title: Heterochrony in the regulation of the developing marsupial limb.
abstract: BACKGROUND
  At birth, marsupial neonates have precociously developed forelimbs. The development of the tammar wallaby (Macropus eugenii) hindlimbs lags significantly behind that of the forelimbs. This differs from the grey short-tailed opossum, Monodelphis domestica, which has relatively similar fore- and hindlimbs at birth. This study examines the expression of the key patterning genes TBX4, TBX5, PITX1, FGF8, and SHH in developing limb buds in the tammar wallaby.
  
  
  RESULTS
  All genes examined were highly conserved with orthologues from opossum and mouse. TBX4 expression appeared earlier in development than in the mouse, but later than in the opossum. SHH expression is restricted to the zone of polarising activity, while TBX5 (forelimb) and PITX1 (hindlimb) showed diffuse mRNA expression. FGF8 is specifically localised to the apical ectodermal ridge, which is more prominent than in the opossum.
  
  
  CONCLUSIONS
  The most marked divergence in limb size in marsupials occurs in the kangaroos and wallabies. The faster development of the fore limb compared to that of the hind limb correlates with the early timing of the expression of the key patterning genes in these limbs.
authors.affiliation: Department of Zoology, The University of Melbourne, Victoria, Australia.
authors.forename: Keng Yih
authors.initials: KY
authors.lastname: Chew
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Shaw
authors.forename: Hongshi
authors.initials: H
authors.lastname: Yu
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pask
authors.forename: Marilyn B
authors.initials: MB
authors.lastname: Renfree
mesh_terms: D000367:Age Factors; D000818:Animals; D019521:Body Patterning / Q000235:genetics*; D017931:DNA Primers / Q000235:genetics; D005346:Fibroblast Growth Factors / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D053823:Hedgehog Proteins / Q000378:metabolism; D006652:Histological Techniques; D017403:In Situ Hybridization; D018878:Limb Buds / Q000254:growth & development* / Q000378:metabolism* / Q000648:ultrastructure; D007614:Macropodidae / Q000254:growth & development* / Q000378:metabolism; D008855:Microscopy, Electron, Scanning; D013045:Species Specificity; D020825:T-Box Domain Proteins / Q000378:metabolism
chemical_list: D017931:DNA Primers; D053823:Hedgehog Proteins; D020825:T-Box Domain Proteins; D005346:Fibroblast Growth Factors
keywords: heterochrony; marsupial limb; species-specific differences