A Spatial and Temporal Gradient of Fgf Differentially Regulates Distinct Stages of Neural Development in the Zebrafish Inner Ear
Open Access
- 15 November 2012
- journal article
- research article
- Published by Public Library of Science (PLoS) in PLoS Genetics
- Vol. 8 (11), e1003068
- https://doi.org/10.1371/journal.pgen.1003068
Abstract
Neuroblasts of the statoacoustic ganglion (SAG) initially form in the floor of the otic vesicle during a relatively brief developmental window. They soon delaminate and undergo a protracted phase of proliferation and migration (transit-amplification). Neuroblasts eventually differentiate and extend processes bi-directionally to synapse with hair cells in the inner ear and various targets in the hindbrain. Our studies in zebrafish have shown that Fgf signaling controls multiple phases of this complex developmental process. Moderate levels of Fgf in a gradient emanating from the nascent utricular macula specify SAG neuroblasts in laterally adjacent otic epithelium. At a later stage, differentiating SAG neurons express Fgf5, which serves two functions: First, as SAG neurons accumulate, increasing levels of Fgf exceed an upper threshold that terminates the initial phase of neuroblast specification. Second, elevated Fgf delays differentiation of transit-amplifying cells, balancing the rate of progenitor renewal with neuronal differentiation. Laser-ablation of mature SAG neurons abolishes feedback-inhibition and causes precocious neuronal differentiation. Similar effects are obtained by Fgf5-knockdown or global impairment of Fgf signaling, whereas Fgf misexpression has the opposite effect. Thus Fgf signaling renders SAG development self-regulating, ensuring steady production of an appropriate number of neurons as the larva grows. Neurons of the statoacoustic ganglion (SAG), which innervate the inner ear, are derived from neuroblasts originating from the floor of the otic vesicle. Neuroblasts quickly delaminate from the otic vesicle to form dividing progenitors, which eventually differentiate into mature neurons of the SAG. Fgf has been implicated in initial neuroblast specification in multiple vertebrate species. However, the role of Fgf at later stages remains uncertain, because previous studies have not been able to evaluate the effects of changing levels of Fgf, nor have they been able to clearly distinguish the effects of Fgf at different stages of SAG development. We have combined conditional loss of function, misexpression, and laser-ablation studies in zebrafish to elucidate how graded Fgf coordinates distinct steps in SAG development. Initially moderate Fgf in a spatial gradient specifies neuroblasts within the otic vesicle. Later, mature SAG neurons express Fgf5 and, as additional neurons accumulate outside the otic vesicle, rising levels of Fgf terminate further specification. Elevated Fgf also slows maturation of progenitors, maintaining a stable progenitor pool in which growth and differentiation are evenly balanced. This feedback facilitates steady production of new neurons as the animal grows through larval and adults stages.This publication has 60 references indexed in Scilit:
- Conditions that influence the response to Fgf during otic placode inductionDevelopmental Biology, 2012
- Fgf and Hh signalling act on a symmetrical pre-pattern to specify anterior and posterior identity in the zebrafish otic placode and vesicleDevelopment, 2011
- Sox2 is required for maintenance and regeneration, but not initial development, of hair cells in the zebrafish inner earDevelopmental Biology, 2010
- Inactivation of fibroblast growth factor receptor signaling in myelinating glial cells results in significant loss of adult spiral ganglion neurons accompanied by age‐related hearing impairmentJournal of Neuroscience Research, 2009
- Spatial and temporal segregation of auditory and vestibular neurons in the otic placodeDevelopmental Biology, 2008
- Pathfinding in a large vertebrate axon tract: isotypic interactions guide retinotectal axons at multiple choice pointsDevelopment, 2008
- Fgf signaling instructs position-dependent growth rate during zebrafish fin regenerationDevelopment, 2005
- Fibroblast growth factor 2 negatively regulates the induction of neuronal progenitors from neural stem cellsJournal of Neuroscience Research, 2005
- Age- and Size-Related Changes in the Inner Ear and Hearing Ability of the Adult Zebrafish (Danio rerio)Journal of the Association for Research in Otolaryngology, 2002
- Stages of embryonic development of the zebrafishDevelopmental Dynamics, 1995