Overexpression of a Zebrafish ARNT2-like Factor Represses CYP1A Transcription in ZLE Cells

Abstract:

Aryl hydrocarbon receptor nuclear translocator (ARNT) factors belong to a novel basic-helix-loop-helix–PAS (bHLH-PAS) transcription factor family that controls a variety of physiological and developmental processes. In a previous study, we obtained a partial complementary DNA fragment of an ARNT2-like factor from zebrafish embryo, liver, and other tissues by reverse transcription–polymerase chain reaction. In an effort to characterize the function of this factor, we screened an embryonic complementary DNA library and obtained a complete cDNA of this ARNT2-like factor, zARNT2A. The deduced protein sequence of zARNT2A encompasses the basic-helix-loop-helix and PAS-A/B motifs and shares highest sequence similarity with the amino-terminal half of mouse ARNT2 factor. However, it lacks a carboxy-terminal transactivation motif following the PAS-A/B motifs. Transient expression of zARNT2A in cultured cells resulted in repression of TCDD-dependent CYP1A transcription. Whole-mount in situ hybridization revealed that zARNT2A is expressed in brain and pronephros at prime-5 stages. In adult fish, zARNT2A messenger RNA is transcribed in a wide range of tissues, which indicates that zARNT2A and its corresponding signal transduction mechanisms have important roles in fish development and other physiological aspects.