1/MEK/MAPK pathway following fertilization is crucial for embryonic cell cycle progression. Inappropriate reactivation of MAPK activity by microinjection of oncogenic Raf-1 RNA results in metaphase cell cycle arrest and, consequently, embryonic lethality. Our findings demonstrate an absolute requirement, in vivo, for inactivation of the MAPK signaling pathway to allow normal cell cycle progression during the period of synchronous cell divisions which occur following fertilization. Further, we show that cytostatic factor effects are mediated through MEK and MAPK.
Daiichi Research Center, Cardiovascular Research Institute, University of California at San Francisco 94143, USA.
A M
AM
MacNicol
A J
AJ
Muslin
E L
EL
Howard
A
A
Kikuchi
M C
MC
MacNicol
L T
LT
Williams
D000818:Animals; D001755:Blastocyst / Q000502:physiology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002453:Cell Cycle; D002875:Chromosomes / Q000502:physiology / Q000648:ultrastructure; D004625:Embryo, Nonmammalian / Q000166:cytology / Q000502:physiology*; D004789:Enzyme Activation; D005260:Female; D005306:Fertilization; D006706:Homeostasis; D007700:Kinetics; D008297:Male; D008677:Metaphase; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D014158:Transcription, Genetic; D014982:Xenopus laevis / Q000196:embryology*
D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases