Abstract:Hemoglobin is the main component of haemolymph, which is widely distributed in vertebrates and some invertebrates. It has many biological functions, including transporting oxygen, storing energy, sustaining osmotic pressure, immunological functions, and so on. According to previous reports, the functions of hemoglobin from different organisms are varied, especially in invertebrate animals, because of less conservation in gene structure. However, the study of the immune function of hemoglobin in mollusks is limited. The ark shell, Scapharca broughtonii, is one of the important economic marine shellfishes in China, Korea, and Japan, and other places. In particular, previous studies showed that there were three types of hemocytes in S. broughtonii: red blood cells, white blood cells, and thrombus cells. To determine the structure, distribution, and immunological activity of the hemoglobin gene, the cDNA sequence of hemoglobin (named SbHbⅠ) was obtained using EST and RACE methods. Sequence analysis revealed that the cDNA was 867 bp in length, including an open reading frame (ORF) of 483 bp encoding a polypeptide of 160 amino acid residues. The predicted molecular weight was 17.5 kDa and isoelectric point (pI) was 9.68. The mRNA expression analysis of SbHbⅠin tested tissues by quantitative real-time PCR (qRT-PCR) revealed that the mRNA of SbHb I could all be detected in the foot, gill, mantle, adductor muscle, haemocytes, hepatopancreas, and the larvae aged from oosperm to 23 d. The expression level of SbHbⅠin haemocytes was more than 70 folds that in the adductor muscle. The expression of SbHbⅠin the larvae from the oosperm to 23 d was basically showed a declining tendency at the beginning and increased later, with a sharp increase at 12 d (P<0.05). After being stimulated in Vibrio anguillarum, SbHbⅠfirst showed an upgraded tendency and later descended, and the same tendency occurred during hypoxia stress, during which SbHbⅠreached the maximum (P<0.05) at 16 h at three dissolved oxygen levels (4.5 mg/L, 2.5 mg/L, and 0.5 mg/L). Basic data were provided from the study of hemoglobin in mollusks.
