Abstract
Fishes rely on both chemical and tactile senses to orient themselves to avoid predators, and to detect and taste food. This is likely achieved by highly coordinated reception of signals by mechano- and chemosensory receptors in fish. A small co-receptor from zebrafish, receptor activity modifying protein (RAMP)-like triterpene glycoside receptor (RL-TGR), was previously found to be involved in recognition of triterpene glycosides, a family of naturally occurring compounds that act as chemical defenses in various prey species. However, its localization, function, and how it impacts sensory organ development in vivo is not known. Here we show that RL-TGR is expressed in zebrafish in both i) apical microvilli of the chemosensory cells of taste buds including the epithelium of lips and olfactory epithelium, and ii) mechanosensory cells of neuromasts belonging to the lateral line system. Loss-of-function analyses of RL-TGR resulted in significantly decreased number of neuromasts in the posterior lateral line system and decreased body length, suggesting that RL-TGR is involved in deposition and migration of the neuromasts. Collectively, these results provide the first in vivo genetic evidence of sensory cell-specific expression of this unusual co-receptor and reveal its additional role in the lateral line development in zebrafish.
Highlights
Animals use diverse sensory systems for mediating critical ecological relationships, for example between predators and their prey[1]
Reverse transcriptase quantitative PCR (RT-qPCR) analysis in zebrafish whole embryos showed that rltgr starts to be expressed at 8 hours post fertilization with a major increase at 3 days post fertilization onwards (Fig. 1a)
The observation that RAMP-like triterpene glycoside receptor (RL-TGR) is expressed in chemosensory tissues in vivo such as lip epithelium, taste buds, and olfactory epithelium (Fig. 2) supports its role as a chemoreceptor which was previously indicated by heterologous expression in Xenopus oocytes[5]
Summary
Animals use diverse sensory systems for mediating critical ecological relationships, for example between predators and their prey (food)[1]. These systems help animals locate food, gauge its nutritional value, and avoid noxious items. One challenge with aversive chemoreception is that toxic and deterrent compounds are structurally diverse, likely more so than the common taste molecules that cue fishes to palatable foods[2]. Fish genomes appear to encode fewer chemoreceptors than one might expect when compared with other vertebrates[4] One such system of chemoreception involving receptor and co-receptor was recently discovered in zebrafish. We performed morpholino-mediated knockdown of RL-TGR to reveal its physiological effects on early development of zebrafish
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