During evolution the vertebrate head has acquired a number of unique features including specialized paired sense organs and cranial sensory ganglia. These evolutionary novelties arise from discrete thickenings of the head ectoderm known as cranial placodes. They include the adenohypophyseal, olfactory, lens, trigeminal, profundal, otic, epibranchial and lateral line placodes. While distinct in the derivatives and cell types they will form, all cranial placodes originate from a common preplacodal domain surrounding the anterior neural plate. Recent evidence suggests that the induction of this pre-placodal domain and its subsequent subdivision into individual placodes with specific identities is a multi-step process. Here we describe the development of these placodes and their derivatives and summarize recent advances in the characterization of the repertoire of transcription factors underlying their development. We also review recent studies that have started to address the role of several classes of signaling molecules in placode induction and segregation, including Bone Morphogenetic Proteins, Fibroblast Growth Factors and Wnt molecules.
Table of Contents
Cranial Placodes and Their Derivatives
Molecular Identity of Cranial Placodes
Induction and Segregation of the Cranial Placodes
About the Author(s)Byung-Yong Park
, Chonbuk National University, College of Veterinary Medicine
Byung-Yong Park was born in Jeonju (South Korea) where he grew up. He did his graduate education at Chonbuk National University where he received his Veterinary and PhD degrees. As part of his graduate work Byung-Yong studied the mechanisms of mouse craniofacial development in the laboratory of Dr. In-Shik Kim. After graduation Byung-Yong joined the laboratory of Dr. Jean-Pierre Saint-Jeannet at the University of Pennsylvania, to study the factors regulating otic placode development in Xenopus. Byung-Yong recently accepted a position in the Department of Anatomy, College of Veterinary Medicine at Chonbuk National University in Korea where he will continue his work on placode induction and differentiation. Byung-Yong is the proud father of two children Kunook (Kevin) and Sayun (Helen). Jean-Pierre Saint-Jeannet
, University of Pennsylvania, School of Veterinary Medicine
Jean-Pierre Saint-Jeannet was born in Mirande and grew up in the small town of L'isle de Noe (Gers, France). Jean-Pierre received his education in France. He obtained a Ph.D. in Developmental Neurobiology from Paul Sabatier University in Toulouse where he worked with Dr. Anne-Marie Duprat on the mechanisms underlying neural induction in the salamander Pleurodeles waltlii. He subsequently trained as a postdoctoral fellow in the laboratory of Dr. Jean Paul Thiery at the Ecole Normale Superieure in Paris, studying cadherin-mediated cell-cell adhesion during development. Jean-Pierre then performed a second postdoc with Dr. Igor B. Dawid at the National Institutes of Health in Bethesda studying the role of canonical Wnt signaling pathway in neural crest formation. Jean-Pierre is currently a Charge de Recherche at the CNRS and an Associate Professor of Developmental Biology in the Department of Animal Biology at the University of Pennsylvania, School of Veterinary Medicine in Phildalephia. Research in his laboratory focuses on the molecular mechanisms controlling neural crest and placodes formation using Xenopus laevis as a model system.