EXPRESSION PATTERNS OF ZEBRAFISH NR1D4A AND NR1D4B AND THEIR TRANSCRIPTIONAL RESPONSES TO DIFFERENT ENVIRONMENTAL STRESSES

We cloned the cDNAs of zebrafish nr1d4a and nr1d4b, performed sequence alignment and phynogenetic analyses, and characterized the expression patterns and their transcriptional responses to several environmental stresses by using real time quantitative RT-PCR (qPCR). The results indicated that zebrafish nr1d4a and nr1d4b genes are paralogs generated by genomic duplication. The DNA binding domain and ligand binding domain of these two paralogs are highly conserved, but these genes possess distinct expression patterns. The abundance of nr1d4a mRNA was quite low during the early stages of embryogenesis and markedly increased at 72hpf; however, nr1d4b was found to be maternally expressed and the mRNA abundance decreased at 6hpf and significantly increased at 72hpf as well. As for tissue-specific expression, the highest expression of zebrafish nr1d4a was found in brain and kidney, followed by gill, ovary, testis and eye, and liver was the organ with the lowest expression. The highest abundance of nr1d4b mRNA was found in ovary, followed by testis and brain, and the lowest expression was found in intestine and heart. The expression of both nr1d4a and nr1d4b could be induced by multiple environmental stresses. The up-regulation of zebrafish nr1d4a and nr1d4b could be detected at as early as 0.5h after exposed to cold stress (16℃). However, the inductive effect of cold stress decreased and gradually disappeared after 6h of exposure. In addition to cold stress, the expression of zebrafish nr1d4a and nr1d4b was also induced by heavy metal (2 mol/L cadmium), hypoxia (5% oxygen) and salinity (5), indicating the involvement of these genes in the acclimation to various environmental stresses. Thus, these findings have laid the foundation for further investigation of nr1d4a and nr1d4b functions and mechanisms underlying the regulation of their expression in fish.