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First published online 7 January 2004
doi: 10.1242/dev.00950

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The role of actin cables in directing the morphogenesis of the pharyngeal pouches

Robyn Quinlan¹, Paul Martin^2,* and Anthony Graham^1,

¹ MRC Centre for Developmental Neurobiology, 4th Floor New Hunts House, Guys Campus, Kings College London, London SE1 1UL, UK
² Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK

Author for correspondence (e-mail: anthony.graham{at}kcl.ac.uk)

Accepted 27 October 2003

The pharyngeal arches are separated by endodermal outpocketings, the pharyngeal pouches. These are structures of considerable importance; they are required to segregate the mesenchymal populations of each arch and to induce the formation of arch components, and they generate specific derivatives, including the parathyroid and the thymus. The pharyngeal pouches are first evident as localised sites at which the endoderm contacts the ectoderm, and they then expand along the proximodistal axis to generate the narrow, tight morphology of the mature pouch. We currently have no knowledge of the morphogenetic mechanisms that direct formation of the pharyngeal pouches. Here, in chick, we show that cells within the pharyngeal pouch endoderm have an abundance of apically located actin fibres that are networked within the endodermal sheet, via their insertion into N-cadherin adherens junctions, to form a web of supra-cellular actin cables. Cytochalasin D disruption of these actin structures results in the formation of aberrant pouches that fail to generate their normal slit-like morphology. This suggests that the process of pharyngeal pouch morphogenesis involves the constraining influence of these actin cables that direct expansion, within the pouch, along the proximodistal axis. These results, importantly, provide us with vital insights into how the pharyngeal pouches form their normal morphology. They also give evidence, for the first time, of actin cables functioning as constraints during complex vertebrate morphogenetic episodes.

Key words: Pharyngeal pouches, Pharyngeal endoderm, Actin cables, Morphogenesis, Chick

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