Sonic Hedgehog-Signalling Patterns the Developing Chicken Comb as Revealed by Exploration of the Pea-comb Mutation

• The genetic basis and mechanisms behind the morphological variation observed throughout the animal kingdom is stillrelatively unknown. In the present work we have focused on the establishment of the chicken comb-morphology byexploring the Pea-comb mutant. The wild-type single-comb is reduced in size and distorted in the Pea-comb mutant. Peacombis formed by a lateral expansion of the central comb anlage into three ridges and is caused by a mutation in SOX5,which induces ectopic expression of the SOX5 transcription factor in mesenchyme under the developing comb. Analysis ofdifferential gene expression identified decreased Sonic hedgehog (SHH) receptor expression in Pea-comb mesenchyme. Byexperimentally blocking SHH with cyclopamine, the wild-type single-comb was transformed into a Pea-comb-likephenotype. The results show that the patterning of the chicken comb is under the control of SHH and suggest that ectopicSOX5 expression in the Pea-comb change the response of mesenchyme to SHH signalling with altered combmorphogenesis as a result. A role for the mesenchyme during comb morphogenesis is further supported by the recentfinding that another comb-mutant (Rose-comb), is caused by ectopic expression of a transcription factor in combmesenchyme. The present study does not only give knowledge about how the chicken comb is formed, it also adds to ourunderstanding how mutations or genetic polymorphisms may contribute to inherited variations in the human face.

Ämnesord

LANTBRUKSVETENSKAPER  -- Bioteknologi med applikationer på växter och djur -- Genetik och förädling inom lantbruksvetenskap (hsv//swe)

AGRICULTURAL SCIENCES  -- Agricultural Biotechnology -- Genetics and Breeding in Agricultural Sciences (hsv//eng)

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