iguana encodes a novel zinc-finger protein with coiled-coil domains essential for Hedgehog signal transduction in the zebrafish embryo

Abstract

Signaling by lipid-modified secreted glycoproteins of the Hedgehog family play fundamental roles during pattern formation in animal development and in humans; dysfunction of Hedgehog pathway components is frequently associated with a variety of congenital abnormalities and cancer. Transcriptional regulation of Hedgehog target genes is mediated by members of the Gli zinc-finger transcription factors. The relative nuclear concentrations of Gli activator (Gli act ) and repressor (Gli rep ) forms, together with their nucleocytoplasmic trafficking, appear to be critical determinants for target gene expression. Whereas such stringent controls of Gli activity are critical in ensuring appropriate levels of pathway activation, the mechanisms by which these processes are regulated remain inadequately understood. Here, using genetic analysis, we show that the zebrafish iguana gene product acts downstream of the Smoothened protein to modulate Gli activity in the somites of the developing embryo. Positional cloning reveals that iguana encodes the zebrafish ortholog of Dzip1, a novel zinc-finger/coiled-coil domain protein that we show can shuttle between the cytoplasm and nucleus in a manner correlated with Hedgehog pathway activity.[Keywords: Iguana; Gli; hedgehog signaling; zebrafish; muscle; DzipI] Supplemental material is available at http://www.genesdev.org.

Stabilization of Speckle-type POZ Protein (Spop) by Daz Interacting Protein 1 (Dzip1) Is Essential for Gli Turnover and the Proper Output of Hedgehog Signaling

“…In iguana mutants, there is a global reduction of Hh target gene expression (31,32). More recent studies indicate that the reduced Hh signaling in iguana mutants is likely a consequence of impaired ciliogenesis (34 -36).…”

“…In zebrafish, the Hh signaling inhibitory effect of the you-too (yot) allele, which encodes a dominant negative mutant of Gli2 due to a nonsense mutation at Arg-929 (64), is markedly enhanced in iguana mutants (31,32). The molecular mechanisms underlying this perplexing finding remain unclear.…”

“…Interestingly, although global Hh signaling activity is reduced in iguana mutant embryos, low levels of ectopic expression of Hh-responsive genes, ptc1 and engrailed 1, were also observed. This suggests that Dzip1 can regulate the Hh signaling pathway in a positive and negative manner (31)(32)(33). Subsequent investigations revealed that the positive role of Dzip1 in the Hh pathway is due to its requirement for ciliogenesis (34 -37).…”

“…Dzip1 is a C2H2 zinc finger domain protein with coiled-coil domains and a nuclear localization signal. Requirements for Dzip1 during embryonic development have been best studied using zebrafish iguana mutants, which harbor specific mutations in the Dzip1 gene (31,32). Iguana mutants exhibit midline and somitic muscle defects, both hallmark phenotypes of Hh loss of function in zebrafish.…”

Gene expression analysis of the hedgehog signaling cascade in the chick midbrain and spinal cord

“…Further regulation of the HH signaling cascade occurs at the level of GLI transcription factors (Jiang, 2002). Several genes (e.g., SUFU, DZIP) complex with the GLI/Ci genes and are involved in the nucleocytoplasmic shuttling and cytoplasmic sequestration of the latter (Kogerman et al, 1999;Murone et al, 2000;Sekimizu et al, 2004;Vokes and McMahon, 2004;Wolff et al, 2004;Huangfu and Anderson, 2006;Svard et al, 2006). In addition, some genes (e.g., BTRC/ SLIMB) that are not solely dedicated to HH signaling also regulate this signaling cascade by targeting GLI genes for hyperphosphorylation and eventual degradation (Jiang, 2002).…”