Sonic hedgehog specifies flight feather positional information in avian wings.

Lara Busby,Constance A Rich,Caitlin Mcqueen,Matthew Towers,Cristina Aceituno,Maria A Ros

doi:10.1242/dev.188821

Abstract

ABSTRACTClassical tissue recombination experiments performed in the chick embryo provide evidence that signals operating during early limb development specify the position and identity of feathers. Here, we show that Sonic hedgehog (Shh) signalling in the embryonic chick wing bud specifies positional information required for the formation of adult flight feathers in a defined spatial and temporal sequence that reflects their different identities. We also reveal that Shh signalling is interpreted into specific patterns of Sim1 and Zic transcription factor expression, providing evidence of a putative gene regulatory network operating in flight feather patterning. Our data suggest that flight feather specification involved the co-option of the pre-existing digit patterning mechanism and therefore uncovers an embryonic process that played a fundamental step in the evolution of avian flight.

Highlights

Much is known about the molecular pathways involved in the induction, positioning and morphogenesis of feathers (Chen et al, 2015; Chang et al, 2019), little is known about how different types of feathers are specified
When cyclopamine is systemically applied to chick embryos at HH18-20, it causes the loss of posterior structures in both wings and legs (Scherz et al, 2007; Towers et al, 2008, 2011) and closely mimics the genetic inactivation of Sonic hedgehog (Shh) signalling in chicken oligozeugodactyly mutants (Ros et al, 2003)
Elongated flight feather buds expressing Ptch1 [a direct target of Shh signalling that is involved in feather morphogenesis (Harris et al, 2002, 2005; McKinnell et al, 2004)] are found along the posterior margin of untreated day 13 wings, but not in the wings of embryos that were treated with cyclopamine (Fig. 1D)

Summary

Introduction

Much is known about the molecular pathways involved in the induction, positioning and morphogenesis of feathers (Chen et al, 2015; Chang et al, 2019), little is known about how different types of feathers are specified. Grafts of prospective chick thigh mesoderm made to the wing result in the formation of feathers characteristic of those found in the leg These findings show that the cells of the morphologically indistinct wing bud mesoderm, which give rise to the dermis, have non-equivalence (have a different intrinsic character), and carry positional information that determines feather identity in the overlying ectoderm (Lewis and Wolpert, 1976).

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Conclusion