The Fgf8 signal causes cerebellar differentiation by activating the Ras-ERK signaling pathway.
The mes/metencephalic boundary (isthmus) is an organizing center for the optic tectum and cerebellum. Fgf8 is accepted as a crucial organizing signal. Previously, we reported that Fgf8b could induce cerebellum in the mesencephalon, while Fgf8a transformed the presumptive diencephalon into mesencephalon. Since lower doses of Fgf8b exerted similar effects to those of Fgf8a, the type difference could be attributed to the difference in the strength of the signal. It is of great interest to uncover mechanisms of signal transduction pathways downstream of the Fgf8 signal in tectal and cerebellar development, and in this report we have concentrated on the Ras-ERK pathway. In normal embryos, extracellular-signal-regulated kinase (ERK) is activated at the site where Fgf8 mRNA is expressed. Fgf8b activated ERK while Fgf8a or a lower dose of Fgf8b did not activate ERK in the mes/metencephalon. Disruption of the Ras-ERK signaling pathway by a dominant negative form of Ras (RasS17N) changed the fate of the metencephalic alar plate from cerebellum to tectum. RasS17N canceled the effects of Fgf8b, while co-transfection of Fgf8a and RasS17N exerted additive effects. Disruption of Fgf8b, not Fgf8a, by siRNA resulted in posterior extension of the Otx2 expression domain. Our results indicate that the presumptive metencephalon receives a strong Fgf8 signal that activates the Ras-ERK pathway and differentiates into the cerebellum.
Department of Molecular Neurobiology, Graduate School of Life Sciences, Tohoku University, Seiryo-machi 4-1, Aoba-ku, Sendai 980-8575, Japan.
Tatsuya
T
Sato
Harukazu
H
Nakamura
D000818:Animals; D001483:Base Sequence; D002454:Cell Differentiation; D002531:Cerebellum / Q000196:embryology* / Q000378:metabolism; D002642:Chick Embryo; D018076:DNA, Complementary / Q000378:metabolism; D018274:Electroporation; D004789:Enzyme Activation; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors / Q000502:physiology*; D005799:Genes, Dominant; D005822:Genetic Vectors; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors
D018076:DNA, Complementary; D034741:RNA, Small Interfering; D051524:Fibroblast Growth Factor 8; D005346:Fibroblast Growth Factors; D020928:Mitogen-Activated Protein Kinases