Hedgehog signaling is required for primary motoneuron induction in zebrafish.
Sonic hedgehog (Shh) is crucial for motoneuron development in chick and mouse. However, zebrafish embryos homozygous for a deletion of the shh locus have normal numbers of motoneurons, raising the possibility that zebrafish motoneurons may be specified differently. Unlike other vertebrates, zebrafish express three hh genes in the embryonic midline: shh, echidna hedgehog (ehh) and tiggywinkle hedgehog (twhh). Therefore, it is possible that Twhh and Ehh are sufficient for motoneuron formation in the absence of Shh. To test this hypothesis we have eliminated, or severely reduced, all three Hh signals using mutations that directly or indirectly reduce Hh signaling and antisense morpholinos. Our analysis shows that Hh signals are required for zebrafish motoneuron induction. However, each of the three zebrafish Hhs is individually dispensable for motoneuron development because the other two can compensate for its loss. Our results also suggest that Twhh and Shh are more important for motoneuron development than Ehh.
Lewis
K E
KE
Institute of Neuroscience, 1254 University of Oregon, Eugene, OR 97403, USA.
Eisen
J S
JS
D000818:Animals; D004627:Embryonic Induction; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins / Q000096:biosynthesis; D060850:LIM-Homeodomain Proteins; D009046:Motor Neurons; D018657:Muscle Fibers, Slow-Twitch; D009132:Muscles / Q000196:embryology; D009154:Mutation; D009419:Nerve Tissue Proteins; D016376:Oligonucleotides, Antisense; D010641:Phenotype; D015398:Signal Transduction; D013116:Spinal Cord / Q000196:embryology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins
D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D060850:LIM-Homeodomain Proteins; D009419:Nerve Tissue Proteins; D016376:Oligonucleotides, Antisense; D015534:Trans-Activators; D014157:Transcription Factors; D029961:Zebrafish Proteins; C509233:ihhb protein, zebrafish; C063843:insulin gene enhancer binding protein Isl-1; C509240:shhb protein, zebrafish