title: Mathematical modelling of digit specification by a sonic hedgehog gradient.
abstract: BACKGROUND
  The three chick wing digits represent a classical example of a pattern specified by a morphogen gradient. Here we have investigated whether a mathematical model of a Shh gradient can describe the specification of the identities of the three chick wing digits and if it can be applied to limbs with more digits.
  
  
  RESULTS
  We have produced a mathematical model for specification of chick wing digit identities by a Shh gradient that can be extended to the four digits of the chick leg with Shh-producing cells forming a digit. This model cannot be extended to specify the five digits of the mouse limb.
  
  
  CONCLUSIONS
  Our data suggest that the parameters of a classical-type morphogen gradient are sufficient to specify the identities of three different digits. However, to specify more digit identities, this core mechanism has to be coupled to alternative processes, one being that in the chick leg and mouse limb, Shh-producing cells give rise to digits; another that in the mouse limb, the cellular response to the Shh gradient adapts over time so that digit specification does not depend simply on Shh concentration.
authors.affiliation: Wolfson Centre for Mathematical Biology, Mathematical Institute, University of Oxford, Radcliffe Observatory Quarter, Oxford, United Kingdom; Oxford Centre for Collaborative Applied Mathematics, Mathematical Institute, University of Oxford, Oxford, United Kingdom.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Woolley
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Baker
authors.forename: Cheryll
authors.initials: C
authors.lastname: Tickle
authors.forename: Philip K
authors.initials: PK
authors.lastname: Maini
authors.forename: Matthew
authors.initials: M
authors.lastname: Towers
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000502:physiology*; D002642:Chick Embryo; D004058:Diffusion; D053823:Hedgehog Proteins / Q000378:metabolism*; D051379:Mice; D008962:Models, Theoretical; D013045:Species Specificity; D014921:Wings, Animal / Q000196:embryology*
chemical_list: D053823:Hedgehog Proteins
keywords: Shh; chick wing; diffusion; digits; gradient; growth; limb; mathematical modelling; morphogen