Molecular and Cellular Endocrinology 157 (1999) 67 – 73 Cloning of putative piscine (Sparus aurata) transthyretin: developmental expression and tissue distribution Bruria Funkenstein a, *, Valerie Perrot a , Christopher L. Brown b a Israel Oceanographic and Limnological Research, National Institute of Oceanography, PO Box 8030, Tel -Shikmona, Haifa 31080, Israel b Hawaii Institute of Marine Biology, School of Ocean and Earth Science and Technology, Uniersity of Hawaii, Box 1346 Coconut Island, Kaneohe, HI 96744, USA Received 30 June 1999; accepted 16 July 1999 Abstract cDNA encoding putative transthyretin (prealbumin, TTR) was cloned from liver of the marine fish Sparus aurata. The cDNA contains an open reading frame of 453 nt, encoding for a TTR precursor of 151 amino acids. The deduced amino acid sequence of S. aurata TTR shows identity of 54, 57.3 and 54.1% with lizard, chicken and rat TTR, respectively. Northern blot analysis revealed a TTR transcript of about 700 nt, highly expressed in liver, but also in skin. Low expression was detected in 12 other tissues by using RT-PCR. The ontogeny of TTR expression during early stages of larval development of S. aurata was examined by Northern blot analysis using poly(A + )RNA from larvae collected on different days after hatching. TTR mRNA was seen already on the first day after hatching and its steady-state levels increased from Day 15 onwards. Molecular cloning of a TTR-like cDNA from fish suggests that TTR evolved earlier in vertebrate development than previously thought. Furthermore, its expression in liver exceeds by several-fold that found in brain, yet high expression is also found in skin. These results suggest that in fish, liver is the main site of TTR synthesis, but that TTR may have an important function in fish skin. © 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Fish; Larva; Liver; Transthyretin cDNA; RNA blot hybridization www.elsevier.com/locate/mce 1. Introduction Numerous studies have demonstrated the presence of thyroid hormones (TH), both T 3 and T 4 , in extracts from whole unfertilized and developing embryos from a variety of teleostean species (Brown et al., 1987; Kobuke et al., 1987; Tagawa and Hirano, 1987; Cyr and Eales, 1996 and references therein). During the course of development, TH in eggs decrease before hatching and increase at the completion of yolk absorp- tion (Brown et al., 1987; Sullivan et al., 1987; Tagawa and Hirano, 1987; Greenblatt et al., 1989; Leatherland et al., 1989a,b; Tagawa et al., 1990a,b). The source of TH in eggs is probably from the maternal circulation, partly because injection of TH into gravid females increased TH levels in unfertilized eggs (Brown et al., 1988; Brown and Bern., 1989; Ayson and Lam, 1993). Thyroid hormones are known to be involved in the regulation of early development throughout verte- brates. Experimental treatment of fish during early stages of development with TH in appropriate doses induced earlier hatching and accelerated yolk absorp- tion, growth and morphological differentiation in many fish species (Lam, 1980; Nacaraio, 1983; Lam and Sharma, 1985; Lam et al., 1985; Reddy and Lam, 1987; Brown et al., 1988; Brown and Bern., 1989; Reddy and Lam, 1992a,b; Brown and Kim, 1995; Tachihara et al., 1997). Furthermore, TH induces metamorphosis in flounder, Paralichthys oliaceus (Inui and Miwa, 1985; Miwa and Inui, 1987). These reports raise two major questions: first, how are TH transferred from the maternal circulation to the developing oocyte and second, how are TH in the developing embryos and larvae transported to their target organs. Exogenous TH administered to larval fish can enter the vascular compartment via skin or * Corresponding author. Tel.: +972-4-8515202; fax: +972-4- 8511911. E-mail address: bruria@ocean.org.il (B. Funkenstein) 0303-7207/99/$ - see front matter © 1999 Elsevier Science Ireland Ltd. All rights reserved. PII:S0303-7207(99)00160-4