The evolutionary history of vertebrate cranial placodes--I: cell type evolution.
Vertebrate cranial placodes are crucial contributors to the vertebrate cranial sensory apparatus. Their evolutionary origin has attracted much attention from evolutionary and developmental biologists, yielding speculation and hypotheses concerning their putative homologues in other lineages and the developmental and genetic innovations that might have underlain their origin and diversification. In this article we first briefly review our current understanding of placode development and the cell types and structures they form. We next summarise previous hypotheses of placode evolution, discussing their strengths and caveats, before considering the evolutionary history of the various cell types that develop from placodes. In an accompanying review, we also further consider the evolution of ectodermal patterning. Drawing on data from vertebrates, tunicates, amphioxus, other bilaterians and cnidarians, we build these strands into a scenario of placode evolutionary history and of the genes, cells and developmental processes that underlie placode evolution and development.
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK. Electronic address: cedric.patthey@gmail.com.
Cedric
C
Patthey
Zoology, School of Natural Sciences & Regenerative Medicine Institute (REMEDI), National University of Ireland, Galway, University Road, Galway, Ireland.
Gerhard
G
Schlosser
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK.
Sebastian M
SM
Shimeld
D000818:Animals; D005075:Biological Evolution; D019521:Body Patterning; D002454:Cell Differentiation; D002465:Cell Movement; D004475:Ectoderm / Q000166:cytology / Q000196:embryology*; D008954:Models, Biological; D012679:Sense Organs / Q000166:cytology / Q000196:embryology*; D014714:Vertebrates / Q000145:classification / Q000196:embryology*
Amphioxus; Cell type; Ciona; Development; Evolution; Neural crest; Placode