The characterization of RHEB gene and its responses to hypoxia and thermal stresses in the small abalone Haliotis diversicolor

RHEB (Ras Homolog Enriched in Brain) is a GTP-binding protein that is ubiquitously expressed in humans and other mammals. The protein is largely involved in the mechanistic target of rapamycin (mTOR) pathway, and regulates the cell cycle progression and growth. The goal of this study was to characterize the RHEB gene in the small abalone Haliotis diversicolor, and identify the responses of RHEB gene to stresses of hypoxia or/and thermal. The objectives were to: 1) clone the full-length cDNA RHEB gene in the H. diversicolor (HdRHEB); 2) quantify the expression of HdRHEB gene in tissues of haemocytes, mantle, kidney, gill, digestive tract, colleterial gland, and hepatopancreas by using RT-PCR, and 3) evaluate the responses of HdRHEB in gill and haemocyte to stresses of hypoxia (0.2 mg/l00 ml), thermal (31 °C), and combination of hypoxia (0.4 mg/l00 ml) and thermal (30 °C) at exposure time of 0, 4, 24, 96, and 192 h. The full length cDNA of HdRHEB was 1044 bp encoding a peptide of 182 amino acid residues. Expression of HdRHEB gene was detected in all of the 7 tissues and showed the highest in mantle (P < 0.05). Under hypoxia, expression of HdRHEB in gill increased significantly at 4 h, 24 h and 96 h (P < 0.05), and that in haemocyte increased significantly at 24 h, 96 h and 192 h (P < 0.05). Under thermal stress, expression of HdRHEB gene in gill decreased significantly at 4 h and 24 h, while expression in haemocyte decreased significantly all the time. Under thermal and hypoxia stresses, expression of HdRHEB gene in gill and haemocyte was up-regulated significantly at 24 h and 96 h (P < 0.05). The results in this study demonstrated for the first time that RHEB gene in abalones is able to response to stress stimuli of hypoxia or/and thermal.