Dev Genes Evol (2009) 219:391–398 DOI 10.1007/s00427-009-0302-z ORIGINAL ARTICLE Induction of otic structures by canonical Wnt signalling in medaka Baubak Bajoghli & Narges Aghaallaei & Gerlinde Jung & Thomas Czerny Received: 7 April 2009 / Accepted: 30 August 2009 / Published online: 16 September 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com Abstract The Wnt family of signalling proteins is known to participate in multiple developmental decisions during em- bryogenesis. We misexpressed Wnt1 in medaka embryos and observed anterior truncations, similar to those described for ectopic activation of canonical Wnt signalling in other species. Interestingly, when we induced a heat-shock Wnt1 transgenic line exactly at 30% epiboly, we observed multiple ectopic otic vesicles in the truncated embryos. The vesicles then fused, forming a single large ear structure. These “cyclopic ears” filled the complete anterior region of the embryos. The ectopic induction of otic development can be explained by the juxtaposition of hindbrain tissue with anterior ectoderm. Fibroblast growth factor (Fgf) ligands are thought to mediate Communicated by T. Hollemann Baubak Bajoghli and Narges Aghaallaei contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s00427-009-0302-z) contains supplementary material, which is available to authorized users. B. Bajoghli : N. Aghaallaei : T. Czerny (*) Department for Biomedical Sciences, University of Veterinary Medicine, Veterinärplatz 1, 1210 Vienna, Austria e-mail: thomas.czerny@vu-wien.ac.at G. Jung : T. Czerny Department for Applied Life Sciences, University of Applied Sciences, FH Campus Wien, Viehmarktgasse 2A, 1030 Vienna, Austria Present Address: B. Bajoghli : N. Aghaallaei Max-Planck Institute of Immunobiology, Stuebeweg 51, 79108 Freiburg, Germany the otic-inducing properties of the hindbrain. However, signals different from Fgf3 and Fgf8 are necessary to explain the formation of the ectopic ear structures, suggesting that Wnt signalling is involved in the otic induction process in medaka. Keywords Wnt1 . Otic induction . Cyclopic ear . Medaka Introduction In teleost fish, the inner ear originates from an ectodermal placode located at the level of rhombomere 4 (r4) of the hindbrain, and the otic placode then cavitates to form the otic vesicle (reviewed in Whitfield et al. 2002). Classical transplantation experiments demonstrated a prominent role of the hindbrain in the otic induction process. In zebrafish, grafting hindbrain tissue to the ventral side of the embryo induces ectopic otic vesicles (Woo and Fraser 1998). Members of the fibroblast growth factor (Fgf) family of secreted ligands are the best candidates for otic-inducing factors (reviewed in Riley and Phillips 2003; Whitfield et al. 2002), but the role of other modulating factors such as Wnt signalling in this process is not clear. Experiments with lithium chloride treatment by Gutknecht and Fritzsch (1990) in Xenopus embryos led to multiple expanded otic vesicles. Since lithium is a potent inhibitor of GSK3; these experiments can be interpreted as a first indication of otic-inducing effects by canonical Wnt signal- ling. A model for induction of the chick inner ear was proposed in which Fgf19 cooperates with Wnt8c to induce ectopic otic placodes (Ladher et al. 2000). Neither Fgf19 nor Wnt8c was able to induce the expression of all otic markers in explants of uncommitted ectoderm, whereas a combina- tion of both genes strongly induced the full range of markers genes. Loss of Wnt8 function experiments in zebrafish suggest