JONZ, M.G.*; NURSE, C.A.*; McMaster University, Hamilton, ON, Canada: Merkel-like cells of the zebrafish gill arch and oral epithelium

The identity of receptors that line the buccal cavity and gill arches in fish sensitive to mechanical stimuli is unknown. Neurosecretory cells in these regions, similar in morphology to mechanoreceptive Merkel cells of higher vertebrates, have been described but their function and innervation pattern are poorly understood. Using a whole-mount preparation and confocal immunofluorescence, we have begun a characterization of Merkel-like cells (MLCs) of the zebrafish oral epithelium and gill arches. A zebrafish-specific neuronal marker (zn-12) was used to label nerve fibers, and antisera against serotonin (5-HT) and the synaptic vesicle protein SV2 labeled MLCs of the gill arch and oral epithelium. Reconstruction of optical sections facilitated a detailed description of MLC morphology, distribution and pattern of innervation. Four populations of MLCs were identified based on the following criteria: location, 5-HT and SV2 expression, the presence of microvilli and innervation by zn-12-immunoreactive (IR) nerve fibers. Most MLCs were located at the base of taste buds, associated with taste cells, and were oriented toward the buccal cavity. Our initial findings indicate that MLCs of the zebrafish oral epithelium and gill arches share some characteristics with Merkel cells of higher vertebrates, and highlight the potential of the zebrafish preparation for the study of MLC function.