Role of crustacean hyperglycemic hormone (CHH) in the environmental stressor-exposed intertidal copepod Tigriopus japonicus

Abstract

To identify and characterize<em> CHH (TJ-CHH)</em> gene in the copepod Tigriopus japonicus, we analyzed the full-length cDNA sequence, genomic structure, and promoter region. The full-length <em>TJ-CHH</em> cDNA was 716 bp in length, encoding 136 amino acid residues. The deduced amino acid sequences of <em>TJ-CHH</em> showed a high similarity of the <em>CHH</em> mature domain to other crustaceans. Six conserved cysteine residues and five conserved structural motifs in the <em>CHH</em> mature peptide domain were also observed. The genomic structure of the<em> TJ-CHH </em>gene contained three exons and two introns in its open reading frame (ORF), and several transcriptional elements were detected in the promoter region of the <em>TJ-CHH</em> gene. To investigate transcriptional change of <em>TJ-CHH</em> under environmental stress, <em>T. japonicus</em> were exposed to heat treatment, UV-B radiation, heavy metals, and water-accommodated fractions (WAFs) of Iranian crude oil. Upon heat stress, <em>TJ-CHH </em>transcripts were elevated at 30 °C and 35 °C for 96 h in a time-course experiment. UV-B radiation led to a decreased pattern of the <em>TJ-CHH</em> transcript 48 h and more after radiation (12 kJ/m²). After exposure of a fixed dose (12 kJ/m²) in a time-course experiment,<em> TJ-CHH</em> transcript was down-regulated in time-dependent manner with a lowest value at 12 h. However, the <em>TJ-CHH</em> transcript level was increased in response to five heavy metal exposures for 96 h. Also, the level of the<em> TJ-CHH</em> transcript was significantly up-regulated at 20% of WAFs after exposure to WAFs for 48 h and then remarkably reduced in a dose-dependent manner. These findings suggest that the enhanced <em>TJ-CHH</em> transcript level is associated with a cellular stress response of the <em>TJ-CHH</em> gene as shown in decapod crustaceans. This study is also helpful for a better understanding of the detrimental effects of environmental changes on the CHH-triggered copepod metabolism.