Mouse Disp1 is required in sonic hedgehog-expressing cells for paracrine activity of the cholesterol-modified ligand

Abstract

There was a reanalysis of data required to support the findings in Development 132, 133-142.We have repeated the facial analysis reported in Fig. 2 to provide the data required to support some of the original findings of this study (see Publisher's note). Our findings substantiate the original conclusions drawn from Fig. 2 of a dose-related genetic interaction between Disp1 and Shh alleles, and of the function of Disp1 within Shh-producing cells. Some differences are reported below, which might reflect slight differences in embryonic staging or increased sensitivity of the whole-mount in situ hybridization procedure here. Importantly, they do not alter the key conclusion that reducing Disp1 levels in Shh-producing cells results in a phenotype similar to that of genetically matched embryos with reduced Disp1 activity throughout the embryo. These data support the overall conclusions of the paper, and, together with other data in the same report, support a model in which the principal requirement for Disp1 activity is in Shh-producing cells. Ptch1 and Shh expression was evident in midline cell populations rostral to the optic lobes in wild-type embryos (arrows in P and U). Their expression was either markedly reduced or lost, depending on the specific combination of Disp1 and Shh alleles (Q-T and V-Y). Ptch1 and Shh expression was detected in the midbrain region (indicated by arrowheads in P and U) of all genotypes, albeit at reduced levels.

Region-specific requirement for cholesterol modification of sonic hedgehog in patterning the telencephalon and spinal cord

“…Pax7 is a class II factor that is repressed by Shh and is expressed in all dorsal progenitor domains, whereas Nkx6.1 (Nkx6-1 -Mouse Genome Informatics) is a class I factor that is induced by Shh and expressed in the broad ventral progenitor domains of V2 (p2) mutants, all ventral cell types were generated at defined locations (Fig. 6), in agreement with previously reported ShhN function in the spinal cord (Tian et al, 2005). The number of floorplate cells labeled by Foxa2 was comparable between control and Shh N/-embryos (Fig.…”

“…Accordingly, it has been proposed that cholesterol modification is required for the formation of Shh multimers involved in long-range signaling and proper vertebrate forebrain patterning (Feng et al, 2004). However, a more recent study suggested that ShhN retained some paracrine activity because it was capable of inducing several ventral neuronal cell types in the spinal cord (Tian et al, 2005). Given this controversy, the role of the cholesterol moiety in Shh function has been re-assessed recently in the limb bud (Li et al, 2006).…”

“…The hydrophobic nature of lipids indicates that there might be a dedicated release mechanism for Shh. Disp1, a multi-pass transmembrane protein, appears to fulfil this mechanistic requirement (Caspary et al, 2002;Kawakami et al, 2002;Ma et al, 2002), as its function is necessary only for lipidated Shh secretion (Li et al, 2006;Tian et al, 2005). Lipidmodified Shh has also been shown to form a large multimeric complex in vitro (Chen et al, 2004a;Zeng et al, 2001).…”

Pattern formation in the vertebrate neural tube: a sonic hedgehog morphogen-regulated transcriptional network

“…Thus, ShhN, which lacks the cholesterol moiety, would be expected to spread more rapidly and to penetrate further into the tissue. Surprisingly then, ventral neural tube patterning is compacted in mice that express ShhN in place of wild-type Shh (Huang et al, 2007;Tian et al, 2005). This might reflect a decreased range for ShhN as compared with fully processed ShhNp and/or a reduced activity of the monomeric form.…”

“…How Disp1 promotes the release of ShhNp remains to be determined, but its requirement is limited to lipidated Shh; Shh lacking cholesterol (ShhN) undergoes Disp1-independent secretion ( Fig. 3) (Tian et al, 2005). One possible action of Disp1 is to facilitate the assembly of soluble ShhNp multimers that are long-range, high-activity signaling complexes (Goetz et al, 2006;Zeng et al, 2001).…”