The torso receptor tyrosine kinase can activate Raf in a Ras-independent pathway.
Activation of the receptor tyrosine kinase (RTK) torso defines the spatial domains of expression of the transcription factors tailless and huckebein. Previous analyses have demonstrated that Ras1 (p21ras) operates upstream of the D-Raf (Raf1) serine/threonine kinase in this signaling pathway. By using a recently developed technique of germline mosaics, we find that D-Raf can be activated by torso in the complete absence of Ras1. This result is supported by analysis of D-Raf activation in the absence of either the exchange factor Son of sevenless (Sos) or the adaptor protein drk (Grb2), as well as by the phenotype of a D-Raf mutation that abolishes binding of Ras1 to D-Raf. Our study provides in vivo evidence that Raf can be activated by an RTK in a Ras-independent pathway.
Hou
X S
XS
Department of Genetics, Harvard Medical School, Boston, Massachusetts 02115, USA.
Chou
T B
TB
Melnick
M B
MB
Perrimon
N
N
D000818:Animals; D004268:DNA-Binding Proteins / Q000235:genetics; D004330:Drosophila / Q000196:embryology / Q000201:enzymology / Q000502:physiology; D029721:Drosophila Proteins; D018507:Gene Expression Regulation, Developmental; D018095:Germ-Line Mutation; D007301:Insect Hormones / Q000502:physiology; D008565:Membrane Proteins / Q000502:physiology; D008954:Models, Biological; D009030:Mosaicism; D010641:Phenotype; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D012097:Repressor Proteins / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*; D020664:Son of Sevenless Proteins
D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; C087725:Hkb protein, Drosophila; D007301:Insect Hormones; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D020664:Son of Sevenless Proteins; C074090:TLL protein, Drosophila; C080530:drk protein, Drosophila; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; C080148:tor protein, Drosophila; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras)