Cloning of SsAkt in Sebastes schlegelii and Its Expression Pattern after Bacterial Stimulation

Sebastes schlegelii is a cold temperate ovoviviparous fish found near the seabed layer and is widely distributed in the Yellow Sea and Bohai Sea of China, as well as in the coasts of South Korea and Japan. It is characterized by its tender meat, delicious taste, rich nutrition, and high medicinal value, thus it is an economically important marine fish species in the northern coastal areas of China. In recent years, deep-water cage cultures have rapidly developed in China. Among the economically important fish species suitable for cage culture in northern China, S. schlegelii is the most important local breed with excellent quality and characteristics. However, with the expansion of the scale of the aquaculture industry, aquaculture diseases including those caused by Vibrio harveyi, Vibrio anguillarum, and Photobacterium damselae subsp. damselae, occur frequently. The authors isolated and identified a dominant pathogenic bacterium, the P5W of V. harveyi, from the lesions of diseased S. schlegelii and studied the response of S. schlegelii to V. harveyi infection. Multitissue transcriptome analysis screened the immune differential gene protein kinase B. Protein kinase B, also known as Akt protein, is a serine or threonine protein kinase, which mainly conducts signal transduction by phosphorylating other proteins. It plays an important role in various biological processes such as cell metabolism, transcriptional regulation, cell cycle regulation, immune defense, and embryonic development. Many studies have shown that during viral infection of cells, the Akt pathway is activated, thereby inhibiting viral proliferation. To clarify the sequence information, evolutionary characteristics, and biological functions of the Akt gene in S. schlegelii and to understand the immune response mechanism of S. schlegelii to bacterial invasion, the full-length cDNA of the SsAkt gene was obtained using molecular biology, and the sequence characteristics, tissue expression rules of the gene, and the response rules to Micrococcus luteus and V. anguillarum were studied. The results showed that the length of the open reading frame was 1 440 bp. The predicted relative molecular mass of the SsAkt protein was 55.80 kDa and the isoelectric point was 5.64. Sequence analysis revealed that the SsAkt protein contains three conserved domains: the PH domain (residues 6–109), serine/threonine protein kinase catalytic (S_TKc) domain (residues 148–405), and serine/threonine protein kinase (S_TK_