title: Transcriptional heterochrony in talpid mole autopods.
abstract: BACKGROUND
  Talpid moles show many specializations in their adult skeleton linked to fossoriality, including enlarged hands when compared to the feet. Heterochrony in developmental mechanisms is hypothesized to account for morphological evolution in skeletal elements.
  
  
  METHODS
  The temporal and spatial distribution of SOX9 expression, which is an early marker of chondrification, is analyzed in autopods of the fossorial Iberian mole Talpa occidentalis, as well as in shrew (Cryptotis parva) and mouse (Mus musculus) for comparison.
  
  
  CONCLUSIONS
  SOX9 expression is advanced in the forelimb compared to the hind limb in the talpid mole. In contrast, in the shrew and the mouse, which do not show fossorial specializations in their autopods, it is synchronous. We provide evidence that transcriptional heterochrony affects the development of talpid autopods, an example of developmental penetrance. We discuss our data in the light of earlier reported pattern heterochrony and later morphological variation in talpid limbs.
  
  
  CONCLUSIONS
  Transcriptional heterochrony in SOX9 expression is found in talpid autopods, which is likely to account for pattern heterochrony in chondral limb development as well as size variation in adult fore- and hind limbs.
authors.affiliation: Paläontologisches Institut und Museum, Universität Zürich, Karl-Schmid-Strasse 4, Zürich 8006, Switzerland. constanze.bickelmann@pim.uzh.ch.
authors.forename: Constanze
authors.initials: C
authors.lastname: Bickelmann
authors.forename: Christian
authors.initials: C
authors.lastname: Mitgutsch
authors.forename: Michael K
authors.initials: MK
authors.lastname: Richardson
authors.forename: Rafael
authors.initials: R
authors.lastname: Jiménez
authors.forename: Merijn Ag
authors.initials: MA
authors.lastname: de Bakker
authors.forename: Marcelo R
authors.initials: MR
authors.lastname: Sánchez-Villagra