Current Biology
Volume 22, Issue 7, 10 April 2012, Pages 601-607
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The Medaka zic1/zic4 Mutant Provides Molecular Insights into Teleost Caudal Fin Evolution

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Summary

Teleosts have an asymmetrical caudal fin skeleton formed by the upward bending of the caudal-most portion of the body axis, the ural region [1, 2, 3]. This homocercal type of caudal fin ensures powerful and complex locomotion and is regarded as one of the most important innovations for teleosts during adaptive radiation in an aquatic environment [4, 5, 6]. However, the mechanisms that create asymmetric caudal fin remain largely unknown. The spontaneous medaka (teleost fish) mutant, Double anal fin (Da), exhibits a unique symmetrical caudal skeleton that resembles the diphycercal type seen in Polypterus and Coelacanth. We performed a detailed analysis of the Da mutant to obtain molecular insight into caudal fin morphogenesis. We first demonstrate that a large transposon, inserted into the enhancer region of the zic1 and zic4 genes (zic1/zic4) in Da, is associated with the mesoderm-specific loss of their transcription. We then show that zic1/zic4 are strongly expressed in the dorsal part of the ural mesenchyme and thereby induce asymmetric caudal fin development in wild-type embryos, whereas their expression is lost in Da. Comparative analysis further indicates that the dorsal mesoderm expression of zic1/zic4 is conserved in teleosts, highlighting the crucial role of zic1/zic4 in caudal fin morphogenesis.

Highlights

► Medaka mutant Da is an enhancer mutant of the zic1 and zic4 genes (zic1/zic4) ► A large transposon impairs the mesoderm-specific transcription of zic1/zic4 in Dazic1/zic4 expression in the dorsal ural mesenchyme induces asymmetric caudal fin

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Present address: Sars International Centre for Marine Molecular Biology, 55 Thormøhlensgate, Bergen N-5008, Norway