Neurotrophin receptors in taste buds of adult zebrafish (Danio rerio) A. Germana a,1 , T. Gonza ´lez-Martı ´nez b,1 , S. Catania a , R. Laura a , J. Cobo c,d , E. Ciriaco a , J.A. Vega b,e, * a Dipartmento di Morfologia, Biochimica, Fisiologia e Produzione Animale, Universita di Messina, Messina, Italy b Departamento de Morfologı ´a y Biologı ´a Celular, Universidad de Oviedo, Facultad de Medicina, C/Julia ´n Claverı ´a, s/n, E-33006 Oviedo, Spain c Departamento de Cirugı ´a y Especialidades Me ´dico-Quiru ´ rgicas (Estomatologı ´a), Universidad de Oviedo, Facultad de Medicina, C/Julia ´n Claverı ´a, s/n, E- 33006 Oviedo, Spain d Instituto Asturiano de Odontologı ´a, Oviedo, Spain e Instituto Universitario de Oncologı ´a del Principado de Asturias, Universidad de Oviedo, Facultad de Medicina, C/Julia ´n Claverı ´a, s/n, E-33006 Oviedo, Spain Received 27 June 2003; received in revised form 26 September 2003; accepted 7 October 2003 Abstract TrkB plays crucial roles in the development and maintenance of taste buds in mammals. In this study we investigated the presence and cell localization of Trks (TrkA, TrkB and TrkC) in taste buds of the zebrafish (Danio rerio) using Western blot and immunohistochemistry. Proteins of 140 and 145 kDa, identified as full-length TrkA and TrkB, were detected. Conversely, the anti-TrkC antibody recognized a protein lower than expected (100 kDa). In agreement with these results the sensory cells of taste buds, displayed TrkA- and TrkB-like, but not TrkC-like, immunoreactivity. TrkA and TrkB co-existed in the same taste buds, but remains to be clarified whether or not they are co- expressed in the same cells. Present results demonstrate that as for mammals neurotrophins might play a role in sensory cells of the teleostean taste buds. q 2003 Elsevier Ireland Ltd. All rights reserved. Keywords: Taste buds; Neurotrophins; Trk neurotrophin receptors; Zebrafish The neurotrophins (NTs) are a family of growth factors that promote development, survival and phenotypic differen- tiation of discrete neuronal populations, and of some non- neuronal tissues, acting throughout specific transmembrane receptors with tyrosine kinase activity denominated Trk (see for a review refs. [1,10]). Both NTs and their signal transducing Trk receptors are highly preserved during vertebrate evolution [6], and mammalian-like or specific NTs and Trks have been detected in fishes (see for a review ref. [9]). The mammalian taste buds express brain derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), two members of the NTs family, and TrkB. BDNF, acting throughout TrkB, plays a key role in the formation and maintenance of gustatory papillae-taste buds nervous apparatus and the taste bugs themselves (see ref. [2]). The zebrafish (Danio rerio) has become in the last times an ideal and common model for genetic analysis, exper- imental embryology and cell biology studies. BDNF and TrkB, but also other NTs and Trk receptors, have been characterized in developing zebrafish [9,13]. However, little is known about the tissue distribution and cellular expression of these molecules in sensory organs of the teleosts (see ref. [7]). In particular, BDNF is expressed in the sensory cells of the neuromasts [5,13], co-localized with TrkB [5]. Whether or not TrkB occurs in the taste buds of this teleost, and whether it is the only present, as it occurs in mammals, is still unknown. The only available data claim for the occurrence of TrkA-like immunoreactivity in the oral taste buds of alevins of Dicentarchus labrax [7]. The present study was designed to analyze the expression of Trks in taste buds of adult zebrafish. The morphology, structure and body distribution of taste buds in the zebrafish has been described in detail earlier [8]. Adult, 6 months old, zebrafish (D. rerio; n ¼ 15, 30–35 mm length) were used throughout the study. The animals were obtained from the aquarium of the Department of 0304-3940/03/$ - see front matter q 2003 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2003.10.017 Neuroscience Letters 354 (2004) 189–192 www.elsevier.com/locate/neulet 1 Both authors contributed equally to this paper. * Corresponding author. Tel./fax: þ 34-95-103-671. E-mail address: javega@sci.cpd.uniovi.es (J.A. Vega).