![]() ![]() A role for the mesenchyme during comb morphogenesis is further supported by the recent finding that another comb-mutant ( Rose-comb), is caused by ectopic expression of a transcription factor in comb mesenchyme. ![]() The results show that the patterning of the chicken comb is under the control of SHH and suggest that ectopic SOX5 expression in the Pea-comb change the response of mesenchyme to SHH signalling with altered comb morphogenesis as a result. By experimentally blocking SHH with cyclopamine, the wild-type single-comb was transformed into a Pea-comb-like phenotype. Analysis of differential gene expression identified decreased Sonic hedgehog (SHH) receptor expression in Pea-comb mesenchyme. Pea-comb is 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. The wild-type single-comb is reduced in size and distorted in the Pea-comb mutant. In the present work we have focused on the establishment of the chicken comb-morphology by exploring the Pea-comb mutant. The genetic basis and mechanisms behind the morphological variation observed throughout the animal kingdom is still relatively unknown. ![]()
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