Amino Acids (2012) 42:1317–1327 DOI 10.1007/s00726-010-0826-6 O R I G I N A L A R T I C L E Cloning, tissue and ontogenetic expression of the taurine transporter in the ﬂatﬁsh Senegalese sole (Solea senegalensis) Wilson Pinto • Ivar Rønnestad • Ann-Elise Olderbakk Jordal • Ana S. Gomes • Maria Teresa Dinis • Cla´udia Araga˜o Received: 23 September 2010 / Accepted: 20 December 2010 / Published online: 6 January 2011 The Author(s) 2011. This article is published with open access at Springerlink.com Abstract Flatﬁsh species seem to require dietary taurine for normal growth and development. Although dietary taurine supplementation has been recommended for ﬂat- ﬁsh, little is known about the mechanisms of taurine absorption in the digestive tract of ﬂatﬁsh throughout ontogeny. This study described the cloning and ontogenetic expression of the taurine transporter (TauT) in the ﬂatﬁsh Senegalese sole (Solea senegalensis). Results showed a high similarity between TauT in Senegalese sole and other vertebrates, but a change in TauT amino acid sequences indicates that taurine transport may differ between mam- mals and ﬁsh, reptiles or birds. Moreover, results showed that Senegalese sole metamorphosis is an important developmental trigger to promote taurine transport in lar- vae, especially in muscle tissues, which may be important for larval growth. Results also indicated that the capacity to uptake dietary taurine in the digestive tract is already established in larvae at the onset of metamorphosis. In Senegalese sole juveniles, TauT expression was highest in brain, heart and eye. These are organs where taurine is usually found in high concentrations and is believed to play important biological roles. In the digestive tract of juve- niles, TauT was more expressed in stomach and hindgut, indicating that dietary taurine is quickly absorbed when Electronic supplementary material The online version of this article (doi:10.1007/s00726-010-0826-6) contains supplementary material, which is available to authorized users. W. Pinto (&) M. T. Dinis C. Araga˜o CIMAR/CCMAR, Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal e-mail: wpinto@ualg.pt I. Rønnestad A.-E. O. Jordal A. S. Gomes Department of Biology, University of Bergen, Pb 7803, 5020 Bergen, Norway digestion begins and taurine endogenously used for bile salt conjugation may be recycled at the posterior end of the digestive tract. Therefore, these results suggest an enter- ohepatic recycling pathway for taurine in Senegalese sole, a process that may be important for maintenance of the taurine body levels in ﬂatﬁsh species. Keywords Taurine transporter TauT Senegalese sole Flatﬁsh Ontogeny SLC6A6 Introduction Taurine is an amino sulphonic acid that is among the most abundant low molecular weight organic constituents of animal tissues. For instance, taurine alone accounts for approximately 0.1% of total body weight in humans. Although often considered an amino acid (AA), taurine lacks a carboxyl group and is not incorporated into pro- teins. Instead, taurine is freely distributed throughout cytosol, and is particularly accumulated in excitable tissues. Taurine plays a vital role in several important biological functions such as bile salt conjugation, osmo- regulation, membrane stabilisation, modulation of neuro- transmitters, antioxidation, and early development of visual, neural and muscular systems (Huxtable 1992). Due to its abundance in animal tissues, taurine is highly available in carnivorous and omnivorous diets. Several animals may temporarily or permanently depend on a die- tary source of taurine, due to limited endogenous rate of taurine biosynthesis caused by an inherent deﬁciency on the enzyme cysteine sulﬁnate decarboxylase. For instance, cats are completely unable to biosynthesise taurine and off- spring of female cats that are fed taurine-deﬁcient diets may not survive or may develop neurological defects and retinal 123