Molecular cloning and characterization of thyroid hormone receptors in teleost fish

Abstract

Thyroid hormones are pleiotropic factors important for many developmental and physiological functions in vertebrates. Their effects are mediated by two specific receptors (TR and TR ) which are members of the nuclear hormone receptor superfamily. To clarify the function of these receptors, our laboratory has started a comparative study of their role in teleost fish. This type of approach has been hampered by the isolation of specific clones for each fish species studied. In this report, we describe an efficient reverse transcription/PCR procedure that allows the isolation of large fragments corresponding to TR and TR of a wide range of teleost fish. Phylogenetic analysis of these receptors revealed a placement consistent with their origin, sequences from teleost fish being clearly monophyletic for both TR and TR . Interestingly, this approach allowed us to isolate (from tilapia and salmon) several new TR or TR isoforms resulting from alternative splicing. These isoforms correspond to expressed transcripts and thus may have an important physiological function. In addition, we isolated a cDNA encoding TR in the Atlantic salmon (Salmo salar) encoding a functional thyroid hormone receptor which binds specific thyroid hormone response elements and regulates transcription in response to thyroid hormones.

Waterborne exposure to PFOS causes disruption of the hypothalamus–pituitary–thyroid axis in zebrafish larvae

“…The biological activities of THs are predominantly mediated at the level of gene transcription, by binding to TRs in the HPT axis in fish (Liu et al, 2000;Marchand et al, 2001;Yang et al, 2007). TRa and TRb were up-and down-regulated, respectively, indicating a different response of TR isoforms to PFOS exposure.…”

The history of a developmental stage: Metamorphosis in chordates

“…The same conclusions were drawn for actinopterygian fishes: their TRs are high affinity T 3 -dependent transcription factors. This was shown both in flatfishes that exhibit drastic metamorphic changes (Marchand et al, 2001, as well as in some other fishes (Essner et al, 1999;Yamano and Miwa, 1998). In the most basal chordate lamprey, the two known TRs are not orthologous to TRa and TRb, and instead are derived from a lamprey-specific duplication (Escriva et al, 2002).…”

Thyroid hormone receptor expression during metamorphosis of Atlantic halibut (Hippoglossus hippoglossus)

“…The teleosts also possess TR and TR but, in contrast to mammals, Japanese flounder, conger eel (Conger myriaster) and Atlantic salmon (Salmo salar) have two distinct TR genes (Yamano et al, 1994;Marchand et al, 2001;Jones et al, 2002;Kawakami et al, 2003a). Conger eel also has two TR genes, and whilst only a single TR gene has been found in other teleosts examined to date, further TR isoforms have been described that result from alternative splicing (Yamano and Inui, 1995;Marchand et al, 2001;Kawakami et al, 2003b).…”