An inversion involving the mouse Shh locus results in brachydactyly through dysregulation of Shh expression

Abstract

Short digits (Dsh) is a radiation-induced mouse mutant. Homozygous mice are characterized by multiple defects strongly resembling those resulting from Sonic hedgehog (Shh) inactivation. Heterozygous mice show a limb reduction phenotype with fusion and shortening of the proximal and middle phalanges in all digits, similar to human brachydactyly type A1, a condition caused by mutations in Indian hedgehog (IHH). We mapped Dsh to chromosome 5 in a region containing Shh and were able to demonstrate an inversion comprising 11.7 Mb. The distal breakpoint is 13.298 kb upstream of Shh, separating the coding sequence from several putative regulatory elements identified by interspecies comparison. The inversion results in almost complete downregulation of Shh expression during E9.5-E12.5, explaining the homozygous phenotype. At E13.5 and E14.5, however, Shh is upregulated in the phalangeal anlagen of Dsh/+ mice, at a time point and in a region where WT Shh is never expressed. The dysregulation of Shh expression causes the local upregulation of hedgehog target genes such as Gli1-3, patched, and Pthlh, as well as the downregulation of Ihh and Gdf5. This results in shortening of the digits through an arrest of chondrocyte differentiation and the disruption of joint development.

Receptor tyrosine kinase-like orphan receptor 2 (ROR2) and Indian hedgehog regulate digit outgrowth mediated by the phalanx-forming region

“…The Dsh/+ phenotype is due to an up-regulated Pthlh expression from ectopic Shh expression, leading to a suppressed Ihh expression in distal phalanges (11), hence a mechanism comparable to the Ihh E95K/E95K mice (6). Immunolabeling for pSMAD1/5/8 also showed a reduced signal in the PFR of Dsh/+ mice (Fig.…”

Gli3 acts as a repressor downstream of Ihh in regulating two distinct steps of chondrocyte differentiation

“…Sections were counterstained with Toluidine Blue. Probes for in situ hybridization were as follows: Col10a1 (Minina et al, 2001), Ihh (Bitgood and McMahon, 1995); Ptch (Goodrich et al, 1996), Pthr1 Gli3 regulates chondrocyte differentiation (Abou-Samra et al, 1994); PTHrP (Koziel et al, 2004), Fgfr1 and Fgfr3 (Minina et al, 2005), Gli1 and Gli3 (Hui et al, 1994); Gli2 (Niedermaier et al, 2005).…”

Analysis of a new allele of limb deformity (ld) reveals tissue- and age-specific transcriptional effects of the Ld Global Control Region

“…From a genetic standpoint, there are a small number of mouse single gene mutants that have proved suitable for the analysis of mouse limb development, including mutants such as extra-toes (Gli3), brachypodism (Gdf5), syndactylism (Serrate2) and mutations affecting members of the Hox genes such as synpolydactyly (Hoxd13) (reviewed in Gurrieri et al, 2002, Zelzer andOlsen, 2003). There are also other genes shown to be crucial for limb development such as Trp63 or Sonic hedgehog (Shh), although mice lacking these genes are not viable (Mills et al, 1999, Yang et al, 1999, Niedermaier et al, 2005. Tissue specific knockouts such as those generated using Msx2-cre (Sun et al, 2000) have provided another means for investigation and confirmation of important signaling pathways affecting limb development, as these mice can often circumvent embryonic lethality caused by global gene disruption (Pan et al, 2005).…”