Abstract
Numerous molecular factors orchestrate the development of the peripheral taste system. The unique anatomy/function of the taste system makes this system ideal for understanding the mechanisms by which these factors function; yet the taste system is underutilized for this role. This review focuses on some of the many factors that are known to regulate gustatory development, and discusses a few topics where more work is needed. Some attention is given to factors that regulate epibranchial placode formation, since gustatory neurons are thought to be primarily derived from this region. Epibranchial placodes appear to arise from a pan-placodal region and a number of regulatory factors control the differentiation of individual placodes. Gustatory neuron differentiation is regulated by a series of transcription factors and perhaps bone morphongenic proteins (BMP). As neurons differentiate, they also proliferate such that their numbers exceed those in the adult, and this is followed by developmental death. Some of these cell-cycling events are regulated by neurotrophins. After gustatory neurons become post-mitotic, axon outgrowth occurs. Axons are guided by multiple chemoattractive and chemorepulsive factors, including semaphorins, to the tongue epithelium. Brain derived neurotrophic factor (BDNF), functions as a targeting factor in the final stages of axon guidance and is required for gustatory axons to find and innervate taste epithelium. Numerous factors are involved in the development of gustatory papillae including Sox-2, Sonic hedge hog and Wnt-β-catenin signaling. It is likely that just as many factors regulate taste bud differentiation; however, these factors have not yet been identified. Studies examining the molecular factors that regulate terminal field formation in the nucleus of the solitary tract are also lacking. However, it is possible that some of the factors that regulate geniculate ganglion development, outgrowth, guidance and targeting of peripheral axons may have the same functions in the gustatory CNS.
Highlights
The unique morphology of the taste system makes it ideal for the study of the molecular factors regulating sensory development
After E16.5, neurons are no longer lost but are added to the geniculate ganglion in Ntf5-/mice. These findings indicate that Brain derived neurotrophic factor (BDNF) regulates geniculate neuron survival for a prolonged embryonic period that begins during target innervation while NT4/5 regulates neuron number at several distinct stages
/- mice, even through NT4/5 binds to the same receptors as BDNF. These findings demonstrate that BDNF functions as a short range chemoattractant which allows facial gustatory neurons to locate and innervate taste epithelia during development
Summary
The unique morphology of the taste system makes it ideal for the study of the molecular factors regulating sensory development. The factors regulating the development and innervation of the peripheral target of gustatory neurons, the fungiform papillae and taste buds will be reviewed. In Ntf5-/- mice, the initial loss of geniculate neurons occurred before E12.5, preceding the loss of the nodose/petrosal complex in these animals These results are consistent with an early role for NT4/5 in gustatory ganglion development. It is not clear whether these factors influence geniculate neuron development, removal of GDNF does reduce the number of neurons in the nodose/petrosal ganglion [69] It remains unclear, whether any of these neurons innervate taste buds. The fact that initial targeting is very accurate suggests that some factor must be expressed in the developing fungiform papillae to signal the correct location to innervating chorda tympani axons. The transcription factor Tlx is expressed by rostral NST, and it may regulate the development of specific NST neuron phenotypes
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
