Gli function is essential for motor neuron induction in zebrafish

• Published in: Developmental biology Vol. 282; no. 2; pp. 550 - 570
• Main Authors: Vanderlaan, Gary, Tyurina, Oksana V., Karlstrom, Rolf O., Chandrasekhar, Anand
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-06-2005
• Subjects: Animals; Danio rerio; Embryonic Induction - physiology; Gene Expression Regulation, Developmental; Genotype; Gli; Green fluorescent protein; Hedgehog; Hedgehog Proteins; Hindbrain; Immunohistochemistry; Induction; Morpholino; Motor neuron; Motor Neurons - physiology; Multigene Family - genetics; Mutation - genetics; Oligonucleotides, Antisense; Patched Receptors; Patched-1 Receptor; Receptors, Cell Surface - metabolism; Rhombomere; Signal Transduction - physiology; Trans-Activators - metabolism; Transcription factor; Transcription Factors - genetics; Veratrum Alkaloids; Zebrafish; Zebrafish - embryology; Zebrafish - metabolism; Zebrafish Proteins - genetics; Zinc Finger Protein Gli2; Hedgehog; Induction; Gli; Green fluorescent protein; Zebrafish; Hindbrain; Motor neuron; Rhombomere; Transcription factor; Morpholino
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1016/j.ydbio.2005.04.010

The Gli family of zinc-finger transcription factors mediates Hedgehog (Hh) signaling in all vertebrates. However, their roles in ventral neural tube patterning, in particular motor neuron induction, appear to have diverged across species. For instance, cranial motor neurons are essentially lost in zebrafish
detour (
gli1
−
) mutants, whereas motor neuron development is unaffected in mouse single
gli and some double
gli knockouts. Interestingly, the expression of some Hh-regulated genes (
ptc1,
net1a,
gli1) is mostly unaffected in the
detour mutant hindbrain, suggesting that other Gli transcriptional activators may be involved. To better define the roles of the zebrafish
gli genes in motor neuron induction and in Hh-regulated gene expression, we examined these processes in
you-too (
yot) mutants, which encode dominant repressor forms of Gli2 (Gli2
DR), and following morpholino-mediated knockdown of
gli1,
gli2, and
gli3 function. Motor neuron induction at all axial levels was reduced in
yot (
gli2
DR
) mutant embryos. In addition, Hh target gene expression at all axial levels except in rhombomere 4 was also reduced, suggesting an interference with the function of other Glis. Indeed, morpholino-mediated knockdown of Gli2
DR protein in
yot mutants led to a suppression of the defective motor neuron phenotype. However,
gli2 knockdown in wild-type embryos generated no discernable motor neuron phenotype, while
gli3 knockdown reduced motor neuron induction in the hindbrain and spinal cord. Significantly,
gli2 or
gli3 knockdown in
detour (
gli1
−
) mutants revealed roles for Gli2 and Gli3 activator functions in
ptc1 expression and spinal motor neuron induction. Similarly,
gli1 or
gli3 knockdown in
yot (
gli2
DR
) mutants resulted in severe or complete loss of motor neurons, and of
ptc1 and
net1a expression, in the hindbrain and spinal cord. In addition,
gli1 expression was greatly reduced in
yot mutants following
gli3, but not
gli1, knockdown, suggesting that Gli3 activator function is specifically required for
gli1 expression. These observations demonstrate that Gli activator function (encoded by
gli1,
gli2, and
gli3) is essential for motor neuron induction and Hh-regulated gene expression in zebrafish.