Neurogenic and non‐neurogenic placodes in ascidians
- 7 September 2004
- journal article
- research article
- Published by Wiley in Journal of Experimental Zoology Part B: Molecular and Developmental Evolution
- Vol. 302B (5), 483-504
- https://doi.org/10.1002/jez.b.21013
Abstract
The late differentiation of the ectodermal layer is analysed in the ascidians Ciona intestinalis and Botryllus schlosseri, by means of light and electron microscopy, in order to verify the possible presence of placodal structures. Cranial placodes, ectodermal regions giving rise to nonepidermal cell types, are classically found exclusively in vertebrates; however, data are accumulating to demonstrate that the nonvertebrate chordates possess both the genetic machinery involved in placode differentiation, and ectodermal structures that are possible homologues of vertebrate placodes. Here, the term “placode” is used in a broad sense and defines thickenings of the ectodermal layer that can exhibit an interruption of the basal lamina where cells delaminate, and so are able to acquire a nonepidermal fate. A number of neurogenic placodes, ones capable of producing neurons, have been recognised; their derivatives have been analysed and their possible homologies with vertebrate placodes are discussed. In particular, the stomodeal placode may be considered a multiple placode, being composed of different sorts of placodes: part of it, which differentiates hair cells, is discussed as homologous to the octavo‐lateralis placodes, while the remaining portion, giving rise to the ciliated duct of the neural gland, is considered homologous to the adenohypophyseal placode. The neurohypophyseal placode may include the homologues of the hypothalamus and vertebrate olfactory placode; the rostral placode, producing the sensorial papillae, may possibly be homologous to the placodes of the adhesive gland of vertebrates. J. Exp. Zool. (Mol. Dev. Evol.) 302B:1–22, 2004.Keywords
This publication has 68 references indexed in Scilit:
- Novel, secondary sensory cell organ in ascidians: In search of the ancestor of the vertebrate lateral lineJournal of Comparative Neurology, 2003
- The Draft Genome of Ciona intestinalis : Insights into Chordate and Vertebrate OriginsScience, 2002
- Epidermal receptor development and sensory pathways in vitally stained amphioxus (Branchiostoma floridae)Acta Zoologica, 2002
- The colonial urochordate Botryllus schlosseri: from stem cells and natural tissue transplantation to issues in evolutionary ecologyBioEssays, 2002
- The dorsal strand of Polyandrocarpa misakiensis (Protochordata: Ascidiacea): a light and electron microscopic studyActa Zoologica, 2002
- AChE localization in adhesive papillae of ascidian larva: effects of citral, a retinoic acid synthesis inhibitorInvertebrate Reproduction & Development, 2001
- Vertebrate Cranial Placodes I. Embryonic InductionDevelopmental Biology, 2001
- Conduction and coordination in deganglionated ascidiansCanadian Journal of Zoology, 2000
- The Genesis of Neural Crest and Epidermal Placodes: A Reinterpretation of Vertebrate OriginsThe Quarterly Review of Biology, 1983
- Development of the sense organs of the larva of Botryllus schlosseriJournal of Morphology, 1935