A floor plate enhancer of the zebrafish netrin1 gene requires Cyclops (Nodal) signalling and the winged helix transcription factor FoxA2.
The floor plate is an organising centre that controls neural differentiation and axonogenesis in the neural tube. The axon guidance molecule Netrin1 is expressed in the floor plate of zebrafish embryos. To elucidate the regulatory mechanisms underlying expression in the floor plate, we scanned the netrin1 locus for regulatory regions and identified an enhancer that drives expression in the floor plate and hypochord of transgenic embryos. The expression of the transgene is ectopically activated by Cyclops (Nodal) signals but does not respond to Hedgehog signals. The winged-helix transcription factor foxA2 (also HNF3beta, axial) is expressed in the notochord and floor plate. We show that knock-down of FoxA2 leads to loss of floor plate, while notochord and hypochord development is unaffected, suggesting a specific requirement of FoxA2 in the floor plate. The transgene is ectopically activated by FoxA2, and expression of FoxA2 leads to rescue of floor plate differentiation in mutant embryos that are deficient in Cyclops signalling. Zebrafish and mouse use different signalling systems to specify floor plate. The zebrafish netrin1 regulatory region also drives expression in the floor plate of mouse and chicken embryos. This suggests that components of the regulatory circuits controlling expression in the floor plate are conserved and that FoxA2-given its importance for midline development also in the mouse-may be one such component.
Rastegar
Sepand
S
Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, B.P. 10142, 67404, Illkirch Cedex, C.U. de Strasbourg, France.
Albert
Stephanie
S
Le Roux
Isabelle
I
Fischer
Nadine
N
Blader
Patrick
P
Müller
Ferenc
F
Strähle
Uwe
U
D000818:Animals; D030801:Animals, Genetically Modified; D002642:Chick Embryo; D003001:Cloning, Molecular; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic; D051542:Hepatocyte Nuclear Factor 3-beta; D047908:Intracellular Signaling Peptides and Proteins; D007438:Introns; D051379:Mice; D008845:Microinjections; D009414:Nerve Growth Factors / Q000235:genetics*; D009420:Nervous System / Q000196:embryology*; D000075388:Netrin-1; D009687:Nuclear Proteins / Q000378:metabolism*; D015398:Signal Transduction; D014157:Transcription Factors / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D025521:Tumor Suppressor Proteins; D015027:Zebrafish / Q000196:embryology / Q000235:genetics*; D029961:Zebrafish Proteins
D017931:DNA Primers; D004268:DNA-Binding Proteins; C496503:Foxa2 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D009414:Nerve Growth Factors; D009687:Nuclear Proteins; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; D029961:Zebrafish Proteins; C512832:ndr2 protein, zebrafish; D051542:Hepatocyte Nuclear Factor 3-beta; D000075388:Netrin-1