4 years ago

Sonic hedgehog antagonists reduce size and alter patterning of the frog inner ear

Sanam Zarei, Karen L. Elliott, Bernd Fritzsch, Kasra Zarei
Sonic Hedgehog (Shh) signaling plays a major role in vertebrate development, from regulation of proliferation to the patterning of various organs. In amniotes, Shh affects dorsoventral patterning in the inner ear but affects anteroposterior patterning in teleosts. Currently, it remains unknown the function of Shh in inner ear development in terms of how morphogenesis changes in the sarcopterygian/tetrapod lineage coincide with the evolution of limbs and novel auditory organs in the ear. In this study we used the tetrapod, Xenopus laevis, to test how increasing concentrations of the Shh signal pathway antagonist, Vismodegib, affects ear development. Vismodegib treatment dose dependently alters the development of the ear, hypaxial muscle, and indirectly the Mauthner cell through its interaction with the inner ear afferents. Together, these phenotypes have an effect on escape response. The altered Mauthner cell likely contributes to the increased time to respond to a stimulus. In addition, the increased hypaxial muscle in the trunk likely contributes to the subtle change in animal C-start flexion angle. In the ear, Vismodegib treatment results in decreasing segregation between the gravistatic sensory epithelia as the concentration of Vismodegib increases. Furthermore, at higher doses, there is a loss of the horizontal canal but no enantiomorphic transformation, as in bony fish lacking Shh. Like in amniotes, Shh signaling in frogs affects dorsoventral patterning in the ear, suggesting that auditory sensory evolution in sarcopterygians/tetrapods evolved with a shift of Shh axis specification of the ear. This article is protected by copyright. All rights reserved.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/dneu.22544

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