Development of sensory and neurosecretory cell types: Vertebrate cranial placodes, Volume 1

Our senses provide us with a richness of experiences that we all too often take for granted. Without our sense organs, our world would be a silent and dark place (not a place at all, really). Yet, we share our sophisticated ears, eyes and noses only with our fellow vertebrates. The senses of their closest living relatives, the tunicates (including sea squirts) and lancelets (or amphioxus), are much simpler. Accordingly, these animals live in a much simpler sensory world. Many other animals get around with an even more basic outfit of sensory cells - isolated cells scattered through their outer tissues - which do not form complex sense organs at all. So how did the vertebrate head become equipped with these complicated new sensory organs? How do they develop in the vertebrate embryo? And how did they evolve from the simpler sensory system of our invertebrate ancestors? These are the core questions that this book and its companion try to answer. The first of these 2 volumes will deal with development, whereas the second volume will cover evolutionary origins. Most of the cranial sense organs of vertebrates arise from embryonic structures known as cranial placodes, which in turn arise from a common embryonic precursor in development. In addition to sense organs, cranial placodes also give rise to sensory neurons that transmit the sensory information to the brain as well as to many neurosecretory cells – neuron-like cells that produce hormones (including the cells of the anterior pituitary, the major hormonal control organ of the vertebrate body). Due to the close developmental and evolutionary links between sensory, neuronal and neurosecretory cells derived from cranial placodes, they will be considered jointly in this set of two books. While the photoreceptors of the vertebrae retina and pineal organ are not derived from cranial placodes, they will nevertheless be briefly discussed here. The main reason is the close evolutionary relationship between photoreceptors and other sensory cell types (e.g. mechano- and chemoreceptors) that develop from placodes. The first volume of this set will focus on the development of sensory and neurosecretory cell types from the cranial placodes in vertebrates. Chapter 1 introduces the vertebrate head with its sense organs and neurosecretory organs. Chapter 2 then provides an overview of the various cranial placodes and their derivatives. Chapter 3 presents evidence that all cranial placodes develop from a common embryonic primordium and discusses how the latter is established in the early embryo. How individual placodes develop from the common primordium is addressed in chapter 4. Chapters 5 to 8 then review, how the various placodally derived sensory and neurosecretory cell types as well as photoreceptors are specified and differentiate (i.e. adopt their peculiar phenotype).

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CRC Press

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Attribution-NonCommercial-NoDerivatives 4.0 International

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