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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)
Gene Review

Hx  -  hemimelic extra toes

Mus musculus

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Disease relevance of Hx

  • The loss of digits that we observed in mice with reduced Lmbr1 activity is in contrast to the gain of digits observed in Hx mice and human polydactyly patients [1].
  • This region is homologous to a segment of mouse chromosome 5, where the mutations hammer toe (HM) and hemimelic extra toes (HX) have been mapped [2].

High impact information on Hx

  • These and three other mutants, namely, Rim4, Hx, and Xt1, which we described in our previous study, all appeared to form a duplicated zone of polarizing activity (ZPA) at the anterior margin of the limb bud [3].
  • In mice the dominant Hemimelic extra toes (Hx) and Hammertoe (Hm) mutations map to a homologous chromosomal region and cause similar limb defects [1].
  • The mouse Hemimelic extra-toes (Hx) mutation maps to a homologous chromosome segment and has been proposed to affect a homologous gene [4].
  • The open reading frame of both genes is intact in mutant mice, but the expression of the Lmbr1 gene is dramatically altered in developing limbs of Hx mutant mice [4].
  • A novel candidate gene for mouse and human preaxial polydactyly with altered expression in limbs of Hemimelic extra-toes mutant mice [4].

Biological context of Hx

  • Msx1 is close but not allelic to either Hm or Hx on mouse chromosome 5 [5].
  • The Lmbr1 gene is entirely within the small critical intervals recently defined for both the mouse and human mutations and is misexpressed at the exact time that the mouse Hx phenotype becomes apparent during limb development [1].
  • This location is closely linked but distinct from the murine limb mutation Hx and syntenic to human chromosome 7q36 [6].
  • In Hx mice we found a down-regulation of Gli3 in the anterior region of the limb bud [7].
  • Absence of the conserved sequence in limbless reptiles and amphibians and a cis- trans test using the Hx and Shh KO alleles suggest that the sequence is a cis-acting regulator that controls the polarized expression of Shh [8].

Anatomical context of Hx


Other interactions of Hx

  • Il6 did not recombine with either Hm or Hx and, therefore, provides a point of access for the analysis of these mutations at the molecular level [5].
  • Hm and Hx are very tightly linked loci [5].
  • Embryos from this strain exhibit little difference in Shh expression compared to Hx simple mutants [10].
  • Hx, a dominant mutation that causes deformities in limb development, maps approximately 2 cM proximal to Emv-1 [11].
  • In contrast, a significant expansion of Dac expression are observed in the anterior mesenchyme of the limb buds of hemimelic extra toes (Hx/+) mice [12].


  1. Reciprocal mouse and human limb phenotypes caused by gain- and loss-of-function mutations affecting Lmbr1. Clark, R.M., Marker, P.C., Roessler, E., Dutra, A., Schimenti, J.C., Muenke, M., Kingsley, D.M. Genetics (2001) [Pubmed]
  2. A complex bilateral polysyndactyly disease locus maps to chromosome 7q36. Tsukurov, O., Boehmer, A., Flynn, J., Nicolai, J.P., Hamel, B.C., Traill, S., Zaleske, D., Mankin, H.J., Yeon, H., Ho, C. Nat. Genet. (1994) [Pubmed]
  3. Multigenic control of the localization of the zone of polarizing activity in limb morphogenesis in the mouse. Masuya, H., Sagai, T., Moriwaki, K., Shiroishi, T. Dev. Biol. (1997) [Pubmed]
  4. A novel candidate gene for mouse and human preaxial polydactyly with altered expression in limbs of Hemimelic extra-toes mutant mice. Clark, R.M., Marker, P.C., Kingsley, D.M. Genomics (2000) [Pubmed]
  5. Msx1 is close but not allelic to either Hm or Hx on mouse chromosome 5. Robert, B., Montagutelli, X., Houzelstein, D., Ferland, L., Cohen, A., Buckingham, M., Guénet, J.L. Mamm. Genome (1994) [Pubmed]
  6. Cloning, expression, and chromosomal location of SHH and IHH: two human homologues of the Drosophila segment polarity gene hedgehog. Marigo, V., Roberts, D.J., Lee, S.M., Tsukurov, O., Levi, T., Gastier, J.M., Epstein, D.J., Gilbert, D.J., Copeland, N.G., Seidman, C.E. Genomics (1995) [Pubmed]
  7. Expression profile of Gli family members and Shh in normal and mutant mouse limb development. Büscher, D., Rüther, U. Dev. Dyn. (1998) [Pubmed]
  8. Phylogenetic conservation of a limb-specific, cis-acting regulator of Sonic hedgehog ( Shh). Sagai, T., Masuya, H., Tamura, M., Shimizu, K., Yada, Y., Wakana, S., Gondo, Y., Noda, T., Shiroishi, T. Mamm. Genome (2004) [Pubmed]
  9. Quantitative metabolic profiling of testicular steroid secretions with bonded-phase capillary gas chromatography. Chubb, C., Nolan, C. J. Chromatogr. (1984) [Pubmed]
  10. Unusual pattern of Sonic hedgehog expression in the polydactylous mouse mutant Hemimelic extra-toes. Blanc, I., Bach, A., Robert, B. Int. J. Dev. Biol. (2002) [Pubmed]
  11. Synteny on mouse chromosome 5 of homologs for human DNA loci linked to the Huntington disease gene. Cheng, S.V., Martin, G.R., Nadeau, J.H., Haines, J.L., Bucan, M., Kozak, C.A., MacDonald, M.E., Lockyer, J.L., Ledley, F.D., Woo, S.L. Genomics (1989) [Pubmed]
  12. Mouse Dac, a novel nuclear factor with homology to Drosophila dachshund shows a dynamic expression in the neural crest, the eye, the neocortex, and the limb bud. Caubit, X., Thangarajah, R., Theil, T., Wirth, J., Nothwang, H.G., Rüther, U., Krauss, S. Dev. Dyn. (1999) [Pubmed]
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